Biology · MICROBES IN HUMAN WELFARE

Consider the following statements regarding secondary sewage treatment and sludge processing: (A) The effluent is passed into aeration tanks where growth of aerobic microbes forms flocs. (B) The BOD of sewage is significantly reduced during the aeration tank process. (C) A small part of the activated sludge is pumped back into the aeration tank to serve as inoculum. (D) Anaerobic sludge digesters produce gases such as methane, hydrogen sulphide and carbon dioxide. How many of the above statements are correct?

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