A) cyclic treatment
B) primary treatment
C) activated sludge treatment
D) tertiary treatment
Correct Answer: C
Solution :The word activated sludge system is derived from the practice of adding to the incoming sewage some of the sludge from a previous batch. This sludge inoculum contains large numbers of metabolizing bacteria, together with yeasts, molds and Protozoa. An especially important ingredient of the sludge are species of Zoogloea bacteria, which form flocculant masses (floe) in the aereation tanks. The activity of these aerobic micro-organisms oxidizes much of the effluent's organic matter into carbon dioxide and water. When the aeration phase is completed, the floe (secondary sludge) is allowed to settle to the bottom, just as the primary sludge settles in primary treatment.
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