Microbiological Characterisics of Sewage

Microbiological Characteristics of Sewage

	Microbiological Characterestics of Sewage - The composition of sewage varies depending upon the source of wastewater. This also causes variation in the microbial flora of sewage. Almost all groups of microorganisms, algae, fungi, protozoa, bacteria and viruses are present. Raw sewage may contain millions of bacteria per ml. The bacterial group comprises mainly the soilborne organisms, Bacillus subtilis, Bacillus megaterium, Bacillus mycoides, Pseudomonas fluorescens, Achromobacter spp. and Micrococcus spp. Bacteria of intestinal origin also occur in sewage in large numbers.
Mostly these are harmless organisms. Examples of this type are Escherichia coli, and other coliforms, Proteus and Serratia species. Potential pathogens include enterococci (Streptococcus faecalis) and Clostridium perfringens. Pathogenic bacteria which cause serious illness like Vibrio cholerae, Salmonella typhi, Salmonella paratyphi and Shigella dysenteriae may also occur in sewage. Viruses which are released in the faeces from infected host are also occasionally found in sewage, for example, poliomyelitis virus, infectious hepatitis virus and coxsackie virus. Bacteriophages also occur in comparatively large numbers. During treatment process the microbial flora may be dominated by the corresponding physiological groups.