Module 3

◼ Water pollution

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 The Importance of Water
◼ All living things need
water
◼ Composes majority of
the body of organisms
◼ Habitat for many
organisms
◼ Helps regulate climate
◼ Shapes earth’s surface
◼ Dilutes & degrades
wastes
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 Use of water
◼ Uses of Freshwater Water resources are used in various fields such as
agricultural, industrial, domestic, recreational, and environmental
activities. Most of the uses require fresh water.
◼ However, around 97 percent of the water on the earth is saltwater and
only three percent is freshwater. About two-thirds of the available
freshwater is frozen in glaciers and polar ice caps. The remaining
freshwater is found underground and a negligible portion of it is
present on the ground or in the air.The following are detailed views on
how water is used in different sectors.

Water footprint

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 Agricultural Use
◼ Agriculture accounts for about 69
per cent of all water consumption
especially in agricultural economies like
India. Agriculture thereby becomes the
largest consumer of the Earth’s available
freshwater. By 2050, the global water
demand for agriculture is estimated to
increase by an additional 19% due to
irrigation needs. Increasing irrigation
needs are likely to put immense pressure
on water storage. It is still not concluded
whether further expansion of irrigation
and additional water withdrawals from
rivers and groundwater is possible in the
future.
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 Industrial Use
◼ Water is the lifesaver of the industry. It is
used for various purposes such as a raw
material coolant, a solvent, a transport
agent, and as a source of energy.
Manufacturing industries are considered to
have a considerable share of the total
industrial water consumption. Besides, paper
and allied products, chemicals, and primary
metals are major industrial users of water.
Worldwide, the industry consumes around 19
percent of total water consumption. In
industrialized countries, the industries use
more than half of the water available for
human use.

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 Domestic Use
◼ Itincludes usages like drinking, cleaning, personal hygiene,
garden care, cooking, washing of clothes, dishes, vehicles, etc.
Since the end of World War II, there has been a trend of
people migrating out of the country to the ever-expanding cities.
This trend has an important role in our water resources.The
government and communities are in a need to provide large
water-supply systems to deliver water to new growing
populations and industries. Comparing all water consumption in
the world, domestic uses about 12 percent of the total water
consumed.

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 Use for Hydropower
◼ Electricity generated from
water is called hydropower.
Hydropower is one of the highly
renewable sources of electricity
in the world. It accounts for
around 16 percent of the total
electricity generated globally.
There are numerous
opportunities for hydropower
development around the
world.At present, the leading
hydropower generating
countries are China, the US,
Brazil, Canada, India, and Russia.

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 Use for Navigation and
Recreation
◼ Navigable waterways are defined as
watercourses that can be used to
transport interstate or foreign
commerce. Moving of agricultural and
commercial goods on the water is done
on a large scale around various parts of
the world. Water is also used for
recreational purposes like boating,
swimming, and sporting activities.
These usages affect the quality of
water and pollute it. The highest
priority should be given to public
health and drinking water quality while
permitting such activities in
reservoirs, lakes, and rivers.

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 Water on Earth
◼ About 97% Earth’s water is salty–less than 1%
of the planet’s water is available fresh H2O

◼ Fresh water is distributed unevenly

◼ 2025: 1/3 human population will live in areas
lacking fresh water
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 Types of water resources

◼ Marine water or saline water

◼ Surface water
◼ Groundwater Fresh water

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 Water, water, everywhere?
(NOT)
➢ Comparison of
population sizes and
shares of the world’s
freshwater among the
continents. (Only 7
countries account for
60% of global water
availability)
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 Water Wars

➢ Many countries in the

Middle East, which
has one of the world’s
highest population
growth rates, face
water shortages.
➢ Desalinization
➢ Rainwater
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The Hydrologic
Cycle

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 Surface Water
◼ Streams, rivers,
lakes, ponds,
reservoirs, wetlands
◼ Runoff replenishes
surface water
◼ Watershed
(A watershed is an
area of land that
drains or “sheds” A watershed is an area of land that drains
water into a specific all the streams and rainfall to a common
outlet such as the outflow of a reservoir,
waterbody. mouth of a bay, or any point along a stream
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channel. CEE101
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 Groundwater
◼ Supply of fresh water found under
Earth’s surface--recharged when water
at surface infiltrates into the ground
◼ Stored in under
ground aquifers
◼ Discharged into
rivers, springs,
etc…

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Infiltration - Process of water percolating
through the soil and into cracks and
permeable rocks.
Zone of Aeration -
Upper soil layers
that hold both air
and water.
Zone of Saturation
Lower soil layers
where all spaces are
filled with water.
Water Table -
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 Precipitation Unconfined Aquifer Recharge Area
Flowing Evaporation and transpiration
Confined artesian well
Recharge Area Evaporation

Infiltration Runoff

Well requiring a pump

Unconfined aquifer
Water table

Less permeable material Confined aquifer

such as clay
Confining permeable rock layer

• Recharge Zone - Area where water infiltrates

into an aquifer.
-Recharge rate is often very slow.
-Presently, groundwater is being removed
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faster than it can be replenished.
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◼ Aquifers - Porous layers of sand, gravel,
or rock lying below the water table.

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 Water Resource Problems
◼ Too much water
◼ Too little water
◼ Poor-quality water

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 Tanushree Bhattacharya. CEE101
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According to the Water (Prevention and Control
of Pollution) Act, 1974, ―

◼ water pollution means such contamination of water or such alteration of

the physical, chemical or biological properties of water or such
discharge of any sewage or trade effluent or of any other liquid,
gaseous or solid substance into water (whether directly or indirectly) as
may or is likely to, create a nuisance or render such water harmful or
injurious to public health or safety or to domestic, commercial,
industrial, agricultural or other legitimate uses, or the life and health
of animals or plants or of aquatic organisms.
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 SOURCES OF WATER
POLLUTION
1, Domestic wastes
2. Industrial wastes
3. Agricultural wastes, insecticides and
pesticides
4. Radioactive wastes.
 Domestic source

◼ Domestic wastewater contains a great variety

of pollutants, such as nutrients, oil and grease,
detergents, biowastes, household chemicals,
heavy metals, bathing and kitchen waste,
salts, pathogens, medicinal constituents, and
soluble and particulate organic matter.

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 Causes..
◼ Growing Population
◼ Every year we add millions of
people to the world
population and our country is
no exception. The earth is
now overcrowded and
consumption habit of the
people is on the rise. The
growth of population gave
rise to increase in wants and
demands of mankind and has
succeeded in creating acute
problem of water pollution.

