Microbes in Sewage Treatment — Prelims Questions

Which of the following statements is INCORRECT regarding the role of microbes in sewage treatment?

A sample of wastewater has a BOD of $300,\text{mg/L}$. After secondary treatment, its BOD is reduced to $30,\text{mg/L}$. What percentage of BOD has been removed?

Which of the following gases is NOT a major component of biogas produced during anaerobic sludge digestion?

The activated sludge is pumped back into the aeration tank to:

Which of the following microbial groups is primarily responsible for the formation of flocs in the aeration tank during secondary sewage treatment?

If the BOD of a river water sample is very high, it indicates that the water is: