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Chapter – 18
Waste water Story
Waste water: Black-brown water whichis rich in lather , mixed withoil that goesdown the drains from skins, showers, toilets, laundries iscalled wastewater.
Wastewater isgenerated in homes, industries, agricultural fields and in otherhuman activities. Thisis called sewage.
Sewage is a liquid waste which causes water and soil pollution. Wastewater is treated ina sewage treatment plant.
Treatment plants reduce pollutants inwastewater to a level where nature can takecare of it.
Where underground sewerage systems andrefuse disposal systems are not available, the low coston-site sanitation system can be adopted.
By-products of wastewater treatment are sludge and bio gas.
Open drain system is a breeding place for flies, mosquitoes and organisms which cause diseases.
We should notdefecate in theopen. It ispossible to havesafe disposal ofexcreta by
low costmethods.
Sewage Treatment:
Aeration: Air is bubbled through the wastewater while it is continuously stirred. Filtration: Aerated water passes through a deep filter of layered sand,fine gravel andmedium gravel.
Chlorination: Chlorine isadded and mixed to the filtered water until wateris clear.
Wastewater Treatment Plant (WWTP):
Wastewater passes through screens to remove large objects. Togo to a grit andsand removal tankat low speed.
Water is allowed to settle inlarge tank.
Floating solids are removed withskimmer. Settled solids (sludge) are removed with scraper.
Clear water is called clarified water. Water is then decomposed by anaerobic bacteria in a tank and air is passed. Microbes settled at bottom as activated sludge and water fromtop is removed.
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