CIE 442 ENVIRONMENTAL ENGINEERING

LECTURE FIVE
LECTURER: ENG. GOODSON MASHEKA

1
Introduction
 Water is the essential element that makes life on earth possible.
 Without water there would be no life.
 We usually take water for granted.
 It flows from our taps when they are turned on.
 Most of us are able to bathe when we want to, swim when we choose and
water our gardens.
 Like good health we ignore water when we have it.

2
Introduction
 Although 71% of the earth’s surface is covered by water only a tiny
fraction of this water is available to us as fresh water.
 About 97% of the total water available on earth is found in oceans and is
too salty for drinking or irrigation.
 The remaining 3% is fresh water. Of this 2.997% is locked in ice caps or
glaciers.

3
Availability of water
Thus only 0.003% of the earth’ total volume of water is easily available to us
as soil moisture, groundwater, water vapour and water in lakes, streams,
rivers and wetlands.
This makes water a very precious resource.
The future wars in our world may well be fought over water.
By the middle of this century, almost twice as many people will be trying to
share the same amount of fresh water the earth has today.

4
Availability of water

As freshwater becomes more scarce access to water resources will be a

major factor in determining the economic growth of several countries
around the world.
Water availability on the planet: Water that is found in streams, rivers,
lakes, wetlands and artificial reservoirs is called surface water.
Water that percolates into the ground and fills the pores in soil and rock is
called groundwater.

5
Availability of water
 Porous water-saturated layers of sand, gravel or bedrock through which ground water flows
are called aquifers.
 Most aquifers are replenished naturally by rainfall that percolates downward through the soil
and rock.
 This process is called natural recharge.
 If the withdrawal rate of an aquifer exceeds its natural recharge rate, the water table is
lowered.

6
 Water Pollution

Any pollutant that is discharged onto the land above is also pulled into the
aquifer and pollutes the groundwater resulting in polluted water in the
nearby wells.
The same pollutant may also pollute the surface water through the surface
runoff
When the quality or composition of water changes directly or indirectly as
a result of man’s activities such that it becomes unfit for any purpose it is
said to be polluted.
7
Sources and categories of water pollutants

8
Sources of water pollution
Point sources of pollution
When a source of pollution can be readily identified because it has a definite source and place where it enters
the water it is said to come from a point source. Eg. Municipal and Industrial Discharge Pipes.

9
Sources of water pollution
Non-point sources of pollution
When a source of pollution cannot be readily identified, such as agricultural runoff, acid
rain, etc, they are said to be non-point sources of pollution

10
Categories of water pollution
There are several categories of common water pollutants.
Disease causing agents
 These are disease-causing agents (pathogens) which include bacteria, viruses, protozoa and
parasitic worms that enter water from domestic sewage and untreated human and animal
wastes.
 Human wastes contain concentrated populations of coliform bacteria such as Escherichia
coli and Streptococcus faecalis.
 These bacteria normally grow in the large intestine of humans where they are responsible
for some food digestion and for the production of vitamin K.

11
Categories of water pollution
Disease causing agents
 These bacteria are not harmful in low numbers.
 Large amounts of human waste in water, increases the number of these bacteria which
cause gastrointestinal diseases.
 Other potentially harmful bacteria from human wastes may also be present in smaller
numbers.
 Thus the greater the amount of wastes in the water the greater are the chances of
contracting diseases from them.

12
Categories of water pollution
Oxygen depleting wastes
 Another category of water pollutants is oxygen depleting wastes.
 These are organic wastes that can be decomposed by aerobic (oxygen requiring)
bacteria.
 Large populations of bacteria use up the oxygen present in water to degrade these
wastes.
 In the process this degrades water quality.
 The amount of oxygen required to break down a certain amount of organic matter is
called the biological oxygen demand (BOD).