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◼ Industrialization
◼ Rapid industrialization is another cause
of worry as far as water pollution is
concerned. Immediately after the
independence, major steps were taken in
our country in its stride for development
in order to give its economy a big push.
◼ Industrialization along with development
brought with it a danger to the human
civilization- the problem of environmental
pollution
◼ Urbanization
◼ big cities also developed just near the water
courses particularly besides the big rivers
subsequently attracted the establishment of
industrial and commercial basis in and around
the cities.
◼ Since many towns and cities lack a proper
sewerage system, the condition worsened
further.
◼ Nature of Modern Technology
◼ The nature of productive technology in
recent years has been largely responsible
for the generation of synthetic and non
biodegradable substances such as
plastics, chemical nitrogen fertilizers,
synthetic detergents, synthetic fibres,
petrochemical and other environmentally
injurious industries and ―disposable
culture.
◼ Modern Agricultural Practices
◼ Fertilizers like phosphates and nitrates
cause widespread damage when applied
carelessly to crops. The fertilizers can be
transmitted to groundwater by leaching and
to surface waters by natural drainage and
storm run-off.
◼ In addition to fertilizers various kinds of
pesticides and insecticide also applied.
Almost all the pesticides those are used are
toxic to human and animals
◼
 Radioactive wastes

◼ Natural sources and man made sources

like, atomic explosions and nuclear fall
out.

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 Point source and non point
source

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 Changes in Surface Runoff
◼ Prior to 1970 about 10%
of stormwater became
runoff
◼ Now 55% of stormwater
is transported as runoff
as development exceeds
75% of the permeable
soil area

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 Stormwater Runoff
(greatest contributor to nonpoint
source pollution) contains:
◼ Nutrients*
◼ Metals*
◼ Suspended solids*
◼ Pesticides
◼ Hydrocarbons
◼ Microorganisms

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 Types of water pollution
◼ Types of water pollution
◼ Surface water:- Water resources like huge oceans, lakes, and rivers etc. are called
surface waters. Contaminants such as chemicals, nutrients, and heavy metals are
carried from farms, factories, and cities into streams and rivers and then to seas and
oceans. Our seas are also sometimes spoiled by oil spills.
◼ Marine pollution: Marine pollution is a combination of chemicals and trash, most of
which comes from land sources and is washed or blown into the ocean. This pollution
results in damage to the environment, to the health of all organisms, and to economic
structures worldwide.
◼ Ground water:- Water stored underground in aquifers is known as groundwater.
Groundwater gets polluted when contaminants (pesticides, fertilizers) or waste leached
from landfills and septic systems make their way into an aquifer, rendering it unsafe
for human use. It is virtually impossible to remove contaminants from groundwater.
Groundwater can also spread contamination into streams, lakes, and oceans.
◼ Themal Pollution:
◼ Thermal pollution is defined as a sudden increase or decrease in the temperature of a
natural body of water, which may be an ocean, lake, river, or pond, by human
influence., thermal pollution is when an industry or other human-made organization
takes water from a natural source and cools or heats it before eventually ejecting it
back into the natural resource, which changes the oxygen levels, disastrously affecting
local ecosystems and communities.
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 Major
type of
water
pollutants

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 Classification of pollutants
Emerging water pollutants
These pollutants include a variety of compounds such
as antibiotics, drugs, steroids, endocrine disruptors,
hormones, industrial additives, chemicals, and also
microbeads and microplastics. Emerging pollutants are
chemicals and compounds that have recently been
identified as dangerous to the environment, and
consequently to the health of human beings.
Precisely, they have been labeled “emerging” because
of the rising level of concern linked to them. In
addition, many of these emerging pollutants have not
been regulated under national or international
legislation, hence posing a greater risk to our
livelihood.

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Concept of water quality
According to UNEP / WHO 1996 “Water quality” is a term used here to express
the suitability of water to sustain various uses or processes. Any use will have
certain requirements for the physical, chemical or biological characteristics of
water, for example, if the water is for drinking purpose then contaminants should
not be present, as well as the water should be acceptable, that is devoid of any
colour or objectionable odour and taste.
Water quality plays a pivotal role in public health, habitat protection, agriculture,
and industry. Water requirements have emerged over time for drinking, hygiene,
fisheries, irrigation, livestock, and industries, cooling in fossil fuel power plants,
nuclear power plants, hydropower generation, and recreational activities.
Drinking water supplies and specialized industrial manufacturers exert the most
sophisticated demands on water qualitatively but largest demands for water
quantity, such as for agricultural irrigation and industrial cooling, require the least
in terms of water quality.

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 Water quality parameters that imparts several problems in industrial water use.

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 Type of Pollutants
Oxygen-Demanding Substances

◼Dissolved oxygen is a key element in water

quality that is necessary to support aquatic life.
◼A demand is placed on the natural supply of
dissolved oxygen by many pollutants in
wastewater. This is called biochemical oxygen
demand, or BOD,

◼ Organic matter and ammonia are “oxygen-

demanding” substances. Oxygen-demanding
substances are contributed by domestic sewage
and agricultural and industrial wastes of both
plant and animal origin, such as those from
food processing, paper mills, tanning, and
other manufacturing processes.

◼These substances are usually destroyed or

converted to other compounds by bacteria if
there is sufficient oxygen present in the water,
but the dissolved oxygen needed to sustain fish
life is used up in this break down process.

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 Dissolved oxygen
◼ The oxygen dissolves by diffusion from the surrounding
air; aeration of water that has tumbled over falls and
rapids; and as a waste product of photosynthesis.
As dissolved oxygen levels in water drop
below 5.0 mg/l, aquatic life is put under
stress.

How Dissolved Oxygen Affects Water

Supplies
A high DO level in a community water
supply is good because it makes drinking
water taste better. However, high DO levels
speed up corrosion in water pipes. For this
reason, industries use water with the least
possible amount of dissolved oxygen.
Water used in very low pressure boilers
have no more than 2.0 ppm of DO, but
most boiler plant operators try to keep
oxygen levels to 0.007 ppm or less.
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Biochemical oxygen demand (BOD) is the amount of
dissolved oxygen needed by aerobic biological organisms
in a body of water to break down organic material present in
a given water sample at certain temperature over a specific
time period.
BOD 5 test.
CBOD
NBOD

COD
Chemical oxygen demand (COD) is defined as “a measure
of the oxygen equivalent of the organic matter content of a
sample that is susceptible to oxidation by a strong chemical
oxidant.* ” Trivalent manganese (Mn III) is a strong, non-
carcinogenic chemical oxidant that changes quantitatively
from purple to faint pink when it reacts with organic matter.
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 Oxygen sag curve
Point source

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 Pathogens

◼ Infectious micro-organisms, or
pathogens, may be carried into
surface and groundwater by sewage
from cities and institutions, by
certain kinds of industrial wastes,
such as tanning and meat packing
plants, and by the contamination of
storm runoff with animal wastes
from pets, livestock and wild
animals, such as geese or deer.
◼ Humans may meet these pathogens
either by drinking contaminated water
or through swimming, fishing, or other
contact activities.
◼ Modern disinfection techniques have
greatly reduced the danger of
waterborne disease.

