Sewage : Waste water generated from the domestic uses by the people. This includes waste water from bath room, Toilets, Kitchen and Dinning.
Water usage by a man in a day in India is 140 litres. This is called per capita requirement. Sewage generation is roughly 80% of the per capita usage. If Sewage is below 10000 litres per day, then Septic Tank is adequate for its treatment and disposal. If sewage exceeds 10000 litres per day, then Sewage Treatment Plant is required. Now a days, Sewage treatment Plants are provided in Apartments, Hotels, Factories. Municipalities and Corporation are providing Sewage Treatment Plants.
Pollutants in the Sewage:
a. BOD – Biochemical Oxygen Demand
Microorganisms such as bacteria are responsible for decomposing organic waste. When organic matter such as dead plants, leaves, grass clippings, manure, sewage, or even food waste is present in a water supply, the bacteria will begin the process of breaking down this waste. When this happens, much of the available dissolved oxygen is consumed by aerobic bacteria, robbing other aquatic organisms of the oxygen they need to live. Biological Oxygen Demand (BOD) is a measure of the oxygen used by microorganisms to decompose this waste. If there is a large quantity of organic waste in the water supply, there will also be a lot of bacteria present working to decompose this waste. In this case, the demand for oxygen will be high (due to all the bacteria) so the BOD level will be high. As the waste is consumed or dispersed through the water, BOD levels will begin to decline.
b. COD – Chemical Oxygen Demand
The amount of oxygen (measured in mg/L) that is consumed in the oxidation of organic and inorganic matter. It is used to measure the total amount of organic and inorganic pollution in wastewater.
MAJOR CONSTITUENTS OF TYPICAL DOMESTIC WASTEWATER