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• Waste water – Used water contain impurities such as mud and chemicals, which make it unfit for reuse is called wastewater.
• Sewage – The liquid waste present in the wastewater is called sewage.
• Organic impurities – solid and liquid human excreta, animal excreta, oils, fertilizer chemicals, pesticides, herbicides, fruit and vegetable waste, etc.
• Inorganic impurities: chemical substances such as metal particles, acids and bases.
• Sewage also contains microorganisms such as protozoans which cause dysentery, vibrio cholerae which causes cholera, salmonella typhi which causes typhoid, virus such as poliovirus which causes polio.
• Sources of wastewater –
  • Domestic wastewater contain waste from toilets, sinks and bathrooms of homes, schools, hospitals and various public places
  • Industrial wastewater contain bodily waste as well as chemical substances such as oils, acids and bases
  • Run down of water from streets or agricultural areas during heavy rain or flood
  • Even the water flowing from roads and rooftops carries harmful substances
• Sewers are network of pipes that joins to big sewers and ultimately leaves sewage water into water resources
• Wastewater treatment plant –
  • If waste water is mixed with sources of drinking water then it can be harmful.
  • Wastewater from the city is allowed to flow to the waste water plant
  • The cleaning process involve removal of physical, chemical and biological impurities from the wastewater.
  • The lighter solids such as plastic objects, sticks, clothes float on water. To remove these impurities, wastewater is passed through bar screens so that the solid particles get filtered out
  • The heavier solid particles such as sand grit or pebbles can still pass through the bars. Such solids can be removed using grit and sand removal tank. Here the speed of the wastewater is lowered down so as to allow settling of heavier particles at the bottom of the tank.
  • After this process wastewater is passed into a large tank called settling tank which is slopped in the middle. Faecal matter present in water settles at the bottom. It is called sludge
  • It is removed from the tank using scraper. The sludge is transported to the sludge digester tank where anaerobic bacteria decompose the waste and produce biogas. It is used for fuel and electricity generation.
  • Clarified water from the tank is allowed to pass into aeration tank. Here aerobic bacteria consume biodegradable waste that is still remaining in the water. They need air for their growth and digestion, so this tank is supplied with blowers or air compressors that pumps continuous supply of air in the tank. After several hours the waste and the aerobic bacteria settle at the bottom of the tank as activated sludge and clearer water remain on top.
  • The activated sludge contain about 97% of water. A part of this sludge is fed back to aeration tank with incoming wastewater so as to ensure presence of aerobic bacteria. From the remaining part water is removed using machines or sand drying beds. The solid substance so obtained is used as manure.
  • Further water is disinfected and lead into sources of water.
• How to reduce waste generation
  • Solid waste should be thrown in dustbins not in the sink
  • Cooking waste like oil and fats should be thrown in dustbins not in the sink
  • Chemical waste like paints, insecticides should not be released with wastewater
  • Do not throw solid waste in open drains
  • A bucket of water is sufficient for bathing
  • Proper Sanitation is also important in order to reduce the waste
• Sanitation and disease
  • Defecation near the water bodies should be banned
  • Donot wash pets, clothes near water bodies
  • If such impure water is used for drinking then it causes diseases. If such water id used for irrigation it pollutes soil
  • Government is implementing programmes to make toilets for everyone, cleaning drains, streets and roads etc.
  • Advanced technology helped to build low cost onsite sewage disposal systems such as septic tanks, chemical toilets, and composting pits
  • Biogas plants are implemented for proper waste disposal
  • At public places waste disposal must be managed properly
  • As a responsible citizen we should give a helping hand in maintenance of public hygiene
  • Dispose the garbage properly in the dustbin.
  • Make groups and give a helping hand in cleaning the public places as well