What are the biological characteristics of wastewater ?
👉 Biological characteristics are due to the presence in sewage of bacteria and other living micro-organisms such as algae, fungi, protozoa etc. The former are more active.
In the sewage bacteria are present in vast numbers ; 22 -55 billion bacteria is contained by 1 litre of sewage. Most of these bacteria are harmless to man and are largely engaged in the beneficial process of converting the complex organic compounds of sewage into simpler, stable, organic and mineral compounds, resulting in purification of sewage. Therefore, some of the bacteria may be harmful, particularly the disease-producing or pathogenic type, and may constitute a real danger to the health of the public.
The beneficial bacteria are of two types
(i) Prototrophic Bacteria
This type of bacteria obtains food from mineral compounds in the sewage such as carbonates, nitrites etc. and are not important for treatment purposes.
(ii) Metatrophic Bacteria
This type of bacteria obtains food from organic compounds, nitrogenous and carbonaceous. This type, depending upon the manner of satisfying its oxygen requirements and can be further sub-classified as aerobic, anaerobic and facultative.
Aerobic bacteria live on free oxygen of air or on the oxygen dissolved in water. And the anerobic bacteria live and develop in the absence of free oxygen as such their oxygen supply comes from the oxygen radicals of organic compounds and mineral substances as nitrites, nitrates and sulphates. The examples of aerobic type of bacteria are the bacteria contained in organic matter discharged into a body of water and of the anaerobic bacteria in pile of gaibage, dead body and faeces. Facultative bacteria are common to either of the aforesaid type. Besides, there is a particular type of bacteria which abounds in the upper layers of the soil and they are live on the dead organic matter of animal or vegetable origin. This is known as saprophytic bacteria and plays an important part in converting the organic matter into a stable humus like product. The metatrophic group i.e., aerobic anaerobic and facultative bacteria have immense importance in the process of decomposition of sewage.