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 Nutrients

◼ Carbon, nitrogen, and phosphorus are essential to living organisms and are the chief
nutrients present in natural water. Large amounts of these nutrients are also present in
sewage, certain industrial wastes, and drainage from fertilized land.
◼ Conventional secondary biological treatment processes do not remove the phosphorus and
nitrogen to any substantial extent -- in fact, they may convert the organic forms of
these substances into mineral form, making them more usable by plant life.
◼ When an excess of these nutrients overstimulates the growth of water plants, the result
causes excessive growth of algae. Uncontrolled algae growth blocks out sunlight and chokes
aquatic plants and animals by depleting dissolved oxygen in the water at night.
◼ The release of nutrients in quantities that exceed the affected waterbody’s ability to
assimilate them results in a condition called eutrophication.
 Eutrophication

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◼ Causes of Eutrophication
◼ The availability of nutrients such as nitrogen and phosphorus limits the growth of plant life
in an ecosystem. When water bodies are overly enriched with these nutrients, the growth of
algae, plankton, and other simple plant life is favoured over the growth of more complex
plant life.

◼ How do Water Bodies Become Overly Enriched?

◼ Phosphorus is considered one of the primary limiting factors for the growth of plant life in
freshwater ecosystems. Several sources also claim that the availability of nitrogen is an
important limiting factor for the growth of algae.

◼ Phosphates tend to stick to the soil and are transported along with it. Therefore, soil
erosion is a major contributor to the phosphorus enrichment of water bodies. Some other
phosphorus-rich sources that enrich water bodies with the nutrient include:

◼ Fertilizers
◼ Untreated sewage
◼ Detergents containing phosphorus
◼ Industrial discharge of waste.
◼ Among these sources, the primary contributors to eutrophication include agriculture and
industrial wastes.

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◼ What Happens to the Huge Biomass of Algae in
Eutrophic Waters?
◼ The excessive growth of algae in eutrophic waters is
accompanied by the generation of a large biomass of
dead algae. These dead algae sink to the bottom of
the water body where they are broken down by
bacteria, which consume oxygen in the process.
◼ The overconsumption of oxygen leads to hypoxic
conditions (conditions in which the availability of
oxygen is low) in the water. The hypoxic conditions at
the lower levels of the water body lead to the
suffocation and eventual death of larger life forms
such as fish.

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◼ Effects of Eutrophication
◼ Primarily, the adverse effects of eutrophication on aquatic bodies include a
decrease in biodiversity, increase in toxicity of the water body, and change in
species dominance. Some other important effects of this process are listed
below.

◼ Phytoplanktons grow much faster in such situations. These phytoplankton species

are toxic and are inedible.
◼ Gelatinous zooplankton blooms fast in these waters.
◼ Increased biomass of epiphytic and benthic algae can be observed in eutrophic
waters.
◼ Significant changes arise in the species composition of macrophytes and the
biomass.
◼ The water loses its transparency and develops a bad smell and colour. The
treatment of this water becomes difficult.
◼ Depletion of dissolved oxygen in the water body.
◼ Frequent fish kill incidents occur and many desirable fish species are removed
from the water body.
◼ The populations of shellfish and harvestable fish are lowered.
◼ The aesthetic value of the water body diminishes significantly.

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Ecological Effects of Eutrophication
Natural standing waters range from ultra oligotrophic to eutrophic with progressive increase in productivity
and related parameters. In addition to such general changes, eutrophication also affects the vertical
structure of lakes with further implications for the biology of freshwater organisms. The transition from
eutrophic to hypertrophic status is usually the result of human activities, and ultimately affects the whole
ecological balance of the freshwater system.

Decrease in Biodiversity
When an aquatic ecosystem is enriched with nutrients by either natural or artificial means, the conditions
become extremely beneficial to primary producers. Commonly, algae and other similar species utilize these
nutrients and a huge increase in their population (algal bloom) is observed.

These algal blooms hinder the flow of sunlight to the bottom of the aquatic body and also cause wide
swings in the dissolved oxygen levels in the water.

When the dissolved oxygen in the water reduces to an amount below the hypoxic level, many marine
animals suffocate and die. This reduces the effective biodiversity of the water body.

Increase in Water Toxicity

A few algae are toxic to many plants and animals. When these algae bloom in eutrophic waters, they
release neurotoxins and hepatotoxins. These toxins can also move up the food chain via shellfish or other
marine animals and lead to the death of many animals.

Toxic algal blooms can also be harmful to humans and are the root cause of many cases of neurotoxic,
paralytic, and diarrhoetic shellfish poisoning.

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◼ Invasion of New Species
◼ A limiting nutrient corresponding to a water body can be made
abundant by the eutrophication process, leading to a shift in the
species composition of the aquatic body and the ecosystem
surrounding it.

◼ If a nitrogen deficient water body is suddenly enriched with it,

many other competitive species might relocate to the water
body and out-compete the original inhabitants of the ecosystem.
One such example of a new species invading eutrophic conditions
is the common carp, which has adapted to these conditions.

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 Inorganic and Synthetic Organic
Chemicals
◼ A vast array of chemicals are included in this category. Examples
include detergents, household cleaning aids, heavy metals,
pharmaceuticals, synthetic organic pesticides and herbicides,
industrial chemicals, and the wastes from their manufacture.
◼ Many of these substances are toxic to fish and aquatic life and many
are harmful to humans. Some are known to be highly poisonous at very
low concentrations. Others can cause taste and odor problems, and
many are not effectively removed by conventional wastewater
treatment.
 Thermal
◼ Thermal pollution is any deviation from
the natural temperature in a habitat and
can range from elevated temperatures
associated with industrial cooling
activities to discharges of cold water into
streams below large impoundments.
◼ Heat reduces the capacity of water
to retain oxygen.
◼ In some areas, water used for
cooling is discharged to streams at
elevated temperatures from power
plants and industries. Even
discharges from wastewater
treatment plants and storm water
retention ponds affected by summer
heat can be released at
temperatures above that of the
receiving water and elevate the
stream temperature.
◼ Unchecked discharges of waste heat
can seriously alter the ecology of a
lake, a stream, or estuary.
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 Drinking water standards
◼ IS 10500 : 2012,
amended in 2015.

