CHAPTER VIII 



STERILIZATION BY HEAT, CHEMICALS, AND ELECTRICITY 



Removing odour — Metallic salts — Action of manganates and per- 

 manganates — Oxynite process — Chlorine and hypochlorites — • 

 Bleaching powder — Hermite — Electrozone — Oxychloride — 

 Acids — Berge — Ozone — Liernur process — Disposal of refuse — 

 Destructors. 



In the foregoing methods for the mechanical separation of the 

 solids and the production of a clear effluent chemicals were 

 sometimes employed, but almost solely with a view to clarifica- 

 tion. The Rivers Pollution Commission and a large number 

 of legal actions led to attempts at " disinfection " of the raw 

 material or its products by processes aimed at removing or 

 preventing smells or destroying the bacteria, at a time when 

 all organisms were held to be dangerous. Odour and appear- 

 ance were often the only things considered. In these earlier 

 attempts at disinfection on a practical scale disinfectants like 

 mercuric chloride and carbolic acid were soon seen to be too 

 costly when used in effective strength. 



It was therefore found that the complete sterilization of 

 crude sewage was impracticable on a large scale. Later, when 

 it became acknowledged that the attempt was in general on 

 the wrong lines, and that biological change was, on the whole, 

 the most economical and efficient means of purification, and 

 should be encouraged and not inhibited, the bacterial flora of 

 an effluent which was inoffensive to sight and smell and con- 

 formed to certain chemical standards excited little attention. 

 This attitude was generally right, as I have frequently con- 

 tended that it is no part of a sewage scheme to convert sewage 

 into drinking-water, and that where the water of a river must 

 be used for drinking, it is always necessary to purify it by 

 efficient filtration or by other means. In Chapter IV. I have 

 already reviewed the question of the survival of pathogenic 



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