I 



STERILIZATION 169 



organisms in bacterial sewage treatment. Filtration has a marked 

 effect in keeping back B. enteritidis sporogenes (see p. gi), and 

 the number of B. coli is diminished during the stay in a septic 

 tank. A septic tank liquid is inimical to B. coli and to other 

 more delicate pathogenic bacteria. Experiments of my own 

 at Caterham proved that nitrifying filters removed 98*5 per 

 cent, of the coli organisms, and all or nearly all of the enteri- 

 tidis. Fuller states that in America sewage filtered inter- 

 mittently through sand contains only about i per cent, of the 

 bacteria present in the raw liquid.^ So that we were justified 

 in concluding that effluents from an efficient bacterial treatment 

 were, with the limitations I have above indicated, perfectly 

 safe to discharge into rivers, and that the greater the aeration 

 and nitrification, the less the possibility of survival of patho- 

 genic organisms. 



Judged from a bacterial standard, and sometimes from a 



chemical one, there is not a river whose waters are safe to 



tdrink without purification, and my contention many years ago 



fthat a good effluent frequently improved a river has been recog- 



Inised as true, and is conceded in the report of the Royal 



lCommission.2 Therefore there does not seem to be much 



'advantage in insisting, in the language of the Commission, 



^on the *' fundamental difference between the discharge of 



jffluents into drinking-water and non-drinking-water streams." 



In most cases it is only practicable, in the majority it is alone 



[necessary, and in all cases it should be compulsory, to carry 



[the purification of sewage to a stage when, in my words at the 



time mentioned, " such factors as time, light, volume of oxygen, 



[and various life in the river, will be more than sufficient to deal 



[with the effluent," leaving, in the instance of '* drinking-water 



;treams," the removal of the reduced number of bacteria to 



:he water companies, with, as I have indicated elsewhere,^ 



final line of defence in domestic sterilization. 



The suggestion that local authorities should in general be 



[further hampered by increasing their existing burdens in 



I treating sewage, so as to produce efiluents equal to drinking- 



[ water, is obviously absurd and unjust. The means by which 



Isterilization of effluents can be effected when necessary will be 



[presently described. 



^ Transactions of the American Society of Civil Engineers, vol. liv., part E, 

 '.1905. 



^ Vol. iv., part i., 1904, p. 105. 



^ Rideal, Cantor Lectures, vSociety of Arts, 1902, p. 27 ; also Jonrnal of the 

 Society of Arts, December 17, 1897, p. 86. 