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 Water Health Effects Other Effects
Parameters
Temperature Regulates biochemical and Affects photosynthesis, dissolved
metabolic reactions. oxygen.
pH Gastrointestinal irritation. Affects enzyme kinetics; corrosive;
affects aquatic life.
TDS Affects kidney and heart Corrosive to water-supply systems;
functioning, laxative or constipation causes hardness.
effects, gastrointestinal irritation.
Hardness Skin irritation; worsens some health Poor lather with detergent; cloth
conditions (cancer, diabetes, etc.). quality deterioration.
Mg Deficiency- hypertension, cardiac Poor lather with detergent; cloth
and cardiovascular diseases, quality deterioration.
diabetes mellitus, osteoporosis.
Ca Deficiency- osteoporosis, Poor lather with detergent; cloth
hypertension. quality deterioration.
Cl- Laxative effects. Corrosive; deleterious effects on
plants, can clog soil pores if it is in
dissolved condition.
NO3- Methemoglobinemia in infants. Algal bloom; adverse impacts on
aquatic life.
PO43- Digestive problems. Eutrophication.
SO42- Laxative effects, gastrointestinal Acid rain; associated with acid mine
irritation. drainage; corrosive.
Na Hypertension, heart diseases, kidney Can impart salinity hazard in soil if it
related problems. is used for irrigation purpose.
Al Kidney disorders, neurological Prevents nutrient intake by roots;
problems. interferes with gill functioning.
Heavy metals Most of the heavy metals affect liver Most of the heavy metals affects soil
and kidney functioning; ATPase microbial activity; deleterious impact
inhibitor; degrades enzyme on plants; ROS production (stress).
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Biological Oxygen High BOD levels- hazardous. Affects water quality and effluent
Demand biodegradability.
Chemical Oxygen Correlated to ill effect on human Hypoxic water reduces cell
Demand health (algal blooms, sea food functioning, death of aquatic
contamination). organisms.
Bacteria Causes dysentery (Salmonella), Some aquatic animals affected similar
cholera (Vibrio), typhoid to human beings; indicates DO, BOD.
(Salmonella).
Protozoa Causes amoebiasis (Entamoeba Affects plant growth; causes illness in
histolytica), giardiasis (Giardia various animals like horse, zebra, dog
lamblia). etc.
Virus Causes SARS (Coronavirus), Affects various animals, plants and
hepatitis A, polio (Poliovirus), even bacteria.
common cold.
Algae Causes Desmodesmus infection; Algal bloom; disrupts photosynthesis
produces toxic compounds (e.g.- in aquatic plants and phytoplankton;
Anaebaena and Nostoc). affects water colour, odour and taste.
Helminths Causes schistosomiasis Many animals are hosts to such
(Schistosoma japonicum), helminths such as pig, sheep etc.
cysticercosis (Cysticercus
cellulosae).
Pathogenic Mostly harmless; diarrhoea, Mostly harmless; Can contaminate
indicators (e.g.- vomiting, abdominal cramps. young plants; Animals could act as its
Escherichia coli) carrier.
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What is Water Quality index?

To get a comprehensive picture of the overall

quality of groundwater or surface water, the
WQI is used.

WQI is defined as a rating reflecting the

composite influence of different water
quality parameters on the overall quality of
water.

The Indian standard specified for drinking

water (BIS, 1991) is used for the calculation
of WQI.
 WQI

◼ Water Quality Index (WQI) is considered as the most effective method of

measuring water quality. A number of water quality parameters are
included in a mathematical equation to rate water quality, determining the
suitability of water for drinking

◼ The index was first developed by Horton in 1965 to measure water quality
by using 10 most regularly used water parameters.
◼ The method was subsequently modified by different experts. These indices
used water quality parameters which vary by number and types.
◼ The weights in each parameter are based on its respective standards, and
the assigned weight indicates the parameter’s significance and impacts on
the index.
 Calculation
◼ A usual WQI method follows three steps which include
(1) selection of parameters,
(2) determination of quality function for each parameter, and
(3) aggregation through mathematical equation

The index provides a single number that represents overall water quality
at a certain location and time based on some water parameters.
The index enables comparison between different sampling sites.
The single-value output of this index, derived from several parameters,
provides important information about water quality that is easily
interpretable, even by lay people
Calculate wqi for the following
dataset
◼ pH=6.61, TDS=70, TH=70
Bicarbonate 45
Chloride 4.9
Sulphate 1.5
Nitrate 261
Fluoride 1.43
Calcium 1.60
Magnesium 0.24
Iron 1.95
All units except pH is in mg/l

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 Water treatment

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Indian Standards for Discharge
of Sewage in Surface Waters
Tolerance limit for Discharge of
Characteristic of
Sewage in Suface Water Sources
the Effluent
BOD5 30 mg/L
COD 250
TSS 100 mg/L
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 Tanushree Bhattacharya. CEE101
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 Wastewater Treatment Scheme

Disinfectant

WW effluent
WW
influent
Preliminary Primary Secondary Tertiary

sludge Sludge Treatment

and Disposal

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 Wastewater treatment processes:

◼ Preliminary treatment is a physical process that removes

large contaminants.
◼ Primary treatment involves physical sedimentation of
particulates.
◼ Secondary treatment involves physical and biological
treatment to reduce organic load of wastewater.
◼ Tertiary or advanced treatments.

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Preliminary Treatment
As wastewater enters a treatment facility, it typically flows through a step
called preliminary treatment. A screen removes large floating objects, such
as rags, cans, bottles and sticks that may clog pumps, small pipes, and
down stream processes.
• Coarse screens remove large solids, rags, and debris from wastewater,
and typically have openings of 6 mm (0.25 in) or larger.
•Typical opening sizes for fine screens are 1.5 to 6 mm (0.06 to 0.25 in).
•Very fine screens with openings of 0.2 to 1.5 mm (0.01 to 0.06 in)

Screens are generally placed in a chamber or channel and inclined towards

the flow of the wastewater. The inclined screen allows debris to be caught on
the upstream surface of the screen, and allows access for manual or
mechanical cleaning.

Some plants use devices known as comminutors or barminutors which

combine the functions of a screen and a grinder. These devices catch and
then cut or shred the heavy solid and floating material. In the process, the
pulverized matter remains in the wastewater flow to be removed later in a
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 Screens
◼ (a) Coarse Screen :- The spacings of bars are more than 40 mm center to center.
◼ (b) Medium Screen: The spacing are less than 40mm.
◼ (c) Fine Screen: The spacings vary from 1.5 mm to 6 mm.
◼ The screens may be fixed or movable. the inclination of the screen varies from 30°
to 60°. The screens are placed at designed inclination in an oblong rectangular
chamber. The ends of the chamber are tapered. It is constructed with brick masonry.
◼ The inner surfaces are plastered and finished with neat cement polish. A perforated
rectangular channel is provided at the top of the screen for the collection of floating
debrises.

