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have four important effects on receiving water quality: depletion 

 of dissolved oxygen, and introduction of pathogenic organisms, settle- 

 able 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 Dossibility cf 

 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 

 discharged 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 indu strial 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 4,000 of 

 the more than 200,000 manufacturing plants in the coastal states 

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

 the nearly 22 billion gallons of industrial wastes discharged 

 only 29 percent receive any kind of waste treatment. 



Intensification of use of the estuarine zone has resulted in many 

 artificial changes being made in the physical structure. Shoreline 



