CHAPTEE VI 



THE BACTERIOLOGY OF SEWAGE AND THE BACTERIAL 

 TREATMENT OF SEWAGE 



Composition of Sewage — Quantity and Quality of Bacteria in Sewage — Treatment 

 of Sewage : (1) Disposal without Purification ; (2) Chemical Treatment ; 

 (3) Bacterial Treatment — Evolution of Bacterial Methods — -Septic Tank 

 Method— Contact Bed Method — Manchester Experiments — Eifect of Bacterial 

 Treatment on Pathogenic Organisms. 



The relation of bacteria to sewage has during the last twenty-five 

 years assumed a position of the first importance. This is due, 

 generally speaking, to three causes. In the first place, our knowledge 

 of the economic function of bacteria present in sewage has increased 

 in a very large measure in recent years. Secondly, as the population 

 has tended to gravitate to cities, the problem of a pure water supply, 

 free from sewage pollution, has become infinitely more complicated 

 than was the case in rural communities in the past. How often 

 sewage, from sewage or cesspools, gains access by means of direct 

 connection or percolation to drinking water, the history of typhoid 

 epidemics and similar outbreaks in this country only too fully records. 

 And thirdly, practical issues have now arisen in connection with the 

 bacterial treatment of sewage. In order to understand the bacteri- 

 ology of sewage and its practical lessons, we may first briefiy consider 

 the quality and constitution of sewage as regards its bacterial content, 

 and then proceed to discuss its biological treatment. 



The Constitution of Sewage 



It is impossible to lay down any exact standard of the. chemical 

 and bacterial quality of sewage. The quality will differ according to 

 the size of the community, the inclusion or otherwise of trade-effluents 

 and waste products, the addition of rain and storm water, and other 



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