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 Velocity
◼ The velocity of flow ahead of and
through the screen varies and affects
its operation.
◼ Velocities of 0.6 to 1.2 mps through
the open area for the peak flows have
been used satisfactorily.
◼ Further, the velocity at low flows in the
approach channel should not be less
than 0.3 mps to avoid deposition of
solids.
STP
STP
 Grit Removal
After the wastewater has been screened, it may flow
into a grit chamber where sand, grit, cinders, and small
stones settle to the bottom. Removing the grit and
gravel that washes off streets or land during storms is
very important, especially in cities with combined sewer
systems.
Large amounts of grit and sand entering a treatment
plant can cause serious operating problems, such as
excessive wear of pumps and other equipment,
clogging of aeration devices, or taking up capacity in
tanks that is needed for treatment.

In some plants, another finer screen is placed after the

grit chamber to remove any additional material that
might damage equipment or interfere with later
processes. The grit and screenings removed by these
processes must be periodically collected and trucked to
a landfill for disposal or are incinerated.
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 Grit Chambers
Grit chambers are like sedimentation tanks, designed to separate the intended
heavier inorganic materials (specific gravity about 2.65) and to pass forward the
lighter organic materials

Raw
O Effluent
wastewater I
U
N
T
L
L
E
SETTLING ZONE E
T
T
Z
O
Z
O
Figure : Typical View of Grit Channel
N
SLUDGE ZONE
N
E E

Types of Velocity Control Devices

•A sutro weir in a channel of rectangular cross section, with free fall downstream of the
channel
•A parabolic shaped channel with a rectangular weir
•A rectangular shaped channel with a parshall flume at the end which would also help
easy flow measurement
 Design of Grit Chambers
◼ Settling Velocity
 Primary treatment
◼ Primary Treatment The initial stage in the treatment
of domestic wastewater is known as primary
treatment. Coarse solids are removed from the
wastewater in the primary stage of treatment. In
some treatment plants, primary and secondary stages
may be combined into one basic operation. At many
wastewater treatment facilities, influent passes
through preliminary treatment units before primary
and secondary treatment begins.

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 Primary sedimentation
◼Primary Sedimentation With the screening
completed and the grit removed, wastewater
still contains dissolved organic and inorganic
constituents along with suspended solids.
The suspended solids consist of minute
particles of matter that can be removed
from the wastewater with further
treatment such as sedimentation or gravity
settling, chemical coagulation, or filtration.
Pollutants that are dissolved or are very
fine and remain suspended in the
wastewater are not removed effectively by
gravity settling.
◼When the wastewater enters a
sedimentation tank, it slows down, and the
suspended solids gradually sink to the
bottom. This mass of solids is called primary
sludge. Various methods have been devised to
remove primary sludge from the tanks.
Newer plants have some type of mechanical
equipment to remove the settled solids from
sedimentation tanks. Some plants remove
solids continuously while others do so at
intervals.

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 Sedimentation
The objective of primary settling tank is to remove the
large size suspended organic solids present in the
wastewater whose specific gravity is more than 1.

•Factors affecting settling of particles

•Flow velocity
•Shape and size of particle
•Viscosity

Figure: Typical view of primary settling tank

 REMOVAL OF OIL & GREASE
Present day oil separators are provided with inclined plates (plate
settlers) which improve their performance considerably. Such separators
are available from several vendors to whom the size and specific gravity
of the oil globules desired to be removed and their performance
efficiency need to be specified.
Removal of free oil and grease from a wastewater
stream reduces the potential for equipment
problems to occur further downstream. There are
three forms of oil encountered in wastewater
treatment at a refinery. They are:

Free Oil or floating oil is removed by either

skimming the surface in the skim tank or by gravity
separation in the API separator.
Emulsified Oil is comprised of oil droplets in stable
suspension within the wastewater. Removal
requires chemical addition to lower the pH followed Figure: Oil &
by addition of dissolved oxygen or nitrogen to Grease Trap for
remove the emulsified oils as they break free from Intercepting Oil and
the wastewater. Grease at the
Dissolved Oil is a true molecular solution within the Source
water and can only be removed with biological
treatment.
 Coagulation and flocculation
They occur in successive steps intended to overcome the forces stabilizing the suspended
particles, allowing particle collision and growth of floc. If step one is incomplete, the following
step will be unsuccessful.

COAGULATION
The first step destabilizes the particle’s charges. Coagulants with charges opposite those of
the suspended solids are added to the water to neutralize the negative charges on dispersed
non-settlable solids such as clay and color-producing organic substances.
Once the charge is neutralized, the small suspended particles are capable of sticking
together. The slightly larger particles, formed through this process and called micro-flocs, are
not visible to the naked eye. The water surrounding the newly formed micro-flocs should be
clear. If it is not, all the particles’ charges have not been neutralized, and coagulation has not
been carried to completion. More coagulant may need to be added.

A high-energy, rapid-mix to properly disperse the coagulant and promote particle collisions is
needed to achieve good coagulation. Over-mixing does not affect coagulation, but insufficient
mixing will leave this step incomplete. Coagulants should be added where sufficient mixing
will occur. Proper contact time in the rapid-mix chamber is typically 1 to 3 or max 5 minutes.

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 FLOCCULATION

Following the first step of coagulation, a second process called flocculation occurs.
Flocculation, a gentle mixing stage, increases the particle size from submicroscopic
microfloc to visible suspended particles.

The microflocs are brought into contact with each other through the process of slow mixing.
Collisions of the microfloc particles cause them to bond to produce larger, visible flocs
called pinflocs. The floc size continues to build through additional collisions and interaction
with inorganic polymers formed by the coagulant or with organic polymers added.
Macroflocs are formed. High molecular weight polymers, called coagulant aids, may be
added during this step to help bridge, bind, and strengthen the floc, add weight, and
increase settling rate. Once the floc has reached it optimum size and strength, the water is
ready for the sedimentation process.

Design contact times for flocculation range from 15 or 20 minutes to an hour or more.