13
Categories of water pollution
Oxygen depleting wastes
The amount of BOD in the water is an indicator of the level of pollution.
If too much organic matter is added to the water all the available oxygen is
used up.
This causes fish and other forms of oxygen dependent aquatic life to die.
Thus anaerobic bacteria (those that do not require oxygen) begin to break
down the wastes.
Their anaerobic respiration produces chemicals that have a foul odour and
an unpleasant taste that is harmful to human health.
14
Oxygen depleting wastes

Fish kills
15
Categories of water pollution
Inorganic plant nutrients.
 A third class of pollutants are inorganic plant nutrients.
 These are water soluble nitrates and phosphates that cause excessive growth
of algae and other aquatic plants.
 The excessive growth of algae and aquatic plants due to added nutrients is
called eutrophication.
 They may interfere with the use of the water by clogging water intake pipes,
changing the taste and odour of water and cause a buildup of organic matter.
 As the organic matter decays, oxygen levels decrease and fish and other
aquatic species die.
 The quantity of fertilizers applied in a field is often many times more than is
actually required by the plants.
 The chemicals in fertilizers and pesticides pollute soil and water.
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Categories of water pollution
Inorganic plant nutrients
While excess fertilizers cause eutrophication, pesticides cause bioaccumulation and
biomagnification.
Pesticides which enter water bodies are introduced into the aquatic food chain.
They are then absorbed by the phytoplanktons and aquatic plants.
These plants are eaten by the herbivorous fish which are in turn eaten by the carnivorous
fish which are in turn eaten by the water birds.
At each link in the food chain these chemicals which do not pass out of the body are
accumulated and increasingly concentrated resulting in biomagnification of these harmful
substances.
One of the effects of accumulation of high levels of pesticides such as DDT is that birds lay
eggs with shells that are much thinner than normal.
This results in the premature breaking of these eggs, killing the chicks inside.
Birds of prey such as hawks, eagles and other fish eating birds are affected by such
pollution.

17
Categories of water pollution

Water soluble inorganic

 A fourth class of water pollutants is water soluble inorganic
chemicals
 These are acids, salts and compounds of toxic metals such as
mercury and lead.
 High levels of these chemicals can make the water unfit to drink,
harm fish and other aquatic life, reduce crop yields and accelerate
corrosion of equipment that use this water

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Categories of water pollution
Organic chemicals
Another cause of water pollution is a variety of organic chemicals, which
include oil, gasoline, plastics, pesticides, cleaning solvents, detergent and
many other chemicals.
These are harmful to aquatic life and human health.
They get into the water directly from industrial activity either from
improper handling of the chemicals in industries and more often from
improper and illegal disposal of chemical wastes.

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Categories of water pollution
Sediment of suspended matter
Sediment of suspended matter is another class of water pollutants. These are insoluble
particles of soil and other solids that become suspended in water.
This occurs when soil is eroded from the land.
High levels of soil particles suspended in water, interferes with the penetration of sunlight.
This reduces the photosynthetic activity of aquatic plants and algae disrupting the ecological
balance of the aquatic bodies.
When the velocity of water in streams and rivers decreases the suspended particles settle
down at the bottom as sediments.
 Excessive sediments that settle down destroys feeding and spawning grounds of fish, clogs
and fills lakes, artificial reservoirs
20
Categories of water pollution

Water soluble radioactive

 Water soluble radioactive isotopes are yet another source of water pollution.
 These can be concentrated in various tissues and organs as they pass through
food chains and food webs.
 Ionizing radiation emitted by such isotopes can cause birth defects, cancer
and genetic damage

21
Categories of water pollution
Hot water
Hot water let out by power plants and industries that use large volumes of water to cool
the plant result in rise in temperature of the local water bodies.
Thermal pollution occurs when industry returns the heated water to a water source.
Power plants heat water to convert it into steam, to drive the turbines that generate
electricity.
For efficient functioning of the steam turbines, the steam is condensed into water after it
leaves the turbines.
This condensation is done by taking water from a water body to absorb the heat. This
heated water, which is at least 15oC higher than the normal is discharged back into the
water body.
The warm water not only decreases the solubility of oxygen but changes the breeding
cycles of various aquatic organisms.

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Categories of water pollution
Hot water
Heated effluents lower the solubility of oxygen in the water because gas
solubility in water is inversely proportional to temperature, thereby reducing
the amount of dissolved oxygen available to aerobic (oxygen-dependent)
species.
 Heat also increases the metabolic rate of aquatic organisms (unless the water
temperature gets too high and kills the organism), which further reduces the
amount of dissolved oxygen because respiration increases.

