SEWAGE 25 



aerated and well moistened but not saturated with water. By placing the 

 manure, together with the waste materials of the farm and the home, 

 in heaps, designated as composts, the decomposition processes can be 

 controlled so as to lead to heat liberation j this results in the destruction 

 of the injurious organisms and the conservation of the plant nutrient 

 elements. When not properly regulated, the decomposition processes 

 may be wasteful, unsanitary, and unsightly, and may even become a 

 source of infection to man and his domesticated animals. 



SEWAGE 



Disposal of sewage and other home wastes is one of the important 

 sanitary problems of men living in industrial and residential centers. 

 Haphazard methods of disposing of sewage not only lead to conditions 

 most unpleasant to human habitation but they are dangerous from the 

 standpoint of infectious diseases. 



Sewage abounds in microorganisms that originate not only from hu- 

 man excreta but also from other household and industrial wastes. The 

 various saprophytic bacteria present in sewage rapidly attack the or- 

 ganic constituents and bring about their gradual mineralization. The 

 destructive action of saprophytic organisms greatly reduces the number 

 of pathogens (334). Activated sludge, for example, has been shown 

 (853) to possess a definite and consistent bactericidal action against the 

 colon bacteria. In addition to antagonistic organisms, active bacterio- 

 phages against nearly all types of intestinal bacteria are present in sew- 

 age. The destruction of pathogens by bacteriolysis thus readily finds a 

 place in the activated-sludge method of sewage purification. 



Dissolved oxygen is generally present when sewage is diluted with 

 water. As the destruction of the organic matter proceeds rapidly, the 

 oxygen becomes depleted, so that none is left after a few hours. The 

 predominant bacterial flora of the water may then become anaerobic, 

 with the result that the chemical processes of decomposition are com- 

 pletely changed J hydrogen sulfide, mercaptans, and other foul-smell- 

 ing substances are then formed. This is accompanied by a typical 

 anaerobic breakdown of carbohydrates, leading to the formation of vari- 



