Sources of water pollution

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Transcript Sources of water pollution

Water pollution
Water distribution and availability:
75% of earth’s surface
 > 97% is found in oceans
 & 3% is freshwater.
2.997% is in ice caps
or glaciers,
only 0.003% is usable water
Sources of water pollution
Industrial effluents,
Domestic sewage,
Fertilizers and pesticides from agricultural lands,
Leachate from solid waste disposal sites.
Types of sources:
Point sources: discharge pollutants at specific
locations through pipes, ditches, or sewers into bodies
of surface water. E.g. drains
Non-point sources: sources discharge pollution over
large land area. E.g. runoff into surface water
Common types of water Pollutants
Disease causing agents (bacteria, fungi)
Oxygen-demanding wastes (organic waste)
Water soluble inorganic chemicals: acids, salts,
and compounds of toxic metals such as lead
and mercury
Inorganic plant nutrients: water-soluble nitrates
and phosphates (eutrophication)
Organic chemicals (oil, plastics, pesticide,
Sediment or suspended particles (insoluble soil
Radioactive substances (water soluble)
Heat (water from thermal power plants)
Causes of Ground water pollution
1.Urban run-off of untreated or poorly treated waste water
and garbage.
2.Agricultural practices (application of large amounts of fertilizers
& pesticides, animal feeding operations, etc., in the rural sector)
3.Leaks from underground storage tanks containing gasoline
and other hazardous substances.
4. Leachate from landfills.
5. Poorly-designed and inadequately maintained septic tanks.
6. Mining wastes.
Arsenic poisoning (Arsenicosis)
 Toxicity develops after 2-5 years’ exposure to
contaminated drinking water. Initially skin develops to
darken, called “diffuse melanosis”, leads later to spotted
melanosis where darkened spots appear on chest, back
& limbs. Still later, leucomelanosis occurs & body shows
white & black spots.
 Associated complications: liver & spleen enlargement,
cirrhosis of liver, diabetes, goiter & skin cancers.
Arsenic-Laced Well Water Poisoning
Pallava Bagla in New Delhi
for National Geographic News
June 5, 2003
According to the World Health
Organization (WHO) in Geneva,
estimates vary from a low of 28 to 35
million to a high of 77 million—more
than half the population of Bangladesh,
Management of municipal sewage
Commonly used Terms
 Sewer-Pipe line carrying the sewage
 Sewage: Liquid flowing in domestic sewer (usually
refers to domestic sewage)
 Sullage /grey water: water from kitchen & bathrooms
 Sanitary sewage/domestic sewage: from residential
 Storm drainage: Water entering a sewer as a result of
 Outfall sewer: Main sewer carrying the entire
wasterwater collected from an area to the point of
disposal or treatment plant.
 Sewerage: art of collection, treatment & disposal of
 Dry weather flow: quantity of sewage flowing during
summer seasons excluding rainwater.
Management of municipal sewage:
1. Self-cleansing velocity: a minimum velocity of 0.5 m/s is
essential in municipal sewers to keep it clean
2. Systems of sewerage:
(i) Combined system: sanitary sewage & storm sewage are
collected in same sewer. Likely to overflow in rainy season
and unhygenic
(ii) Separate system: Separate systems for sanitary and
storm sewers.
(iii) Partially combined or partially separate system:
Either a portion of storm in sanitary or a portion of sanitary to
storm sewer. For India this is the best choice.
3. Quantity of sewage: water consumed by a city is a function
(80 %) of its population .135 liters per capita per day in small Indian cities
4. Variations in sewage flow rates: knowledge essential for the
design of sewers.( Morning /evening)
5. Characteristics of sewage: aerobic to anaerobic environment
& thus change in color of sewage(dissolved oxygen)
6. Contaminants of concern in sanitary sewage:
(i) Organic matter,
(ii) Solids (suspended and dissolved),
(iii) Refractory organics and pesticides,
(iv) pH
7. Organic matter : To express amount of organic matter in the
terms of amount of oxygen required to biochemically oxidized
by aerobes.
