Water treatment describes those processes used to make water more acceptable for a desired end use. These can include use as drinking water, industrial processes, medical and many other uses. The goal of all water treatment process is to remove existing contaminants in the water, or reduce the concentration of such contaminants so the water becomes fit for its desired end use. Water quality analytical techniques are considered in the context of EEC directives on the quality of the aquatic control of all effluents is entering it. The principal methods of water analysis are reviewed and it indicated in view of destructive and hazardous role of pollution, it become necessary that the very nature of atmosphere, the various air effluent are present there to save the environment from the harmful effect. Effluent can be treated in different ways, it is classified as; preliminary treatment, primary treatment, secondary treatment and complete final treatment. Waste water obtained from industries is generally much more polluted than the domestic or even commercial waste water. Industrial wastewater cannot be always treated easily by the normal methods of treating domestic waste waters. Depending on the quantum, concentration, toxicity and presence of non biodegradable organics in an industrial wastewater, its treatment may consist of any one or more processes such as equalization, neutralization, physical treatment, chemical treatment and biological treatment. The atmosphere contains hundreds of air pollutants from natural or from anthropogenic sources. All such pollutants are called primary pollutants for example; sulphur oxides, carbon monoxide, nitrogen oxides, lead etc. Secondary pollutants are the chemical substances, which are produced from the chemical reactions of primary pollutants or due to their oxidation etc. A high growth in vehicle population brings in its wake urban air pollution problems unless timely appropriate steps to control vehicle emissions are under taken.
Some of the fundamentals of the book are quality and characteristics of effluents, collection of sewage samples for physical and, chemical testing, disposing of effluents, disposal of wastewaters in lakes and management of lake waters, disposal of sewage effluents on land for irrigation, classification of treatment processes, treatment of industrial effluents, methods of treating industrial wastewaters, strategies for management of industrial wastes, combined industrial municipal wastes, a process for upgrading paper mill effluent by water hyacinth, ventilation for controlling indoor air pollution, the environment and its pollution, disposal of environmentally hazardous radioactive effluents and biomedical wastes, air pollution, its control and monitoring, fuels from waste etc.
This book is an effort to put together the various options available to meet the water and air effluent available for the environmental protection. The book presents a concise but through an overview of state of technology for water and air effluent treatment. The water and air effluent treatments are organized into chapters by broad problem area, treatment of industrial effluent, industrial waste management, etc. This will be helpful to technocrats, consultants, educators, architects, industry executive, students and others concerned with saving environment problem.
QUALITY AND CHARACTERISTICS
sewage is discharged into some river stream
floating solids present in the discharged sewage may be washed up on to
shore, near the point of disposal, where they decompose and create foul
and bad odours. The large amount of organic matter present in the
sewage will also consume the dissolved oxygen from the river stream in
and may thus seriously decrease the dissolved oxygen of the river
causing fish kills and other undesirable effects. In addition to these
the discharged sewage will contaminate the river water with pathogenic
bacteria. Hence, even though municipal sewage is 99.9 per
cent water, it
requires treatment, if nuisance is to be avoided.
The extent and
type of treatment required, however, depends
upon the character and quality of both sewage and source of disposal.
example, a small community at the seaside might discharge its unaltered
directly into the ocean without any ill effects, but if this city were
inland on a small stream, a high degree of treatment might be needed.
In the olden
times, the waste waters from a community were
not so much contaminated as they are today. The urbanization,
growth, and the improved standards of living, have increased the
quantity of municipal sewage in recent years to a point where dilution
can no longer be relied upon to prevent the undesirable effects of
In many cases, more advanced treatment of wastewater is essential to
undue pollution. This is much more so, when the disposed sewage is
contain industrial wastewaters.
Hence, it is
absolutely necessary to study the
characteristics and behaviour of sewage, to ensure its safe disposal.
study will help us in determining the degree and type of treatment
be given to a given sewage, and thus avoid the pollution of the source
discuss the various physical, chemical and biological
(bateriological) characteristics of sewage, let us first
discuss as to how
the sewage gets decayed, and what happens to it with the
passage of time.
Decomposition of Sewage
Most of the
organic matter present in sewage is unstable and
decomposes readily through chemical as well as biological
Till the advent of biological methods, chemical treatment of sewage
being adopted to remove the organic matter from the sewage. However,
advent of biological degradation methods, this type of treatment has
bacteria will then utilize the free oxygen as
electron acceptor, thereby
oxidizing the organic matter to stable and unobjectionable end
stable end products like nitrates, carbon dioxide, sulphates
respectively for the three forms of matter, i.e. nitrogenous
and sulphurous matter. Water, heat, and additional bacteria
will also be
produced in this biological oxidation, which can be represented by the
It may also be
noted that during the decomposition of
nitrogenous organic matter, the ammonia formed in the initial stages,
linger on till the end, depending upon the available oxygen, retention
temperature, biological activity, etc., because the
facultative bacteria are
incapable to break ammonia to nitrates.
products formed in
the aerobic oxidation of the three types of organic matter are shown in
respective cycles, in Fig. l (a), (b) and (c). These
cycles are known as
nitrogen cycle, carbon cycle, and sulphur cycle, for nitrogenous,
carbonaceous, and sulphurous organic
Decomposition. If free
dissolved oxygen is not available to the sewage, then anaerobic
putrefaction, will occur. Anaerobic bacteria as well as
bacteria operating anaerobically, will then
flourish and convert the
complex organic matter into simpler organic compounds of nitrogen,
sulphur. These anaerobic bacteria, infact, survive by extracting and
the bounded molecular oxygen present in compounds
like nitrates (NO3) and sulphates
(SO4). Gases like ammonia,
hydrogen sulphide, methane, etc. are also evolved in this
Steps in the
Nitrogen cycle. Nitrogenous
organic matter get oxidized to ammonia, then to nitrites, and finally
which when consumed by plants, through photosynthesis, form
(plant life). The plant proteins, when consumed by animals, form animal
proteins. The wastes produced by animals and their dead bodies, will
nitrogenous organic matter, thus completing the nitrogen cycle.
There may be
some short circuits of
the cycle, as shown by dotted lines say for example, the dead plants
on death, lead to formation of organic matter directly, without
animal protein. Similarly, nitrates on denitrification may
into free nitrogen (and sometimes to ammonia), which may be converted
plant proteins, as it may be used by certain bacteria residing in the
roots. This is called nitrogen fixation.
Steps in the
Sulphur Cycle. This cycle
is similar to nitrogen cycle. The sulphurous organic matter, on
produces H2S gas,
which on further oxidation, changes to sulphur, and then finally to
Sulphates, when consumed by plants through photosythesis, change into
proteins which when eaten by animals, change into animal proteins. The
produced by animals and their dead bodies will again form sulphurous
matter, thus completing the sulphur cycle.
There may be
short circuits in the cycle, as shown by the
dotted lines organic sulphurous matter may be directly formed by the
the plants, without the formation of animal proteins.
sulphates in the absence of oxygen will be
converted into H2S, by the
process of reduction.
Steps in the
Carbon Cycle. The carbonaceous
matter, on oxidation, releases carbon dioxide, which is its final end
This CO2, when used
by plants through photosynthesis, gets converted into plant
and proteins (sugars) which when eaten by animals, change into animal
proteins. The wastes produced by animals and their dead bodies will
carbonaceous organic matter, thus completing the carbon cycle.
There may be
short circuits in the cycle, as shown by the
dotted lines. Organic carbonaceous matter may be directly formed by the
plant life gives off CO2 at
night, and the animal life gives off CO2 during
respiration. Both these respiration
processes are shown by the dotted lines in the above figure. various
which these gases are evolved are shown in Fig. 2. which represents
carbon and sulphur cycles together, for the above anaerobic
final equations, representing this decomposition, are given below
acids including alcohols produced in Eq. 4, are
further converted into methane gas (CH4), carbon
dioxide gas (CO2), etc., if
bacteria are also especially present in the sewage. This conversion is
represented by the equation.
An understanding of these cycles
will help us in determining the stage
of decomposition of sewage by testing for the products of decay. For
well oxidised sewage will contain nitrates and sulphates, but very
ammonia and hydrogen sulphide. On the other hand, lesser oxidised
contain nitrites and sulphur instead of nitrates and sulphates.
Biological Treatment. Numerous
bacteria are found in waste waters of a community. So much so, that
about 5 to
50 billion bacteria are generally present per litre of sewage. Out of
bacteria, only a small number are harmful to man, and are called
a large number of bacteria present in sewage, called non pathogens are,
however, important aids, in the process of decomposition, and are thus
to us in sewage treatment. The fundamental basis of our treatment given
sewage, therefore, is to provide an environment favourable to
the action of
the aerobic and anerobic bacteria, that stabilise the
present in sewage either through aerobic or anaerobic decomposition.
which work on oxidation alone (i.e. aerobic
decomposition) are aeration tanks, contact beds, intermittent
trickling filters, and oxidation ponds.
which work on putrefaction alone (i.e., anaerobic
decomposition) are septic tanks, Imhoff tanks, sludge
digestion tanks, and
CHARACTERISTICS OF EFFLUENTS
The quality of
effluents can be
checked and analyzed by studying and testing its physical, chemical and
bacteriological (biological) characteristics, as explained below
Physical Characteristics of Sewage and Their Testing
examination of sewage is carried out in order to
determine its physical characteristics. This includes tests for
turbidity (ii) colour
(iii) odour and (iv) temperature.
These tests are summarized below
Turbidity. Sewage is normally turbid,
resembling dirty dish water or wastewater from baths having other
matter like fecel matter, pieces of paper, cigarette ends, match
greases, vegetable debris, fruit skins, soaps, etc. The turbidity
sewage becomes stronger. The degree of turbidity can be measured and
turbidity rods or by turbidimeters, as is done for testing raw water
Colour. The colour of sewage can
normally be detected by the naked eye, and it indicates the freshness
colour is yellowish, grey, or light brown, it indicates fresh sewage.
if the colour is black or dark brown, it indicates stale and septic
Other colours may also be formed due to the presence of some specific
Odour. Fresh sewage is practically
odourless. But, however, in 3 to 4 hours, it becomes stale with all
present in sewage being practically exhausted. It then starts omitting
offensive odours, especially that of hydrogen sulphide gas, which is
to decomposition of sewage.
Temperature. The temperature has an
effect on the biological activity of bacteria present in sewage, and it
affects the solubility of gases in sewage. In addition, temperature
affects the viscosity of sewage, which, in turn, affects the
in its treatment.
temperature of sewage is generally slightly higher
than the temperature of water, because of additional heat added during
of water. The average temperature of sewage in India is 20°C, which is
about the ideal temperature for the biological activities. However,
temperature is more, the dissolved oxygen content (D.O.) of sewage gets
Chemical Characteristics of Sewage and Their Testing
for determining the chemical characteristics
of sewage help in indicating the stage of sewage decomposition, its
and extent and type of treatment required for making it safe to the
disposal. Chemical analysis is, therefore, carried out on sewage in
determine its chemical characteristics. It includes tests for
Total solids, suspended solids, and
of fats, greases, and oils.
sulphates and H2S gas.
oxygen demand (C.O.D.)
oxygen demand (BOD).
These tests are
Total Solids, Suspended Solids and Settleable Solids
contains very small
amount of solids in relation to the huge quantity of water (99.9%). It
contains about 0.05 to 0.1 per cent (i.e. 500 to
1000 mg/1) of total
solids. Solids present in sewage may be in any of the four forms
solids, dissolved solids, colloidal solids, and settleable solids.
solids which remain floating in sewage. Dissolved solids are
remain dissolved in sewage just as salt in water. Colloidal
finely divided solids remaining either in solution or in suspension. Settleable
solids are that portion of solid matter which settles out,
if sewage is
allowed to remain undisturbed for a period of 2 hours. The proportion
different types of solids is generally found to be as given below
It has been
estimated that about
1000 kg of sewage contains about 0.45 kg of total solids, out of which
is in solution, 0.112 kg is in suspension, and 0.112 kg is settleable.
DISPOSING OF EFFLUENTS
treatments that may be
given to raw sewage before disposing it of, it shall be worthwhile to
discuss the various methods and sources of disposal of sewage. The
study of the
sources of disposal is important, because the amount of treatment
be given to sewage depends very much upon the source of disposal, its
and capacity to tolerate the impurities present in the sewage
without itself getting potentially polluted or becoming less useful.
There are two
general methods of disposing of the sewage
disposal in water and
Irrigation or Broad Irrigation or Sewage Farming, i.e.
disposal on land.
dilution is more common of these two methods,
which are described below
DISPOSAL BY DILUTION
dilution is the process
whereby the treated sewage or the effluent from the sewage treatment
discharged into a river stream, or a large body of water, such as a
sea. The discharged sewage, in due course of time, is purified by what
as self purification process of natural waters. The degree and amount
treatment given to raw sewage before disposing it of into the river
question, will definitely depend not only upon the quality of raw
also upon the self purification capacity of the river stream and the
use of its water.
Standards of Dilution for Discharge of Waste waters into
The ratio of the
quantity of the diluting water to that of
the sewage is known as the dilution factor and depending upon this
Royal Commission Report on Sewage Disposal has laid down the following
standards and degrees of treatment required to be given to a particular
standards have been operative in England since
1912, and had also been followed in India without much variance.
the increasing pollution of surface streams due
to indiscriminate discharge of domestic and industrial, waste waters without bothering to look
into the available
dilution ratios, it has become imperative to limit the concentrations
various pollutants being discharged in to the surface water sources
the sewage and industrial effluents. The tolerance limits for such
pollutants have therefore been prescribed by various countries,
India. These limits are based upon the desirability of giving full
treatment to sewage and industrial liquid wastes, up to minimum level
The Bureau of
(BIS), previously known as Indian Standard Institution (ISI), has
laid down its guiding standards for sewage effluents, vide IS 4764
for industrial effluents vide IS 2490 1974, as shown in table 2. These
tolerance limits are supposed to be the national guidelines for guiding
various State Pollution Control Boards for prescribing their legally
enforceable standards, depending upon the water quality and dilution
in their respective surface water sources, and the type of effluents
by the different industries.
industrial wastewaters are disposed of in to public
sewers, then also, their quality has to be checked, by following the
prescribed by IS 3306 1974.
Dilution in Rivers and Self Purification of Natural Streams
When sewage is
discharged into a
natural body of water, the receiving water gets polluted due to waste
present in sewage effluents. But the conditions do not remain so for
because the natural fores of purification, such as dilution,
oxidation reduction in sun light, etc., go on acting upon the pollution
elements, and bring back the water into its original condition. This
purification of polluted water, in due course, is called the self
phenomenon. However, if the self purification is not achieved
either due to too much of pollution discharged into it or due to other
the river water itself will get polluted, which, in turn, may also
sea where the river outfalls.
factors on which these natural forces of
purification depend are (a) temperature (b)
hydrography such as the velocity and surface expanse of the river
available dissolved oxygen, and the amount and type of organic matter
(e) rate of reaeration, etc.
affecting the dilution and
sedimentation rates, the temperature also affects the rate of
chemical activities, which are enhanced at higher temperatures and
lower temperatures. The dissolved oxygen content of water, which is
essential for maintaining aquatic life and aerobic conditions (so as to
the anaerobic decomposition and subsequent nuisance) is also influenced
temperature. At higher temperatures, the capacity to maintain the D.O.
concentration is low while the rate of biological and chemical
high, causing thereby rapid depletion of D.O. This is likely to lead to
anaerobic conditions, when the pollution due to putrescible organic
in the body of water
helps in breaking the surface of the stream or lake, and helps in rapid
from the atmosphere. Thus, it helps in maintaining aerobic conditions
river stream, and in keeping it clear. Too much of turbulence, however,
desirable, because it scours the bottom sediment, increases the
retards algae growth, which is useful in reaeration process. Wind and
undercurrents in lakes and oceans cause turbulences which affect their
The Hydrography affects the
velocity and surface expanse of the river stream. High velocities cause
turbulence and rapid reaeration, while large surface expanse (for the
cubic contents) will also have the same effects.
The larger the
amount of dissolved
oxygen presents in water, the better and earlier the self purification
The amount and
the type of organic
matter and biological growth present in water will also affect the rate
purification. Algae which absorbs carbon dioxide and gives out oxygen,
very helpful in the self purification process.
The rate of
reaeration i.e. the
rate at which the D.O. deficiency is replenished, will considerably
self purification process. The greater is this rate, the quicker will
self purification, and there will be no chances of development of
Pollution in a River Stream. A
polluted stream undergoing self purification can be divided into the
Zone of degradation
Zone of active decomposition
Zone of recovery and
Zone of cleaner water
These zones are
of degradation or Zone of pollution. This zone is found for a certain
length just below
the point where sewage is discharged into the river stream. This zone
by water becoming dark and turbid with formation of sludge deposits at
bottom. D.O. is reduced to about 40% of the saturation value. There is
increase in carbon dioxide content reoxygenation (i.e.
occurs but is slower than de oxygenation.
conditions are unfavourable to the
development of aquatic life and as such, algae dies out, but fish life
present feeding on fresh organic matter. Moreover, certain typical
such as Limondrilus and Tubifex appear with sewage fungi, such as
of active decomposition. This zone is marked by heavy
pollution. It is characterized by water
becoming greyish and darker than in the previous zone. D.O.
down to zero and anaerobic conditions may set in with the evolution of
like methane, carbon dioxide, hydrogen sulphide, etc., bubbling to the
with masses of sludge forming an ugly scum layer at the surface. As the
decomposition slackens due to stabilization of organic matter, the re
sets in and D.O. again rises to the original level (i.e.
zone, bacteria flora will flourish. At the upper end, anaerobic
replace aerobic bacteria, while at its lower end, the position will be
reversed. Protozoa and fungi will first disappear and then reappear.
will be absent. Algae and Tubifex will also mostly be absent. Maggots
Psychoda (sewage fly) larvae will, however, be present in all but the
of recovery. In
this zone, the river stream tries to recover from its degraded
condition to its
former appearance. The water becomes fearer, and so the algae reappears
fungi decreases. B.O.D. falls down and D.O. content rises above 40% of
saturation value Protozoa, Rotifers, Crustaceans and large plants like
Bryozons, etc. also reappear. Bottom organisms will include Tubifex,
Snails, etc. The organic material will be mineralised to form nitrates,
sulphates, phosphates, carbonates, etc.
of Cleaner Water. In this zone, the river attains its
original conditions with D.O.
rising up to the saturation value. Water becomes attractive in
Game fish (which requires atleast 4 to 5 mg /1 of D.O.) and usual
prevails. Same pathogenic organisms may still, however, survive and
present, which confirms the fact that when once a river water has been
polluted, it will not be safe to drink it, unless it is properly
Indices of Self
Purification. The stage
of self purification process can be determined by the physical,
biological analysis of the water. Colour and turbidity are the physical
indices, while D.O., B.O.D. and suspended solids are the chemical
can mark the stages of purification. Moreover, the biological growth
water can also indicate the stage of purification process, as different
of micro and macro organisms will exist in polluted water under
conditions, as discussed in the previous sub article.
zones of pollution (i.e. various stages
in the self purification process) and the physical, chemical and
indices, characteristics of each zone, are shown in Fig. 1.
