Table 3A. Total Nitrogen and Phosphorus Concentration (Median) in 

 Wastewater Effluents Following Four Conventional Treatment 

 Processes (after Mancini et al., in press) 



Table 3B. Typical Wastewater Characteristics (after Mueller, et al., 1 976) 



Concentration (mg 1' 1 ) for 



New York City 

 secondary 



effluent 



BOD 5 131 158 36 



Total P 4.70 6.14 3.30 



Total N 21.7 22* 22* 



N:P (weight) 4.62 3.58 6.67 



N:P (atoms) 10.20 7.92 14.73 



'Average of primary and secondary effluent concentrations. 



As far as the marine environment is concerned, control of the phosphorus content 

 of the effluent cannot be expected to limit effectively the excessive plant growths in 

 the environment into which the effluent is discharged. Since nitrogen is commonly 

 the most critical element limiting phytoplankton production in the marine environ- 

 ment, removal of nitrogen from the wastewater effluents would be expected to be the 

 most effective way to prevent excessive phytoplankton growth. Various methods are 

 available for nitrogen removal from sewage effluents. Their effectiveness is summa- 

 rized in Table 5( Mancini et al., in press). Conventional primary and secondary treat- 

 ments remove some of the organic nitrogen from the sewage but have little or no 

 effect on inorganic nitrogen. Various advanced wastewater treatment processes can 

 remove as much as 90 percent of the total nitrogen. Even such comparatively simple 

 treatments as oxidation ponds can be very effective in removing nitrogen, provided 

 the organic material produced in the photosynthetic process in these ponds is re- 

 moved as particulate matter before the effluent is released to the environment. 



If the effluent is released to the environment without control of the elements that 

 stimulate plant growth, the natural photosynthetic process in the environment will 

 recreate the organic material that was removed or decomposed at considerable ex- 

 pense in the treatment process. There is a time lag in achieving this in the environ- 

 ment the duration of which is dependent upon all of the environmental factors that 



74 