BOD : Amount of oxygen required by the aerobic bacteria to
biochemically oxidize the organic matter present in the waste
& is expressed in mg/l.
BOD= depletion in DO * Dilution factor
COD: Chemical oxidants are used instead of aerobes for
oxidation of organic matter.
8. Treatment of sewage:
Primary treatment,
Secondary treatment
Tertiary treatment.
Primary treatment
Grit chamber
Oil and grease trap
Primary sedimentation
Screening of the first operation performed on
incoming sewage for removal of large floating matters (light
weight but big sized wood)
Grit chamber: To remove inorganic suspended particles by
reducing velocity: optimum velocity
Oil and grease trap: Used to remove oil, grease and other
floating matter s before it reached to biological treatment, essential for
efficient working of biological system
Primary Sedimentation:
treatment. Sedimentation tanks
rectangular and design criteria are:
done before biological
are either circular or
1. Surface overflow rate or surface area loading:
ratio of discharge passing through sedimentation tank to the
plan area of the tank.
2. Detention time: Duration for which sewage is retained
in sedimentation tank, ratio of the tank volume to the
discharge passing through the tank.
3. Horizontal flow velocity: necessary to maintain
horizontal flow velocity less than 0.3 m/s in the tank for
laminar flow.
Primary sedimentation:
Secondary treatment
 Consist of biological treatment techniques for removal of BOD.
 Biological treatments are based on types of microbes involved.
e.g aerobic, aerobic and facultative treatment systems
Treatment Process
Aerobic suspended
growth process
Activated Sludge Process •Good efficiency in BOD
Aerobic attached growth
trickling filter, Rotating
biological contractor
•High BOD removal
•lesser energy requirement
compared to ASP
•Occupies large area
Anaerobic suspended
growth process
septic tank
•Incomplete treatment
•no energy
•noxious gases with fuel
Anaerobic attached
growth process
anaerobic filters
•Incomplete treatment
•no energy
•noxious gases with fuel
•High energy requirement
Conventional activated sludge process: aerobic suspended growth
Sewage is aerated in an aeration tanks for long hours
Aerobic bacteria present in tank biochemically oxidize organic matter
in sewage to stable end-products like carbon dioxide, water, nitrates,
sulphates, energy, etc. & large number of bacteria
The excess aerobic bacteria produced will be removed as sludge
A portion of sludge will be returned to aeration tank to maintain active
concentration of bacteria.
Trickling Filter: aerobic attached growth biological treatment system
Sewage after primary sedimentation passes through trickle filtres
Attached microorganisms biochemically oxidize organic matter
Waste water treatment complete process
Septic Tank: anaerobic suspended growth
•Anaerobic bacteria biochemically oxidize organic matter
•Effluent is usually dispersed in the ground using subsurface
dispersion trenches.
•Sedimentation of the suspended solids takes place in same tank
where digestion takes place.
•Usually adopted for small communities of population up to 300.
An Imhoff tank is a two-stage septic system
where the sludge is digested in a separate
tank. This avoids mixing digested sludge with
incoming sewage.
A properly designed and normally operating
septic system is odor free and, besides
periodic inspection and pumping of the septic
tank, should last for decades with no
A well designed and maintained concrete,
fibreglass or plastic tank should last about 50
Oxidation Pond (Lagoons-secondary treatment of wastewater)
Low cost natural treatment system in which oxygen required
by bacteria to biochemically oxidize organic matter is provided
by atmospheric winds and algae present in oxidation pond
Algae utilize nutrients and CO2 provided by bacteria for
photosynthesis and supplement bacteria with O2.
Depth of the pond must be low (0.5M) to keep pond aerobic)
Symbiotic relationship between algae and bacteria- Major
feature of oxidation pond.
Constructed wet land
Engineered marshes
Duplicate natural process to
cleanse water
Two basic types: Free water
surface, subsurface flow
Free water surface: soil support
the roots, shallow (<0.5 m)
Subsurface flow wetlands:
permeable media supports the
roots, depth (04- 0.8m
Successful in Netherlands
Justicia americana
Advanced filtration
 Normal filtration: All medium passes through filter
medium that removes contaminants to produce high
quality water.
