t^.O 



3.0 



to 



5 2.0 



o 



CO 



CO 



I .0 



TYPICAL RAW SEWAGE POND 

 (AUGUST 10, 1955) 



OHIO RIVER - BROMLEY 

 (OCTOBER 3, 1957) 



PHOTOSYNTHESIS 



RESPIRATION 



.■;ovi-' 



H 6 8 10 12 m 16 18 20 22 2>4 

 TIME - DAY 



OXYGEN RELATIONS IN SURFACE WATERS 

 Figure 7 



In sewage stabilization ponds algae are im- 

 portant for the oxygen they produce. California 

 pilot plant studies of such ponds (Gotaas, Oswald 

 and Golueke, 1954) showed an average yield of 

 1 .65 pounds of photosynthetic oxygen for each 

 pound of algae produced. In spite of this benefit, 

 the fact remains that an algal residue is left and 

 must be disposed of. In the pond, or in other re- 

 ceiving waters, the algae continue to draw upon 

 available oxygen for their respiration while alive 

 and are oxidized by bacteria when dead . Experi- 

 ence to date indicates that algae in such effluents 

 generally die and decompose at a sufficiently slow 

 rate that their deoxygenating influences are spread 

 over a long stream reach and, consequently, do 

 not produce acute oxygen depressions. In theory, 

 however, an equitable materials balance must show 

 not only the oxygen produced in growing the algae, 

 but also the oxygen required to oxidize them to a 

 stable state. In such a balance, the benefits of 

 algal photosynthesis appear less attractive . 



The necessity to include in evaluations of the 

 oxygenating benefits of algae the oxygen required 

 to decompose them is shown strikingly by recent 

 developments in Lake Washington (Sylvester, 

 Edmondson and Bogan, 1956). Domestic eutrophi- 

 cation has stimulated an increasing abundance of 



algae. It has been noted that oxygen consumption 

 in the hypolimnion has increased greatly during the 

 past 22 years because of the dropping down of in- 

 creasing quantities of algae and organic derivatives 

 from above. In 1933, 825 tons of oxygen were re- 

 moved per month; in 1950 the rate was 1400 tons, 

 and in 1955, 2190 tons. During the same period 

 the minimum dissolved oxygen concentration near 

 the bottom decreased from 6.4 ppm . to 3.5 ppm. 



Elsewhere in lakes, severe odor problems 

 have been encountered where planktonic blue-green 

 algae, having abandoned their more uniform dis- 

 persion in the water, clump together in windrows 

 and accumulate as a surface scum in protected 

 areas. As they decay, such concentrated algal 

 masses soon exhaust the available oxygen in the 

 immediate surroundings so that gaseous products 

 of anaerobic processes befoul the air. 



In polluted water conducive to intense algal 

 photosynthesis, super- saturation which so com- 

 monly occurs is wasteful, inefficient, and appar- 

 ently even reportedly dangerous. In sewage stabi- 

 lization ponds, oxygen concentrations exceeding 

 400% saturation have been observed. Because the 

 rate of the B.O.D. reaction unfortunately is not ac- 

 celerated by Increasing the oxygen concentration, 

 the surplus oxygen cannot be used for more rapid 



63 



