Page 2 - 3. LESSON NOTE

 Screening: the sewage is screened by passing the wastewater through
screens to remove all large objects such as cans, rags, sticks and plastic
packets that are carried in the sewage stream.
 Grit removal: The screened wastewater is passed through a sand or grit
chamber where sand, grit, stones etc are settling down.
 Sedimentation: After grit removal by passing through large tanks, is
commonly called sedimentation.

Secondary Treatment: -

Secondary treatment is used to decompose the biological content or the organic
waste which are derived from human waste, food waste, toilet water containing
soaps and detergents with the help of bacteria.

Tertiary treatment -

The water undergoes chemical treatment that depends on the composition of water
at this stage. The water is disinfected using chlorine it may also be exposed to
ultraviolet rays to kill disease causing microorganisms. The cleaned water is then
released into rivers or seas.

Uses of treated water and sludge: -

 It can be used as a fertilizer or as landfill.

Sewage sludge and wastewater effluents can provide essential plant nutrients and
water. Since sludge is rich in organic matter, it can improve the physical condition of
the soil

Constituents of sewage-

 Organic impurities
 Inorganic impurities
 Nutrients
 Diseases causing microbes

Alternative method of sewage disposal: -
 Septic Tank: -
 Landfill: -
 Vermicomposting: -

 Incineration: -

 Steps to Prevent water pollution: -
 Industrial waste should be treated and rendered harmless before discharged
into water bodies.

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