Which gases are produced during the sewage treatment process?

Given below are two statements: Based on them,select the correct option.
Statement $I$: Activated sludge is obtained in the grit chamber.
Statement $II$: Activated sludge is pumped into an anaerobic digester.

Secondary sewage treatment is mainly a

In how many stages did the biologists from Humboldt State University perform wastewater treatment?

Select the appropriate option regarding the aeration tank.

Statement $P$: $A$ major portion of organic matter in water is consumed by chemical processes.
Statement $Q$: Microorganisms,including bacteria,consume organic matter present in water.