Deficit of a Polluted River Stream. The oxygen
deficit D at any time in a polluted river stream is the difference
actual D.O. content of water at that time and the saturation D.O.
the water temperature i.e.
order to maintain clean conditions in a river stream, the oxygen
be nil, and this can be found out by knowing the rates of de
oxygenation and re
Curve. In a polluted
stream, the D.O.
content goes on reducing due to decomposition of volatile organic
rate of de oxygenation depends upon the amount of the organic matter
to be oxidised at the given time (i.e. Lt as well as
on the temperature
of reaction (i.e. T). Hence, at a given temperature,
the curve showing
depletion of D.O. with time, i.e. deoxygenation
curve (Refer curve 1 of
Fig. 2) is similar to the first stage B.O.D. curve. It can also be
Curve. In order to
counter balance the
consumption of D.O. due to de oxygenation, atmosphere, supplies oxygen
water, and the process is called re oxygenation. The rate at which the
is supplied by the atmosphere to the polluted water depends upon
The depth of the receiving water
(rate is more in a
The condition of the body of water
(rate is more in
a running stream than in a quiescent pond)
The saturation deficit or the
oxygen deficit (i.e.
the deficit of D.O. below the saturation value) and
temperature of water.
these factors, the rate of re oxygenation can
also be expressed mathematically and plotted in the form of a curve
called re oxygenation
curve (Refer curve II Fig. 2).
Curve. In a running
exposed to the atmosphere, the de oxygenation as well as the re
hand in hand. If de oxygenation is more rapid than the re oxygenation,
oxygen deficit results.
Note. If the D.O.
content becomes zero, aerobic conditions
will no longer be maintained and putrefaction will set in.
The amount of
resultant oxygen deficit can be obtained by
algebraically adding the de oxygenation and re oxygenation curves (see
III Fig. 2). The resultant curve so obtained is called the
oxygen sag curve
or the oxygen deficit curve. From this curve, the oxygen
deficit and oxygen
balance (i.e., 100 D) per cent in a stream after a
certain lapse of
time, can be found out.
It can also be
seen that when the de oxygenation rate exceeds
the re oxygenation rate, the oxygen sag curve shows increasing deficit
oxygen but when both the rates become equal, the critical point is
then finally when the rate of de oxygenation falls below that of re
the oxygen deficit goes on decreasing till becoming zero.
This is the
important first stage equation in which L is the
B.O.D. of the mixture of sewage and stream, and F (KD and
corresponds to the temperature of the mixture of sewage and stream at
equations are of practical value in predicting the
oxygen content at any point along a stream, and thus help us in
degree of waste treatment required, or of the amount of dilution
order to maintain a certain D.O. in the stream.
Disposal of Wastewaters in Lakes and Management of lake Waters
wastewaters in confined
lakes or reservoirs is much more harmful than its disposal in flowing
and rivers. Water quality management in lakes in entirely different
in rivers. It is
infact the phosphorous
(a nutrient largely contained in industrial as well as domestic
which seriously affects the water quality of lakes and is hence
the prime lake pollutant. Oxygen demanding wastes
may be the other
important lake pollutants. The toxic chemicals from industrial
also sometimes very adversely effect some special classes of the lakes.
However, phosphorous (a nutrient) constitutes the most important
lake pollutant, and needs special study in water quality management of
A study of the
lake systems is essential to understand the
role of phosphorous in lake pollution. The study of lakes is called
in Lakes. The water of a
stratified during summers and winters, as discussed below
season, the surface water of a lake gets heated
up by sunlight and warm air. This worm water being lighter, remains in
layers near the surface, until mixed downward by turbulence from winds,
boats and other forces. Since such turbulence extends only to a limited
from below the water surface, the top layers of water in the lake
mixed and aerobic. This warmer, well mixed and aerobic depth of water
epilimnion zone. The lower depth, which remains
cooler, poorly mixed and
anaerobic, is called the hypolimnion zone. There
may also exist an
intermediate zone or a dividing line, called thermocline, as
Fig. 3 (a).
The change from
epilimnion to hypolimnion can be experienced
while swimming in a lake. When you swim in top layers horizontally, you
feel the water warmer and if you dive deeper, you will find the water
The change line will represent monocline. The depth of epilimnion zone
upon the size of the lake for the same temperature changes. It may be
as I m in small lakes and may be as large as 20 m or more in large
depth also depends upon the storm activity in the spring when
developing. A major storm at the right time will mix the warmer water
substantial depth and thus create a deeper epilimnion zone than its
depth. Once formed, lake stratification is very stable, and can only be
by exceedingly violent storms. As a matter of fact, as summer
stability increases the epilimnion continues to warm, while the
remains at a fairly constant temperature.
With the onset
of winter season, the epilimnion cools, until
it is more dense than the hypolimnion. The surface water then sinks,
The water of the hypolimnion rises to the surface, where it cools and
sinks. The lake, thus becomes completely mixed, making it quite
regions of freezing temperatures, when the temperature drops below 4°C,
above process of overturning (or turn over) stops, because water is
at this temperature. Further cooling or freezing of the water surface
in winter stratification, as shown in Fig. 3 (b).
With the passing
of winters and commencement of spring
season, the surface water again warms up and overturns, and lake
completely mixed. The lakes in regions of temperate climate will,
have at least one, if not two, cycles of stratification and turn over
in Lakes. Lakes have been
exhibit distinct zones of biological activity, largely determined by
availability of light and oxygen. The most important biological zones
These zones are
shown in Fig. 4, and briefly discussed below
Euphotic zone. The upper layer
of lake water
through which sunlight can penetrate, is called the euphotic zone. All
growth occurs in this zone. In deep water, algae grow as the most
plants, while rooted plants grow in shallow water near the shore.
The depth of the
euphotic zone is reduced by the turbidity,
which blocks sunlight penetration. In most lakes, the turbidity is due
growth although colour and suspended clays may substantially reduce
penetration in some lakes. It is important to note that the bottom of
zone only rarely coincides with the thermocline.
The depth of the
euphotic zone can be approximated and
measured by a simple device, called the secchi disk,
shown in Fig. 8.5.
This disk is lowered into the lake water until the observer can no
distinguish between the boundaries between its white and black
depth, called the secchi disk depth, does not correspond exactly to the
of euphotic zone, but provides a good approximation of its extent. This
disk depth also provides a measure of the aesthetic quality of water.
greater is the secchi disk depth, the clearer is the water.
Littoral zone. The shallow
water near the shore,
in which rooted plants grow, is called the littoral zone. The extent of
littoral zone depends on the slope of the lake bottom, and the depth of
euphotic zone. The littoral zone cannot extend deeper than the euphotic
as shown in Fig. 8.3.
Benthic zone. The bottom
sediments in a lake
comprises what is called the benthic zone. As the organisms living in
overlying water die, they settle down to the bottom, where they are
by the organisms living in the benthic zone. Bacteria are always
this zone. The presence of higher life forms, such as worms, insects
crustaceans however, depends upon the availability of oxygen at the
a Lake. The
productivity of a lake
is defined as a measure of its ability to support a food chain. Since
form the base of this food chain, which is required by the other forms
living organisms to thrive, its presence measures the lake
Although, more productive lakes will have a higher fish population, yet
such a lake will have to support heavier algal growth, its water
be reduced, because of the undesirable changes that occur as algal
increases. Moreover, due to reduced water quality, the most desirable
which flourish in better quality waters, will be lost.
productivity level may, therefore, be determined by
measuring the amount of algal growth that can be supported by the
nutrients. This productivity level of a lake is thus, reflective of the
quality of the lake. As the productivity of a lake increases, its water
reduces. Because of the important role productivity plays in
quality, it forms a basis for classifying lakes.
the increasing level of its productivity, the
lakes may be classified as
Eutrophic lakes and
There four types
lakes have a low level of productivity due to a severely limited supply
nutrients to support algal growth. The water of such a lake is
enough as to make its bottom visible upto considerable depth. In such a
the euphotic zone often extends into the hypolimnion, which is aerobic.
Oligotrophic lakes, therefore, support cold water game fish. An
example of such a lake is offered by the Tahoe Lake on California
lakes. The lakes
having medium productivity levels, with medium growth of algae and
are usually classified as mesotrophic lakes. In such a lake, although
substantial depletion of oxygen may occur in the hypolimnion, yet it
Eutrophic lakes. Eutrophic
lakes do have a high level of productivity, because of an abundant
algal nutrients. The flourishing growth of algae makes the lake water
highly turbid, so that the euphotic zone may extend only partially into
As the algae
die, they settle to the lake bottom, where they
are decomposed by benthic organisms. In a eutrophic lake, this
sufficient to deplete the hypolimnion of oxygen during summer
hypolimnion is anaerobic during summer, such a
lake will only support warm water fish. As a matter of fact, all types
water fish are driven out of the lake, before the hypolimnion becomes
anaerobic, because they generally require dissolved oxygen levels of at
mg/L. Highly eutrophic lakes may also have large mats of floating algae
typically impart unpleasant tastes and odours to the water.
These are very
old shallow lakes,
having thick organic sediment deposits at their bottoms. Rooted water
abundantly grow in such shallow ponds, which ultimately become marshes.
of Lakes. Eutrophication
is a natural
process under which lakes get infested with algae and silt up gradually
become shallower and more productive through the entry and cycling of
like carbon, nitrogen and phosphorous. The initially clear water
lakes, therefore, gradually turn into mesotrophic, eutrophic, and
stages, due to continuous entry of silt and nutrients.
process of eutrophication infact can always get
its carbon and nitrogen requirements from the atmospheric gases like CO2 and
(NO2) while the
requirement of phosphorous is met by its
presence in natural run off due to disintegration of rocks, which
phosphorous. The increased phosphorous in lake water, entering either
the agricultural use of its drainage area or through the entry of
industrial waste waters, will cause accelerated eutrophication of
lakes, and is
called cultural eutrophication. The natural process of eutriphication
gets intensified by the entry of wastewater discharges into the lakes,
permanent damage to its water quality and siltation. Eutrophic lakes
however, not necessarily polluted, but pollution contributes to
quality management for a lake, therefore, aims at
reducing its eutrophication to atleast at
its natural level, by controlling and
reducing the input
of phosphorous in the lake water. Once the input of phosphorous, (which
directly controls the production of chlorophyll and hence the algal
development) is reduced, the phosphorous concentration will gradually
down, as the existing phosphorous will get buried into the sediment or
flushed out of the lake along with the excess river flow feeding the
suggested for reducing eutrophication by removal
of phosphorous by its precipitation by addition of lime to the lake
water or by
dredging out the phosphorous rich sediment from the lake bottom, will
succeed until the entry of phosphorous is not curtailed. It, therefore,
imperative to stop the entry of sewage and industrial wastewaters,
largely contain phosphorous, into the lakes. Even the treated sewage
be low in phosphorous, since phosphorous can be removed only by costly
methods of waste treatment. The lake waters should, therefore, not be
for discharge of treated sewage. The phosphorous content of the
can, however, be reduced by banning the use of phosphorous rich
in detergents, which presently contribute heavy input of phosphorous in
domestic sewage, as large as twice that contributed by human excreta.
advanced countries have, therefore, banned the use of phosphates in
and soaps. India has yet to follow suit.
entry of seeping septic tank effluents from
cottages and houses built adjoining the lakes, through the sub soil
lake, will also cause phosphorous pollution in the lake, after the soil
too saturated to absorb any further phosphorous, finally passing it on
lake. The time it takes for phosphorous to break through to the lake
the type of soil, the distance to the lake, the amount of wastewater
and the concentration of phosphorous in the seeping wastewater. Entry
phosphorous through such sources should also be controlled to reduce
eutrophication of lakes, by collecting the septic tank effluents in
be carried up to the treatment plants, before disposing it off, safely.
The use of
fertilizers in fields in the drainage area should
also be controlled to reduce the entry of phosphorous through the
off flowing over such fields and finally entering the lakes. Treatment
catchments to reduce soil erosion will also help in reducing
into the surface runoff.
TREATMENT OF EFFLUENTS
Classification of Treatment Processes
being disposed of
either in river streams or on land, has generally to be treated, so as
it safe. The degree of treatment required, however, depends upon the
characteristics of the source of disposal, as discussed in the previous
Effluents can be
different ways. Treatment processes are often classified as
final treatment, as discussed below
treatment consists solely in separating the floating materials (like
animals, tree branches, papers, pieces of rags, wood, etc.), and also
settleable inorganic solids. It also helps in removing the oils and
etc. from the sewage. This treatment reduces the BOD of
by about 15 to 30%. The processes used are Screening for removing
papers, rags, clothes, etc. Grit chambers or Detritus tanks for
and sand and Skimming tanks for removing oils and greases.
treatment consists in removing large suspended organic solids. This is
accomplished by sedimentation in Settling basins.
effluent from primary treatment, often contains a
large amount of suspended organic material, and has a high BOD (about
preliminary as well as primary treatments are
classified together, under primary treatment.
solids, which are separated out in the
sedimentation tanks (in primary treatment), are often stabilised by
decomposition in a digestion tank or are incinerated.
is used for land fills or soil conditioners.
further treatment of the effluent, coming from the primary
This is generally accomplished through biological decomposition of
matter, which can be carried out either under aerobic or anaerobic
In these biological units, bacteria will decompose the fine organic
produce clearer effluent.
reactors, in which the organic matter is
decomposed (oxidised) by aerobic bacteria are known as aerobic
units and may consist of (i)
Filters (intermittent sand filters, as
well as trickling filters) (ii)
Aeration tanks, with the
feed of recycled activated sludge (i.e. the
sludge, which is
settled in secondary sedimentation tank, receiving effluents from the
tank) (iii) Oxidation
ponds and Aerated lagoons. Since
all these aerobic units, generally make use of primary settled sewage,
easily classified as secondary units.
reactors, in which the organic matter is
destroyed and stabilized by anaerobic bacteria, are known as anaerobic
biological units and may consist of Anaerobic lagoons,
Septic tanks, Imhoff
tanks, etc. Out of these units, only anaerobic lagoons make use of
settled sewage, and hence, only they can be classified under secondary
biological units. Septic tanks and Imhoff tanks, using raw
therefore, not classified as secondary units.
from the secondary biological treatment will
usually contain a little BOD (5 to 10% of the original), and may even
several milligrams per litre of DO.
solids/sludge separated out in the primary as
well as in the secondary settling tanks, will be disposed of by
them under anaerobic process in a Sludge digestion tank.
The Final or
Advanced Treatment. This treatment
is sometimes called tertiary treatment, and consists in removing the
load left after the secondary treatment, and particularly to kill the
pathogenic bacteria. This treatment, which is normally carried out by
chlorination, is generally not carried out for disposal of sewage in
is carried out, while using the river stream for collecting water for
re use or
for water supplies. It may, however, Sometimes be adopted, when
the outfall of sewage is very near to the water intake of some nearby
treatment is, therefore, usually confined up to
secondary treatment only. Well in fact, various physical, chemical and
biological processes are available for treatment, depending upon the
requirements. The choice of the treatment methods depends on several
including the disposal facilities available. Actually, the
between primary, secondary and tertiary treatment is rather arbitrary,
many modern treatment methods incorporate physical, chemical and
processes in the same operation.
treatment units, which may be used for treating
sewage, and the extent of BOD, solids and bacteria removed by them,
have been summarized
in Table 1.
operations of these units may be combined in
different ways, depending upon the topography and other local needs, so
create different types of treatment plants.
Fig. 1 shows
diagrammatic sketches of some standard types of
sewage treatment plants, which give full treatment, and may be adopted
different conditions. The first plant [Fig. 1 (a)]
consists of Imholf
tanks and low rate trickling filters, and
may be adopted for very
small towns, although the use of Imhoff tanks has become old and
days. The second plant [Fig. 1 (b)] consists of
sedimentation tanks and
high rate trickling filters, and is suitable for
cities of small and
medium sizes. The third type of treatment plant [Fig. 1 (c)]
a sedimentation tank and an activated
sludge treatment plant, and
is suitable for larger cities, where continuous attendance and
different types of treatment plants contain
different combinations of treatment units. These combinations can also
changed, and some other combination made, depending upon the local
topography and geology will influence the choice of the units to be
For example, the trickling filter plant consumes high head and requires
ground slope to avoid pumping Imholf tanks are vary deep and can not be
constructed economically under adverse underground conditions.
size of the plant will also influence the type of units to be housed in
example, smaller sized plants cannot house such units which require
skilled attendance and supervision, and as such, they should house such
which do not employ complicated mechanical equipment.
treatment units will now be discussed in details.
Screening is the
very first operation carried out at a sewage
treatment plant, and consists of passing the sewage through different
screens, so as to trap and remove the floating matter, such
as pieces of
cloth, paper, wood, cork, hair, fibre, kitchen refuse, fecal solids,
present in sewage. These floating materials, if not removed, will choke
pipes, or adversely affect the working of the sewage pumps. Thus, the
of providing screens is to protect the pumps and other equipments from
possible damages due to the floating matter of the sewage.
preferably be placed before the grit chambers
(described in the next article). However, if the quality of
grit is not of
much importance, as in the case of land fillings, etc., screens may
placed after the grit chambers. They may sometimes be accommodated in
of the grit chambers themselves.
Types of Screens, Their Designs and Cleaning
the size of the openings, screens may be
classified as coarse Screens, medium screens, and fine screens.
screens are also known as
Racks, and the spacing between the Bars (i.e. opening
size) is about 50
mm or more. These screens do help in removing large floating objects
sewage. They will collect about 6 litres of solids per million litre of
The material separated by coarse screens, usually consists of rags,
paper, etc., which will not putrefy, and may be disposed of by
burial, or dumping.
medium screens, the spacing
between bars is about 6 to 40 mm. These screens will ordinarily collect
90 litres of material per million litre of sewage. The screenings
contain some quantity of organic material, which may putrefy and become
offensive, and must, therefore, be disposed of by incineration,
(not by dumping).
shaped coarse and medium screens are now a days
widely used at sewage treatment plants. They are made of steel bars,
parallel to one another at desired spacing on a rectangular steel
are called bar screens. The screens are set in a masonry or R.C.C.
called the screen chamber.
