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Water pollution

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Water is one of the most precious natural resources

Water covers more than 70% of earth’s surface

About 97% of water in the earth is salty

2% of water is locked in glaciers and polar ice caps

Only 1% is useful for direct consumption

Undrinkable

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Use of any resources generates waste

Water pollution is the leading worldwide cause of deaths & diseases

Water pollution accounts for deaths more than 14000 people daily

With rapid increase in human population water resources are polluted so that precious &

unique organisms & ecosystems are being harmed & are even dying at an alarming rate

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Water pollution is the presence of some foreign substances or impurities in water in

such a quantity so as to a constitute healthy hazard by lowering the water quality

and making it unfit for use

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Noticeable signs of water pollution

Offensive odours from rivers, streams, lakes & oceans

Oily & greasy material floating on the surface of water bodies

Unchecked growth of aquatic weeds in water bodies

Bad taste of drinking water

Decrease of aquatic life in freshwater bodies

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Aquatic weeds

Salvinia  in early stages

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Water use cycle

Water source

Water treatment plant

Water distribution system

Water use Wastewater collection

Wastewater treatment plant

Discharge to receiving water

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Sources of water pollution

1. Point source

2. Non point source or diffused source

3. Natural source

4. Anthropogenic source

a. Domestic wastewater b. Agricultural runoff c. Industrial effluent

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1. Point source

Source which can be readily identified at a single location

Source will be directly discharged from a single point

Examples: industrial discharge, municipal sewage, combined sewer discharge etc.

This type of discharge can be easily controlled

Water pollution caused by these sources can be minimised if the effluents from these sources

are controlled, treated up to acceptable levels & disposed off

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2. Non point or diffused source

They are diffused across a broad area

Their contamination cannot be traced to a single discharge point

Location of the source of water pollution cannot be easily identified

Here the pollutants scattered on the ground ultimately reach the water sources & cause pollution

Examples: runoff from agriculture lands, runoff from mining areas etc.

Water pollution caused by diffused source like agriculture can be controlled by changing crop

patterns and advanced farm management practices

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3. Natural sources

Rain water

Atmosphere

Surrounding vegetation

Underground rocks and volcanoes

Natural runoff

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4. Anthropogenic sources

These sources include oil spills, atmospheric deposition, marine dumping, radioactive

waste, global warming and eutrophication

Among these, most important sources are:

a. Domestic wastewater

b. Agricultural runoff

c. Industrial effluent

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eutrophication

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a. Domestic wastewater

It is the wastewater generated from household activities, commercial places, institutions

and other public places

It consists of 99.9% of water and 0.1% of solids

These solids are mostly organic with a small fraction of inorganic matter

It’s decomposition produces large quantities of malodorous gases and contains number

of pathogens

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b. Agricultural wastewater

This is the runoff from agricultural fields and animal farms

This waster water is considerably rich in :

Nitrogen

Phosphate

Organic matter

Pesticides

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Water bodies enriched with nutrients induce rapid growth of microscopic plant life in surface

water

It leads to algal bloom

Thus reducing the oxygen content in the aquatic environment popularly known as

Eutrophication

Eutrophication is most common in stagnant water bodies such as ponds & lakes

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c. Industrial wastewater

They results from industrial operations

Each year world generates around 400 billion tons of industrial waste

Much of these wastes is pumped untreated into rivers, oceans & other waterways

They may have pollutants of almost all kinds ranging from simple nutrients & organic matter to

toxic substances

Nature & composition of industrial wastewater vary widely from industry to industry & even for

same industry depending upon raw materials, processes & operational factors

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Water pollutants & its effects

Pollutants are substances which affect the normal functioning of human life & domesticated

species when introduced into biosphere

Commonly found pollutants in water pollution are:

1. Inorganic salts 2. Acids/Alkalis 3. Organic matter 4. Suspended solids

5. Floating matter 6. Thermal discharges 7. Colouring materials 8. Toxic chemicals

9. Micro organisms 10. Radioactive materials 11. Foam producing matter

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1. Inorganic salts

These includes nitrates, phosphates, carbonates, chlorides, sulphates of Ca, Mg, Fe etc.

