Biology · MICROBES IN HUMAN WELFARE

Consider the following statements regarding secondary sewage treatment: (A) The primary effluent is passed into large aeration tanks where it is constantly agitated mechanically and air is pumped into it. (B) This allows vigorous growth of useful aerobic microbes into flocs. (C) These microbes consume the major part of the organic matter in the effluent, significantly reducing BOD. (D) The BOD test measures the rate of uptake of oxygen by micro-organisms in a sample of water. How many of the above statements are correct?

1. Only two
2. Only three
3. All four
4. Only one