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Each time you flush the toilet or you wash something down the sink's drain, you create sewage (also known in polite society as wastewater). One question that many people might ask is, "Why not simply dump this wastewater onto the ground outside the house, or into a nearby stream?" There are three main things about wastewater that make it something you don't want to release into the environment:
  • It stinks. If you release wastewater directly into the environment, things get very smelly very fast.
  • It contains harmful bacteria. Human waste naturally contains coliform bacteria (for example, E. coli) and other bacteria that can cause disease. Once water becomes infected with these bacteria, it becomes a health hazard. 
  • It contains suspended solids and chemicals that affect the environment.
  • Wastewater contains nitrogen and phosphates that, being fertilizers, encourage the growth of algae. Excessive algae growth can block sunlight and foul the water. 
  • Wastewater contains organic material that bacteria in the environment will start decomposing. When they do, these bacteria consume oxygen in the water. The resulting lack of oxygen kills fish. 
  • The suspended solids in wastewater make the water look murky and can affect the ability of many fish to breathe and see. 
  • The increased algae, reduced oxygen and murkiness destroy the ability of a stream or lake to support wildlife, and all of the fish, frogs and other life forms quickly die. 
Chemical Characteristics of Sewage
Concrete Sanitary Sewers(Image 4learning.org)

Domestic sewage contains 99.9% water, 0.02-0.03% suspended solids and other inorganic (30%) and organic (70%) substances. Inorganic components include ammonia, chloride salts and metals. Metal industries and mines also contribute to the inorganics. Organic components include either nitrogenous compounds like proteins and amino acids and non-nitrogenous compounds like carbohydrates and lipids. Animal sewage is high in protein and lipids and plant sewage is rich in cellulose and lignin. Lipids in the form of fatty acids which escape digestion in the digestive system account for the lipids in the faeces.






 
About the Author


Mohsin Hanif Awan He is B.Sc in Civil Engineering from "University of Engineering and Technology Peshawar,Pakistan"








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