Microorganisms and sewage treatment

In water streams, spontaneous self-purification processes take place with an active participation of microorganisms. By the metabolic activities of these, 

Problems and techniques of the treatment of domestic and industrial wastewaters are described in Section 4.5.2. Some microbiological aspects of the processes are considered here. 

The majority of bacteria are Gram-negative organisms and the coli-aerogenes group account for only a small fraction. Bdellovibrio bacteri-ovorus which attacks bacteria reduces the bacterial numbers. Antibiotic-resistant aeromonads have been isolated from some samples. Nitrosomonas spp. are also present and are responsible for nitrification of ammonia. 

The bacterial population may vary with the waste being treated. In antibiotic wastes Pseudomonas may be dominant. With fellmongery and tannery effluents, the activated sludge was dominated by Pseudomonas and Acinetobacter. 

Protozoa are present in large numbers and may influence positively the quality of the effluent and may also play a part in flocculation (Fig. 4.14). 

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