Question

Explain the steps involved in preliminary treatment of sewage.

Answer 1

1. Screening: Sewage and waste water contain plenty of suspended, floating materials, coarse, and solid particles, along with dissolved substances. The suspended objects are filtered and removed. This is done in screening chambers. The sewage is passed through screens or net in the chambers. Larger suspended or floating objects are held in the screening chambers. These have to be removed before the biological treatment.
2. Grit Chamber: After screening, the filtered sewage is then passed into a series of grit chambers. These chambers contain large stones (pebbles) and brick-ballast. Coarse particles settle down by gravity. Thus, passage of filtered sewage removes much of the coarse particulate matter.