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Flocs start to form during the neutralization step as particle collisions occur. ...
Sweep flocculation occurs when colloidal contaminants are entrained or swept
down by the precipitates as they settle in the suspension. The optimal pH range
for coagulation is 6 to 7 when using alum and 5.5 to 6.5 when using iron.
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 Commonly used coagulant and
flocculants
The following natural
products are used as
flocculants:
Chitosan.
Isinglass.
Moringa oleifera seeds
(Horseradish Tree)
Gelatin.
Strychnos potatorum seeds
(Nirmali nut tree)
Guar gum.
Alginates (brown seaweed
extracts)
Apart from these, polymers
or polyelectrolytes
originating from starches
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 Clarification

Clarification is the removal of suspended solids and floc from

chemically treated water, before its application to filters.

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 Filtration –a part of tertiary treatment but used after
primary treatment for municipal or industrial water
supply
What happens to water during filtration? The second
step in a conventional water treatment system is
filtration, which removes particulate matter from water
by forcing the water to pass through porous media.
The filtration system consists of filters with varying
sizes of pores, and is often made up of sand, gravel
and charcoal. The diameter of a grain of fine sand is
approximately 0.1 millimetre, so only particles with
diameters less than 0.1 millimetre would pass through
the fine sand layer. Filtration would not be able to
produce safe drinking water, if many contaminants are
much smaller than 0.1 millimetre (such as viruses,
which can be as small as 0.000001 millimetre in
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There are two basic types of sand filtration:
Slow sand filtration and
Rapid sand filtration

Slow sand filtration is a biological process, because it uses bacteria to treat the water. The
bacteria establish a community on the top layer of sand and clean the water as it passes
through, by digesting the contaminants in the water. The layer of microbes is called a
schumtzdecke (or biofilm), and requires cleaning every couple of months, when it gets too
thick and the flow rate declines. After the schumtzdecke is removed, the bacteria must be
allowed several days to reestablish a community before filtering can resume.

Slow sand filtration systems have been used for many years; the first systems operated in
London in the 19th century. However, slow sand filtration systems require large areas of
land to operate, because the flow rate of the water is between 0.1 and 0.3 metrecube per
hour. Due to the land area that is required and the down-time for cleaning, rapid sand filters,
which were developed in the early 20th century, are much more prevalent today.

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Rapid sand filtration is a physical process that removes suspended solids from
the water. Rapid sand filtration is much more common than slow flow sand
filtration, because rapid sand filters have fairly high flow rates and require
relatively little space to operate. In fact, during rapid sand filtration, the water
flows at a rate up to 20 metrecube per hour. The filters are generally cleaned
twice per day with backwashing filters and are put back into operation
immediately.

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 Equalization

A well - mixed vessel with

fluctuating input flow rates
and / or concentration with
fairly constant output flow
rates and/or concentrations.

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 Secondary Treatment
After the wastewater has been through Primary Treatment processes, it flows
into the next stage of treatment called secondary. Secondary treatment
processes can remove up to 90 percent of the organic matter in wastewater by
using biological treatment processes. The two most common conventional
methods used to achieve secondary treatment are attached growth processes
and suspended growth processes.

If the BOD/COD ratio for untreated wastewater is 0.5 or greater, the waste is
considered to be easily treatable by biological means. If the ratio is below about
0.3, either the waste may have some toxic components or acclimated micro-
organisms may be required in its stabilization.

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 F/M Ratio
The term Food to Microorganism Ratio (F/M) is actually a measurement of the amount of
incoming food ( Lbs of Influent CBOD) divided by the Lbs of Microorganisms in your system.

To determine the amount of incoming food (F), you need to know the CBOD of the influent
into your activated sludge(aeration) system. You also need to know the flow(MGD).
So to calculate the amount of food we do the following calculation:

F= Influent Flow (MGD) X Influent CBOD Concentration (mg/l) X 8.34 pounds/gallon waste
water

To determine the volume of microorganisms (M), you need to know the volume of your
aeration system and you need to know the concentration of Volatile Solids in your aeration
system (MLVSS) or Mixed Liquor Volatile Suspended Solids.

M= Aeration System Volume (in Millions of Gallons) X MLVSS X 8.34 pounds/gallon waste
water

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Types of secondary treatment
Attached Growth Processes
In attached growth (or fixed film) processes, the microbial growth occurs on the
surface of stone or plastic media. Wastewater passes over the media along with
air to provide oxygen. Attached growth process units include trickling filters,
biotowers, and rotating biological contactors. Attached growth processes are
effective at removing biodegradable organic material from the wastewater.

Suspended growth process

In suspended growth processes, the microbial growth is suspended in an
aerated water mixture where the air is pumped in, or the water is agitated
sufficiently to allow oxygen transfer. Suspended growth process units include
variations of activated sludge, oxidation ditches and sequencing batch reactors.

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A trickling filter is simply a bed of media (typically
rocks or plastic) through which the wastewater passes. The media ranges
from three to six feet deep and allows large numbers of microorganisms to
attach and grow. Older treatment facilities typically used stones, rocks, or
slag as the media bed material. New facilities may use beds made of
plastic balls, interlocking sheets of corrugated plastic, or other types of
synthetic media. This type of bed material often provides more surface
area and a better environment for promoting and controlling biological
treatment than rock. Bacteria, algae, fungi and other microorganisms
grow and multiply, forming a microbial growth or slime layer (biomass) on
the media. In the treatment process, the bacteria use oxygen from the air
and consume most of the organic matter in the wastewater as food. As
the wastewater passes down through the media, oxygen-demanding
substances are consumed by the biomass and the water leaving the
media is much cleaner. However, portions of the biomass also slough off
the media and must settle out in a secondary treatment tank.

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Biotowers
A biotower is used to reduce the BOD value of a liquid effluent. A
biotower is an above-ground cylindrical tank or rectangular
structure that contains plastic media with a high surface area,
such as randomly filled polypropylene shapes or modular blocks
of corrugated PVC. Effluent is pumped to the top of the tower and
distributed over the surface of the media using rotating
distributors, troughs, or nozzles and splash plates. The effluent
trickles down over the media, which become coated with
microbial films that consume the organic material.

The treated liquid may be recycled over the biotower before the
biological solids are settled out. Biotowers can be arranged in
series with inter-stage settlement. Fan ventilation may be
incorporated where the biomass must be highly aerobic, for
example where nitrification is required.

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 Rotating biological contactor
The RBC process involves allowing the
wastewater to come in contact with a
biological medium in order to
remove pollutants in the wastewater before
discharge of the treated wastewater to
the environment, usually a body of water
(river, lake or ocean). A rotating biological
contactor is a type of secondary treatment
process. It consists of a series of closely
spaced, parallel discs mounted on a
rotating shaft which is supported just above
the surface of the waste water.
Microorganisms grow on the surface of the
discs where biological degradation of the
wastewater pollutants takes place.

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 Suspended growth process
Suspended Growth Processes Similar to the microbial processes in attached
growth systems, suspended growth processes are designed to remove
biodegradable organic material and organic nitrogen-containing material by
converting ammonia nitrogen to nitrate unless additional treatment is provided.

The suspended growth process speeds up the work of aerobic bacteria and other
microorganisms that break down the organic matter in the sewage by providing a
rich aerobic environment where the microorganisms suspended in the
wastewater can work more efficiently. In the aeration tank, wastewater is
vigorously mixed with air and microorganisms acclimated to the wastewater in a
suspension for several hours. This allows the bacteria sequencing and other
microorganisms to break down the organic matter in the wastewater. The
microorganisms grow in number and the excess biomass is removed by settling
before the effluent is discharged or treated further. Now activated with millions of
additional aerobic bacteria, some of the biomass can be used again by returning
it to an aeration tank for mixing with incoming wastewater.
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 Activated Sludge Process Activated Sludge
Process - ASP

• Raw Effluent In
• Aeration
• Sedimentation
• Treated water out
• Sludge Recirculation
• Sludge withdrawal
The activated sludge process, like most
other techniques, has advantages and
limitations. The units necessary for this
treatment are relatively small, requiring
less space than attached growth
processes. In addition, when properly
operated and maintained, the process is
generally free of flies and odors. However,
most activated sludge processes are more
costly to operate than attached growth
processes due to higher energy use to run
the aeration system. The effectiveness of
the activated sludge process can be
impacted by elevated levels of toxic
compounds in wastewater unless complex
industrial chemicals are effectively
controlled through an industrial
pretreatment program.

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ASP
 Upflow Anaerobic Sludge Blanket Reactor (UASB)

The Up flow Anaerobic Sludge Blanket reactor (UASB)

maintains a high concentration of biomass through
formation of highly settleable microbial aggregates. The
sewage flows upwards through a layer of sludge.

• The sludge in the UASB is tested for pH, volatile fatty acids (VFA), alkalinity, COD and SS. If
the pH reduces while VFA increases, the sewage should not be allowed into the UASB until the pH
and VFA stabilise.
• The reactor may need to be emptied completely once in five years, while any floating material
(scum) accumulated inside the gas collector channels may have to be removed every two years to
ensure free flow of gas.
• All V-notches must be cleaned in order to maintain the uniform withdrawal of UASB effluent
coming out of each V-notch. The irregular flow from each V-notch results in the escape of more
solids washout. Similarly, blocking of the V-notches of the effluent gutters will lead to uneven
distribution of sewage in the reactor.
Up – Flow Anaerobic Sludge Blanket Rector (UASB) Flow
Anaerobic Sludge Blanket Rector (UASB) Flow Diagram
Advantages UASB
• Requires less power than aerobic processes
• Biogas generated can be used as fuel or electricity.
Disadvantages
• UASB alone does not treat the sewage to desirable limits,
therefore downstream aerobic treatment is compulsory
• Requires very large space due to post treatment
• Recovery of biogas is not sufficient to produce substantial
electricity in case of municipal
 Description of Oxidation Ditch
Oxidation ditch is an extended aeration activated sludge
process. An oxidation ditch is a large holding tank in a
continuous ditch with oval shape similar to that of a
racetrack. The ditch is built on the surface of the ground
and is lined with an impermeable lining. This allows the
waste water to have plenty of exposure to the open air for
the diffusion of oxygen. The liquid depth in the ditches
is very shallow, 0.9 to 1.5 m, which helps to prevent
anaerobic conditions from occurring at the bottom of
the ditch. The oxidation ditch effluent is clarified in a
secondary clarifier and the settled sludge is returned to
maintain a desirable MLSS concentration. The MLSS
concentration in the oxidation ditch generally ranges
from 3,000 mg/ L to 5,000 mg/ L; however, this is
dependent upon the surface area provided for
sedimentation, the rate of sludge return, and the aeration
process. Longer retention time within the ditch will allow
for a greater amount of organic matter to be broken down
by the aerobic bacteria. After treatment, the waste water
is pumped to a secondary settling tank where the sludge
and the water are allowed to separate. From there the
effluent goes on to other treatment processes or disposal.
The sludge that has accumulated on the bottom of the
secondary settling tank is then removed and a portion of
it is returned CEE101
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Lagoons
A wastewater lagoon or treatment pond is a scientifically constructed pond,
three to five feet deep, that allows sunlight, algae, bacteria, and oxygen to
interact. Biological and physical treatment processes occur in the lagoon to
improve water quality. The quality of water leaving the lagoon, when
constructed and operated properly, is considered equivalent to the effluent
from a conventional secondary treatment system. However, winters in cold
climates have a significant impact on the effectiveness of lagoons, and winter
storage is usually required.
Lagoons have several advantages when used correctly. They can be used for
secondary treatment or as a supplement to other processes. Treatment ponds
require substantial land area and are predominantly used by smaller
communities. Lagoons remove biodegradable organic material and some of
the nitrogen from wastewater.

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Sequencing batch reactor (SBR)
A sequencing batch reactor (SBR) is used in small package plants and also for
centralized treatment of sewage. The SBR system consists of a single completely
mixed reactor in which all the steps of the activated sludge process occurs. The
reactor basin is filled within a short duration and then aerated for a certain period of
time. After the aeration cycle is complete, the cells are allowed to settle for a duration
of 0.5 h and effluent is decanted from the top of the unit which takes about 0.5 h.
Decanting of supernatant is carried out by either fixed or floating decanter
mechanism. When the decanting cycle is complete, the reactor is again filled with raw
sewage and the process is repeated. An idle step occurs between the decant and the
fill phases. The time of idle step varies based on the influent flow rate and the
operating strategy. During this phase, a small amount of activated sludge is wasted
from the bottom of the SBR basin. A large equalization basin is required in this
process, since the influent flow must be contained while the reactor is in the aerating
cycle.

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 Tanushree Bhattacharya. CEE101
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 The Use or Disposal of
Wastewater Residuals
and Biosolids
When pollutants are removed from water, there is always something left over.
It may be rags and sticks caught on the screens at the beginning of primary
treatment. It may be the solids that settle to the bottom of sedimentation
tanks.
Whatever it is, there are always residuals that must be reused, burned,
buried, or disposed of in some manner that does not harm the environment.

Biosolids are processed wastewater solids (“sewage sludge”) that meet

rigorous standards allowing safe reuse for beneficial purposes.

Currently, more than half of the biosolids produced by municipal wastewater

treatment systems is applied to land as a soil conditioner or fertilizer and the
remaining solids are incinerated or landfilled.

