question_answer 17)

  Waste water treatment generates a large quantity of sludge, which can be treated by (a) an aerobic digesters (b) floe                 (c) chemicals                      (d) oxidation pond         

Answer:

                  (a) Sludge is further treated by anaerobicdigesters. These are large heated tanks in which its chemical decomposition is catalyzed by microorganisms. The liquid is treated by bacteria which breakdown the organic matter remaining in solution. It is then sent to oxidation ponds where heterotrophic bacteria continue the breakdown of the organics and solar UV light destroys the harmful bacteria. Chemical are not used in there treatments.