These salts makes water hard

Hard water increases soap consumption & deposits scales on pipelines

Iron causes spots and stains on white fabrics

Water bodies enriched with nitrates & phosphates cause Eutrophication

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2. Acids/Alkalis

They are discharged into streams by chemical industries & other industrial plants

Mosh freshwater bodies have natural pH in the range of 6 to 8

High concentration of acid, sufficient to lower the pH to below 7 causes eye irritation to

swimmers, rapid corrosion of ship’s hull & deterioration of fishermen's net etc.

When pH of water goes below 5, fish population begins to disappear

Efficiency of waste treatment plants are affected by acidity

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Alkalis appear in wastewater from soap manufacturing, textile dyeing, rubber reclamation,

leather tanning etc.

High pH is also detrimental to aquatic life

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3. Organic matter

Organic pollution occurs when large quantities of organic compounds which act as substrates

for microorganisms are released into water sources

During decomposition of organic pollutants, the dissolved oxygen in receiving water may be

used up at greater rate than it can be replenished

Critical range of dissolved oxygen in water for sustenance of fish life is 3 to 4 mg/L

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4. Suspended solids

They either settle to bottom or remains suspended in water body

These solids increases turbidity of water body

Solids that gets deposited on the banks decompose &causes odours

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5. Floating matter

These includes oils, greases & other materials which float on the surface

They make the river unsightly & obstruct the passage of light through water

Presence of floating matters hinders the self-purification processes of water bodies

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6. Thermal discharges

Increase in normal temperature of natural waters is caused by nuclear power plant/

boiler/ industrial discharges

warmer water is lighter than cold

Stratification occurs in water body

This causes most of aquatic life to retreat to stream bottom

Bacterial action increases

It results in accelerated depletion if stream’s dissolved oxygen content

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7. Colouring materials

Colour in water is the indicator of pollution

Colour interferes with the transmission of sunlight into stream, thus reducing its natural

disinfection action

Colour in water is contributed by the effluents discharged from textile industries, paper

mills, tanneries, slaughter houses etc.

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8. Toxic chemicals

Highly complex organic & inorganic toxic compounds produced by various chemical

industries are toxic to aquatic life

They include cyanides, sulphides, acetylene, alcohol etc.

Many of these have cumulative effect on flora & fauna

Hexavalent chromium found in wet cement is water soluble & can soak into skin &

produce allergic reaction

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9. Micro-organisms

Domestic sector, food processing industries and slaughter houses usually discharge

wastes containing bacterial

These bacteria are generally of 2 significant types:

1. Bacteria which assist in the degradation of organic matter

2. Bacteria which are pathogenic

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10. Radioactive materials

They comprises of a number of radio isotopes emitting ionizing radiation that are

harmful to human & environment

This radiation is not readily detectably by methods usually employed to determine the

presence of contaminants in environment

Exposure to high levels of radioactive waste may cause mutation & cancer

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11. Foam producing matter

Presence of foam producing matters are usually discharged by textile mills, pulp and

paper mills & some chemical plants

Presence of foam producing matter leads to undesirable appearance of receiving streams/

water bodies

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Water bone diseases caused by pathogens

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Sustainable wastewater treatment

Wastewater is a combination of liquid or water carried wastes, removed from domestic,

commercial & industrial establishments together with surface/ ground/ storm water

Both wastewater collection systems & centralized & decentralized wastewater treatment

systems are designed & managed primarily to protect human & environment health

The current wastewater management system is a “disposal-based linear system”

This traditional wastewater management systems needs to be transformed into a

sustainable, closed-loop wastewater management system

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Various unit operations & processes in conventional wastewater treatment can be

grouped as:

1. Preliminary treatment

2. Primary treatment

3. Secondary/ Biological treatment

4. Tertiary/ Advanced treatment - Advanced

Conventional

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1. Preliminary treatment – Large floating matters such as rags & sticks are removed

2. Primary treatment – Materials those settle at bottom are removed

3. Secondary treatment – Dissolved & finely divided are degraded biologically with the help of micro

organisms

4. Tertiary/ Advanced treatment – Additional treatment needed to remove impurities in wastewater

which remains even after conventional secondary treatment

Treated effluents using above methods are either disposed on to a nearby water body or onto a land

which happens in conventional “disposal-based linear system”

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Sustainable wastewater treatment methods Conventional methods have its own mistakes

So now more emphasis is given not only to treat wastewater but also to reuse & recycle

the treated effluents coming out from conventional wastewater treatment plants

Commonly followed sustainable wastewater treatment methods:

1. Wastewater ponds

2. Constructed wetlands

3. Upflow Anaerobic Sludge Blanket (UASB)

4. Soil Aquifer Treatment (sat)

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1. Wastewater ponds

Wastewater treatment using ponds or lagoons

It is a well known technology

The extensive treatment process relies on suspended bacterial growth cultures

This purification requires long retention time

Require a lot of space compared to other energy intensive wastewater treatment system

They are high performance, low cost, low energy, low maintenance process, especially

suitable in warm climates

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Wastewater ponds connected in series

They are very efficient in removing pollutants when compared to a single wastewater pond

The first pond is facultative pond & it is designed to remove the major part of organic impurities

Subsequent ponds in series are maturation ponds & are designed for the removal of nutrients &

pathogens

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2. Constructed wetlands They are natural systems in which the wastewater flows through a planted soil filter bed

The filter bed contains filter materials like sand or gravel & is sealed to the ground

The treatment relies on bacterial activity taking place in the bio-film in the bed

Mechanism of pollutant removal is based on processes such as sedimentation, filtration, biological degradation,

adsorption, precipitation, nitrification, plant uptake etc.

To enhance the process the soil filter bed is planted with plants, typically reed

Hence often known as reed bed filters

Commonly this method comprises a pre-treatment step for sedimentation of organic impurities to avoid clogging

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3. Upflow Anaerobic Sludge Blanket Can use this method if there is shortage of land

Anaerobic bacteria degrade organic materials in the absence of oxygen & produce methane & carbon

dioxide

Methane can be used as an alternative energy source – biogas

Other benefits:

Reduction of total bio-solids volume up to 50% - 80%

Final waste sludge that is biologically stable which serves as rich humus for agriculture

This method can be applied on a very small to large scales44

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4. Soil Aquifer Treatment It is a geo-purification system

Here partially treated sewage effluent is introduced into groundwater through soil percolation under

controlled conditions

During percolation, natural soil filtration occurs & partially treated sewage effluent enters aquifer where

mixing & possibly some physical & chemical reactions may occur

By recharging through unsaturated soil layers, the effluent achieves additional purification before it mixed

with natural groundwater beneath the soil

In water scarce areas, treated effluents become a considerable resource for improved groundwater sources

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SAT systems are inexpensive, efficient for pathogen removal & are not highly technical to operate

Biggest advantage- it breaks the pipe to pipe contact of directly reusing treated wastewater from

wastewater treatment plant

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Importance of sustainable wastewater treatment method:

The effluents from all the above methods may be reused in agricultural, industry, groundwater recharge,

toilet flushing, landscape irrigation & fire protection

This methods transform wastewater technology into a closed loop management system

Treated wastewater from sustainable wastewater treatment provides essential plant nutrients as well as trace

nutrients

Use of nutrient rich water for agricultural & landscaping may lead to a reduction or elimination of fertilizer

applications

The wastewater reuse leads to reduced water consumption & treatment needs, with associated cost savings 49

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Reuse of treated wastewater for various applications:

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Model showing three dimensions of sustainable wastewater treatment