32 



I'x^th December ^ 1898. 



Mr. Thomas Workman, J.P., President, in the Chair, 



THE PURIFICATION OF SEWAGE BY BACTERIA. 



By Arthur J. Martin, Assoc. M.Inst. C.E. 



(Abstract.) 



I CANNOT pass on to the special side of my subject without first 

 referring briefly to the nature and properties of sewage, as a 

 proper understanding of these is absolutely necessary for the 

 comprehension of a process of purification. There is often a 

 disposition to regard sewage as consisting, either wholly or in 

 great part, of excremental matter. This is very far from being 

 the case. There are, for instance, many towns in the North of 

 England where the excreta are dealt with on the dry-earth or 

 privy system, and do not find their way into the sewers ; but 

 in such cases, as the Rivers Pollution Commissioners have 

 shown, the sewage differs very slightly in composition and 

 strength from that of water-closeted towns, in which the whole 

 of the excrement is admitted to the sewers. 



Fresh sewage is generally comparatively free from smell ; but 

 when it has lain about for any length of time, as it does in the 

 depressions of badly-laid sewers, it often becomes exceedingly 

 offensive. In other words, it begins to decompose. This 

 process of decomposition serves a definite purpose of supreme 

 importance in the economy of nature. The materials which 

 are suitable as food for the vegetable and animal world exist in 

 extremely limited quantities, and must therefore be used over 

 and over again. But the refuse of animal life has to be 



