Biological Sewage Disposal 239 



such wastes as those derived from a packing house, for example, 

 might add nutrients which would encourage microbial multi- 

 plication in sewage. 



When human excreta contain enteric pathogens, these organisms 

 survive for varying periods of time, depending upon the competi- 

 tion with saprophytic organisms. Enteric pathogens usually come 

 out second best when saprophytic competition is keen. 



The problem of safe disposal of potentially harmful organisms 

 commonly revolves around dumping the sewage into large bodies 

 of water or processing the material, usually biologically, to make it 

 odorless and harmless. Sanitary engineers have determined that 

 sewage can usually be adequately handled without creating a 

 public nuisance if one part of sewage is diluted in not less than 

 fifty parts of water, but some form of pre-treatment is required 

 by certain state and federal laws, before sewage can be dumped 

 into such bodies of water. This ratio usually allows proper 

 biological decomposition without overloading the water. 



The term sewerage is applied to the pipes, mains, tanks, etc., 

 which comprise a disposal system. The designation does not in- 

 clude the liquid wastes themselves. Sewage may contain matter 

 in solution, substances in colloidal suspension, and large and small 

 gross particles which must undergo decomposition to make them 

 soluble. 



TYPES OF SEWAGE DISPOSAL SYSTEMS 



It is estimated that more than half of the people in the United 

 States must dispose of their own sewage since no central system 

 is available to them. The procedures employed for the disposal 

 of human wastes in rural areas include sanitary pit privies, cess- 

 pools, or septic tanks. The latter two are generally used where 

 running water and flush toilets are involved. 



SANITARY PIT PRIVIES 

 The "outhouse," so common in rural areas, has served, and is 

 serving, a useful function in the disposal of human wastes. If 

 properly constructed to prevent a fly problem, these pit privies 