Now a days, these
screens are generally kept inclined at
about 30 to 60° to the direction of flow, so as to increase
area, and to reduce the flow velocity and thus making the screening
effective. While designing the screens, clear openings should have
total area, so that the velocity through them is not more than 0.8 to 1
This limit, placed on velocity, limits the head loss through the
thus, reduces the opportunity for screenings to be pushed through the
collected on bar screens can be removed either
manually or mechanically. Manual cleaning is practised at small plants
hand operated rakes. The inclined screens help in their cleaning by the
stroke of the rake. Large plants, however, use mechanically operated
which move over the screens, either continuously or intermittently.
The cleaning of
screens by rakes will be hindered by cross
bars, if at all provided. They are, therefore, generally avoided.
sometimes classified as fixed or movable, depending
upon whether the screens are stationary or capable of motion.
are permanently set in position. A most
commonly used bar type screen is shown in Fig. 2.
Movable screens are stationary
operating periods. But they can be lifted up bodily and removed from
positions for the purpose of cleaning. A common movable bar medium
screen is a
3 sided cage with a bottom of perforated plates. It is mainly used in
ahead of pumps.
Screens have perforations of
1.5 mm to 3 mm in size. The installation of these screens proves very
effective, and they remove as much as 20% of the suspended solids from
These screens, however, get clogged very often, and need frequent
They are therefore, used only for treating the industrial wastewaters,
treating those municipal wastewater, which are associated with heavy
industrial wastewaters. These screens will considerably reduce the load
further treatment units.
Brass or Bronze
plates or wire mesh is generally used for
constructing fine screens. The metal used should be resistant to rust
The fine screens
may be disc or drum type, and are operated
continuously by electric motors. Fig. 3 shows a typical disc type of
screen, which is cleaned by a cone brush.
Comminutors or Shredders are
devices, which break the larger sewage solids to about 6 mm in size,
sewage is screened through them. Such a device consists of a revolving
drum, through which the sewage is screened (Fig. 4). Cutters mounted on
drum, shear the collected screenings against a comb, until they are
enough to pass through 5 mm to 10 mm wide slots of the drum. These are
arranged in pairs to facilitate repairs and maintenance. Comminutors
recent origin, and eliminate the problem of disposal of screenings, by
the solids to a size which can be processed elsewhere in the plant.
always be preceded by grit chambers to prevent their excessive wear.
Such devises are
used only in developed countries like USA,
and generally not adopted in our country.
Disposal of Screenings
separated by screens is called the screenings.
It contains 85 to 90% of moisture and other floating matter. It may
contain some organic load which may putrefy, causing bad smells and
To avoid such possibilities, the screenings are disposed of either by
or by burial, or by dumping. The dumping is avoided when screenings are
medium and fine screens, and are likely to
contain organic load, as pointed out earlier. The screenings may also
sometimes be broken up by a comminutor and then passed on to the grit
Burning of the
screenings is done in the incinerators, similar
to those used for burning garbage. The process of burning is called Incineration.
The screenings are first dried with suns heat by spreading on
ground or by
compressing through hydraulic or other presses, so as to reduce the
content to about 60%. The incineration is carried out at temperatures
760 to 815°C. This will avoid bad smells.
may also be disposed of by burial. The
process is technically called Composting. In this
screenings are buried in 1 to 1.5 m deep trenches, and then covered
with 0.3 to
0.45 m of porous earth. In due course of time, oxidation reduction of
screenings will take place, and the contents can be used as manure.
of disposing of the screenings is by dumping
them in low lying areas (away from the residential areas) or in large
water, such as sea. Dumping in sea will be
suitable only where strong
forward currents do exist to take the dumped material away from the
The dumping on land for raising low lying areas is
also adopted only
when screenings are from the course screens, and not from the medium or
screens, and as such not containing much organic load.
screenings along with the sewage sludge in a
sludge digestion tank has also been tried, but not found successful.
GRIT REMOVAL BASINS
also called grit channels, or grit basins, are
intended to remove the inorganic particles (specific gravity about
as sand, gravel, grit, egg shells, bones, etc. of
size 2 mm or larger to
prevent damage to the pumps, and to prevent their accumulation in
digestors. Girt chambers are, infact nothing but like sedimentation
designed to separate the intended heavier inorganic materials by the
sedimentation due to gravitational forces, and to pass forward the
organic materials. They may be placed either before or after the
engineers, howevers, prefer to place them before the screens, as to
silting of the screen chambers.
A grit chamber
is an enlarged channel or a long
basin, in which the cross section is increased, so as to
reduce the flow
velocity of sewage to such an extent that the heavy inorganic materials
settle down by gravity, and the lighter organic materials remain in
and, thus, go out along with the effluent of the grit basin. The
point in the design of the grit basins is that the flow velocity should
be too low as to cause the settling of lighter organic matter, nor
should it be
so high as not to cause the settlement of the entire silt and grit
sewage. The flow velocity should also be enough to scour out
organic matter, and reintroduce it into the flow stream. Such a
scourting velocity is, infact, given by the modified Shields formula,
states that Critical scour velocity.
particles of 0.2 mm (d), the
formula gives critical velocity values of 0.11 to 0.25 m/sec. This
limits for optimum flow velocity for design of
grit basins. In practice
a flow velocity of about 0.25 to 0.3 m/sec is adopted for the design of
In order to
prevent large increase in flow velocity at peak
hours, due to increased discharge, and thus, to avoid the scouring of
settled grit particles from the bottom, it is preferable to design the
chambers for D.W.F. (Dry weather flow), and to provide additional units
taking increased discharge at peak hours. If, however, a single unit is
designed, or there are large variations in discharge, then the grit
designed for generating optimum velocity at peak discharge and a
section, such as a proportional flow weir or a
parshall flume (venturiflume),
is provided at the lower (effluent) end of the grit channel, which
varying the flow area of the section in direct proportion to the flow,
thus, helps to maintain a constant velocity in the channel (within the
permissible limits of 5 to 10% over the designed value), even at
It has also been
proved that when a proportioning flow weir
is used as a velocity control device, then a rectangular cross section
required for the grit channel but however, when a pars hall
used as a velocity control device, then a parabolic cross
required for the grit channel, inorder to keep the flow velocity
shown in Fig. 5 (a) and (b).
and detention time provided for a
grit basin are inter dependent, and are based on the considerations of
settling, Velocity of inorganic particles through water. A detention
about 40 to 60 seconds (1 minute) is generally sufficient for a water
about 1 to 1.8 m. After fixing the depth and the detention time we can
design the tank dimensions, as its length will then be equal to
earlier generally two to three separate chambers in
parallel (as shown in Fig. 6.) should be provided one to pass the low
the other to pass (along with the first of course) the high flow. This
also help in manual cleaning of the chambers, as one unit can work
other is shut down for cleaning.
The grit chambers
can be cleaned periodically at about 3 weeks interval, either manually,
mechanically or hydraulically Hand cleaning is done only in case of
plants (of capacity less than about 4.5 million litres per day), while
mechanical or hydraulic cleaning is adopted for larger plants. In manual
cleaning, grit is removed by shovels, etc., by hand in mechanical
cleaning, grit is removed with the help of machines and in hydraulic
cleaning, grit is removed by the force of water jet directed
from a central
point and removed through the pipes in the side walls or bottom of the
The removed grit
may contain some organic matter, and can be
washed prior to its disposal, if necessary, by using certain patented
and the wash water returned to the plant influent. Washed grit may
contain about 1 to 5% of putrescible organic matter.
The silt and
grit, etc. removed by the grit chambers can be
easily disposed of either by burial or burning (incineration) or for
low lying areas by dumping. It cannot be used for preparation of
it contains sufficient organic matter
are nothing but grit chambers designed to flow
with a smaller flow velocity (of about 0.09 m/sec) and longer detention
(about 3 to 4 minutes) so as to separate out not only the larger grit,
but also to separate out the very fine sand particles, etc. Due to
large amount of organic matter will also settle out along with the
sand, etc. This organic material is then separated from the grit by
currents in the tank through baffles, or by controlled aeration of the
through the tank. The rising air bubbles will then separate the lighter
matter from the descending
grit. The grit is removed continuously by means of scraper mechanism.
details of detritus tanks remain the same as those of a grit chamber.
Design of ParaboIic Grit Chamber provided with a Par shall
Parshall Flume. A parshall
flume, also called a
venturi flume, is a horizontally constricted vertical throat in an open
channel, as shown in Fig. 8. Such a venturi flume, as we know, can be
used as a
discharge measuring device, and also as a velocity control device. This
is made use of for its latter purpose in a grit channel.
flume, as a velocity control device, is
preferable to the proportional flow weir, etc., as it involves
loss, and can also work under submerged conditions for certain limits.
of submergence are 50% in case of 0.15 m throat width, and
70% for wider
throat widths upto 1 m. Another advantage of a venturiflume is that one
section can be installed for 2 to 3 grit chambers. Moreover, the
is a self cleaning device, and there is no problem of clogging.
TANKS FOR REMOVING OILS AND GREASE
are sometimes employed for removing oils and
grease from the sewage, and placed before the sedimentation tanks. They
therefore, used where sewage contains too much of grease or oils, which
fats, waxes, soaps, fatty acids, etc. These materials may enter into
from the kitchens of restaurants and, houses, from motor garages, oil
refineries, soap and candle factories, etc. They are, thus, normally
large amounts in the industrial wastewaters.
If such greasy
and oily matter is not removed from the sewage
before it enters further treatment units, it may form unsightly and
scums on the surface of the settling tanks, or interfere with the
sludge treatment process, and inhibit biological growth on the
These oil and
greasy materials may be removed in a skimming
tank, in which air is blown by an aerating device through the bottom.
rising air tends to coagulate and congeal (solidify) the grease, and
to rise to the surface (being pushed in separate compartments), from
details of a skimming tank are shown in Fig. 10.
It consists of a long trough shaped structure divided into two or three
compartments by means of vertical baffle walls (having slots in them)
short distance below the sewage surface, as shown. The baffle walls
pushing the rising coagulated greasy material into the side
(called stilling compartments). The rise of oils and grease is brought
blowing compressed air into the sewage from diffusers placed
bottom of the tank. The collected greasy materials are removed (i.e.
off) either by hand or by some mechanical equipment. It may then be
either by burning or burial.
TREATMENT OF INDUSTRIAL EFFLUENTS
obtained from industries are generally much more
polluted than the domestic or even commercial Wastewaters. Still,
several industrialists try to discharge their effluents into our
streams, through unauthorized direct discharges. Such a tendency on the
the industries may pollute the entire river water to a grave extent,
making its purification almost an impossible task. Sometimes, the
discharge their polluted wastewates into municipal sewers, thereby
task of treating that municipal sewage, a very difficult and a costly
generally prevented by legal laws, from discharging their untreated
It therefore, becomes necessary for the industries to treat their
in their individual treatment plants, before discharging their
on land or lakes or rivers, or in municipal sewers, as the case may be.
Methods of Treating Industrial Wastewaters
wastewaters, as pointed out above, usually contain
several chemical pollutants and toxic substances in too large
characteristics of the produced wastewater will usually vary from
industry, and also vary from process to process even in the same
industrial wastewaters cannot always be treated easily by the normal
treating domestic wastewaters, and certain specially designed methods
of methods may be necessary.
In order to
achieve this aim, it is generally always
necessary and advantageous to isolate and remove the troubling
the wastewaters, before subjecting them to usual treatment processes. The
sequence of treatment processes adopted should also be such as to help
useful by products. This will help economize the pollution
measures, and win encourage the industries to develop such treatment
the quantum, concentration, toxicity and
presence of non biodegradable organics in an
industrial wastewater, its
treatment may consist of any one or more of the following processes
Chemical treatment and
are briefly discussed below
consists of holding
the waste water for some pre determined time in a continuously mixed
produce a uniform wastewater. Such an arrangement will, of course be
when the wastewater produced by the industry varies in characteristics
quantity over the entire day.
the excessive acidity or alkalinity of the particular wastewater, by
or acid, respectively, to the wastewater. This may be achieved either
in the equalisation
tank, where possible, or a separate neutralisation
tank may be used.
treatment consists of
separating the suspended inorganic matter by physical processes, like
as we know, is employed to separate
heavier settleable solids, and hence sedimentation tank may be provided
when the wastewater contains a high percentage of such heavy inorganic
Floatation. Floatation consists of
creation of fine air bubbles in the waste tank, by introduction of air
tank from the bottom. The rising air bubbles, attach themselves to the
suspended particles, increasing their buoyancy, and finally lifting
liquid surface for consequent removal by skimming.
treatment is often
necessary before the biological treatment, though sometimes, it may not
required at all. Sometimes, it may however, serve as the final stage of
treatment is a costly and expensive exercise,
care should be taken to see, if it could be avoided altogether, to
treatment is used to recover the dissolved organic
matter from the wastewater, and may consists of one or more of the
osmosis or hyper filtration
coagulation or chemical precipitation
processes are briefly pointed out below
reverse osmosis treatment process, the wastewater containing dissolved
are filtered through semipermeable membranes at a pressure higher than
osmotic pressure, as discussed in article 9.29.6(3) Vol. 1. Such a
requires pre treatments like (a) activated
carbon adsorption or
precipitation followed by some kind of
electrodialysis treatment process, dissolved salts from wastewater are
separated by passing an electriccurrent through the wastewater tank,
with ion exchange membranes, as discussed in article 9.29.6(2) Vol. I. This treatment
process also requires
some pretreatment, as is required in reverse osmosis process.
chemical oxidation, chemicals like chlorine and
ozone are used to
reduce substances like ammonia and cyanid
etc. from the
wastewater, in addition
BOD load on biological treatments.
coagulation, as we know, is adopted in treating raw water supplies, and
in sedimentation of unsettleable micro and colloidal impurities, which
absorbed in the gelatinous flocs, formed by the chemical reactions
coagulants, or between the coagulant and the alkalies present in raw
treatment of industrial wastewaters is necessary,
when they contain large quantities of biodegradable substances. Such
treatment may be used either with or without acclimatisation.
on wastewater for determining its
ratio, will help in determining the type of
treatment required. Say for example, if this ratio is more than 0.6,
wastewaters are biologically treatable without acclimatisation and if
is less than 0.6 and upto 0.3, then acclimatisation is needed for
treatment and if the ratio is less than 0.3, biological treatment may
consists of the gradual exposure of the waste
water in increasing concentration to the seed or initial
population under a controlled condition.
The criteria for
selecting a particular conventional
biological treatment process, may differ
for different types of
industrial was tewaters.
parameters for a given type of industrial wastewater may be determined
In the absence
of any actual test data, the performance data
of a similar type of industrial wastewater may be used for design.
It has also been
observed that most of the industrial
wastewaters do not contain sufficient nutrients for micro biological
hence nutrients like urea (containing nitrogen), superphosphates
phosphorous) etc. may have to be added to the reactors. For balanced
micro organisms in a biological treatment reactor, the ratios of BOD
Phosphorous should be 100 5 1 for aerobic systems, and 100 2.5 0.5 for
cases, special types of micro organisms are found
to cause better biological oxidation, since commonly available
population may fail to achieve oxidation.
be handled with special care and specific treatments. Say for example,
wastes, like cyanides, formaldehydes, phenols, etc. may need
of special type of bacteria. Toxic metals, like copper, zinc, chromium
need pre separation chemically, as otherwise, they may interfere with
biological oxidation by tying up the enzymes, essentially required for
from weak wastewaters may also sometimes help in reducing problems in
industrial wastewater treatment plants.
it can be stated
that the selection of a sequence of particular treatment processes
the characteristics of the wastewaters, and also upon the permissible
requirements of the effluents.
processes needed for
different industries will, therefore, generally vary from one industry
made for treating
industrial wastewaters, simply by biological methods, though cheaper,
generally failed in the absence of making efforts for pre recovery of
pollutants or chemicals from the wastewater by using chemical methods.
use of simple biological methods have fairly succeeded in industries, like
fruit processing, dairies, slaughterhouses, and
prior to biological treatment, for separation of troubling pollutants,
chromium, arsenic, cyanide, mercury, several nitrogenous substances,
etc., is very necessary and important for industries like fertilizers,
and pigments, pesticides, electroplating, paper and pulp, etc.
treatments to the wastewaters of such industries, before
subjecting them to
the biological treatment is thus, the prime requirement for designing
planning the treatment plant for a particular industry.
scale re use of the
treated water in the industry is another important factor, which must
considered, while deciding the sequence of treatment processes for a
industry. Such a possible reuse, if can be made possible, will help in
scale economy in the industry.
certain typical Indian industries along with suggested
treatments with flowcharts
are broadly reflected in Tables 11.1 and 11.2 so as to serve as a first
guide to the design engineers. For detailed planning and design of the
treatment works, however, the design engineer will have to be well
with the detailed operations and stages involved in the given industry,
the characteristics of the wastewaters generated at different places in
industry, and to finally work out the most satisfactory and economical
of treatment processes for that industry, using his intuition,
experience, and of course, ingenuity.
INDUSTRIAL WASTE WATER EFFLUENTS
huge quantities of the nations waters and are
the major factor in the continuing rise in water pollution. They
trillion gallons of water but,
prior to discharge, treat less than 5 trillion gallons. In terms of a
pollution parameter, BOD, the waste generated by industries is
that generated by a
over 360 million people. Even more undesirable than the BOD loads of
effluents are the enormous quantities of mineral and chemical wastes
factories which steadily become more complex and varied. They include
such as iron, chromium, nickel, and copper salts such as compounds of
calcium, and magnesium acids such as sulfuric and hydrochloric
and brines phenols cyanides ammonia toluene blast furnace wastes
varieties of suspended and dissolved solids and numerous other waste
These wastes degrade the quality of receiving waters by imparting
and color and through excess mineralization, salinity, hardness, and
plant and animal life.
The variety and
complexity of inorganic and organic
components contained in industrial effluents present a serious liquid
treatment control problem in that the pollution and toxicity effects of
these constituents are of greater
significance than those found in domestic
waste water treatment technology which is often
barely adequate for existing waste types offers even less promise of
type and degree of treatment which will be required in the near future.
Therefore, industrial pollution control technology must be developed to
effective and economical control of pollution from such varied
those producing metals and metal products, chemicals and allied
and allied products, petroleum and coal products, food and kindred
textiles and leather goods.
Several of the
more common terms encountered in sewage treatment
technology are given below to assist the reader in developing his
this field and in understanding what follows.
organic matter from
sewage by saturating it with air and biologically active sludge.
Adsorption is an advanced
way of treating
wastes in which carbon removes organic matter not responsive to
or biological treatment.
Aeration tank serves as a
chamber for injecting
air into water.
Algae are plants which
grow in sunlit waters.
They are a food for fish and small aquatic animals and, like all
oxygen into the water.
Bacteria are the smallest
living organisms which literally eat
the organic parts of sewage.
BOD, or biochemical
oxygen demand, is the amount of oxygen
necessary in the water for bacteria which consume the organic sewage. It
is used as a measure in telling
how well a sewage treatment plant is working.
