Environmental

Engineering
By: Dr. Saadat

Water
Pollution

References:
Principles of Environmental Engineering and
Science
Mackenzie L. Davis
Susan J. Masten

References:
Introduction to Environmental Engineering
Mackenzie L. Davis
David A. Cornwell

Introduction

How we use the water in lakes, rivers, ponds, and streams is

greatly influenced by the quality of the water found in them.

Activities such as fishing, swimming, boating, shipping, and

waste disposal have very different requirements for water
quality.

Water of a particularly high quality is needed for drinking

water supplies.

In many parts of the world, the introduction of pollutants

from human activity has seriously degraded water quality.

Water Pollutants and Their Sources

Point Sources
Domestic

sewage and industrial wastes act as point

sources because they are conveyed to a single point
of discharge into the receiving water.

In

general, point source pollution can be reduced or

eliminated through waste minimization and proper
wastewater treatment prior to discharge to a natural
water body.

Water Pollutants and Their Sources

Nonpoint Sources

Urban and agricultural runoff are characterized by

multiple discharge points and are called nonpoint
sources.

Reduction of agricultural nonpoint source pollution

generally requires changes in land use practices.

Urban storm water (including that from streets, parking

lots, golf courses, and lawns) can transport pollutants
such as nitrogen and phosphorus from fertilizers,
herbicides applied to lawns and golf courses, oil,
grease, ethylene glycol (used in antifreeze), and cut
grass and other organic debris.

Water Pollutants and Their Sources

Oxygen-Demanding Material

Anything that can be oxidized in the receiving water

resulting in the consumption of dissolved molecular
oxygen is termed oxygen-demanding material.

This material is usually biodegradable organic matter

but also includes certain inorganic compounds.

The consumption of dissolved oxygen, DO, poses a

threat to fish and other forms of aquatic life.

Oxygen-demanding materials in domestic sewage come

primarily from human waste and food residue.

Water Pollutants and Their Sources

Oxygen-Demanding Material

Two important industries that release oxygendemanding wastes are the food-processing and paper
industries.

Almost any naturally occurring organic matter, such as

animal droppings, crop residues, or leaves, which is
released into the water from nonpoint sources, will
contribute to the depletion of DO.

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Water Pollutants and Their Sources

Nutrients

Nitrogen and phosphorus, two nutrients of primary

concern, are considered pollutants when they become
too much of a good thing.

They must be present in rivers and lakes to support the

natural food web.

Problems arise when nutrient levels become excessive.

Excessive nutrients often lead to large growth of algae,

which in turn become oxygen-demanding material
when they die and settle to the bottom.

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Water Pollutants and Their Sources

Nutrients

Some major sources of nutrients are phosphorus-based

detergents, fertilizers, food-processing wastes, as well
as animal and human excrement.

The loss of nutrients in runoff or seepage from

croplands is the major source of nutrient release from
agricultural operations.

The pollution of groundwater with nitrate is widespread

in agricultural areas.

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Water Pollutants and Their Sources

Pathogenic Organisms
o

Pathogenic microorganisms found in wastewater

include bacteria, viruses, and protozoa excreted by
diseased person or animals.

When discharged into surface water, they make the

water unfit for drinking.

If the concentration of pathogens is sufficiently high,

the water may also be unsafe for swimming and
fishing.

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Water Pollutants and Their Sources

Suspended Solids
Organic

and inorganic particles that are carried by

wastewater into a receiving water are termed
suspended solids (SS).

When

the speed of the water is reduced by flow

into a pool or a lake, many of these particles settle
to the bottom as sediment.

Colloidal

particles, which do not settle readily,

cause the turbidity found in many surface waters.

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Water Pollutants and Their Sources

Suspended Solids

Organic suspended solids may also exert an oxygen

demand.

Inorganic suspended solids are discharged by some

industries but result mostly from soil erosion.

As excessive sediment loads are deposited into lakes

and reservoirs, the turbidity increases, light penetration
decreases, the bacterial population often increases, and
the solids deposit on the bottom of the water body,
destroying the habitat for many benthic organisms.

