WATER POLLUTION

Definition
o Water pollution means undesirable changes in physical, chemical or biological properties of
water that makes it unfit for use by human and other living beings.
o There are certain symptoms of water pollution: changed colour, offensive smell, bad taste,
unchecked growth of aquatic weeds, oily material floating on surface, and death of fish and
other aquatic organisms.
Water pollutants: Types
Water pollutants have been classified into following categories:
o Organic pollutants: Majority of them are derivatives of living beings while some compounds are
synthetic. They include (a) Natural organic pollutants, (b) Sewage and industrial effluents, (c)
Synthetic organic chemicals (SOCs), (d) Microbiological pollutants, and (e) Oils.
o Inorganic pollutants: These include variety of inorganic chemicals like mineral acids, bases,
salts, metals, heavy metals etc. They come from natural sources (rocks) as well as man made
sources (industries).
o Radioactive pollutants: These include different radioactive substances which are released into
water from natural sources (rocks) as well as man made sources (nuclear waste, weapons etc.).
o Suspended solids and sediments: These include insoluble impurities like soil, sand and other
solid particles which either remain as suspension in water or form sediments. Sources include
soil erosion (by agriculture, mining, construction), sewage and other effluents.
o Heat or thermal pollution: Heated water from thermal power plants and industries is often
discharged in water bodies. This increases temperature of water and decreases dissolved oxygen.
Sources of water pollution
o Major sources of water pollution include: Nature (death and decay of plants and animals), soil
erosion, agricultural run-off, mining (acid mine drainage), municipal sewage, industrial
effluents, accidental spillage etc.
o There are two types of sources of water pollution:
 Point sources: Sources whose location can be identified as single point. e.g., sewage and
industrial effluent
 Non-point or diffused or area sources: Sources that are scattered over a large area or that
can not be identified as single point. e.g., run-off from agricultural land, forests, construction
etc
Effects of water pollution
Water pollution has following types of adverse effects on properties of water:
o Physical effects: It includes increased temperature, depletion of dissolved oxygen (DO),
increased turbidity, altered colour, oily surface etc. This results in reduced photosynthesis and
loss of aquatic life.
o Oxidation effects: It includes biological and chemical oxidation. As a result of this different
impurities get oxidized (e.g., sulphides into sulphate, ammonia into nitrite and nitrates) at the
cost of dissolved oxygen.
o Toxic chemical effects: This includes poisonous effects of different compounds which results
into fatal diseases or deaths of living beings. e.g., toxic metals like cadmium, mercury,
chromium cause damage to liver, kidney and brain. Similarly pesticides, acids, dioxins cause
damage.
o Nutrient effects and Eutrophication: Agricultural run-off brings lots of nutrients (nitrates and
phosphates) to water bodies. This results into excessive growth of water weeds (chiefly algae) all
over the surface and death of underlying organisms due to oxygen shortage. Finally the aquatic
ecosystem collapse (destroyed). This is called Eutrophication.
o Micro-organism effects: Different micro-organisms (e.g., bacteria, virus) found in dirty water
cause a number of water borne diseases e.g., cholera, typhoid, hepatitis, dysentery etc.
Control measures and prevention of water pollution
o Following strategies are adopted for controlling water pollution:
 Two approaches are used: input control and output control. Input control means ‘reducing
generation of pollutants’ while output control means ‘controlling pollutants after being
produced’.
 Output control further involves two strategies: volume reduction and strength reduction.
Volume reduction means reducing total volume of pollutant while strength reduction means
reducing harmful effects of pollutants.
 Both, volume and strength of the polluted water can be reduced by different types of water
treatment plants (WTP). This includes Sewage Treatment Plants (STP) and Effluent Treatment
Plants (ETP).
 In these treatment plants, pollutants are removed through sequential steps that include:
Primary treatment, Secondary treatment and Tertiary treatment.
 In Primary treatment bigger impurities are removed using physical processes (sedimentation,
filtering, decanting).
 In Secondary treatment organic compound are oxidized by biological oxidation (in presence of
bacteria).
 In Tertiary treatment, the remaining impurities are oxidized by chemical oxidants and
disinfection is done by UV-rays, ozone etc.
o Besides it, there are certain common measures to control pollution like:
 Domestic and industrial waste waters should be discharged into rivers only after proper
treatment through STPs and ETPs.
 Solid wastes must not be mixed with liquid wastes and should not be thrown into to water
bodies. They should be separately managed.
 Sources of drinking water should be protected from pollution. Polluting activities (e.g.,
industrial use, discharging effluents, bathing, washing, cattle rearing etc.) must be avoided
in vicinity of source of drinking water.
 Water bodies should be regularly cleaned of aquatic weeds, plants and other crude impurities
like polythene, metals, garbage etc. Special breeds of fish, which feed on mosquito eggs and
bacteria, can be cultured in water bodies.
 Afforestation must be done for reducing soil erosion and improving local soil hydrology. Use
of agrochemicals need to be minimized.
 Public awareness regarding water pollution and its control measures should be created.

 Water/wastewater Treatment Plant