134 Bacteria in Relation to Country Life 



Sanitary efficiency of sewage-purification. — The various 

 methods of biological treatment of sewage are, to a great 

 extent, effective, in that they destroy the organic matter 

 and produce a non-putrescible effluent. Purified effluents 

 of this character do not seem to affect injuriously the 

 potable qualities of the surface waters to which they 

 are added. Instances are even recorded in which they 

 actually improved the water into which they were 

 discharged. The water that drains away from the 

 sewage-irrigated lands near Paris is clear and sparkling. 

 It is used for drinking and fish thrive in it. 



When sewage-purification is considered as a means 

 for the destruction of the disease germs contained in it, 

 there is no certainty of its absolute reliability. In this 

 case it is not so much the number as the kind of bacteria 

 that survive the purification process, that is of impor- 

 tance. Much work has been done in the study of this 

 problem, but the results are somewhat conflicting. It has 

 been shown that the growth of the sewage bacteria is 

 inimical to the survival of typhoid germs. Cultures of the 

 latter, introduced into unsterilized sewage, tended to dis- 

 appear rapidly, and only an occasional individual survived. 



In order to eliminate any possible contamination of 

 drinking-water by the disease germs, it has been pro- 

 posed to treat the effluents with what Rideal calls 

 finishers, that is, substances that will effect the steriliza- 

 tion when added to the purified sewage at the rate of a 

 few grains per gallon. Ozone could probably be used 

 for the same purpose, as recent experiments indicate. 

 It remains to be demonstrated whether large volumes of 

 effluents can be thus treated effectively and economically. 



