Question

Write a report on treatment of sewage in cities and towns

Answer 1

The process of treating the sewage before discharging it in the waterways is termed as sewage treatment. Sewage consists of excessive amount of nitrogen, phosphorus, metal compounds and organic matter. Microorganisms breaks down the chemical and biological waste present in the sewage, digesting the organic matter present in it. They feed on the organic matter and releases an enzyme which helps in its degradation removing the organic matter from the sewage

Sewage treatment is a process in which sewage is treated in order to remove its harmful constituents and making it environmentally safe. Its main purpose is to clean wastewater for discharge into streams or other receiving waters and for reuse.

Sewage treatment generally involves three stages: primary, secondary and tertiary treatment.

Primary treatment: In primary treatment sewage is kept in a basin where heavy solids from the sewage get settled down into the bottom while lighter solids float at the surface. These settled and floating materials are removed and the remaining liquid sewage is subjected to secondary treatment.
Secondary treatment: This treatment is carried by certain microorganisms which remove all the suspended and dissolved biological matter. Chlorination is done to remove microorganisms from the effluent prior to its discharge for the tertiary treatment.
Tertiary treatment: Treated water is then disinfected chemically (for example: de chlorination) or physically (for example: micro filteration) before discharging it into a stream, river, etc. The treated water may also be used for irrigation of fields, parks and golf course and if it is sufficiently clean, it can be used for groundwater recharge or agricultural purposes.