Chlorinator is a device for
adding chlorine gas
to sewage to kill infectious germs.
Coagulation is the clumping
together of solids
to make them settle out of the sewage faster. Coagulation of solids is
about with the use of certain chemicals such as lime, alum, or
Combined sewer carries both
sewage and storm water
Comminutor is a device for
the catching and
shredding of heavy solid matter in the primary stage of waste treatment.
Diffused air is a technique
by which air under
pressure is forced into sewage in an aeration tank. The air is pumped
the sewage through a pipe and escapes through holes in the side of the
Digestion of sludge takes
place in heated
tanks where the material can decompose naturally and the odors can be
Effluent is the liquid
that comes out of a treatment plant
after completion of the treatment process.
Electrodialysis is a process by
attracts or draws the mineral salts from sewage.
Floc is a clump of
solids formed in sewage when certain
Flocculation is the process
by which certain
chemicals form clumps of solids in sewage.
Incineration consists of
burning the sludge to
remove the water and reduce the remaining residues to a safe,
The ash can then be disposed of safely on land, in some waters, or into
or other underground locations.
Interceptor sewers in a
combined system control
the flow of the sewage to the treatment plant. In a storm, they allow
the sewage to flow directly into a receiving stream. This protects the
treatment plant from being overloaded in case of a sudden surge of
the sewers. Interceptors are also used in separate sanitation systems
collect the flows from main and trunk sewers and carry them to the
Ion is an
electrically charged atom or group of atoms
which can be drawn from waste water during the electrodialysis process.
Lateral sewers are the pipes
that run under the
streets of a city and
into which the
sewers from homes or businesses empty.
scientifically constructed ponds in which
sunlight. algae, and oxygen interact to restore water to a quality
effluent from a secondary treatment plant.
aeration begins by
forcing the sewage up
through a pipe in a tank. Then it is sprayed over the surface of tank,
the waste stream to absorb oxygen from the atmosphere.
Microbes are minute
living things, either plant or animal. In
sewage, microbes may be germs that cause disease.
Mixed liquor is the name
given the effluent that
comes from the aeration tank after the sewage has been mixed with
sludge and air.
Organic matter is the waste
from homes or industry
which is of plant or animal origin.
Oxidation is the consuming
or breaking down
of organic wastes or chemicals in sewage by bacteria and chemical
Oxidation pond is a manmade
lake or body of water
in which wastes are consumed by bacteria. It is used most frequently
waste treatment processes. An oxidation pond is basically the same as a
treatment removes the
material that floats or
will settle in sewage. It is accomplished by using screens to catch the
floating objects and tanks for the heavy matter to settle in.
Pollution results when
vegetable, or mineral reaches water, making it more difficult or
use for drinking, recreation, agriculture, industry, or wildlife.
chemicals used to
speed the removal of solids from sewage. The chemicals cause the solids
coagulate or clump together more rapidly than chemicals like alum or
lakes, oceans, or other
water courses that receive treated or untreated waste waters.
Salts are the minerals
that water picks up as it passes
through the air, over and under the ground, and through household and
Sand filter removes the
organic wastes from
sewage. The waste water is trickled over the bed of sand. Air and
decompose the wastes filtering through the sand. The clean water flows
through drains in the bottom of the bed. The sludge accumulating at the
must be removed from the bed periodically.
in a separate
system, are pipes in
a city that carry only domestic waste water. The storm water runoff is
care of by a separate system of pipes.
treatment is the second
step in most waste treatment
systems in which bacteria consume the organic parts of the wastes. It
accomplished by bringing the sewage and bacteria together in trickling
or in the activated sludge process.
tanks help remove
solids from sewage. The
waste water is pumped to the tanks where the solids settle to the
float on top as scum. The scum is skimmed off the top, and solids on
are pumped out to sludge digestion tanks.
Septic tanks are used to
treat domestic wastes.
The underground tanks receive the waste water directly from the home.
in the sewage decompose the organic waste and the sludge settles on the
of the tank. The effluent flows out of the tank into the ground through
The sludge is pumped out of the tanks, usually by commercial firms, at
Sewers are a system of
pipes that collect and deliver waste
water to treatment plants or receiving streams.
Sludge is the solid
matter that settles to the bottom of
sedimentation tanks and must be disposed of by digestion or other
complete waste treatment.
Storm sewers are a separate
system of pipes that
carry only runoffs from buildings and land during a storm.
are the wastes
that will not sink
or settle in sewage.
is a bed of
rocks or stones. The
sewage is trickled over the bed so the bacteria can break down the
wastes. The bacteria collect on the stones through repeated use of the
plant is a series of
filters, and other processes by which pollutants are removed from water.
There are at
present two basic
methods of treating wastes. They are called primary and
primary treatment, solids are allowed to settle and are removed from
Secondary treatment, a further step in purifying waste water, uses
As sewage enters
a plant for primary treatment it flows
through a screen which removes large floating objects such as rags and
that may clog pumps and pipes. The screens vary from coarse to fine
consisting of parallel steel or iron bars with openings of about half
or more to screens with much smaller openings.
generally placed in a chamber or channel in a
position inclined with respect to the flow of the sewage to make
easier. The debris caught on the upstream surface of the screen can be
off manually or mechanically. Some plants use a device known as a
which combines the functions of a screen and a grinder. These devices
then cut or shred the heavy solid material. In this method the
material remains in the sewage flow to be removed later in a settling
After the sewage
has been screened, it passes into what is
called a grit chamber where sand, grit, cinders, and small stones are
to settle to the bottom. A grit chamber is especially important for
combined sewer systems because it will remove the grit or gravel that
off streets or land during a storm and ends up at the treatment plants.
unwanted grit or gravel from this process is usually disposed of by
land near a treatment plant.
In some plants,
another screen is placed after the grit
chamber to remove any further material than might damage equipment or
with later processes.
screening completed and the grit removed, the sewage
still contains suspended solids. These are minute particles of matter
be removed from the sewage by treatment in a sedimentation tank. When
of the flow of sewage through one of these tanks is reduced, the
solids will gradually sink to the bottom. This mass of solids is called
have been devised for removing sludge from
the tanks. In older plants it was removed by hand. After a tank had
service for several days or weeks, the sewage flow was diverted to
tank. The sludge in the bottom of the out of service tank was pushed or
with water to a nearby pit and then removed for further treatment or
plants built within the past 30 years have
included mechanical means for removing the sludge from sedimentation
some plants it is removed continuously and in others at intervals. To
the primary treatment the sludge free effluent is chlorinated to kill
bacteria and then discharged into a stream or river. The chlorination
helps to reduce odors.
Although 30 per
cent of the municipalities in the United
States give only primary treatment to their sewage, this process by
considered entirely inadequate for most needs. Municipalities and
faced with increased amounts of wastes and wastes that are more
remove from water, have turned to secondary and even advanced waste
treatment removes up to 90 per cent of the organic
matter in sewage by making use of the bacteria it contains. The two
processes for secondary treatment are trickling filters and
sludge process. The effluent from the sedimentation tank in
stage of treatment flows or is pumped to a facility using one or the
Filter. A trickling
filter is simply a bed
of stones from three to ten feet deep through which the sewage passes.
gather and multiply on these stones until they can consume most of the
matter in the sewage. The cleaner water trickles out through pipes in
bottom of the filter for further treatment. The sewage is applied to
the bed of
stones in two principal ways. One method consists of distributing the
intermittently through a network of pipes laid on or beneath the
surface of the
stones. Attached to these pipes are smaller, vertical pipes which spray
sewage over the stones. Another much used method consists of a vertical
the center of the filter connected to rotating horizontal pipes which
sewage continuously upon the stones.
Process. The trend
today is toward the use of the activated sludge process instead of
filters. The former process speeds up the work of the bacteria by
and sludge heavily laden with bacteria into close contact with the
In the activated
sludge process the sewage from the settling
tank in primary treatment is pumped to an aeration tank where it is
air and sludge loaded with bacteria and allowed to remain for several
During this time, the bacteria break down the organic matter. From the
tank the sewage, now called mixed liquor, flows to another
to remove the solids. Chlorination of the effluent completes the basic
secondary treatment. The sludge, now activated with additional millions
bacteria and other tiny organisms, can be used again by returning it to
aeration tank for mixing with new sewage and ample amounts of air.
sludge process, like most other techniques, has
advantages and limitations. The size of the units needed is small so
require comparatively little land space. Also, the process is free of
odors. But it is more costly to operate than the trickling filter, and
sometimes loses its effectiveness when faced with difficult industrial
supply of oxygen is necessary for the activated sludge
process to be effective. Air is mixed with sewage and biologically
sludge in the aeration tanks by three different methods. The first,
is accomplished by drawing the sewage from the bottom of the tank and
it over the surface, thus causing the sewage to absorb large amounts of
from the atmosphere. In the second method, large amounts of air under
are piped down into the sewage and forced out through openings in the
third method is a combination of mechanical aeration and the forced air
The final phase
of the secondary treatment consists of the
addition of chlorine to the effluent coming from the trickling filter
activated sludge process. Chlorine is usually purchased in liquid form
injected into the effluent as a gas 15 to 30 minutes before it is
into a watercourse. If done properly, chlorination will kill more than
cent of the harmful bacteria in an effluent.
treatment is used when the
waste stream must meet strict requirements governing recreational
water, or must approach drinking water standards. This may require one
several of the following processes slow filtration rapid filtration
activated carbon adsorption by activated carbon application of ozone
chlorination or use of other oxidizing chemical or lagooning.
At each plant
the question may arise as to what degree of
treatment is actually required. Water quality criteria imposed by
waste stream discharges may vary widely. Even within the same state, or
particular river basin, different limits for each of the contaminants
set for the section of the river under consideration.
LAGOONS AND SEPTIC TANKS
There are many
well populated areas
in the United States that are not served by any sewer systems or waste
plants. Lagoons and septic tanks are the usual alternatives in such
A septic tank is
simply a tank buried in the ground to treat
the sewage from an individual home. Waste water for the home flows into
tank where bacteria in the sewage break down the organic matter and the
water flows out of the tank into the ground through subsurface drains.
Periodically the sludge or solid matter in the bottom of the tank must
removed and disposed of.
In a rural
setting, with the right kind of soil and the
proper location, the septic tank is a safe and effective means of
strictly domestic wastes. Septic tanks should always be located so that
the effluent can seep into wells used for drinking.
Lagoons or, as
they are sometimes called, stabilization or
oxidation ponds, also have several advantages when used correctly. They
give sewage primary and secondary treatment or they can be used to
other processes. A lagoon is a scientifically constructed pond, usually
to five feet deep, in which sunlight, algae, and oxygen interact to
water to a quality equal to or better than effluent from secondary
Changes in the weather affect how well a lagoon will break down the
When used with
other waste treatment processes lagoons can be
very effective. A good example is the Santee, California, water
project. After conventional primary and secondary treatment by
sludge, the towns waste water is kept in a lagoon for 30 days. Then the
effluent, after chlorination, is pumped to land located immediately
series of lakes and allowed to trickle down through sandy soil into the
The resulting water is of such good quality that the residents of the
swim, boat, and fish in the lake water.
TYPES OF INDUSTRIAL WASTES
wastes exceed if one includes the steam electric
generating industry the combined total of all other liquid wastes of
activities in terms of volume, probably averaging over 200 billion
day and they contain thousands of potentially polluting elements and
often in high concentrations.
Because of the
large gaps in the information base, it is not
possible to hypothesize with any certainty that industrial wastes are
damaging on a national basis than the effects of unconstrained runoff
the Western States, damages from intense irrigation and water
practices may or may not exceed damages caused by industrial wastes.
need be no hesitation in making the judgement that for the nation as a
routine discharges of industrial wastes exceed in polluting impact,
domestic wastes, urban runoff, mining, transportation, or accidental
Their sheer volume and the directly toxic influences of many kinds of
industrial wastes (acids, heavy metals, some persistent organic
sufficient to justify the judgement, even though no comprehensive
waste inventory has been compiled.
variety of industrial pollutants argues against an
attempt to catalog them, but for the purposes of general description we
recognize at least five distinct categories of wastes from industrial
materials wasted to water by industrial processes have been calculated
amount to 29.7 billion pounds of five day chemical oxygen demand (BOD5) per year having an aggregate
discharged strength, after treatment, of
11 billion pounds of BOD5 per
year. The estimate, then, places the
oxygen demand of industrial wastes before treatment at 3.5 times that
sewered domestic wastes, and the after treatment strength at 5.5 times
the after treatment strength of domestic wastes.
and suspended solids wasted to water by industrial processes are
amount to about 24 billion pounds per year before treatment, over 7
pounds after treatment, with the relationship between industrial and
wastes quite similar to that for BOD.
materials which impart acidity or alkalinity or which contain
added to water in undeterminable amounts by manufacturing activities.
these are directly toxic. Such materials cause a permanent change in
quality that is not reduced by natural assimilation. Dilution and
neutralization the latter usually adding to the concentration of total
dissolved solids are the only remedies in such cases.
the amount of about 9,152,000 million Btus is currently discharged
into water by industrial processes, most of it by the electrical
industry. Although some control is exercised through recycling
particularly in arid areas, the major part of the nations industrial
water is discharged directly to streams. Waste heat is a pollutant in
reduces the utility of water for additional cooling and may radically
aquatic ecology. It also contributes to the polluting effect of water
materials by accelerating chemical reaction rates and by reducing the
solubility of gases including oxygen.
compounds occur in water as a result
of industrial processes, either through direct discharge by
producing such compounds (e.g., factories engaged in the
production of pesticides or pharmaceuticals),
by the synergistic interaction
materials in water, or through the food chain. Again, no quantitative
assessment is available, and for the second category of toxins, even
determining probability of occurrence cannot be attempted.
general categories of pollutants are included
most of the possible sources of recognized water quality problems. Only
and viral presences fall outside of the group of polluting effects to
industry contributes materially. (Although these are not entirely out
range of parameters to be included in the polluting activities of
packing plants, and other food processors in lesser measure, contribute
presence and viability of water borne bacteria.) Manufacturing must
the top, and it very probably leads, in any list of potential sources
And for any
possible strategy of water pollution control,
industrial wastes are of critical importance. Over the last ten years,
amount and composition of industrial output has been such that for
incremental pound of BOD that has been generated directly by population
increase, twenty more have been generated by increased industrial
Increased per capita production is the essence of improvement in the
of living, and the production of wastes is an inescapable concomitant
production of goods. So that as population and per capita production
to advance, we can anticipate a continuing and unavoidable advance in
volume of wastes to be managed.
industry has added rapidly to its inventory of
waste treatment facilities over the last decade and a half, and it
provision for waste treatment is routinely designed into new plants and
additions. Estimated daily discharge of BOD from all sources in 1968
greater than in 1957, in spite of significant increase in population,
incidence of sewering, and industrial production. While additional
municipal wastes had an unquestionable influence on the economys
contain the level of waste discharges, the preponderance of industrial
and their more rapid rate of increase would have made containment
incremental industrial waste treatment effectiveness had not occurred
advanced rates than incremental industrial production.
Strategies for Management of Industrial Wastes
public sector, where only variations on a single
theme of waste treatment are possible, industrial pollutants can be
through at least four distinct strategies. (1) The obvious procedure is
installation of industrial waste treatment plants. Treatment
through factory operated plants is estimated to have been increasing at
per cent annual rate (in terms of BOD reduction) since the early
(2) A second and increasingly prevalent procedure is to discharge
wastes to public systems for treatment. The aggregate amount of BOD
industrial sources discharged to public sewers is estimated to have
at an 8.4 per cent annual rate through the late nineteen sixties and
is estimated to account for half of the current BOD loading to
area waste treatment plants. (3) Process modification and changed
formulations are probably the most effective as well as the most
means of reducing wastes. The outstanding example is the shift of the
paper industry from the sulfite pulping process to the sulfate process,
calculated to have been responsible for a greater reduction in the
level of BOD than the combination of all of the waste treatment plants
U.S. More recent example include the rising prevalence of cooling water
development of biodegradable detergents, and substitution of
hydrochloric acid for sulphuric acid in metal pickling liquors. (4) In
absence of alternative control procedures, industry has on occasion
product line or production procedure. At the present time, phosphorus
detergents, DOT, mercury battery production of chlorine and alkali, and
process for production of soda ash all seem likely candidates for
QUANTITY OF INDUSTRIAL WASTES
Table. 1 shows
reported quantities of industrial waste waters
discharged in 1967. Waste load estimates, based upon an estimate of the
quantity of pollutant per product unit, indicate that the chemical,
food and kindred industrial groups generated about 90 per cent of the
industrial wastewater before treatment.
statistics on net waste load discharges are not
completely available. However, indications are that the extent of
waste water treatment is not greater than that currently practiced for
municipal waste waters.
wastes differ markedly in chemical composition,
physical characteristics, strength, and toxicity from wastes found in
domestic sewage. Every conceivable toxicant and pollutant of organic
inorganic nature can be found in industrial waste waters. Thus, the BOD5 or
solids content often are not adequate
indicators of the quality of industrial effluents. For example,
wastes frequently contain persistent organics which resist the
treatment procedures applied normally to domestic sewage. In addition,
industrial effluents require that specific organic compounds be
that trace elements be removed as part of the treatment process.
It is therefore
necessary to characterize each industrial
waste water to permit comparative pollutional assessments to be made
individual industries as well as industry groups. Characterization will
classifying the components of industrial waste waters into as few as
classes of pollutants to more readily collate pollution statistics and
evaluate economics of methods of treatment as well as to project least
methods. Proposed generalized basic classification parameters are BOD,
and TDS into which all known pollutants can be classed. Also required
establishment of a relative pollution comparative index for all
pollutants. This index, in combination with the known characteristics
volume of a waste water, will determine the relative gross pollution
of all industrial wastes and establish a basis for comparing the
pollution from different industries.
Table 3 presents
permissible criteria for surface water for
public supplies as obtained from the Report of the Committee on Water
Criteria, April 1, 1968. The addition of an assumed BOD5 value
of 5 mg/l to these criteria permits
comparisons of the listed pollutants to be made against a unit of BOD.
these circumstances it is relatively apparent that pollutants such as
and phenol (on a mg/l concentration equivalent basis) are 5000 times
critical as pollutants than BOD. Further work in this area will permit
establishment of more accurate priorities in terms of our nations most
industrial groups and industries suspected of
making significant contributions to water pollution. These have been
on the basis of a process water intake of at least 1 billion gallons
and with regard to the potential for pollution from the process use of
number approximately 150 and potentially
represent equally numerous waste waters of significantly different
characteristics for which treatment technology must either be developed
upgraded. The inter changeability of treatment technology between
of waste waters is anticipated.
A wide spectrum
of technology is available for controlling
and treating industrial water pollution. Some of the more important
and unit processes are given in Table 5.
