The two different categories of microbes naturally occuring in sewage water are bacteria and fungi.
The following three treatments are carried out for purifying sewage water.
a. Primary treatment : 1. separation of large debries, 2. sedimentation in tanks.
b. Secondary treatment :
- Waste water is pumped in shallow stabilization or oxidation ponds, where microbes oxidize its organic matter.
- The process results in release of carbon dioxide and formation of sludge.
- Sludge is continuously aerated further for its oxidation.
c. Teritary treatment :
- Removal of turbidity in waste water caused by the presence of nutrients in dissolved organic matter, metals or pathogens.
- It involves chemical oxidation by strong oxidising agents such as chlorine gas, perchlorate salts, ozone gas, UV radiations.