Consider the following statements about secondary sewage treatment.\ I. In secondary treatment, use

Question

Consider the following statements about secondary sewage treatment.\ I. In secondary treatment, useful aerobic microbes grow rapidly and form flocs. Flocs are masses of bacteria associated with fungal filaments to form mesh-like structures.\ II. The growing microbes consume organic matter and reduce the biochemical oxygen demand. When BOD of sewage has reduced, the effluent is passed into settling tank.\ III. In settling tank, the bacterial flocs settle and the sediment is called activated sludge.\ IV. A small part of the sludge is used as an inoculum in the aeration tank and the remaining part is passed into large tanks called anaerobic sludge digesters.\ V. In the digesters, heterotropic microbes anaerobically digest bacteria and fungi in sludge producing mixture of gases such as, carbon dioxide, nitrogen and methane which form the biogas.\ Which of the given statements are correct?\

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(d)