explain the main step involved in sewage treatment
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Answer:
Sewage treatment
Sewage treatment generally involves three stages, called primary, secondary and tertiary treatment. Primary treatment consists of temporarily holding the sewage in a quiescent basin where heavy solids can settle to the bottom while oil, grease and lighter solids float to the surface.
The sewage treatment consists of three processes:
1) Primary treatment: In this process, the effluent or the sewage flows through huge tanks called the primary sedimentation tanks.
In these tanks, the sludge settles down while grease and oil float on the surface and are removed.
These tanks have scrapers that continuously push the sludge that is collected, towards the hopper in the base of the tank
2) Secondary treatment: In this process, the biological waste from human waste, soap, food waste, and detergent are substantially degraded.
Most of the municipal sewage water treatment plants treat the sewage that is settled through the aerobic process.
The effluent after the primary treatment has dissolved biological matter is then converted into clean water by making use of the bacterial and waterborne aerobic micro-organisms that absorb the pollutants.
The effluents from this process are clean enough to be discharged into the rivers.
3) Tertiary treatment: This is the final stage of filtration where the effluent is treated further to its best quality before being discharged to the environment.
The tertiary treatment has to ensure very high standards of treating the effluents to be cleaner than the stream or river water.
It reduces the phosphorous and ammoniacal nitrogen.