Bacterial aerobic oxidation of polluted water in biological oxidation ponds is done to purify it. Presence of bacteria helps in____________________?

A. Coagulation and flocculation of colloids
B. Oxidation of carbonaceous matter to CO2
C. Nitrification or oxidation of ammonia derived from breakdown of nitrogenous organic matter
to the nitrite and eventually to the nitrate
D. All A., B. and C. (Correct)