Biological Charactors

It is due to the presence in sewage of bacterias and other micro-organisms ( algae, fungi, protozoa, etc. The former are much more active. Bacteria are present in vast number in sewage. Each liter of sewage may contain 5- 50 billion bacterias. Most of these bacterias are harmless to man and are largely engaged in converting complex organic compounds of sewage into simpler, stable organic and mineral compounds, thereby resulting in purification of sewage. some of the bacterias, particularly the disease-producing or pathogenic type constitute a real danger to the health of the public.

The bacterias are two types.

1. Prototrophic: – which obtain food from minerals like nitrites, carbonates, etc.
2. Metatrophic :- which obtain food from organic compounds- nitrogeneous and carbonaceous. They are two types, depending upon the manner of satisfying their oxygen demands.

• Aerobic Bacterias live on free oxygen of air or an oxygen dissolved in sewage/water.
• Anaerobic Bacterias live and develop in the absence of free oxygen. They extract oxygen from oxygen-containing-radicals of organic compound and minerals such as nitrates, nitrites and sulphates.

The Bacterias are of immense importance in the process of decomposition of sewage.