23
Effects of water pollution

24
Effects of water pollution

Water pollution adversely affects the fish and other aquatic life.
The presence of acids/alkalis in water destroys micro-organisms, thereby
disturbing the self purification process in rivers.
The toxic materials in water cause serious health hazards in human beings
and other animals.
Polluted water causes spread of epidemics, such as cholera, tuberculosis,
jaundice, dysentery, typhoid and diarrhoea in human beings.
High treatment cost for purification of water for drinking
25
Effects of water pollution
 The use of polluted water from lakes, ponds and rivers for irrigation of
agricultural fields, damages crops severely and decreases agricultural
production.
 The use of water contaminated with salts increases alkalinity of the soil.
 Heavily polluted water affects the soil, decreases its fertility and kills soil
micro-organisms and even certain useful bacteria.
 Contamination of sea water due to oil slicks caused by the leakage of crude
oil from oil tankers causes ecological disasters which results in the death of
sea organisms including fishes.
26
Some major disturbances in the ecosystem due to water pollution
Pollutant Sources Cause Effect
Nitrates, Agricultural Plant Nutrients Eutrophication
Phosphates, fertilizers,
ammonium salts Sewerage, manure
Animal manure and Sewerage, paper Oxygen deficiency Depth of aquatic
plant residues mills, food animals
processing wastes
Heat Power plants and Thermal discharge Death of fish
industrial cooling
Oil Slick Leakage from oil Petroleum Death of marine
life due to non-
availability of
oxygen dissolved
in water

27
Effects of water pollution

 Fertilizers and pesticides are widely used in agriculture.

 Their excessive use for increasing agricultural yield has led to
the phenomenon of eutrophication and biomagnification.

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Eutrophication
With the use of high yielding varieties of crops, the use of
fertilizers and pesticides has increased a lot.
Excess fertilizers may mix with surface water and may get drained
into water bodies (surface runoff).
The enrichment of water with nutrients such as nitrates and
phosphates that triggers the growth of green algae is called
eutrophication.
This fast growth of algae followed by decomposition depletes the
water body of its dissolved oxygen. As a result aquatic animals die
of oxygen shortage.

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Eutrophication

30
Eutrophication
Sewage and/or fertilizer run off from fields

Enriched nutrient content in water bodies (Eutrophication)

Algae multiply to produce an ‘algal bloom’

Algae use up oxygen and begin to die

Decomposers (bacteria) multiply and use more oxygen

Organisms (such as fish) die due to lack of oxygen

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Biomagnification
 Non-biodegradable pesticides, such as DDT are widely used for crop protection.
 Once they enter the food chain, their concentration keeps on increasing with each
trophic level (steps of a food chain).
 As a result, accumulation of these compounds takes place in the body of top
consumers over a period of time.
 Entry of harmful non-biodegradable chemicals in small concentrations and their
accumulation in greater concentrations in the various levels of food chain is called
biomagnification.

32
Biomagnification
 Consider the following food chain. Is there any difference in the concentration of DDT
in water and that in the body of the Pelican bird?
 Water ® Algae ® Fish ® Pelican bird (top consumer)
0.2 ppm 77 ppm 500-600 ppm 1700 ppm

(ppm = parts per million)

 DDT used in small quantities to kill mosquitoes can enter the food chain and may get
concentrated in large concentration due to its non-biodegradable nature in the body of
birds (top) consumer.
 This causes adverse effects, such as weak egg shells, resulting in decreased population

33
Sources of industrial pollution

Type of Inorganic pollutants Organic pollutant

Industry
Mining Chlorides, various metals, ferrous sulphate, sulphuric acid,
hydrogen sulphide, ferric hydroxide surface wash offs,
suspended solid, chlorides and heavy metals

Iron and Steel Suspended solids, iron cyanides, thiocyanate, sulphides, oxides Oil, phenol and naphtha.
of copper, chromium., cadmium and mercury.