In spite of the
complexity and magnitude of industrial
pollution, initial estimates of the costs for clean waters from
sources have been made. Table 2 gives the types of treatments and costs
industries, while Table 3 presents the estimated industrial capital
requirements to abate pollution by 1973 to the extent of providing 85
treatment effectiveness. It is seen that the capital requirements for
are substantially less than the estimated capital requirements for
treatment or collection facilities for separating combined sewers,
gross pollution load contributed is substantially greater than either.
indicates that the average cost of industrial waste treatment is
less than for municipal waste treatment when based on treatment cost
BOD. If these estimates are reasonably accurate it would appear that
most part industrial pollution control to an equivalency with secondary
is within reach at a reasonable cost.
waste water treatment are However by product
recovery and utilization techniques can reduce the cost of treatment
frequently prove to be less expensive than other methods of disposal.
ultimately may be the most valuable product
due to supply shortages, increasing water supply costs, increasing
costs, and mounting municipal sewerage charges. The recovery of product
useable water, and thermal energy are key methods of reducing over all
treatment costs and must always be considered.
waste streams can be eliminated or significantly
reduced by process modifications. One notable example is the
save rinse and spray rinse tanks in plating lines. This measure brings
substantial reduction in waste volume as well as a net reduction in
RECLAMATION OF TEXTILE EFFLUENTS
Phenols due to
their wide spread
usage are often found in the effluents from certain industrial plants.
examples of their usage include the intermediates in the production of
plastics, drugs dyes etc. Effluents of coking plants, brown coal
plants, pulps and paper industry, textile processing plants are the
source of phenols in the environment. Thus a wide variety of phenols
introduced into aquatic environment. Chlorinated phenols are one of the
environmentally harmful compounds, having been proved to be toxic to
organisms even at 0.1 ppm level. Furthermore, 0.01 ppm level of
suffices to impart an extremely disagreeable taste and odour to water.
becomes necessary to process such waters in order to eliminate phenols.
of phenols and chlorinated phenols by activated charcoals has been
the most efficient process. In view of the high cost and tedious
the regeneration of activated carbon there is a continuing search for
efficient adsorbents. Recently, we have reported some guar derivatives
potential utility in removing colour from the textile effluents. As a
our research programme for the reclamation of textile effluents we
the sorption and desorption characteristics of phenol and some
the guar derivatives. These phenols are added to the thickenings used
textile printing as preservative.
Adsorbents. The adsorbents
used in this study
are quaternary aminised trimethyl and tripropyl aminohydroxypropyl
referred onwards as TMAHP, TEAHP and TPAHP guars. These were
Phenols. Phenol, 2
chlorophenol, 2, 4 dichloro phenol, 2,4.6 trichlorophenol
and pentachlorophenol were of
LR grade and were purified
distillation or by repeated crystallisation, there purity was chec ked
samples of textiles
effluents were collected from two open drains of Jodhpur industrial
area at a
specific point marked for this purpose. The effluents were collected in
bottles by standard procedure. The effluents were highly coloured,
foul smelling. The detailed analysis of it has been, already, reported.
other chemicals were of Analar grade and were used as such. All the
were prepared in double distilled water obtained from an all glass
technique. The adsorption
obtained by agitating 0.05 to 0.5 g of the adsorbent with 100 ml
solution of phenols in skrew cap jars. The agitation was continued for
at ambient temperature (25 + 0.2°C). The initial pH of the solution was
adjusted by adding requisite amount of dilute acid or alkali solution.
equilibrated solutions were centrifuged for 10 min at 10,000 RPM in a T
model (GDR) centrifuge and analysed for the residual
phenol concentration by 4 aminoantipyrene method as described in ASTM.
The waste water
samples were allowed to stand for 4 hr
supernatant liquid was decanted,
adjusted for pH and 100 ml of it was
agitated for 1 hr with the different amount of guar
The waste waters
were than centrifuged
and analysed for residual total phenol concentrations by 4 amino
method using Shimadzu model 240 spectrophotometer.
Results and Discussion
guar derivatives show favourable adsorption
for phenol and chlorophenols from their aqueous solutions. The sorption
desorption of phenols in our case may be better explained using
Effect of pH. The
introduction of trialkylamino substituent on to guar imparts it a
basic an ion exchange character that permit the adsorption of phenol
ion/molecule by the ion exchange process over a wide range of pH 3 10.
effect of pH on the adsorption of phenol on guar derivatives was
for 2, 4 dichlorophenol
pentachlorophenol on TMAHP guar in the pH range 3.5 10.0. The values of K and 1/n at
different pH were
calculated from the linear
log x/m and logC, these are given in the Table 2. From these values it
apparent that the adsorption is favoured in the pH range of 4 7 (Fig.
is probably due to the neutralisation of the anionic sites and negative
potential of the surface of guar derivatives at lower pH. The reduced
adsorption at higher pH may be attributed to
the abundance of hydroxyl ion and
consequent ionic repulsion between the surface partial negative charge
Effect of the
initial phenol concentration. The effect
of the initial phenol concentration on the sorption and desorption
the guar derivatives was investigated for 2, 4 dichlorophenol and
at 50 and 100 mg/1 initial concentrations.
The values of K
and 1/n were calculated from the linear plots
of log x/m and log C (Fig. 3). The adsorption capacity, K, was found
the initial lower concentration of phenol concerned. This appears due
larger adsorbent surface available to the phenolate ions at lower
with textile effluents the adsorption of total phenol in the textile
on TMAHP guar was studied at pH 3,4 and 8.5. The percentage decrease in
total phenol concentration in the effluent was plotted against the
TMAHP guar added. The per cent decrease in the phenol concentration was
proportional to the amount of the guar derivative up to a certain
then approaches to a limiting value (Fig. 4). The removal was maximum
at pH 4.
This is in accordance to our previous results obtained for the
anionic dyes and phenols on TMAPH guar. Approximately 70 90% of the
phenol was removed in the first half an hour and no significant removal
The removal of
the individual phenol by the guar derivative
was evaluated by treating 1litre textile effluent with TMAHP guar at pH
estimated the residual phenol concentration by high performance liquid
chromatography (HPLC). The textile effluent was subjected to the
with methylene chloride before and after treatment with guar
separately, the extract was then concentrated and re dissolved in
isocratic elutions were made with mobile phase being methanol water
(5545, v/v) at a flow rate of 1 ml per minute. The detection limit of
detector was kept 2, as calculated from the noise to signal ratio. Fig.
the chromatographic separation of the phenolic compounds in the
chloride extract. These results show that all the chlorophenols are
equally well and the derivative show no preferential adsorption to a
phenol. The per cent decrease in the concentration of individual phenol
evaluated from the calibration curves, obtained by chromatographing
sample of phenol and chlorophenols under identical experimental
These values have been given in Table 3.
A PROCESS FOR UPGRADING PAPER MILL EFFLUENT BY WATER HYACINTH
A novel and
effective low cost treatment for pulp and paper mill
effluent is discussed in this paper. The effluent is treated in
lagoons with water hyacinth, Eichhornia crassipes (Mart)
abundantly in tropical and humid countries of the world. Since large
effluent are generated in a pulp and paper mill, the need for an
economic and simple process for its treatment is of primary
the paper industry.
Some of the
conventional methods of treatment, i.e.,
activated sludge, Trickling filteration and stabilization lagoons,
well known. Due to heavy capital investment and high operational costs,
methods are generally uneconomical to install and operate. Even the low
waste treatment process based on lagoon stabilization requires
areas since the detention time necessary to achieve the desired
reduction is very high, ranging from 30 to 40 days, has been observed
several investigators that water hyacinth possesses the ability to
substantially reduce the concentrations of organic matter, minerals and
metals present in the waste waters.
which has rapidly spread throughout the warm
regions of the world, is considered as one of the most noxious weeds
problem in its eradication. However, this weed possesses good potential
reduction of pollution load of sewage and industrial effluents, and
also as a
source of energy food and livestock food, fertilizers, and other
Wolverton and McDonald have rightly mentioned that the neglected water
has now begun to gain its respectability by offering a relatively
economically attractive solution to some of the most pressing problems.
atropical plant of exquisite beauty with
broad glossy green leaves and light lavender flowers splotched with
yellow, is found in ditches, ponds and streams. The plant is highly
and reproduces mainly by vegetative offsprings. Its growth rate is so
it can double its number every 8 10 days in warm, nutrient enriched
forming a huge floating mat.
Details of life
cycle of water hyacinth have been studied.
Its ecological adoptibility throughout the warm regions of the world
reviewed by Holm Chatterjee studied the details of chemical composition
water hyacinths whereas Wolverton and McDonald reported chemical
water hyacinths grown in sewage lagoons.
For reduction of
pollutants from the industrial and domestic
waste water by water hyacinth culture, Sinha have carried out
investigations by growing in oxidation ponds with digested sugar wastes
effluents from septic tanks. MC Donald studied the effect of this plant
nutrient and pollutant removal from sewage and industrial effluent
Neuse performed an experiment at the Willamson Creek Plant in Austin,
USA involving hydraulic testing of water hyacinth culture unit
designed to remove algae from stabilization pond effluent. Widyanto
studied the effects of agriculture, domestic and industrial pollutants
Space Technology Laboratory (NSTL), Mississippi,
has also carried out extensive studies on the utilization of water
for treatment of various sewage and industrial effluents.
Experimental Procedure and Results
mentioned reports indicate that there is
considerable scope for utilizing water hyacinths for upgrading
effluents but no work has so far reported methods for treating the pulp
paper mill effluent with water hyacinth. The present work on upgrading
paper mill effluent was initiated with the following objectives
study the techno economic feasibility
of water hyacinth utilization in the upgrading of combined paper mill
identify, evaluate and optimize the
influencing parameters responsible for the treatment of paper mill
with water hyacinth.
of pollution load, COD estimations have been
carried out throughout the studies. BOD measurements have not been
in the belief that if the process could be effective for removal of
constituents contributing to COD, it would be easier control BOD values
desired levels. The combined effluent from an integrated pulp and paper
has been used for various studies reported here.
the plant. Effluents with
varying pH were collected. For obtaining the high
and low range of pH,
dilute NaOH and HC1 were added in calculated doses. In each
of the pots,
plants were grown and their survivability was observed. Intermittently,
of the effluent was also noted (Fig. 1).
survivability at different pH values, 2 to
12, showed that water hyacinth could survive and grow well within a
range of 4 10 beyond which it become dry. Furthermore, the dried plants
rejuvenate even after placing them in a suitable nutrient medium. It is
interesting to note that in the case of plants which survived in the pH
of 4 10, the final pH of the effluent was always
around 7 (neutral) within
a week, irrespective of the initial pH of the
In general, the
growth of water hyacinth was rapid in the
combined pulp and paper mill effluent. It was also observed that
small quantities of sewage waters accelerated the plant growth.
detection period vs reduction in pollution load. Effluent
was kept for stabilization with a predetermined quantity of water
at odays as well as at different time intervals during treatment were
analysed for pH (Table 1) and COD (Fig. 2).
It is seen that
the treated effluent (760 ppm COD) showed
around 70 per cent of COD reduction within 9 days as compared to only
cent without hyacinth treatment.
the surface area coverage by water hyacinth. The surface area
experimental pots was divided into four equal sections. After filling
with effluent, approximately 25%, 50%, 75% and 100% of the area was
with water hyacinth in one, two, three and four sections respectively.
were analysed for pH and COD (Table 2).
coverage of 75 per cent of the area available by
water hyacinth can be considered as adequate since beyond this no
reduction in COD is observed. Also, full coverage of the surface area
the growth of the plant and aeration of the surface.
were followed in the subsequent phases of
Detection period. The
effluent after 4 hours of settling was fed with water hyacinth covering
surface area. Samples were analysed for pH and COD
initially as well as
after different days (Table 3).
tanks (200 litres) COD reduction was low as compared to earlier
the laboratory using smaller tanks of 30 litres because of the high
effluent to be treated in proportion to the plant content. In a typical
experiment, it is seen that the reduction of COD achieved is almost two
when 1.5 kg wet biomass of hyacinth is added to 200 litres of effluent.
Recycling of the
possibility of the same stock of hyacinth was studied by repeatedly
same set of hyacinth for seven consecutive treatments by changing the
in the container. The samples were analyzed for pH and
COD in the
beginning and after 3 days for each set.
For recycling it
has been seen that
the same stock of hyacinths can be used without any decrease in
more than seven cycles keeping the detention period at 3 days in each
effluent to plant. To study
the effect of volume (height) of the effluent
on the efficiency of treatment, studies were carried out in experiment
which were filled with the effluent to different volumes, i.e.,
75% and 50% to which a fixed quantity of hyacinth was added. Samples
analyzed for pH and COD after different detention periods (Table 4).
The extent of
COD reduction obtained with different volumes
of effluent showed that the overall reduction has an increase relation
height of the effluent. The lesser the height per plant, the higher the
pollution reduction, i.e., the reduction in COD is
to the total volume of effluent treated.
effluent with high pollution load. To study if
longer detection would be helpful for treatment of effluents with high
pollution loads, experiments were carried out for longer durations
(approximately for a month). Samples were analyzed for pH and
different days of detention (Fig. 3).
A maximum of 60%
reduction in COD could be obtained within a
detention period of one month in case of a typical effluent having
effluent from paper machines. Unsettled
effluent from the paper machine was also collected as it contains very
suspended matter and high inorganic content, and is, therefore, quite
in characteristics and its composition from the combined paper mill
and allowed to settle for 4 hours before treating with water hyacinth.
Reduction in pH and COD was noted
Around 90% of
COD reduction was achieved within a short
detention time of 6 days. Beyond 6 days the reduction in COD was
Based on the
encouraging results obtained in Phase I and
Phase II it was decided to carry out large scale trials on experimental
A pilot lagoon
was constructed (Fig. 5) and the effluent was
filled to a height of 1 m, allowed to settle for 4 hr and then 75% of
area of the lagoon was covered with water hyacinth. After settling, the
values of pH and COD of the effluent were measured and subsequent
were carried out for different periods for progressive treatment with
hyacinths. Samples were collected from the top and bottom surfaces for
different days of detention (Fig. 6).
To simulate the
working of a pilot lagoon with a detention
period of 15 days in actual operation in the mills l/15th of the
effluent was removed from bottom and the same quantity of fresh
added from the top to make up the volume. The incoming effluent was
for its COD after settling. This process was continued for 7 days and
samples collected from the bottom of the ponds were analyzed for pH
COD (Table 5).
The results in
the pilot lagoon were quite encouraging with a
healthy growth of the hyacinth. The per cent reduction was quite
with the earlier experimental results. Approximately 70 80% COD
be achieved in the lagoon within 15 days for the combined effluent with
600 ppm of COD.
Our results on
percentage of pollution reduction are quite
encouraging. Around 70 80% of COD reduction has been achieved within 15
detention in a lagoon treatment with hyacinth in a batch process or
process. Similar trends in the reduction of pollution load were also in
different effluents. Around 80% of suspended solids were removed from
treated effluent in comparison to the 15% in the untreated one within
biological treatment processes, the
biological degradation and subsequent assimilation of impurities are
carried out by phytoplanktonic algae. But because of the easy
algal cells, algae laden effluent is considered as the most undesirable
features of stabilization ponds. Water hyacinth is found to check the
algae and has been considered as one of the tools for removing algae
lagoons. Although, water hyacinth does not produce oxygen through its
purifies the waste by means of a complicated mechanism, regarding which
considered that cellular enzyme system accomplishes oxidation without
removal of hydrogen. They also found that roots of hyacinths contain
dehydrogenation enzymes which possibly absorb hydrogen and also act as
transferring agents to accomplish the higher rate of oxidation. Along
biodegradation of the organic matter, water hyacinth can also remove
metals. In the static laboratory experiments as reported by NSTL scientist
Eichhornia rapidly absorbs gold, silver, cobalt strontium,
lead and mercury very efficiently. Water hyacinth can also absorb or
phenols and other organic toxic compounds from effluents and drinking
supplies. Hence, removal of toxic material by absorption leads to
the toxicity of the system. Further, treatment with water hyacinth also
the overall turbidity of the water.
Whatever may be
the probable cause of biodegradation and
removal of toxic materials water hyacinth gives a new dimension in the
upgrading the industrial wastes with special reference to the waste
and Paper Industry.
DISPOSAL OF SOLID EFFLUENTS AND REUSE
Definition, Classification, Quantity and Composition of Refuse
All solid and
semi solid wastes of a community, except human
excreta and sullage is classified under the general term refuse,
represents the dry wastes or solid
wastes of the society, and includes
garbage, ashes, rubbish, dust, etc. as defined below
Garbage. It includes all sorts of putrescible
organic wastes, obtained from kitchens, hotels, restaurants,
etc. All waste
food articles, vegetable peelings, fruit peelings, etc., are thus,
this term. These wastes are organic in nature, and thus, likely to
quickly, producing foul odours and health hazards. They may also result
breeding of flies, mosquitoes, insects, etc. Hence, garbage must be
of, properly and quickly. When it is scientifically processed and composted,
then it is possible to obtain valuable products, like grease,
fertiliser, etc. from garbage. The density of garbage usually varies
450 to 900 kg/m3.
Ashes. Ashes as all of us know
denote the incombustible waste products from
furnaces, and houses or industries. The density of ashes generally
between 700 to 850 kg/m3. Its quantity is getting
reduced in modern days due to the increasing use of cooking gas and
oil, and lesser use of cooking coal, in houses. In industrial towns,
this quantity may be quite appreciable.
Rubbish. Rubbish includes all non
wastes except ashes. It, thus, includes all combustible and
wastes, such as rags paper pieces, broken pieces of glass and
furniture, card boards,
broken crockery, etc. Rubbish is lighter, and normally has a density
between 50 to 400 kg/m3. It may create greater nuisance
during the autumn and summer, as it
may be scattered by high winds.
density of refuse (mixture of all types of dry
wastes) generally varies between 300 to 600 kg/m3.
above technical classification based on the type of
wastes, the refuse may also be classified, depending on its source, as (i)
house refuse (ii) street refuse and (iii)
trade refuse. All these
terms are quite apparent, and known to all of us, and hence need no
The quantity of
solid wastes (refuse) produced
by a society depends upon the living standards of its residents. The
of modern society has resulted in a vast increase in the amount of
generated per person.
In an average
modern city, each citizen produces about 0.3 to
0.8 kg of solid domestic waste per day. The quantity generated is
found to be on a lower side, when the degree of commercialization and
is on a lower level. Say for example, a city like Delhi, produces about
tonnes/day of solid wastes whereas. New York produces as much as 25,000
tonnes/day of solid wastes.
The quantity of
refuse produced in a city not only depends
upon the type of the city and on the living standards of the residents,
also depends upon the seasons. Say for example, in India, average
is about 25% higher than the yearly average, due to larger carriage and
consumption of fruits, like mangoes, melons, etc.
composition of refuse (by
weight) is estimated to be as shown in Table 1.
