name the two different categories of microbes naturally occuring in sewage water. explain thie role in cleaning sewage into usable water.

Hi
Bacteria and fungi are two categories of naturally occurring microbes present in sewage.

The above microbes forms bubbling flocks during thorough mixing, by whic all the air (O2) is consumed causing decrease in the BOD of the sewage.
Due to this all the harmful microbes die.

Similarly anaerobic microbes (non air absorbing microbes) digest the aerobic bacteria and fungi and produce gases like CH4, C02, H2S, etc.
It makes the water less polluted to be released in the water bodies.