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Water Pollutants and Their Sources

Salts

All water contain some salt.

These salts are often measured by evaporation of a

filtered water sample.

The salts and other matter that dont evaporate are

called total dissolved solids (TDS).

In many cases the water is naturally saline because salts

dissolve in the water as it percolates through the soil or
rock formations.

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Water Pollutants and Their Sources

Salts

However the widespread use of water for irrigation in

arid or semiarid areas has increased salinity problems.
Evaporation of water from open reservoirs and canals
and during application to plants increases salinity.

Salt accumulation in agricultural soils can lead to a

reduction in crop yield.

Some saline soils can be reclaimed by applying

sufficient water to leach the solutes from the root zone.
However, the leaching process may degrade
groundwater quality.

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Water Pollutants and Their Sources

Pesticides

Pesticides are chemicals used by farmers, households,

or industry to regulate and control various types of
pests or weeds.

The presence of pesticides in surface and groundwater

is ubiquitous in the United States.

Pesticides have been linked to a wide range of human

health hazards, ranging from short-term impacts such
as headaches and nausea to chronic impacts like cancer,
reproductive harm, and endocrine disruption.

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Water Pollutants and Their Sources

Pharmaceuticals and Personal Care Products

Pharmaceuticals and Personal Care Products (PPCPs)

are a class of compounds that are applied externally or
ingested by humans, pets, and other domesticated
animals.

They are released to the environment through the

disposal of expired, unwanted, or excess medications to
the sewage system by individuals, pharmacies, or
physicians.

Another source of PPCPs in the environment is through

metabolic excretion products in urine and feces.

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Water Pollutants and Their Sources

Pharmaceuticals and Personal Care Products

PPCPs, such as deodorants and sunscreens, can be

washed into our waterways during bathing, washing
and swimming.

PPCPs can also migrate into the environment from

poorly engineered landfills and cemeteries.

Most of the PPCPs are polar chemicals, which means

that they will tend to migrate to our waterways and not
be sorbed onto soils and sediments.

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Water Pollutants and Their Sources

Pharmaceuticals and Personal Care Products

Numerous PPCPs have been detected in municipal

wastewater and surface waters.

Conventional municipal wastewater treatment is not

designed to remove PPCPs and many of these
chemicals may pass through the treatment plant
unaltered.

Little is known about the environmental effects of

PPCPs. Researchers found that most pharmaceuticals
do not produce acute toxic effects, however, research
needs to be done on the chronic effects of PPCPs on
aquatic life.

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Water Pollutants and Their Sources

Other Organic Chemicals
o

Hydrocarbons from combustion processes: methane,

benzene, and polycyclic aromatic hydrocarbons

Solvents used in dry cleaning and metal washing:

trichloroethane, tetrachlorethane,

Most of the above chemicals are known as human

carcinogens.

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Water Pollutants and Their Sources

Arsenic
o

Arsenic is a naturally occurring element in the

environment.

Its occurrence in groundwater is largely the result of

minerals dissolving naturally from weathered rocks and
soils.

Arsenic poisoning from groundwater can have

numerous health effects, ranging from gastrointestinal
upsets, diabetes and skin lesions.

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Water Pollutants and Their Sources

Toxic Metals

Heavy metals enter aquatic environment through the

discharge of industrial waste and wastewater treatment
plants, storm-water runoff, mining operations and

The most commonly occurring heavy metals are

arsenic, cadmium, chromium, copper, nickel, lead, and
mercury.

As heavy metals persist in the environment, they tend

to accumulate in soils, sediments, and biota.

Heavy metals can also bioaccumulate.

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Water Pollutants and Their Sources

Heat

Water released by many industrial processes are much

warmer than the receiving waters.

Increases in water temperature can have negative

effects.

Many important commercial fish such as salmon and

trout, live only in cool water.

Higher temperatures also increase the rate of oxygen

depletion in areas where oxygen-demanding wastes are
present.