Microbes in Sewage Treatment — Prelims Questions

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

The primary purpose of aeration in the secondary treatment of sewage is to:

What is the approximate percentage reduction in BOD typically achieved during secondary sewage treatment?

Biogas produced in anaerobic sludge digesters is primarily a mixture of:

A student observes a sample from an aeration tank under a microscope. Which of the following would they most likely observe?

If the BOD of a wastewater sample is $200,\text{mg/L}$ and after secondary treatment, it is reduced by $90\%$, what is the final BOD of the treated effluent?