The quantity of
rubbish in Indian refuse, as compared to that
in U.S.A. is very small as in India, large quantities of papers,
plastics, synthetic polymers, rags, etc. are picked up and removed
the rag pickers (men, women and children) before the refuse reaches the
disposal site. This, infact, reduces the calorific value of Indian
the other hand, the quantity of garbage in U.SA is very small, because
use of garbage grinders, and use of tinned and readymade packed
Collection, Removal and Carriage of Refuse
In India, the
refuse is generally collected in individual
houses in small containers, and from there, it is collected by sweepers
small hand driven lorries/carts, and then dumped into the masonry
constructed along roadsides, by municipalities. The refuse is finally
away by municipal trucks, for further disposal during some day time.
methods adopted here are highly unsatisfactory, and need tremendous
improvements and changes.
house sweepers and street scavangers, do not
bother much for carrying refuse properly, and they go on scattering it
there, while carrying it up to the municipal chambers. Many of them do
bring hand lorries even. Even at the entrance point of the municipal
chamber, they just throw the refuse, scattered alround in and out of
The street animals would further scatter it, leading to all round
the refuse, almost everywhere, resulting in highly insanitary
municipal trucks, do not generally clear and
clean the refuse chambers properly, and the residual refuse remains
a long time, resulting in its composition and evolution of obnoxious
consequently causing health hazards. Even municipal trucks, while
refuse, are generally not closed bodied, and hence go on throwing
way, and also giving pungent smell. This is happening so, even in
capital of India.
The process of
refuse collection and its carriage, therefore,
needs vast changes in this country. The refuse, should, therefore,
collected by municipal trucks directly from the houses. Roadside
collection masonry chambers, need complete elimination. Municipal
should be completely closed, and should visit homes and houses, twice a
once in the morning and once in the evening, to collect household
trucks (vehicles) should also be of high
quality, of special design and be properly maintained. They should be
durable, and water tight, and be made of stainless steel with smooth
having round corners and edges, for facility of cleaning. They should
low loading line, say upto about 1.5 m, so that minimum of time and
required in filling them. They should have a cover, which should be
made as a
part of the body with hatches which can be opened during collection.
devices should be installed in these vehicles, for lifting the body to
sides or back, or for pushing the refuse out, so that they can be
The practice of
open burning of tree leaves and grass
clippings, as prevailing in our country, also needs to be stopped. Such
and grasses, instead of being burnt, should be mulched and used for
Refuse by Sanitary Land Filling. In this
method of refuse disposal, refuse is carried and dumped into the low
under an engineered operation, designed and operated
according to the
acceptable standards, as not to cause any nuisance or
hazards to public
health or safety.
The refuse is
dumped and compacted in layers of 0.3 0.6 m
or so, and after the days work when depth of filling becomes about 1.5
m, it is
covered by good earth of about 15 cm to 30 cm thickness, so that the
not directly exposed. This filling is done by dividing the entire site
smaller portions, as explained in article 184.108.40.206. The compaction is
movement of bull dozers, trucks, etc. before starting filling the
Filling of low
lying areas should generally be done by
leaving a minimum distance of 6 m from the surrounding area.
DDT, creosote, cresol, etc. should also be sprayed on the layers to
breeding of mosquitoes and flies. A final cover of about 0.6 metre of
laid and compacted at the top of the filled up land to prevent rodents
burrowing into the refuse.
With the passage
of time, the filled up refuse will get stabilized
due to the decomposition of organic matter and subsequent conversion
stable compounds. The land filling operation is essentially a
method of waste treatment, since the waste is stabilized by aerobic as
anaerobic bacterial processes.
bacterial decomposition occurs under the aerobic
conditions, because a certain amount of air is trapped within the
However, the oxygen in the trapped air is soon exhausted within a few
the long term decomposition occurs under anaerobic conditions.
period of refuse stabilisation can infact, be
divided into five distinct phases (i) During the
first phase of
operation, aerobic bacteria and fungi, which are dominant, deplete the
available oxygen to effect oxidation of organic matter. As a result of
respiration, the temperature in the fill increases, (ii)
In the second
phase, anaerobic and facultative bacteria develop to decompose the
matter and H2 and
evolved through acidogenic activity. (iii) In
the third phase,
methanogenic bacteria develop to cause evolution of methane gas. (iv)
In the fourth phase of decomposition, the methanogenic
activity gets stabilized.
(v) In the fifth stage, the methanogenic activity
depletion of the organic matter and ultimately, the system returns to
conditions within the land fill.
biological degradation, the moisture content of
the dumped material should be high, say not less than 60% or so, which
sometimes maintained by the aerobic decomposition brought out by fungi,
sometimes by sub soil water.
The refuse, in
managed landfills, may usually get stabilized,
generally within a period of 2 to 4 months and settle down by 20 40% of
original height. The filled up land can infact, be used for developing
green land, parks, or other recreational spots. Unequal settlement and
trouble, may however, be there, and hence, normally, for the first 1 2
the land is grassed or planted, fenced, and left out as reserved green
This can, on a later date, be preferably used for developing some
grounds, or picnic spots. Such sites may also sometimes be used for
constructing houses though they are not generally preferred, because
constructions may prove to be costly due to their deeper foundations
avoiding unequal settlements. Such houses, may further pose problems
of bad odours and cracks in walls and plasters, on a later date.
This method of
refuse disposal is very suitable to the
heavier type of Indian refuse, and also to the rural communities,
camps, etc. Hence, it is widely adopted in our country. So much so,
Indian refuse is disposed of in
The area method
is used when it is not possible to further
excavate at the chosen land fill site, especially when the groundwater
In this method, the entire land fill site is first of all divided into
of sub areas by constructing embankments and roads. The sub areas are
division cells or sometimes simply as cells. However,
differentiate them from smaller heaps of waste fill, which are filled
the site and are called cells, it is preferable to call these sub
areas as sub division cells.
of roads on the embankments will help in
moving the trucks bringing the solid waste from the city over them, as
their being emptied in any of the sub division cells. These sub
may be numbered, and may be taken up for filling with waste, one after
The work of
filling in a chosen sub division cell is started
by bringing and filling the refuse (solid waste) along one of the cross
embankment or bundi, such as the one shown in Fig. 12.1, and marked as
waste is simply brought and dumped on the ground, spread in layers of
m thickness, and compacted. Another layer of 0.5 m thickness is then
top of the previous layer, and also compacted. Layering and compacting
repeated until a height of about 1.5 m is reached. At this point and at
of a working day, a cover of earth of about 0.15 to 0.3 m thickness is
on the top and side slopes of the compacted heap, which is called a
cover is called the daily cover.
Fig. 1 shows the
prospective view of such a land filling
site, in which you can locate the cross earthen levee (AB). To the
side of this levee is a completed unit of compacted solid waste or
shaded, which is bound by the daily earth cover on side as well as on
small fill unit is called a cell. Another cell to
the right of the
previous cell is then filled on the next day and completed in the same
The daily cell filling, then proceeds to the right, until the entire
most horizontal span (length) gets filled. In the figure, a total of
horizontal cells are filled in the span. Cells are then further
top of the previous cells to complete another horizontal span of cells
second lift. A partially filled second lift is shown in Fig. 1 itself.
earth cover existing between the bottom cells (1st lift) and the cells
above them (2nd lift) is known as the intermediate cover. The
height of the horizontal cells of a given lift including the top cover,
known as the lift.
VENTILATION FOR CONTROLLING INDOOR AIR POLLUTION
we all understand, is nothing but our
surroundings, which can be badly affected by smokes,
gases, oxygen deficits, noises, and vibrations, etc. When such
substances or actions hazardously affect our environment, we
call them as
pollutants, and the process whereby the surroundings get adversely
known as environmental pollution.
A public health
engineer, who is responsible for removing all
kinds of wastes of a society, is evidently responsible for cleaning the
from such pollutants, and, thus, to ensure a healthy and wholesome
surroundings, to ensure health and happiness for the people.
sanitation, which evidently means cleaning
of the environment, therefore, becomes the major task of a
engineer, and this task primarily, includes collection and
refuse and sewage from houses, buildings, and other public areas, the
subject which has already been dealt in the earlier chapters of this
of sufficient and wholesome air to the buildings and residents for
controlling indoor air pollution, is also included as a work of
sanitation, and hence, usually, included in the subject of Public
Engineering more so, because it is the wholesome air, on which depends
health of the public.
we discuss design aspects governing
ventilation of buildings, we shall first describe the harmful effects
indoor air pollution and its present status.
Sources, Effects and Status of Indoor Air Pollution
In a developing
country like India, the most important source
of indoor air pollution is combustion of domestic fuel (such as cow
wood, and crop residues) used
for cooking, on which 80% (1991
census) of our population relies. It has further been estimated by Indian
Council of Medical Research (ICMR) New Delhi that globally
30 lakh people
die every year due to air pollution, out of which 18 lakh people die
indoor air pollution in developing countries. In India alone, 5.89 lakh
die annually due to indoor air pollution (4.96 lakh in rural areas and
lakh in urban areas).
The indoor air
pollution has infact, been found to be much
worse than the outdoor air pollution, since a pollutant released indoor
thousand times more likely to reach the lungs than a pollutant
released outdoors. It is generally
the women and young children and
infants who face the maximum adverse effects of indoor air pollution.
households, there is no separate kitchen, and people usually
stay in the same room where they cook, or burn fuel to heat during
Moreover, women who work on cooking, and their young children
infants, always necessarily stay at the place of cooking or burning of
traditional fuel. This exposes them to continuous indoor air pollution
long hours. This proves worst for the children (up to the age of about
years), whose lungs are in the developing stages.
Health Scientists of California have, infact,
strongly linked the indoor air pollution, with acute respiratory
chronic obstructive lung disease in children below five years of age.
analysis by Anita Zaidi of Agha Khan Hospital in Islamabad (Pakistan)
shows a strong link between traditional biomass fuel use and infant
The experts have concluded that traditional fuel emits large
dangerous pollutants and are often burnt in poorly ventilated
they are responsible for substantial ill health in the country.
use of cleaner fuels, improved stoves and
better ventilation of homes and kitchens should therefore be given top
to reduce indoor air pollution. Moreover,
children and pregnant
women, who are most susceptible to ill effects of indoor air
to be protected on top priority from indoor air pollution.
Purpose of Ventilation
stated earlier, is
meant for supply of fresh air, and to replace the old hot used up
air. The ventilation ensures the removal of bad effects of occupancy of
By providing necessary oxygen to
deficit caused by respiration
By removing and diluting CO2 in the air
By lowering down the temperature by
used up air and replacing it by colder fresh air
By reducing humidity and
By reducing body odours.
Extent of Ventilation Required and Ventilation Standards
In olden days,
it was thought that
the poisonous CO2
inhabitants is mainly responsible for causing pollution in houses and
public buildings. It was also thought that CO2 content
increasing beyond 0.06% in the room, would cause very harmful effects.
Accordingly, the ventilation standards were framed on limiting the CO2 of
the used up air to 0.06%, as against the
normal content of 0.04% of fresh air.
purification standard of 0.06%
of CO2 means
that the air gets contaminated when its
increases from 0.04% to 0.06%. In
other words, addition of 0.02% of CO2 in
the air by
respiration will contaminate the air, which further means that the
0.02 cum of CO2 will
contaminate the air of a room of 100 cum
an adult person
releases 17 litres (0.017 cum) of CO2 per
can, conclude that 0.02 cum of CO2 will
released by an adult in minutes. Hence, an adult person, if kept in a
room of 100 cum volume, will contaminate its air in 70.6 minutes.
If we consider a
room of an average
size 10 ft. × 10 ft. × 10 ft. i.e. 1000 ft3 =
volume, we find that such a room of 28 cum capacity will be
contaminated by a
single adult in
In other words,
a room of 28 cum
volume will be contaminated by the presence of a single individual in
minutes, and hence air of this room will need to be changed at
minutes i.e. 3 changes per hour will be required, with
requirement of 3 x 28 = 84 cum per hour.
however, be true only if
there is no automatic ventilation through the loose door and window
and also the ventilation that takes place when the doors of a room are
occasionally opened. Due to such automatic ventilations, the
of air will get reduced. On the other hand, the requirement of air will
increase if the number of inhabitants is more than 1, or if the room
occupied per person is less than 28 cum. Moreover, this requirement of
based upon the assumption that 0.06% CO, content will start causing
to the inhabitants, needing air replacement whereas, infact, in these
has been established that CO2 contents
upto 1% or so, can be easily
withstood. Due to these reasons, the air requirement was considered
in olden times than in modern days. The air requirement of as high a
50 cum per hour per person was not considered infrequent in olden days.
requirement has, nowadays, not only been toned down to about 15 30
rather the entire concept of ventilation has undergone a change.
Now a days, it
has been established
that maximum air change is required not for keeping CO2 under
control, but is to ensure proper heat
dissipation and cooling of the human body, as explained below
in all living beings
produces heat, which is partly (20%) consumed in their different
chemical activities. The remaining 80% heat has to be dissipated
convection, and evaporation, so as to
maintain the thermal
equilibrium of the body.
The blood in the
body carries the heat to fine capillaries
near the skin, and from there, it dissipates into the atmosphere by conduction.
Due to this, the temperature of the surrounding air rises,
which sets up
the convection currents. Fresh air comes nearby, and carries
away heat. If
the rate of its passage is slow, the body feels discomfort whereas if
passage is accelerated through fans, etc. more relief is secured.
season, the temperature difference between the
body (at 37°C) and the surrounding air, becomes very low, and the heat
becomes very flat, and hence the rate of conduction falls down.
ventilation then becomes most essential.
surrounding temperature increases even beyond the
body temperature, as happens in a tropical country like India, where 40
°C temperature is quite common during summers, both conduction and
stops functioning. The evaporation of the body sweat can only cause
The rate of this evaporation also reduces when humidity is high. Hence,
hot and humid day, body feels more discomfort. The comfort can then be
increased by Increasing the air movement by using fans, and also by
the surface area of evaporation by removing clothings. Lungs also help
of heat through convection and evaporation. In hot weather, deeper and
breathing expels more heat.
It thus becomes
evident that ventilation is mainly required
to control the body heat, and not to overcome CO2 alone.
of ventilation required for body cooling exceeds the rate required for
other bad effects of occupancy, such as decrease of O2, increase of
Hence, the air
changes are required and provided these days
on the basis of body cooling alone, and not on the consideration of CO2.
consideration and in actual practice, the fresh
air is supplied at the rate of 15 to 30 cum per hour per person, depending
upon the type of building. When the number of occupants cannot be
determined, the rate of air supply may be based upon the number of air
to be provided.
Table 1 gives
some common accepted standards in this regard.
On minimum side,
a window area of 0.052 m2 per
person should generally be provided, so as
to ensure admission of atleast 28 cum (i.e. 1000
cft) of air per
hour with a velocity not greater than 9 m/min.
recommendation is to provide about th of the floor
area in the living rooms for windows. Every room should preferably be
with atleast 2 windows, and at least one of them should face open space
varandah. Kitchens must be provided with more window area.
deflectors (also called fan lights) of 30 cm
height at the bottom or top of a window, opening inward, permits
ventilation of the room, even when windows are closed, as shown in Fig.
In case of slopy
roofs, ridge ventilators may be provided, as
shown in Fig. 2. Such ventilators are useful in
taking out used vitiated
air from large halls.
In hot summer
months, during day time, hot outside air may be
warmer than the inside room air, and the ventilators may then reverse
functions. In other words, the bottom openings may start letting out
air, whereas the top openings may start admitting outside air to fill
partial vacuum created thereby. The inside of room will, therefore,
worse, unless the admitted air is cooled down by some method. Khas
may, therefore, be hanged at the roof level ventilators to cool the air
evaporation. But during night time, when outside temperature falls, all
and ventilators may have to be kept open for allowing them to function
THE ENVIRONMENT AND ITS POLLUTION
Biosphere and Environment
knowledge of Geology, we know that the solid earth
and its interior is known as lithosphere, and the gaseous layers
the earth upto a distance of about 700 km, composes the atmosphere. The
atmosphere is further sub divided into (i)
stratosphere and (iii)
ionosphere, depending upon the
distance of the gaseous layers from the surface of the earth.
collection of water over the earth as well as
inside the earth is called the hydrosphere.
narrow belt of lithosphere and atmosphere, a
little below and above the surface of the land, and in water and air,
largely contains living organisms (such as plants and animals,
life), is called the biosphere. Biosphere is, therefore, that
zone on earth, where the lithosphere, the hydrosphere, and the
into contact with one another. It is, in fact, that portion
on the earth,
where alone, life is in existence.
There is a
continuous exchange of matter between these three elements
lithosphere, hydrosphere, and atmosphere). Say for example,
their food from the nutrients and moisture found in the soil layers of
lithosphere. Similarly, plants use carbon dioxide from the atmosphere,
sunlight for their growth. Dead plants and animals are decomposed by
and become soil nutrients. Some of this may be dissolved by the running
and added to the hydrosphere. The evaporation of water from the
and subsequent condensation of water vapour in the atmosphere and
rainfall on the earth, provide water supply for the organisms in the
Physical and Biological Environment
The four major
elements, i.e. (i)
water, (iii) air, and
(iv) living organisms (plants
and animals), together constitute what is known as environment or
be further sub divided into
or Biological environment
Land, water, and
air together, infact, forms one group of
environment, called physical environment whereas, the living
another group of environment, called biological environment.
physical environment (land, water and air) is
essential for existence of life in various forms the biological
provides the necessary food, so very essential for the sustenance of
man on the
earth. Man, as a matter of fact, cannot survive on the earth without
Ecosystem and Ecological Balance of Nature
living organisms constituting the biological environment
are, infact, dependent upon each other for their survival, and each,
depends on the physical environment of the area in which it lives.
as stated earlier, is the physical environment together with the
which live therein. Ecology is the science which deals with the inter
between the various organisms and their relationship with the physical
on land and in water provide food for herbivorous
animals (generally smaller and weaker, plant eating
elephant) and these herbivorous animals, inturn, become the food for
animals (flesh eating animals, like lions). The relative
number of these
different types of organisms in the biosphere is, however, such that
no scarcity of food for any organism. The smaller organisms are much
more in number
and their growth and reproduction is also much faster than those of
organisms, which are fewer in number and reproduce slowly. This ensures
availability of sufficient food for larger animals.
In the natural
environment, in the biosphere, there, infact,
exists a perjeet balance or equilibrium between the various organisms,
is known as ecological
balance. In this equilibrium state, the
relative numbers of different organisms in a particular environment
constant. This ecological balance may, however, get
disturbed, when changes
take place in the natural environment, which may
consequently change the
relative numbers of the different organisms in the biosphere. If the
ratio balance between the different organisms is disturbed, then
there becomes a dearth of food for certain particular organisms, which
ultimately lead to large scale mortality of those particular organisms.
new equilibrium is finally re established under the changed conditions.
this period of readjustment, evidently, certain old species get
new species may be born. This process of evolution of new species and
extinction of old species is a continuous process.
existing pattern of organisms in the biosphere
has been reached as a result of gradual evolution and extinction over
million years of earths history. During the changing physical
various organisms adapted themselves, and survived but still however,
particular species which could not tolerate the changing environment,
and became extinct. New species were also born in the new changing
Man, infact, came into existence, as a result of large scale
changes that took place about one to two million years ago.
Impact of Man on Biosphere
arrival and reproduction of man on the earth, a
large scale impact has been caused on the biosphere, due to his
actions. Say for example, large scale deforestation of
residential and agricultural land uses has changed the habitat of
living in the forests. His hunting of animals, has
led to the extinction
of certain animal species. He has also developed new types of
animals as well as plants to serve his own needs. His using pesticides
insecticides in the agriculture farms have also affected the relative
proportion of various organisms in the biosphere. Such continuing
the biosphere, if not checked, will certainly prove disastrous to the
existence of man himself, because it is the biosphere, on
which depends, the
life as well as the progress of human civilization.
Pollution and Conservation of Environment
of civilization and rapid industrialization
by man has caused a great damage to the ecosystem. Things have worsened
no attention or a very little attention has been paid towards
environment, while executing industries and other developmental
any development, there is bound to be some
amount of environmental degradation. An ecological survey and effective
measures for protecting the environment, are therefore, essentially
before any developmental project is undertaken. But unfortunately,
developing any industry or commercial or even urban properties, we have
bothered to look at the environmental degradation, likely to be caused
establishments, either through our ignorance or through our sheer
not spending any money on things which do not immediately affect us,
individually. There are infact, people among us who believe
that there is
more money in destroying the environment (such as those who felt trees,
kill wild animals, unauthorized), rather than in conserving it.
Tomorrow is not
their immediate concern.
of mans interference with the natural equilibrium
may be mentioned. The excessive use of coal, petroleum, and natural gas
industries, automobiles, and power generation, has created enormous
pollution of environment.
Pollution of air
marked in the
industrial and congested cities of U.S., Europe, Japan, and even in
from factories, coke ovens and furnaces,
steam engines, etc. exhaust fumes from
automobiles, power plants, etc.,
injurious chemical fumes from oil refineries, zinc
industries, metallurgical plants, iron and steel plants, incineration
etc. evolution of radioactive gases and suspended radiactive dusts from
explosions and accidental discharges from nuclear reactors, etc. have
the air to such an extent that special steps are now required at
for reducing such air pollutions.
The increase in
environment has been responsible for gradual heating up of our globe,
process called greenhouse effect. The CO2 layer,
acts like a glass cover used for a green house, which
allows the outside
heat to enter the green house, but does not allow the inside heat to go
to a glass house, CO2 layer
is transparent to short wave radiation
from the sun, but absorbs the longer wave radiation from the earth. The net
result is , gradual heating up of the earth. It is feared that by the
atmosphere will be doubled, leading to 40C rise in the
world temperature. Such continuous
warming of earth may cause the glaciers to recede and ice to melt at
This may cause a rise in sea level by about 0.65 m. which ultimately
submerge most of our islands and coastal cities.
The salty sea
water spreading to land may also lead to
infertility of soil and spoil the underground water.
water is another aspect of environmental
pollution. The waters of rivers, lakes, and oceans are, now a days
polluted on a large scale, by the outflow of effluents from factories
industries. Water pollution also results from the disposal of solid
wastes, such as plastics, rubbers, paper,
untreated wastewaters and
sewage, etc. Water pollution also interferes with the growth of
living in the water bodies, thus retarding the natural purification
caused by such organisms.
environmental pollutions, lead to the spread of
diseases through polluted air and water. The use of insecticides and
has led to the concentration of DDT and other harmful chemicals in
animal food products, which when consumed by man, cause diseases.
In order to
check such drastic ill effects of environmental
pollution on the health of the people as well as the plants and the
it is extremely necessary that we wake up from our long slumber, and
some drastic remedial measures to protect our natural wholesome
Legislative laws and their effective implementation is
most important to
stop the greedy and/or ignorant people from spoiling our environment.
Status of Administrative Control on Environment in India
In our country,
no attention was paid for controlling the
environmental effects of developmental projects, almost till the year
so. It was in the 4th five year plan period (1968 1973), when, for the
time, environmental aspects were introduced for harmonious development.
In the year
1970, the Government of India, appointed a
committee under the chairmanship of Pandit Pitamber Pant (a member of
planning commission), which prepared a country report for presenting in
U.N. Conference on Human Environment, in 1972. Soon thereafter, a
Committee on Environmental Protection and Coordination was set up in
of Science and Technology, for advising the G.o.I. on environmental
The 5th five
year plan (1973 1977) continued to stress upon
the environmental considerations. During this plan period, a central
enacted, under the name of Water (Prevention and Control of
Pollution) Act, 1974.
This law was meant for checking and preventing
water pollution, which
had become quite prominent by that time, at several places in the
As a result of
this legislative enactment of 1974, a central
board, called Central Board for the Prevention and Control of
was constituted for monitoring and detecting
water bodies, and for initiating remedial measures, including
courts, so as to prevent the influential industrialists and
throwing their industrial wastes and sewages into our precious water
This act of 1974
also stipulated that the various States of
India will separately constitute such pollution control boards in their
respective States, and the central board will serve as a watchdog body
advice and watch the performance of State boards, besides exercising
separate authority in respect of union territories, which are directly
by the centre.
important act, called the Water (Prevention and
Control of Pollution) Cess Act, 1977, was also passed by the
which has proved quite effective in reducing the quantities of
wastes, as the act promotes recycling and reuse
of the wastes.
further stressed in the 6th five year plan (1980 1985), which contained
separate chapter on Environment and Development. During this plan
separate Department of Environment was set up on
November 1, 1981, at
the level of central cabinet. Air pollution was also recognised, and a
legislation, called Air (Prevention and Control of Pollution) Act,
enacted. The water pollution control boards were given the additional
looking after air pollution control also.
A third act,
called The Environment
(Protection) Act, 1986 has also been promulgated by the Parliament
occurrence of the Bhopal gas tragedy. This act
extends to whole of
India, and central Government has been empowered for taking any
in its opinion are necessary for improving and protecting the
Under section 9 of this act, it has also been made obligatory on the
industries to prevent and mitigate environmental pollution, which may
due to any accident or unforseen act at their industry. Under section
10 and 11
of this act, Government officers, empowered by the Central Government,
enter the premises of the industries and collect samples, and/or carry
reasonable action deemed fit for environmental protection.
Severe fines and
including imprisonments upto 5 years have been prescribed for failures
continued failures on the part of industries failing to comply with the
under section 5 of the act.
order to check the
emitted smokes from badly maintained automobiles, containing too much
carbon monoxide and paniculate matter, a fourth legislation, called
Vehicles Act, 1988 has been passed by the parliament. The
exhaust standards framed under Central Motor Vehicles Rules
tol come into force w.e.f. 1 7 1989. However, due to non availability
monitoring equipments, like smoke meters and gas
checking the quality of exhaust emissions, and also due to political
influences, this act largely remains on the statue books of the country.
Even after five
years of the
enactment of this legislation, nothing serious is being done to check
prevent the polluting vehicles, barring a few pollution checks carried
private cars, in Delhi. The authorities are thus, simply ralaxing,
interference from the politicians and the courts.
In order to
prevent loopholes in
the effective implementation of these environmental laws, the
Government is now
thinking to constitute special environmental courts, for
speedy trial of
the offenders of anti pollution laws and also to carry out annual environmental
audits, to easily detect disobedience of such laws by
industries. The earlier it is done the better.
DISPOSAL OF ENVIRONMENTALLY HAZARDOUS RADIOACTIVE EFFLUENTS
Radioactive Elements and Radioactive Radiations
elements like thorium, strontium, iodine,
plutonium, phosphorous, carbon, manganese, radium, cobalt, zinc, etc.
as radioactive isotopes of different designation numbers, when present
natural environment, disintegrate, releasing
ionised radiations or rays.
These emitted radiations are very powerful and contain enormous energy.
rays are even capable of penetrating through thick steel sheets.
disintegration may be defined as the
spontaneous breakup of the nucleus of an atom of a
or its isotope. The breakup of nucleus itself is important here, as
that of the entire atom or the molecule in other types of hazardous
dimensions of radioactivity, the nucleus of a radioactive atom itself
large, making it unstable. This unstable nucleus breaks up, and the
changes to another one, which is lower in mass. The radiations or the
radioactivity generated due to such breakup of the nucleus of the
atom, which is found to be extremely hazardous to life, consists of (i)
particles (ii) beta particles and
radiations, as discussed below
Radiations. The release of
from the nucleus of a radioactive element is equivalent to the release
positively charged helium nucleus, consisting of two neutrons
protons. This release causes the parent atom to loose four atomic
an atomic mass (also called atomic mass number) is the sum of the
protons and the number of neutrons in the nucleus. The loss caused in atomic
number in such a break up will be equal to 2, because atomic
equal to the number of protons in the nucleus.
of Uranium 238 to release alpha particles,
given by eq. (1) can be quoted as an example of this type of breakup of
radiactive element, which is explained below
When U 238
releases the alpha particles, the atomic number
decreases by 2, and atomic mass (or atomic mass number) decreases by 4.
atomic number of Uranium is 92. From the periodic table (given at the
the book as Appendix Table A 8), the atom with an atomic number of 90
(Th). Hence, the equation is written as
particles released in the above equation, are slow
particles, possessing weak penetration power, and can be
stopped even by 8
cm of air or by thin sheets. They are deflected by electric and
but are strongly ionising with a doubly ionised helium nucleus, as
are the release
of electrons from a radioactive nucleus, caused by the
breakup of a neutron
into a proton and an electron. Due to this break up of one neutron, the
will have one increased proton, and hence one increased positive charge
increase in its atomic number. Since the mass of the released electron
small, the reaction will not change the atomic mass, which equals to
of protons and number of neutrons (here the total number of neutrons
protons remains unchanged, since one neutron is changed into one proton
the release of one electron). However, due to change in charge
charge), the parent atom changes to another atom of higher atomic
an electron, beta radiation has a negative charge.
are hence defined as high velocity
electrons, which can penetrate thin aluminium sheets, and
deflected by electric and magnetic fields.
Radiations. Gamma radiation
or gamma ray, as it
is also called, has no charge or mass, being simply an electromagnetic
radiation that travels at the speed of light. Being an electromagnetic
radiation, gamma radiation may be thought of as a wave or
a photon having
very short wave length in the range of 103 to
When an electron
in an atom moves from a higher energy level
(excited state) to the lower stable level, energy
is radiated. An
analogous phenomenon also occurs in a nuclear reaction a nucleus
excited state releases the gamma rays when it transforms into a more
lower form. Gamma radiation may accompany either alpha or
beta radiation. X
rays are also a sort of gamma rays.
Gamma rays are
hence defined as very high frequency
photons, which can penetrate several cm thick lead, and are
by magnetic fields.
Nuclear Fission. When an orbital
electron goes from
a higher unstable energy level to a lower stable energy level, energy
liberated. This is what happens in a nuclear reaction, where
Fissions to transform to a lower stable form, releasing energy, which
Since a fission
is a breakup of the nucleus, at least two
fission fragments shall form in the process. In 1 out of 10,000
fission fragments are formed instead of two.
fission reaction using
Uranium 235 (U 235). In the process, the Uranium atom captures a
making the nucleus unstable, causing break up. Since the atomic mass of
neutron is 1, the sum of the atomic masses of the product species must
be 235 +
1 = 236, as illustrated below
Mo and La are
the two fission fragments. The total of atomic
masses on reactants and products of reaction, both totalling 236.
Since they are
too small to emit alpha particles, fission
fragments are beta or gamma emitters only. Reaction (17.3)
yields 204 MeV
fission fragments are formed (1 in 10,000 cases),
the third fragment is tritium (H 3).
Since it is a
chemical form of hydrogen, it exchanges freely with the non radioactive
hydrogen in the cooling water used in nuclear reactors. Containment of
fragment is, thus, difficult. Tritium (H3) has a long life of 12.3
Table 1. lists
the fission fragments that can be produced in
the fission reactor. Some of the products are very harmful to life. Say
example, Cs 137 concentrates in muscles, Sr 90 concentrates in bones,
and 1 131
concentrates in thyroid gland. The safe disposal of
radioactive wastes is
therefore of paramount importance and is hence discussed below in brief.
Impacts of Radioactivity on Life and Environment
When human body
is subjected to the ionised radiations, large
scale hazards, like cancers, shortening of life span,
genetic changes may occur, depending upon the quantum of
exposure although, however, smaller and calculated doses of such
used on human body for medical diagonosis through X rays, etc. for
the mal functioning of different organs of the body.
The quantum of
radiation, which determines the time of
exposure, is generally measured in several units.
commonly used unit of measuring radiation dose is
rad. 1 millirad is equal to 103 ×
rad, and one kilo rad is 1000 rad. 100 rad
is represented by another latest unit, called gray (Gy). Numerically 1
equals the old unit of 1 rem (roentogen). Roentogen is represented by R
All these units depend directly or indirectly on the capability of the
radioactive materials to cause ionisation in their environment. All the
units used in radiation are given in Appendix Table A 7 at the end of
ensure that such radiations do not cause harmful
effects on the body, it is necessary that the quantum of these
which the body is subjected to, be restricted to safe standards. International
Commission on Radiological Protection, by their research and
experience on the use of X rays and radium, has stipulated the limiting
radiation exposures per year per normal person.
values of annual radiation exposure are given below in
concentrations of radio activity not only proves
dangerous to humans, but also to plants, animals, and birds. It
becomes imperative for man to watch and control the presence of such
radiations in the environment.
however, radio activity emissions in natural
environment have not been detected anywhere, going above or even nearer
permissible limits, except at places where atomic weapons are exploded,
some accidental discharges eminate from nuclear reactors/ stations.
atomic accidental discharge in Russia, which
occurred on April 26, 1986, is well known to all of us. This accidental
discharge had not only killed around 30 people, but had scattered
fallout over a vast area, the large scale genetic effects of
yet to come up. Its radioactive fallouts have been detected far and
over a vast area of Europe. Inspite of several measures taken to avoid
range genetic effects of radioactivity in these areas, and more than 50
people being constantly undergoing regular medical checkups, the crisis
confidence is, growing up, as birth defects in farm animals and
health among children and villagers, are being reported.
In a British
Medical Research Council (BMRC) study, it
has been concluded that two atomic isotopes, named Strontium 90 and
are generally produced from fallouts from nuclear weapon testings and
power stations. Strontium 90, like calcium, gets incorporated into the
and as such, the milk produced by animals into whose bodies strontium
been concentrated, may become radioactively contaminated.
Iodine 131 is
another highly dangerous isotope. This element
can enter the food chain at any level, and become concentrated in human
consuming such foods. Once within the body, it can damage white blood
bone marrow, spleen lymph nodes, and can cause lung tumors, skin
sterilities, defective eye sights, etc.
isotopes have, thus, been singled out for
contaminating the pasture milk and air, and thereby posing radioactive
In the above
British M.R.C. study, a dose called Emergency
Reference Level (E.R.L.) has also been defined, as the concentration of
radioactivity, which different parts of the body can tolerate, varying
to 60 rads. This reference level is a guide to
initiate counter measures
like evacuation, etc., as and when the
radioactivity in a particular
area is detected to be more than the reference level. Other counter
like giving anti atomic drugs to remove the bad effects of
also sometimes be adopted say for example, contamination of Iodine 131
removed by treating the affected people with ordinary iodine tablets.
radioactivity released in the natural
environment, under normal conditions, known as the
radiation, is found to be hardly 100 200 milli rads, a value much lower
the tolerance limits. However, in case of accidental nuclear
discharges, anti radioactivity
measures may have to be initiated, as pointed out above.
Nuclear Wastes in India. The
position of disposal of nuclear wastes in India is, though not very
present, but is liable to become so in future, as our nuclear programme
momentum. We have three sources of nuclear wastes i.e.
nuclear mines (ii) the nuclear
power plants and (iii)
the nuclear research reactors.
Our nuclear mines for extracting
uranium ore are
located at Jaduguda village in Bihar state. Once
the uranium ore is
extracted at these mines it is sent to a facility centre in Hyderabad
processing to secure uranium. Earlier, the waste from the processing
being dumped in a nearby pond, but since it
AIR POLLUTION, ITS CONTROL AND MONITORING
Air Pollutants, Their Effects, and Sources of Origin
Air, as we all
know, is most essential for life. It has been
established that man can hardly survive for 5 minutes without air
however, he can survive for 5 days without water, and for 5 weeks
supporting important natural element sometimes becomes
our bitter enemy, as and when it gets polluted, since it causes a
diseases in our body. The harmful effects caused to human body by the
air depends upon the type and concentration of the pollutants present
air, not only is harmful to man, but is also
harmful to all types of life, including plants, animals, and birds. It
harmful to non living materials, like metals,
marbles and other stones,
woods, paints, papers, etc. which get spoiled by the contact with
either due to the mere physical corrosive action of polluted air,
or/and due to
the chemical attack of the pollutants on such materials.
as a matter of fact, contains hundreds of air
pollutants from natural or from anthropogenic sources. All such
called primary pollutants.
important primary pollutants are H2S, H2F and other
fluorides, methyl and ethyl mercaptans, etc., which are
found in our general atmosphere, although if present, may prove quite
pollutants often react with one another or with
water vapour, aided and abetted by the sunlight, to form entirely a new
pollutants, called secondary pollutants. These secondary pollutants are
chemical substances, which are produced from the chemical reactions of
or anthropogenic pollutants or due to their oxidation, etc., caused by
energy of the sun. These new pollutants are often more harmful than the
original basic chemicals that produce them.
formed by the simple chemical reaction
H2O vapour, and is
a much more toxic
pollutant than SO2, having
far reaching effects on environment, since it causes acid rains.
pollutants like ozone, formaldehyde, PNA, etc.
are formed by photochemical reactions, caused by sun light between two
pollutants. Say for example, O3 is
formed due to photochemical reaction
between hydrocarbons (HC) and nitrogen oxide (NO). Similarly, aldehydes
formed by photochemical oxidation of hydrocarbons in the atmosphere.
All these major
air pollutants are now discussed below in
details, mentioning their hazardous effects on human body, and
sources of origin.
is an irritant gas,
and when inhaled, affects our mucous membranes. It increases
rate and causes oxygen deficits in the
body, leading to bronchial
spasms in some of the affected persons. Patients
of asthma are very
badly affected by this pollutant.
