Explain the different steps involved during the primary treatment phase of sewage.

Hint: The process of removing contaminants from the municipal wastewater is called sewage treatment. The municipal waste mainly contains the household sewage and the industrial wastewater.

Complete Answer:
The sewage treatment involves physical, chemical and biological processes for removing contaminants from wastewater so that it becomes safe for releasing it in the environment.

The sewage treatment has three steps- primary, secondary and tertiary treatment.
1. Primary treatment- This is the first step of the treatment and it involves settling the heavy solids at the bottom by temporarily holding the sewage in the quiescent basin. Some of the lighter waste particles remain floating to the surface. Both the settled waste and the floating waste in the water are removed and the remaining water is left for the secondary treatment. So filtration and sedimentation are the two basic techniques used in this step. The sewage is passed through a series of filters with sequentially small pores sizes that remove floating objects in it. Then it is left for sedimentation and the effluent is taken then for the secondary treatment.
2. Secondary treatment- It involves the removal of dissolved particles and biological matters in the water. It involves the use of water-borne and indigenous microorganisms.
3. Tertiary treatment- It involves the chemical and physical disinfection of the water before discharging it in the river, stream, lagoon or wetland.

Note: The sludge obtained from the waste water must also be properly treated before discharging it in the environment. The wastewater after treatment can also be used for agricultural purposes.