Table 23. Average Efficiency of Primary and Secondary Sewage 

 Treatment Plants (Source: Reference 93) 



dead organic matter on estuarine bottoms. In serious cases, the 

 nutrients remaining after conventional secondary treatment may have 

 to be removed by an additional process before discharge of the efflu- 

 ent to typical estuarine waters. 



Ocean dispersal of treated sewage may be feasible if properly 

 designed and controlled, and provided that high concentrations of toxic 

 substances are absent. The pripcipal advantage of the ocean as a disposal 

 site is a reduction of costs compared to the advanced treatment required 

 for disposal in estuarine waters (Table 24) L98J. The ocean rapidly 

 disperses and dilutes the effluent because of its volume and mixing 

 capabilities, thus reducing the potential for ecological damage. The 

 location and physical configuration of ocean effluent outfalls should be 

 determined by depth, distance from shore, circulation and mixing features 

 of the particular ocean location, and factors influencing interactions 

 of wastes with the environment [99]. But it must be clearly understood 

 that high concentrations of sewage released at a single point anywhere 

 In the ocean may overwhelm its assimilative capacity and cause extensive 

 local damage, particularly to bottom life. 



137 



