"That it destroyed any pathogenic organisms which there might be in the sewage."
"32. As regards the first of these claims, it is now clearly established that, in practice, all the organic solids are not digested by septic tanks, and that the actual amount of digestion varies to some extent with the character of the sewage, the size of the tanks relative to the volume treated, and the frequency of cleansing."
"At Huddersfield, Mr. Campbell estimated that about 38 per cent. of the solids were converted into gas or digested; * * * while at Birmingham, Messrs. Watson and O'Shaughnessy say that the figures available indicated a digestion of not more than 10 per cent. of the suspended matter entering the tanks."
"33. As regards the second claim, we find as a result of a very large number of observations that the sewage issuing from the septic tanks is, bacteriologically, almost as impure as the sewage entering the tanks."
Messrs. Winslow and Phelps, in their interesting paper, "Investigations on the Purification of Boston Sewage," [8] quote a suggestion made by Stoddart (1905):
[8] Water Supply and Irrigation Paper No. 185, p. 125.
"He finds, in a septic tank of several compartments, a considerable deposit of sludge in the first compartment, giving a fairly clear supernatant liquid, which in the last chamber of all undergoes a secondary decomposition, leading to the throwing down of an additional precipitate of offensive sludge."
What took place in the case referred to by Stoddart corresponds to the author's observations of the liquid leaving the tanks in a clarified condition, but the secondary decomposition must take place in some manner, and, when it does, a nuisance seems to be unavoidable where no provision is made to care for it.
In view of the experience of others, some further treatment seems to be necessary. Such treatment should include disinfection, as no method of disposal yet devised has succeeded in reducing materially the pathogenic germs usually to be found in sewage and tank effluents.
If the crops to be irrigated are to be eaten, uncooked, by mankind, then disinfection at least is imperative.