Water Supply and Seivage Disposal. 219 



Sewage disposal. The disposal of house sewage by 

 water carriage is not only a matter of great convenience 

 but a hygienic necessity. Through the use of the ordi- 

 nary open vault there is not only opportunity for the pol- 

 lution of the well water but the disease-producing bac- 

 teria may be carried from the privy vault to the kitchen, 

 the milk room, and elsewhere by means of the common 

 house fly. If the sewage can be disposed of in a conven- 

 ient way and yet avoid the danger of pollution of water 

 and food much will be done for the comfort and health of 

 the home. 



Cities that are located on a body of water often dis- 

 charge their sewage into the river or lake. Others less- 

 favorably located find it necessary to dispose of the 

 wastes in other ways, utilizing different methods of puri- 

 fication that shall render the sewage comparatively harm- 

 less. Most of these methods of purification depend on 

 the work of bacteria. The sewage contains organic mat- 

 ter of various kinds, which will be decomposed in the 

 same manner as has been shown to occur in the soil. The 

 final products will be harmless, and in the process of de- 

 composition the disease-producing bacteria will be de- 

 stroyed. 



The methods of sewage purification seek to establish 

 conditions favorable : (1) for the growth of anaerobic bac- 

 teria that shall render soluble all solid matter contained 

 in the sewage just as the solids are made soluble in the 

 soil ; (2) for the development of the aerobic bacteria that 

 shall complete the work of decomposition, and the nitri- 

 fying bacteria that change the ammonia to nitric acid. 

 Modifications of the types of plants used by cities in 

 the disposal of large quantities of sewage can be used on 

 the farm for the safe and convenient disposal of the 