Ocean dumping of these solids is no longer allowed.

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Prior to utilization or disposal, biosolids are stabilized to control odors and
reduce the number of disease-causing organisms. Sewage solids, or sludge,
when separated from the wastewater, still contain around 98 percent water.
They are usually thickened and may be dewatered to reduce the volume to be
transported for final processing, disposal, or beneficial use.

Dewatering processes include drying beds, belt filter presses, plate and frame
presses, and centrifuges. To improve dewatering effectiveness, the solids can
be pretreated with chemicals such as lime, ferric chloride, or polymers to
produce larger particles which are easier to remove wastewater, still contain
around 98 percent water.

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 Incineration
Incineration consists of burning the dried solids to reduce the organic residuals to
an ash that can be disposed or reused. Incinerators often include heat recovery
features.

Undigested sludge solids have significant fuel value as a result of their high
organic content.

However, the water content must be greatly reduced by dewatering or drying to

take advantage of the fuel potential of the biosolids.

For this reason, pressure filtration dewatering equipment is used to obtain

biosolids which are sufficiently dry to burn without continual reliance on auxiliary
fuels. In some cities, biosolids are mixed with refuse or refuse derived fuel prior
to burning. Generally, waste heat is recovered to provide the greatest amount of
energy efficiency.

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 Biosolids and its uses

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 Disinfection
Untreated domestic wastewater contains
microorganisms or pathogens that produce human
diseases. Processes used to kill or deactivate these
harmful organisms are called disinfection. Chlorine is
the most widely used disinfectant but ozone and
ultraviolet radiation are also frequently used for
wastewater effluent disinfection.

Chlorine

Chlorine kills microorganisms by destroying cellular

material. This chemical can be applied to wastewater
as a gas, a liquid or in a solid form similar to
swimming pool disinfection chemicals. However, any
free (uncombined) chlorine remaining in the water,
even at low concentrations, is highly toxic to
beneficial aquatic life. Therefore, removal of even
trace amounts of free chlorine by dechlorination is Tanushree Bhattacharya. CEE101
module 3, BIT Mesra
often needed to protect fish and aquatic life. Due to
emergency response and potential safety concerns,
chlorine gas is used less frequently now than in the
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past.
 Chlorination

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 Free chlorine and combined
chlorine

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 Chlorine demand

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 Breakpoint Chlorination

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 Disadvantages of Chlorination
The use of chlorine to disinfect water
produces various disinfection
byproducts, which have been classified
mainly as halogenated and non-
halogenated byproducts. These primary
byproducts are trihalomethanes (THMs)
and haloacetic acids. THMs are the
byproducts of chlorination of water that
contains natural organic matter.
The most common THM compounds are
dibromochloromethane (CHClBr2),
bromoform (CHBr3), chloroform (CHCl3),
and dichlorobromomethane (CHCl2Br).
The sum of these four compounds is
referred to as Total Trihalomethanes
(TTHMs).

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 Ozone
Ozone is produced from oxygen exposed
to a high voltage current. Ozone is very
effective at destroying viruses and bacteria
and decomposes back to oxygen rapidly
without leaving harmful by products.
Ozone is not very economical due to high
energy costs.

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 Ultraviolet Radiation
Ultra violet (UV) disinfection occurs when
electromagnetic energy in the form of light
in the UV spectrum produced by mercury
arc lamps penetrates the cell wall of
exposed microorganisms. The UV
radiation retards the ability of the
microorganisms to survive by damaging
their genetic material. UV disinfection is a
physical treatment process that leaves no
chemical traces. Organisms can
sometimes repair and reverse the
destructive effects of UV when applied at
low doses

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 Advanced treatment or
tertiary treatment

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 Membrane filtration

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 Tanushree Bhattacharya. CEE101
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 Tanushree Bhattacharya. CEE101
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 Tanushree Bhattacharya. CEE101
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 Tanushree Bhattacharya. CEE101
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 Nitrogen Control
Nitrogen in one form or another is present in municipal wastewater and is usually not
removed by secondary treatment. If discharged into lakes and streams or estuary
waters, nitrogen in the form of ammonia can exert a direct demand on oxygen or
stimulate the excessive growth of algae. Ammonia in wastewater effluent can be
toxic to aquatic life in certain instances.
By providing additional biological treatment beyond the secondary stage, nitrifying
bacteria present in wastewater treatment can biologically convert ammonia to the
non-toxic nitrate through a process known as nitrification. The nitrification process is
normally sufficient to remove the toxicity associated with ammonia in the effluent.
Since nitrate is also a nutrient, excess amounts can contribute to the uncontrolled
growth of algae. In situations where nitrogen must be completely removed from
effluent, an additional biological process can be added to the system to convert the
nitrate to nitrogen gas. The conversion of nitrate to nitrogen gas is accomplished by
bacteria in a process known as denitrification. Effluent with nitrogen in the form of
nitrate is placed into a tank devoid of oxygen, where carbon-containing chemicals,
such as methanol, are added or a small stream of raw wastewater is mixed in with
the nitrified effluent. In this oxygen free environment, bacteria use the oxygen
attached to the nitrogen in the nitrate form releasing nitrogen gas. Because nitrogen
comprises almost 80 percentTanushree air in the earth’s
of the Bhattacharya. CEE101 atmosphere, the release of
nitrogen into the atmosphere does module
2/16/2024 not cause
3, BITany environmental harm.
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 Biological Phosphorus Control
Like nitrogen, phosphorus is also a necessary nutrient for the growth of
algae. Phosphorus reduction is often needed to prevent excessive algal
growth before discharging effluent into lakes, reservoirs and estuaries.
Phosphorus removal can be achieved through chemical addition and a
coagulation sedimentation process discussed in the following section.
Some biological treatment processes called biological nutrient removal
(BNR) can also achieve nutrient reduction, removing both nitrogen and
phosphorus. Most of the BNR processes involve modifications of
suspended growth treatment systems so that the bacteria in these systems
also convert nitrate nitrogen to inert nitrogen gas and trap phosphorus in the
solids that are removed from the effluent.

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 Carbon adsorption
Carbon adsorption technology can remove organic materials from wastewater
that resist removal by biological treatment. These resistant, trace organic
substances can contribute to taste and odor problems in water, taint fish flesh,
and cause foaming and fish kills. Carbon adsorption consists of passing the
wastewater effluent through a bed or canister of activated carbon granules or
powder which remove more than 98 percent of the trace organic substances.
The substances adhere to the carbon surface and are removed from the water.
To help reduce the cost of the procedure, the carbon granules can be cleaned by
heating and used again.

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 Ion exchange process

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