IV-562 



domestic sewage, many municipal waste discharges also contain 

 significant amounts of industrial wastes, which may add to the 

 variability and complexity of the wastes discharged. Municipal waste 

 discharges have four important effects on receiving water quality: 

 depletion of dissolved oxygen, and introduction of pathogenic 

 organisms, settleable material, and inorganic nutrients. 



Sewage treatment reduces and alters the impact of municipal waste 

 on the environment. Primary treatment with chlori nation will remove 

 part of the decomposable organic material, nearly all of the settle- 

 able and suspended solids, and almost eliminate the possibility of 

 pathogens in the effluent. Secondary treatment can almost eliminate 

 decomposable organic material, and some special processes can 

 eliminate certain kinds of dissolved salts. About one half the 

 municipal wastes discharges to estuarine waters receive secondary 

 treatment, with the most extensive use of secondary treatment being 

 in the Chesapeake Bay estuarine region. 



Associated with the major metropolitan developments are large numbers 

 of industrial complexes with their attendant waste products. Many of 

 these industrial wastes , especially from the chemical industry, are 

 of such a complicated nature that it is difficult both to identify 

 them and to assess their effects on the receiving streams. Only 

 4000 of the more than 200,000 manufacturing plants in the Coastal 

 States account for 97 percent of the total liquid wastes discharged. 



