TREATMENT OF CITY SEWAGE 89 
to-day by communities that need to find some method of sewage 
disposal. 
The Bacterial Treatment of Sewage-—This method is based 
upon exactly the same bacterial activities that we have been con- 
sidering in recent chapters, the sewage being treated in a manner 
that hastens the decomposition power of the bacteria so that they 
will rapidly destroy the organic products in the sewage. The 
method has not been devised by any one person, but has been the 
result of observations and experiments of several, extending over 
many years, and finally crystallized into practical results. 
The bacterial treatment of sewage depends upon the destruc- 
tive action of the decomposition and putrefactive bacteria. 
Putrefactive bacteria decompose all kinds of organic bodies, both 
the nitrogenous and those purely carbonaceous. Most of the 
solid matter in the sewage is composed of these organic bodies, and 
it is evident that if the sewage can be induced to undergo a 
thorough decomposition under the action of microdrganisms, this 
will produce a great effect upon the composition of solid matters 
present. Almost all of them will be reduced to simpler com- 
pounds. The carbonaceous material will be reduced eventually, 
if the process is complete, into COz and water, with the liberation 
of hydrogen or perhaps marsh gas (CH,). Such gases would leave 
the liquid and join the atmosphere. The nitrogenous material 
would suffer the decomposition, resulting in the production of 
ammonia; and denitrification, which would be sure to occur, would 
still further reduce this to free nitrogen. Such gases also would 
be sure to join the atmosphere unless held in solution in the liquids. 
In short, the putrefactive processes, which in the manure heap 
produce a loss deprecated by the agriculturist, would produce 
here exactly the result which the sanitary engineer desires to 
reach, a destruction and dissipation of organic material. 
Such changes will take place as readily in sewage as In manure 
or’ in the soil. Indeed, observation and analysis show that they 
commonly take place much more rapidly. Im the first place, 
