Question

The primary method of treatment of sewage water involves which of the following processes?
(a) Sludge digestion
(b) Aerobic bacterial activity
(c) Anaerobic bacterial activity
(d) Filtration and sedimentation

Answer 1

Hint: Wastewater is passed through several tanks and filters which separate pollutants from water. Then the resulting "sludge" is fed into a digester where more processing occurs. Almost 50 percent of the suspended solids in wastewater are in this main batch of sludge.

Complete answer:
Sewage flows into large tanks in the primary sedimentation stage, generally called "pre-settling basins," "primary sedimentation tanks" or "primary clarifiers." When grease and oils rise to the surface and are skimmed off, the tanks are used to settle sludge. Mechanically powered scrapers are normally fitted with primary settling tanks that continuously push the collected sludge into a hopper at the base of the tank where it is pumped to sludge treatment facilities. For saponification (soap-making), grease and oil from the floating material may often be retrieved.

Additional Information: In several steps, this is achieved. Initially, concurrent filtration removes floating debris and then the grit, i.e. dirt and small pebbles, is removed by sedimentation. The primary sludge forms all the solids which settle down, and the supernatant forms the effluent. Furthermore, the effluent from the main settling tank is taken for secondary therapy.
So, the correct answer is, ‘filtration and sedimentation method.’

Note:
 -The primary and secondary methods of sewage water treatment are continuous processes.
-Primary therapy eliminates material that either floats or gravity settles out readily. The physical processes of screening, comminution, removal of grit, and sedimentation are included.