 Common filters –rough screens, sand filters, multimedia
filters, cartridge filters, removes larger than 0.1 μ
 Cross flow filtration: Operate membrane in cross flow
mode. Results in rejected contaminants carried away
from membrane surface, minimizing contaminant
Membranes for filtration processes
 Polymeric membranes, packaged into membrane
 Pressure is applied to allow liquid to pass through
very small pores in the membrane
Micro filtration: 0.1-1μ, low cost operation
Ultra filtration: medium – large size molecule (20 500Å)
 Membrane filtration process where hydrostatic
pressure forces a liquid against a semipermeable
membrane. Suspended solids and solutes of high
molecular weight are retained, while water and low
molecular weight solutes pass through the membrane
Nano filtration: pore size is close to 1 nm.
 cross-flow filtration technology which ranges somewhere
between ultrafiltration (UF) and reverse osmosis (RO).
Reverse osmosis
Reverse osmosis
•Spirally bound membranes
•Results in removal of 90-99 % NaCl and other impurities
•Filter sizes for comemrcial and residential application generally ranges from 2” X12” tp
8” X 40 “
Semi-permeable membranes- used in water desalinization
 Cellulose acetate (CA)
 Chlorine tolerant
 Non bacteria resistant
 Ideal pH range 6-8
 Good water production rate
 Cellulose tri acetate (CTA)
 Chlorine tolerant: will increase membrane life
 Resistant to most bacteria
 Ideal operating pH 4-8
 Excellent water production rate
 Thin film composite (TFC)
 Chlorine sensitive
 Bacteria resistant
 pH 3-11
 Highest water production rate
 Highest salt rejection
 Longest membrane life
 Most widely used
Total Rural sanitation, Tamil Naidu
A direct relationship exists between water,
sanitation and health. Consumption of unsafe
drinking water, improper disposal of human
excreta and lack of personal and food hygiene
have been the major causes of many diseases
in developing countries like India.
Ganga water
Ganga -unique
Spiritual significance-birth to death.
Congregation (an assembly of persons
brought together for common religious
worship) at banks
Self purification and dilution
The principal sources of pollution of the
Ganga river
1.Domestic and industrial wastes. It has been estimated
that about 1.4 × 106 m3 per day of domestic wastewater and
0.26 × 106 m3 per day of industrial sewage are going into
the river.
2. Solid garbage thrown directly into the river.
3. Non-point sources of pollution from agricultural run-off
containing residues of harmful pesticides and fertilizers.
4. Animal carcasses and half-burned and unburned human
corpses thrown into the river.
5. Defecation on the banks by the low-income people.
6. Mass bathing and ritualistic practices.
Ganga Action plan
Department of Environment, in December 1984, prepared an action plan
for immediate reduction of pollution load on the river Ganga.
The Cabinet approved the GAP (Ganga Action Plan) in April 1985 as a
100 per cent centrally sponsored scheme.
-Started GAP-I for completion by March 1990, but extended it
progressively up to March 2000.
- While the GAP-I was still in progress, the CGA (Central Ganga
Authority) decided in February 1991 to take up the GAP-II,
covering the following pollution abatement works:
(a) On the tributaries of river Ganga, viz. Yamuna, Damodar and
(b) In 25 class-I towns left out in Phase-I.
(c) In the other polluting towns along the river.
•Ph I + II– 1000k crores
•2010- Ganga basin authority was set up.
•Fast track by 2020- he Ganga will be pure and free of pollutants by 2020
Hindustan times, 22nd February 2012
• 75 per cent of the pollution load was from
untreated municipal sewage.
• 88 per cent of the municipal sewage was
from the 25 Class I towns on the main river.
• Only a few of these cities had sewage
treatment facilities (these were very
inadequate and were often not functional).
• All the industries accounted for only 25 per
cent of the total pollution (in some areas, such
as Calcutta and Kanpur, the industrial waste
was very toxic and hard to treat).
Design of waste water treatment plant