82 THE MANURE HEAP AND SEWAGE. 



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 destructive 

 action of the decomposition and putrefactive bacteria. Putre- 

 factive 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 microorganisms, this will produce 

 a great effect upon the composition of solid matters present. 

 Almost all of them will be reduced to simpler compounds. The 

 carbonaceous material will be reduced eventually, if the process 

 is complete, into CO 2 and water, with the liberation of hydrogen 

 or perhaps marsh gas (CH 4 ). 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. In the first place, 

 the organic matter to be acted on is generally in a soluble or partly 

 dissolved condition, and very easily acted upon by bacteria. 

 Secondly, the great abundance of water facilitates the action, for 

 bacteria require an abundance of water for their best growth. Thirdly, 

 the bacteria are present in extreme abundance. All sewage con- 

 tains bacteria in large numbers, although naturally the number 

 varies. A common sewage contains from 7,000,000 to 10,000,000 



