Although waste water treatment in oxidation pond is considered to be aerobic process, both aerobic and anaerobic processes operate together. The aerobic decomposition mainly takes place near the surface and anaerobic process, at the bottom.
The oxygen required for the metabolism of bacteria is obtained from the surface through aeration as well as from the algae present in the pond, and in turn the bacteria supplies CO-, by decomposing the waste. For good supply of oxygen by algae, the ponds are made shallow so that sunlight can penetrate well, helping photosynthesis. The waste thus, present at the upper part of the pond, undergoes aerobic decomposition into CO, and H20.
The bad due to anaerobic decomposition however, creates problem and thus waste water before being released i, the pond should be treated to remove the solid materials which may settle down, and aeration should provided throughout the pond by mechanical stirring. Secondly, in winters when photosynthesis retarded, oxygen supply is reduced creating an anaerobic condition and causes same problem with odors.