Download 2.2 WATER POLLUTION Definition: Any alteration in physical

2.2 WATER POLLUTION
Definition: Any alteration in physical (temperature), Chemical and biological properties of
water, as well as contamination with any foreign substance which would constitute a health
hazard or otherwise decrease the utility of water.
2.2.1 Major Categories of Water Pollutants
1. Infectious agents
Examples: Bacteria, viruses, protozoa and parasitic
Major Human Sources: Human and animal wastes
Harmful Effects: Diseases like jaundice, typhoid and gastrointestinal diseases
2. Oxygen-Demanding Wastes
Examples: Organic wastes such as kitchen waste, animal manure and plant debris that can be
decomposed by aerobic bacteria.
Major Human Sources: Sewage, animal feedlots, paper mills, and food processing facilities.
Harmful Effects: Large population of bacteria decomposing these wastes can degrade water
quality by depleting water of dissolved oxygen. This causes destruction of fish and other form of
aquatic life.
3. Inorganic Chemicals
Examples: acids, compounds of toxic metals such as lead, arsenic and selenium and salts such as
sodium chloride in ocean water and fluorides found in some soils.
Major Human Sources: Surface runoff, industrial effluents and household cleansers.
Harmful Effect: (a) Make fresh water unusable for drinking or irrigation, (b) Cause skin cancers
and crippling spinal and neck damage (F-), (c) Damage the nervous system, liver and kidneys
(Pb and As), (d). Harm fish and other aquatic life, (e) Lower crop yields, and (f) Accelerate
corrosion of metals exposed to such water.
4. Organic Chemicals
Examples: Oil, gasoline, plastics, pesticides, cleaning solvents and detergents.
Major Human Sources: Industrial effluents, household cleansers, surface runoff from farms and
yards.
Harmful Effects: (a) Cause nervous system damage (pesticides), reproductive disorders
(solvents), cancers (gasoline and solvents), (b) Harm fish and wildlife.
5. Plant Nutrients
Examples: Water soluble compounds containing nitrate, phosphate, and ammonium ions.
Major Human Sources: Sewage, manure, and runoff of agriculture and urban fertilizers.
Harmful Effects: can cause excessive growth of algae (eutrophication) and other aquatic plants,
which die, decay, deplete water of dissolved oxygen and kill fish. Drinking the water with
excessive level of nitrates lowers the oxygen-carrying capacity of blood and can kill unborn
children and infants (blue baby syndrome).
6.Sediments
Examples: Soil, silt
Major Human Sources: Land erosion
Harmful Effects: (a) Cloud water and reduce photosynthesis, (b) Disrupt aquatic food web,
(c) Carry pesticides and bacteria, (d) Settle out and destroy feeding and spawning grounds of
fish, and (e) Clog and fill lakes, artificial reservoirs, and harbors.
7. Radioactive Materials
Examples: radioactive isotopes of iodine, radon, uranium, cesium, and thorium.
Major Human Sources: Nuclear power plants, mining and processing of uranium, nuclear
weapon production and testing, natural sources.
Harmful Effects: genetic mutations, miscarriages, birth defects, and certain cancers.
8. Heat (Thermal Pollution)
Examples: excessive heat
Major Human Sources: Water cooling of power plants, and industrial plants.
Harmful Effects: Lowers dissolved oxygen levels and makes aquatic organisms more vulnerable
to disease, parasites and chemicals. Fish and other organisms are killed due to thermal shock.
2.2.2 Sewage
Sewage is a liquid waste, which includes human and house-hold waste waters,
industrial wastes, ground wastes, street washings and storm waters. Sewage, besides about 99.9
percent water contains organic and inorganic matter in dissolved, suspension and colloidal states.
Aerobic and anaerobic decomposition:
Sewage contains both aerobic and anaerobic bacteria, which can bring about oxidation of
organic compounds present in it. In the presence of good amount of dissolved or free oxygen
organic compounds undergo a process of oxidation brought about by aerobic bacteria to nontoxic and inoffensive smelling compounds. This kind of oxidation is called aerobic
decomposition.
C
CO2,
H
H2O,
N
NO3,
S
SO4,
P
PO4
The presence of dissolved or free oxygen is necessary for the livelihood of aerobic
bacteria. As the oxygen content is exhausted the anaerobic bacteria becomes active and
decompose the organic compounds to offensive smelling compounds. This decomposition in the
absence of oxygen is called anaerobic decomposition.
C&H
CO2& CH4,
N
Indicators of pollution load:
NH3,
S
H2S,
P
PH3
The organic pollution load of a wastewater can be measured by two indexes “Biological
Oxygen Demand” (BOD) and “Chemical Oxygen Demand” (COD).
BOD of sewage is defined as amount of free oxygen required by the bacteria, under
aerobic condition, for the decomposition of organic matter at 20oC in 5 days. The unit of BOD is
mg/l or ppm. The average BOD of sewages is between 100 to 150 mg/l.
COD of sewage is defined as the amount of oxygen required for the decomposition of
both oxidisable organic and inorganic compounds under more drastic conditions
The more the BOD and COD values more are the pollution load of the water.
Control measures of water pollution
1. Administration of water pollution control should be in the hands of state or central
government
2. Scientific techniques should be adopted for environmental control of catchment areas of
rivers, ponds or streams
3. Industrial plants should be based on recycling operations as it helps prevent disposal of
wastes into natural waters but also extraction of products from waste.
4. Plants, trees and forests control pollution as they act as natural air conditioners.
5. Trees are capable of reducing sulphur dioxide and nitric oxide pollutants and hence more
trees should be planted.
6. No type of waste (treated, partially treated or untreated) should be discharged into any
natural water body. Industries should develop closed loop water supply schemes and
domestic sewage must be used for irrigation.
7. Qualified and experienced people must be consulted from time to time for effective
control of water pollution.
8. Public awareness must be initiated regarding adverse effects of water pollution using the
media.
9. Laws, standards and practices should be established to prevent water pollution and these
laws should be modified from time to time based on current requirements and
technological advancements.
10. Basic and applied research in public health engineering should be encouraged.