Chemical Various acids and alkalies, chlorides, sulphates, nitrates of Aromatic compounds
Plants metals, phosphorus, fluorine, silica and suspended particles

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Sources of industrial pollution
Type of Inorganic Organic pollutant
Industry pollutants
Pharmaceuticals Protein, carbohydrates,
organic solvents intermediate
products, drugs and antibiotics
Soap and Tertiary ammonium Fats and fatty acids, glycerol,
Detergents compound alkalies. phosphates, polysulphonated
hydrocarbons.
Food processing Highly putrescible
(easily rots) organic matter and
pathogens.
Paper and Pulp Sulphides and Cellulose fibre, bark, wood sugars
bleaching liquors organic acids,

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Industrial pollution

36
Water pollutants, their sources and effect on human health

Pollutant Source Diseases in man

Lead Industrial waste Nervous disorders, Kidney failure. blood poisoning
Tin Industrial dust Affects central nervous system (CNS)
Affects, vision
Mercury Industrial discharge Affects central nervous system and peripheral nervous
system,
kidney failure, Numbness of lips, muscles and limbs,
Blurred vision
Arsenic Industrial discharge Respiratory and skin cancer. Nervous disorder
Nickel Aerosols, industrial dust Pulmonary disorders, dermatitis
Cadmium Industrial discharge Kidney disorders,
Pulmonary and skeletal diseases
Uranium, thorium Radioactive waste Leucoderma, skin cancer
cesium

37
Prevention and control of water pollution
Water pollution can be controlled by
 Treating industrial effluents before discharging into rivers, separate channels for river and
sewage water
 Avoid contamination of rivers, lakes and ponds by washing clothes, bathing.
 Not throwing waste, food materials, paper, biodegradable vegetables and plastic into open
drains.
 Setting up sewage water treatment plants
 Use of septic tanks/sewerage system in houses to avoid direct outlet of faecal matter and
other wastes
 Effluents from distilleries and solid waste containing organic matter diverted to biogas
plants to generate energy
 Maintenance or safety standards for the effluents discharged into the water System 38
EFFECT OF POLLUTION ON STREAMS

39
Effect Of Pollution On Streams
The effect of pollution on streams depends on the type of pollutant. Some compounds are
acutely toxic to aquatic life (e.g., heavy metals), and will cause dead zones downstream
from the pollutant source.
 Some types of pollutants are health concerns to humans, but have little impact on stream
communities.
For example, coliform bacteria are an indicator of animal waste contamination, and are
therefore an important human health concern, but most aquatic organisms are not harmed
by the presence of coliforms

40
EFFECT OF POLLUTION ON STREAMS
 One of the most common types of stream pollutants is the introduction of biodegradable organic material.
 When a high-energy organic material such as raw sewage is discharged into a stream, a number of changes
occur downstream from the point of discharge.
 As the organic components of the sewage are oxidized, oxygen is used at a rate greater than that upstream
from the sewage discharge, and the dissolved oxygen in the stream decreases markedly.
 The rate of reaeration, or solution of oxygen from the air, also increases, but is often not enough to prevent
total depletion of oxygen in the stream.
 If the dissolved oxygen is totally depleted, the stream becomes anaerobic.
 Often, however, the dissolved oxygen does not drop to 0 and the stream recovers without a period of
anaerobiosis

41
Effect Of Pollution On Streams

Dissolved oxygen downstream from a source of organic pollution

42
Effect Of Pollution On Streams
The dip in dissolved oxygen is referred to as a dissolved oxygen sag curve.
Curve A depicts an oxygen sag without anaerobic conditions; curve B shows an oxygen sag
curve when
pollution is concentrated enough to create anaerobic conditions, Do is the oxygen deficit in
the stream after the stream has mixed with the pollutant, and D,
is the oxygen deficit of the upstream water.
The effect of a biodegradable organic waste on a stream's oxygen level may be estimated
mathematically.
Let z (t) = the amount of oxygen still required at time-1 t, in milligrams per liter (mg/L), and
k' = the deoxygenation constant, in days-1.
The deoxygenation constant k ' will depend on the type of waste,
the temperature,
the stream velocity.
The rate of change of z over time is proportional to k

43
Effect Of Pollution On Streams
 The effect of a biodegradable organic waste on a stream's oxygen level may be estimated
mathematically.
Let
z (t) = the amount of oxygen still required at time t , in milligrams per liter (mg/L), and
k1', = the deoxygenation constant, in days -1

𝑑
𝑑 𝑡 = 𝑘 ′1 𝑧(𝑡)
𝑑𝑡
This differential equation has a simple solution:

𝑧 𝑡 = 𝐿0 𝑒 −𝑘′1 𝑡

44
Effect Of Pollution On Streams
 Where Lo is the ultimate carbonaceous oxygen demand, in milligrams per liter (mg/L), or
the amount of oxygen needed to degrade the carbonaceous organic material in the
wastewater at the point where the effluent first enters into and mixes with the stream.
 This equation is plotted for various values of k '1, and with Lo = 30 mg/L.
 Since the ultimate oxygen requirement is Lo and the amount of oxygen still needed at any
given time is z,

45
Computation of Oxygen Demand

Amount of Oxygen required at any time t(z(t)) for various deoxygenation constants (q) when
the ultimate carbonaceous oxygen demand (Lo) is 30mg/L

46
 Computation of Oxygen Demand
The amount of oxygen used after time t, the biochemical oxygen demand (BOD), is simply
the difference between Lo and z(t):
−𝑘 ′ 1 𝑡
𝐵𝑂𝐷 𝑡 = 𝐿𝑜 − 𝑧 𝑡 = 𝐿𝑂 (1 − 𝑒 )

 This relationship is plotted and it can be seen that the BOD asymptotically approaches Lo as time passes.
 Contrasting with this increase in BOD over time is the reoxygenation of the stream by natural forces.
 This will depend on the difference between the current amount of dissolved oxygen, and the maximum
amount of oxygen the water can hold at saturation.
 In other words, if d is the actual amount of dissolved oxygen in the water, and d s is the amount of
dissolved oxygen at saturation, then

𝑑
𝑑 𝑡 = 𝑘′2 𝑑𝑠 − 𝑑 𝑡 = 𝑘′2 𝐷(𝑡)
𝑑𝑡

47
Computation of Oxygen Demand
 where D (t) is the oxygen deficit at time t, in milligrams per liter (mg/L), and k 2'
is the reoxygenation constant, in days -1

Dissolved oxygen used (BOD) at any time t plus the dissolved oxygen still needed at time
t(z(t)) is equal to the ultimate oxygen demand (Lo)
48
Computation of Oxygen Demand
Reaeration constant
Types of water course K2’ at 20̊ C (day -1)
Small ponds or backwaters 0.10-0.23
Sluggish streams 0.23-0.35
Large streams, low velocity 0.35-0.46
Large streams, normal velocity 0.46-0.69
Swift streams 0.69-1.15
Rapids >1.15

NOTE: For temperatures other than 20̊ C, k2’ (T) = k2’(20̊ C)(1.024)T-20

 The value of k2' is obtained by studying the stream using a tracer. If this cannot be done,
a generalized expression (O’Connor 1966) may be used

3.9𝑣 1 2
1.037 𝑇−20
𝑘′2 =
𝐻3 2

49
Computation of Oxygen Demand
where,
 T is the temperature of the water in degrees Celsius
 H is the average depth of flow in meters,
 v is the mean stream velocity in meters per second (m/s ) .
 Alternatively, k'2 values may be estimated from a table like reaeration constant table
 For a stream loaded with organic material, the simultaneous deoxygenation and
reoxygenation of the water forms the dissolved oxygen sag curve, first developed by
Streeter and Phelps in 1925 (Streeter and Phelps 1925).
 The shape of the oxygen sag curve is the sum of the rate of oxygen use and the rate of
oxygen supply.

50
Computation of Oxygen Demand
 Immediately, downstream from a source of organic pollution the rate of use will often
exceed the rearation rate and the dissolved oxygen concentration will fall sharply.
 As the discharged organic matter is oxidized, and fewer high-energy organic
compounds are left, the rate of use will decrease, the supply will begin to catch up with
the use, and the dissolved oxygen will once again reach saturation.

This may be expressed mathematically as:

𝑑
𝐷 𝑡 = 𝑘1 ′ 𝑧 𝑡 − 𝑘′2 𝐷(𝑡
𝑑𝑡

51
 Computation of Oxygen Demand
Which can be solved to give:

𝑘1′ 𝐿𝑂 −𝑘1, 𝑡 −𝑘2, 𝑡 −𝑘2, 𝑡

𝐷 𝑡 = ′ ′ 𝑒 −𝑒 + 𝐷𝑜 𝑒
𝑘2 − 𝑘1

 Where Do is the initial oxygen deficit in the stream at the point of wastewater discharge, after the
stream flow has mixed with the wastewater, in milligrams per liter (mg/L).
 The deficit equation can also be expressed in common logarithms:

𝑘1′ 𝐿𝑂 −𝑘 ,
𝑡 −𝑘 ,
𝑡 ,
𝐷 𝑡 = ′ ′ 10
1 − 10 2 + 𝐷𝑜 10 𝑡
−𝑘2
𝑘2 − 𝑘1

52
 Computation of Oxygen Demand
Since
,
𝑒 −𝑘2 𝑡 = 10−𝑘𝑡 when k =0.043k’

 The initial oxygen deficit (Do) is calculated as a flow-weighted proportion of the initial stream oxygen
deficit and the wastewater oxygen deficit:

𝐷𝑠 𝑄𝑠 + 𝐷𝑝 𝑄𝑝
𝐷𝑜 =
𝑄𝑠 + 𝑄𝑃

Where Ds is the oxygen deficit in the stream directly upstream from the point of discharge, in milligrams
per liter (mg/L); Qs is the stream flow upstream from the wastewater discharge, in cubic meters per second
(m3/s); Dp is the oxygen deficit in the wastewater being added to the stream, in milligrams per liter
(mg/L); and Qp is the flow rate of wastewater, in cubic meters per second (m /s).

53
Computation of Oxygen Demand
Similarly, the ultimate carbonaceous BOD (Lo ) is:

𝐿𝑠 𝑄𝑠 + 𝐿𝑝 𝑄𝑝
𝐿𝑜 =
𝑄𝑠 + 𝑄𝑃

where Ls is the ultimate BOD in the stream immediately upstream from the point of
wastewater discharge, in milligrams per liter (mg/L); Qs is the stream flow
upstream from the wastewater discharge, in cubic meters per second (m3 /s); Lp is
the ultimate BOD of the wastewater, in milligrams per liter (mg/L); and Qp is the
flow rate of the wastewater, in cubic meters per second (m3 /s).

54
 Computation of Oxygen Demand
The most serious water quality concern is the downstream location where the oxygen
deficit will be the greatest, or where the dissolved oxygen concentration is the lowest. By
setting dD/dt = 0, we can solve for the time when this minimum dissolved oxygen occurs,
the critical time, as

1 𝑘2, 𝐷𝑜 𝑘2, − 𝑘1,

𝑡𝑐 = , , In , 1−
𝑘2 − 𝑘1 𝑘1 𝑘1, 𝐿𝑜

 Where tc is the time downstream when the dissolved oxygen concentration is the lowest.

55
Example
Assume that a large stream has a reoxygenation constant k1 ' of 0.4/day, a flow velocity
of 5 miles/h, and at the point of pollutant discharge, the stream is saturated with oxygen
at 10 mg/L. The wastewater flow rate is very small compared with the stream flow, so
the mixture is assumed to be saturated with dissolved oxygen and to have an oxygen
demand of 20 mg/L.
The deoxygenation constant k1' is 0.2/day. What is the dissolved oxygen level
30 miles downstream?
Solution
Stream velocity = 5 miles/h, hence it takes 30/5 or 6 h to travel 30 miles.
Therefore, t = 6 h/24 h/day = 0.25 day, and Do = 0 because the stream is saturated.
20 20
𝐷 𝑡 = 𝑒 − 0.2 0.25
− 𝑒− 0.4 0.25
= 1.0𝑚𝑔/𝐿
0.4 − 0.2
The dissolved oxygen 30 miles downstream will be the saturation level minus the
deficit, or 10 - 1.0 = 9.0 mg/L
56
Effect Of Pollution On Streams
When the rate of oxygen use overwhelms the rate of oxygen reaeration, the
stream may become anaerobic.
An anaerobic stream is easily identifiable by the presence of floating sludge,
bubbling gas, and a foul smell.
The gas is formed because oxygen is no longer available to act as the hydrogen
acceptor, and NH3, H2S, and other gases are formed.
Some of the gases dissolve in water, but others can attach themselves as
bubbles to sludge (solid black or dark benthic deposits) and buoy the sludge to
the surface.
For some distance, the water is usually black or dark, and filamentous bacteria
(sewage "fungus") grow in long slimy filaments that cling to rocks and wave
graceful streamers downstream.

