n — 



e 



Cl 



d 



3 — 



2 — 



OHIO RIVER WATER-DARK 



OHIO RIVER WATER-DAYLIGHT 



2 U 6 8 10 12 



t, DAYS 



INFLUENCE OF ILLUMINATION ON B.O.D. OF SAMPLE CONTAINING ALGAE 



AUGUST 26, 1955 



Figure 10 



m 



period may give an unduly high value because of 

 algal respiration, death, and decay; (b) incubation 

 with illumination as an attempt at improvement may 

 give unduly low or negative B.O.D. (Figure 6) be- 

 cause of the addition of oxygen by photosynthesis; 

 and (c) incubation with intermittent illumination, 

 although superficially attractive, does not suffi- 

 ciently simulate stream conditions in terms of tem- 

 perature, illumination, availability of nutrients , 

 and other factors. 



A number of attempts have been made to mod- 

 ify the B.O.D. procedure to make the result more 

 meaningful with samples containing algae . Abbott 

 (1948) incubated duplicate samples in B.O.D. bot- 

 tles for 48 hours, one bottle of the pair in darkness 



and the other exposed to light at a north window. 

 Test results were expressed as a ratio, L ~ D 



Oo- Od 



when Oq is initial dissolved oxygen, Ol and Od 

 are concentrations after light and dark incubation 

 respectively. Later, the procedure was modified 

 further (Abbott, 1952) to measure the light energy 

 during incubation with a hydrogen iodide actino- 

 meter . 



In studying the influence of blue-green algae 

 on the B.O.D. result, Wisniewski (1958) modified 

 the test to determine separately the influence of 

 living, dead, and variable concentrations of algae. 

 Further studies on this problem are in progress at 

 theUniversity of Wisconsin, the Sanitary Engineering 



66 