Some quantity of
atmospheric sulphur dioxide (SO2) may oxidise to
trioxide (SO3), which
when inhaled, may dissolve in the body fluids to form sulphuric acid (H2SO4), which is a
very strong corrosive acid. SO3, thus, causes
high and worse
irritation even at lower concentrations, leading to severe
also responsible for causing acidity in
fogs, smokes and in rains, and hence is the major source of corrosion
buildings and metal objects.
originates in the atmospheric air from the refineries and
plants, smelting operations, and burning of fuels.
plants may emit SO2 quantities,
as high as 1/10th of the coal
burnt by them. Open burning of
garbage as well as municipal incineration plants may
sulphur dioxide in the air.
standard for SO2 under
Ambient Air quality standards is 80 mg/m3 which
approximates to 0.03 ppm, at 20°C.
possesses about 200
times affinity for blood hemoglobin (Hb,) than oxygen.
Eventually, when inhaled, CO replaces
the hemoglobin, and form what is known as
carboxy hemoglobin (CO.Hb,).This
carboxy hemoglobin is of no use for respiratory purposes, and hence
half of the hemoglobin of the blood is used up in forming carboxy
becomes a certainty.
Persons dying of
carbon monoxide inhalations exhibit
characteristic bright pink colour of the flesh due to the presence of
coloured carboxy hemoglobin in their bloods.
also affects the central nervous system, and
is even responsible for heart attacks, and high
chiefly originates from automobile exhausts,
and is caused by incomplete combustion of organic matter.
In cities, it is
found in as high concentrations as about 60
with still higher concentrations in tunnels, garrages, and near the
intersections and running automobiles.
standard for CO under US Ambient Air Standards
is 10 mg/m3 (9
Nitrogen. Out of seven
known varieties of
oxides of nitrogen, only nitric oxide (NO) and nitrogen
dioxide (NO2) are found to
injurious to human health. NO2 is
considered to be more injurious than NO.
Eye and nasal
irritations are the common
caused by about 28 mg/m3 (15
ppm) of NO2 and
discomfort may occur even with brief exposure, when its
to about 47 mg/m5 (25
Many deaths are
reported to have occurred in a fire in a
clinic in Clevland in U.S.A. in May 1929, due to evolution of NO2 from
the burning of X ray films.
The NO2 mainly
originates into the atmosphere from automobile
exhausts, incineration plant, furnace smokes, etc., as it is
caused by the
combustion of organic matter.
standard for NO2, under U.S.
Ambient Air Quality Standards, is 100
sulphide, as is well known
to all of us, is a foul smelling gas with a typical odour of rotten
Exposure to this gas for short periods may lead to loss of
smell sense. This
gas may also cause headaches, conjunctivitis, sleeplessness, and
the eyes. Its higher concentrations may block
oxygen transfer, and damage
the nerve tissues.
however, is generally not found in any trouble some concentrations in
general atmosphere, mainly because, it is not emitted in automobile
since it gets burnt to SO2. H2S is, therefore,
not included in the Ambient air quality Standards.
this gas is produced in industries, like oil
refining, rubber, tanneries, plants manufacturing sulphur
artificial silk by the viscose process, etc., and may,
therefore, pose a
threat to the people working in those particular plants, and in the
areas, due to chances of its accidental leakages.
Methyl and Ethyl
Mercaptans. These are
other compounds of sulphur, which may be of interest to us in air
because of their strong odours. These compounds, however, are
neither found in our general environment, nor are they harmful to us. As
matter of fact, they are added to domestic and industrial gas supplies,
to detect gas leakages due to their pungent smells.
Fluoride and other Fluorides. Fluorides,
present in air may range from those which are extremely irritant and
like H2F, to
relatively non reactive compounds. Their smaller concentrations may
in cattle and plants. They are, however, less harmful to
They are emitted
into the atmosphere by aluminium plants,
steel plants, phosphate fertiliser plants, etc. They are
also produced by burning
of coal. H2F is also
used in refining and in some chemical industries, and hence its
threats near such plants, always persist.
Fortunately, H2F concentrations
in city air are generally found to be
much lower, and do not pose any problems. Its max.
in most cities is around 0.025 ppm. is, therefore, not included in the
air quality standards.
Lead (Pb). Lead is mainly
injected into the
atmosphere through the exhausts of automobiles, particularly,
automobiles running on petrol. Normally, inorganic lead has been
urban areas in concentrations of about 0 2 ug/m3, with higher
values in areas of heavy traffic. The
concentrations of lead in inhaled air, may cause irritation of mucous
membranes of nose, throat and lungs. Lead poisoning may also
to gastrointestinal tracts, liver and kidney. It may also cause
abnormalities in pregnancy and fertility. Lead poisoning is
also found to
be responsible for retarding mental growth in
standard for lead, under U.S. Ambient Air
Quality Standards, is 1.5 ug/m3.
(HC). Hydrocarbons, as
we all know, are
compounds containing only hydrogen and carbon. The hydrocarbons are
divided into two categories, i.e.
group of hydrocarbons and
group of hydrocarbons.
hydrocarbons include alkanes (methanes),
alkenes (olefins), and alkynes. Out
of these three varieties, the
alkenes (olefins) have
been found to be unsaturated and
highly reactive in atmosphere through photochemical reactions. Alkanes
(methanes) are simply inert hydrocarbons, and do not react photo
The third variety, i.e. alkynes, though quite
reactive, is generally not
found present in the atmosphere, and hence is of no importance to us in
Due to this photochemical
reactionary property of the
alkenes (olefin) type of hydrocarbons, it has become very important to
and monitor the presence of such hydrocarbons in the air.
The presence of
hydrocarbons in the city air, is therefore
attracting a lot of attention, because the olefin type of hydrocarbons
with other pollutant gases, forming new pollutants, which are even more
than the individual original pollutants.
chiefly released into the atmosphere by automobile
exhausts. Paraffins and olefins have been found to be chief
present in large quantities in the air of Los Angeles city of U.S.A.,
heavy number of automobiles ply every day. Hydrocarbons are also
the atmosphere by smokes of incinerators, through
fumes of oil
refineries, and also by evaporation of gasoline at service
Benzene and its
related aromatic hydrocarbons are also
extensively used for solvent extraction purposes, and many of these
hydrocarbons are found to cause body cancers.
ketones may also be considered under hydrocar bons,
because they may also be formed by the oxidation of hydrocar bons in
atmosphere, although they may primarily be released by automobiles and
incinerators along with hydrocarbons. Substances like formaldehyde
of eyes, skins and lungs, and hence,
may be quite injurious to
The presence of
hydrocarbons in the environment may prove to
be quite hazardous, and hence needs to be properly monitored.
standard for non methane types of hydrocarbons
under U.S. Ambient Air Quality Standards is 160 ug/m3 (0.24
Substances. The poly nuclear
aromatic hydrocarbons is considered to be quite important to air
studies, because many of these compounds have been shown to be carcinogenic
to produce cancers). Increase in lung cancers in cities have been
these hydrocarbons, caused by automobile exhaust emissions. Out
varieties of such hydrocarbons, Benzo (a) pyrene has
been found to be
the most carcinogenic hydrocarbon, followed by Benzo (e)
acephenanthrylene, and Benzo (j) flouroranthene. Various
varieties, with less carcinogenic properties are also known.
The Ambient Air
Quality Standards adopted by Environment
Protection Agency (EPA) of USA, does not specify any
for these hydrocarbons. However, attempts are being made to reduce
these benzene compounds in industries from the present level of 10 ppm
(30 mg/m3) to 1 ppm (3
DDT are not only harmful for insects, for killing of which they are
used, but are also harmful to man. The indoor spraying of DDT causes
concentrations in domestic pets as well as in humans. So much so, that
even been found in the milk of mothers. The presence and absorption of
injuriously affect our central nervous system, and
may attack other
organs of the body. For these reasons, the use of DDT has, infact, been
are also quite harmful to human
health. Their growing use in agricultural farming is not without
because, if such substances are absorbed by the expectant mothers, they
cause premature labour, and even abortions.
The recent Bhopal
Gas Leakage Tragedy from the factory
of Union Carbide of India, manufacturing pesticides is a pointer to the
of spontaneous serious air pollutions that may result from such
which utilise or produce poisonous gases in their manufacturing
Insecticides and pesticides do come under such industries and hence,
pose such serious threats to life, even in future.
contained in air, may cause allergic reactions in sensitive human
substances are called aero allergens.
The reactions to
such substances occur in our body mainly in
the skin and the respiratory tract. Sneezing is one symptom of allergy,
followed by skin troubles and/or bronchitis,
allergens have been largely found to originate
from living things like plants, animals, etc., although however, finely
powdered industrial materials may also sometimes cause allergic
and fungal spores from local plants are one of
the worst allergens. About 20 micro metre in diameter, ragweed
usually deposited within 90 m of the parent plant, and hayfever and
sufferers coming within that range are liable to suffer severe allergic
reactions and asthma attacks.
The high degree
of allergy caused by pollens and spores, originating
from the local plants, makes our beautiful city of Bangalore, a dreaded
for asthmatics and allergic persons. Instances have even been cited,
only the asthmatics have had asthma attacks on them in Bangalore, but
normal persons who had never exhibited asthma tendencies earlier, got
of asthma in this city of fine climate. The Asthma Research
infact, identified 75 types of air borne pollens and 120 types of
among which the pollen of parthenium plant was
found to be the highest
(41%), followed by grass pollen (28.8%), and
pollens of cassia
pollens and spores, other important allergens are
animal hairs, furs, feathers, dusts, spices, cotton flakes,
flour, tobacco etc.
besides certain chemical compounds. Say for example, SO2 and
compounds of cabalt and beryilium are
found to cause allergic reactions in certain sensitive persons.
commercial fur dye paraphenylenediamine is an
allergic agent, capable of
causing dermatitis in addition to bronchial asthma. Factories
castor beans for oil extraction, release a powdery material in to the
which is a strong allergen.
Isotopes. The evil effects
substances have been thoroughly discussed under article 16.3. But
however, we would like to repeat here that the three
Cesium 137, and Iodine 131
have been singled out as the main products of atomic explosions and
discharges from atomic and nuclear reactors although, however, other
may also be present.
health hazards caused by such radioactive
emissions are anemia, cancers, shortening of life spans, and
the genetic effects, like sterility, embroyo
malformations, etc. Radioactivity is notorious for its
delayed and long
term evil effects on human health.
Ozone. The presence of
ozone gas in the air may cause irritation
in the respiratory tract, reaching much deeper into the lungs
the oxides of sulphur.
The origin of
this gas into the atmosphere is probably caused
indirectly, by the process of photochemical air pollution. In
two pollutants unite together in the presence of sun light, producing a
Since ozone has
been generally found to occur in the highly
motorised areas, particularly during day time, it is believed that it
produced by the photochemical reaction of hydrocarbons and
formation of such photochemical smogs is
quite high in places where number of plying automobiles is too high,
and where inversion
smog conditions prevail in the atmosphere. Los Angeles city
in USA is
facing such problem of photochemical smog, which also causes intense
irritation, unusual odour, and reduction in the
Delhi city is
also becoming prone to such problems, and
Delhis atmosphere needs to be keenly and immediately watched by the
authorities, before it becomes too late and irreversible.
VEHICULAR AIR POLLUTION AND MEASURES FOR ITS CONTROL
of vehicles in India particularly that of
mopeds, scooters and motorcycles, has been growing at a fast rate, in
recent past. At present, India is the second largest producer of two
after Japan, and the production of these vehicles will almost double to
million vehicles/year in the next five years. During the same period,
production of cars and diesel vehicles is estimated to increase by 60
135,000 and 190,000 vehicles/year respectively.
According to an
estimate the projected population of
different types of vehicles is shown in Fig. l. One sees a totally
picture of vehicle mix in India compared to US and European countries.
The two wheelers
far outnumber the cars and diesel vehicles unlike developed countries.
Directorate General of Technical Department2
a still higher growth in the population of
two wheelers. The pattern of fuel consumption is also very different in
as compared to US and Europe. First scooters, motorcycles, etc. consume
than 50 per cent of total gasoline at present and their share is
grow still further. Secondly, the consumption of diesel fuels is about
times higher than that of gasoline.
A high growth in
vehicle population brings in its wake urban
air pollution problems unless timely and appropriate steps to control
emissions are undertaken. Although the present population of vehicles
cities is much smaller than in US and Europe, the existing vehicle
engine designs, coupled with their older age and congested and slow
traffic, perhaps has aggravated the situation such that the signs of
air pollution are already apparent in the large cities in India.
control measures help to a significant extent in
the development of more efficient engines and also in their efficient
operation. In this paper, emission characteristics of the present
vehicles are given. The type of emission control technology required
and its effects
on vehicle fuel economy are also discussed.
Types of Vehicle Emissions
It is well known
that the gasoline vehicles contribute mostly
to carbon monoxide, un burned hydrocarbons (fuel), nitrogen oxides and
participates to the atmosphere. The diesel vehicles are the primary
emitting black smoke, in addition to the gaseous emissions mentioned
gaseous emissions pose health hazards by themselves as well as generate
hazardous secondary pollutants, e.g. ozone,
peroxyacyl and aryl nitrates
through reactions in the atmosphere. On the other hand, the diesel
considered largely a nuisance and causes poor visibility for the
following the offending diesel vehicle. The diesel exhaust is also
due to presence of traces of aldehydes and other oxygenated
Depending upon the sulphur content of diesel fuels, the diesel vehicles
emit varying amount of sulphur dioxide.1 into
Emission Characteristics of Indian Vehicles
emission control measures have generally been
directed towards carbon monoxide from gasoline vehicles and black smoke
diesel vehicles. This has been followed by the control of unburned
hydrocarbons, nitrogen oxides and lead removal from gasoline. In view
above, a vehicle emission survey comprising of idle carbon monoxide
from gasoline vehicles and free acceleration smoke from diesel vehicle
conducted in Delhi for the Department of Environment, Government of
India3. The main
findings of the survey
are given below.
emissions from gasoline vehicles The carbon
monoxide emissions from about 600 inservice vehicles were measured and
results are shown in Fig. 2. The passenger cars, generally, gave higher
emissions than the two and three wheelers.
The two and
three wheelers in India are mostly powered by crankcase scavenged two
engines. An inherent design feature of these engines is short
fresh air fuel mixture during cylinder scavenging process. The lower
concentration of CO in the exhaust gases of two and three wheelers
cars is largely due to dilution of combustion products by the short
fresh fuel air mixture. However, the fresh mixture short circuiting
very high concentration of un burned hydrocarbons of up to 45,000 ppmc
exhaust gases of 2 stroke engines.
Indian Standards for
CO emissions from gasoline vehicles and the percentage of vehicles
which meet these standards are shown in Table 1.
acceleration diesel smoke The smoke
emissions from buses, trucks and minibuses are shown in Fig. 3. Again
600 vehicles of all categories were tested. The minibuses and trucks
observed to be excessively high emitters of black smoke. The proposed
Standards specify a limit of 65HSU (Hartridge Smoke Unit) under free
acceleration. The srrioke limits ranging from 40 to 60 HSU have been in
in several European countries. Table 2 gives the percentage of the
surveyed which meet the proposed IS Smoke limit. Excessively high smoke
the trucks and minibuses resulted largely from over fuelling and poor
mechanical condition of the engines of these vehicles.
data The idle CO
and free acceleration smoke serve as good indicators of the emission
of the gasoline and diesel vehicles respectively as far as these two
concerned. However, the mass of different pollutants emitted by the
the most accurate measure of its pollution characteristics. Using US
(Environmental Protection Agency) and ECE
(Economic Commission for Europe) driving cycles, which simulate the
urban driving schedules in these countries, the mass emission data from
scooters, motorcycles, mopeds, cars and diesel engines were measured3. Table 3 shows
the average mass
emission characteristics of Indian vehicles.
technology required depends on the type and
design of engine/vehicle, the pollutant to be controlled and the extent
reduction required. Moderate to large reductions in the vehicle
been possible by those technologies which also result in the
vehicle fuel economy. Stringent controls and more so relating to the
oxides, require the technology which may result in the fuel economy
the following sections, the emission control technology which may be
initially in India and their effect on the vehicle fuel economy are
gasoline engine vehicles passenger cars The first
exhaust emission standards in US and uptill now in Europe have been met
primarily through the following techniques.
operation, improved design and calibration of
and faster idle speed, improved spark timing control and use of
ignition systems and
reduction in quench zones in combustion chamber, etc.
50 to 60 per cent reduction in CO and HC and about 20 per cent
reduction in NOX have
resulted through the above improvements.
The design modifications in intake manifolding to improve mixture
and reduce maldistribution amongst different engine cylinders and use
turbulence combustion chamber have made possible to run the engines
of lean mixture operation become obvious from
Fig. 4 which shows the effect of air fuel ratio on the emissions. Lean
operation results in Substantial reductions in CO and HC emissions. NOx emissions
however, peak at about 5 to 10 per
cent leaner than the stoichiometric mixture. The typical variation of
consumption with air fuel ratio is also shown in Fig. 4. The range of
ratios used on cars before 1970, and around 1980 in Europe are also
With the leaner operation of the cars, fuel economy benefits and the
accompanying reductions in CO and HC are evident. With improvements in
combustion chamber design the mixture can be further leaned to obtain
in all the three pollutants as well as the fuel consumption.
operation of the engine results in power loss but
reduces also the octane number requirement. Thus, compression ratio of
burn engines can be increased such that the same power output is
to 10 per cent reduction in fuel consumption and large reductions in
emissions are possible through these changes.
carburettor design, production and calibration have
given significant reductions in emissions. Carburettor metering
cut from 12 % to 6 % richer than the lean limit. Several manufacturers
and Europe maintained only a 3 per cent tolerance band on carburettor
characteristics as shown in Fig. 5.
variations in the carburettor metering
characteristics of even up to 10 to 15% were, common in the pre
control era. Reducing this tolerance through better quality control
low emissions with improvements in the vehicle fuel economy.
technologies, e.g. exhaust gas
recirculation (EGR), exhaust gas treatment by catalytic or thermal
are required to obtain emission reductions of more than 75%. However,
not provide the fuel economy benefits. Use of EGR, in fact,
gasoline engine powered two and three wheelers The
principal advantages of two stroke engines are low cost, high specific
output, low weight, simplicity of design and ease of maintenance.
depending upon the engine operating conditions, 15 to 40 per cent of
the air fuel
mixture supplied to the two stroke engine is short circuited to the
without taking part in combustion. Table 3 also showed that the
emissions from the two stroke engine powered vehicles under urban
conditions amounted to 22 30 per cent of the fuel supplied. Presence of
amount of residual gases in the combustion chamber results in very low
Thus, the main pollutants from 2 stroke
engines are carbon monoxide and hydrocarbons.