57
Effects of aquatic life
 Other adverse effects on aquatic life accompany the unpleasant physical
appearance of an anaerobic stream.
 The types and numbers of species change drastically downstream from the
pollution discharge point.
 Increased turbidity, settled solid matter, and low dissolved oxygen all contribute
to a decrease in fish life.
 Fewer and fewer species of fish are able to survive, but those species that do
survive find food plentiful, and often multiply in large numbers.
 Carp and catfish can survive in water that is quite foul and can even gulp air from
the surface.
 Trout, on the other hand, need very pure, cold, oxygen-saturated water and are
notoriously intolerant of pollution.

58
Effects of aquatic life

 The numbers of other aquatic species are also reduced under anaerobic conditions,
 The remaining species, like sludge worms, bloodworms, and rat-tailed maggots,
abound, often in staggering numbers - as many as 50,000 sludge worms per square
foot.
 The diversity of species may be quantified by using an index, such as the Shannon-
Weaver diversity index (Shannon and Weaver 1949).
𝑠
′
𝑛𝑖 𝑛𝑖
𝐻 = × 𝐼𝑛
𝑛 𝑛
𝑖=1

where H'’ is the diversity index, ni is the number of individuals in the ith species, and n
is the total number of individuals in all S species.
59
Effects of aquatic life

The number of species and the total number of organisms downstream from a
point of organic pollution

60
Effects of aquatic life
Diversity indices can be quite difficult to interpret because they are composed of
two different measurements: species richness (how many different kinds of
organisms are present?) and species equitability (how evenly are the individuals
distributed among the species?).
 One way to overcome this problem is to convert the diversity index into an
equitability index, such as Pielou's J (E.C 1975):

𝐻′
𝐽=
𝐼𝑛𝑆

 Pielou's J is a measure of how close H' is to its maximum value for any givensample,
approaching 1.0 at maximum equitability.
 Although still widely used for general comparisons, both H' and J have been replaced with
more complex indices that take into account the relative abundance of pollution-tolerant or
intolerant species

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Diversity and equitability of aquatic organisms
No. of individuals in samples
Species Pollution Upstream from Downstream
tolerances outfall from outfall
Mayfiles Intolerant 20 5
Rat-tailed Tolerant 0 500
maggots
Trout Intolerant 5 0
Crap Tolerant 1 20
Diversity (H’) = 0.96 0.22
Equitability (J) = 0.87 0.20

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Effects of aquatic life
 As mentioned earlier, nitrogen compounds may be used as indicators of pollution. The
first transformation, in both aerobic and anaerobic decomposition, is
 the formation of ammonia; thus the concentration of ammonia increases as organic
nitrogen decreases.
 As long as the stream remains aerobic, the concentration of nitrate will increase to
become the dominant form of nitrogen.
 These reactions of a stream to pollution occur when a rapidly decomposable organic
material is the waste.
 The stream will react much differently to inorganic waste, as from a metal-plating plant.
 If the waste is toxic to aquatic life, both the kind and total number of organisms will
decrease downstream from the outfall.
 The dissolved oxygen will not fall, and might even rise.
 There are many types of pollution, and a stream will react differently to each. When two
or more wastes are involved, the situation is even more complicated.

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Effects of aquatic life

Typical variations in nitrogen compounds downstream from a point source of pollution

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Groundwater pollution
While oil spills are highly visible and often get a lot of media attention, a
much greater threat to human life comes from our groundwater being
polluted which is used for drinking and irrigation.
While groundwater is easy to deplete and pollute it gets renewed very
slowly and hence must be used judiciously.
Groundwater flows are slow and not turbulent hence the contaminants are
not effectively diluted and dispersed as compared to surface water.
Moreover pumping groundwater and treating it is very and costly.
Hence it is extremely essential to prevent the pollution of groundwater in
the first place.

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Causes of ground water Pollution
 Urban run-off of untreated or poorly treated waste water and
garbage
 Industrial waste storage located above or near aquifers
 Agricultural practices such as the application of large amounts
of fertilizers and pesticides, animal feeding operations, etc. in
the rural sector
 Leakage from underground storage tanks containing gasoline
and other hazardous substances
 Leachate from landfills
 Poorly designed and inadequately maintained septic tanks
 Mining wastes
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