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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