Biology · MICROBES IN HUMAN WELFARE

Consider the following statements regarding sewage treatment: (A) Primary treatment involves the physical removal of particles—large and small—through filtration and sedimentation. (B) Secondary treatment is also known as biological treatment and is carried out by anaerobic bacteria. (C) The effluent from primary settling tank is passed into large aeration tanks for mechanical agitation and air pumping. (D) The greater the BOD of waste water, more is its polluting potential. Which of the above statements are correct?

1. (A), (B) and (C) only
2. (A), (C) and (D) only
3. (B), (C) and (D) only
4. (A), (B), (C) and (D)