e 

 c 

 a. 



o 



— 2 



HEAN B.O.D. 



From Bartsch, 1956 



2 



AM 



8 



II 



t!oo:i 



B 



a. 



(X 



c 



m 



o 

 m 



8 



II 

 PM 



INFLUENCE OF DIFFUSED DAYLIGHT OH B.O.D. SAMPLE 

 CONTAIN IMG ALGAE - AUGUST 26, 1955 



Figure I I 



Center, and perhaps elsewhere. 



Three areas of relationship between algae 

 and the B.O.D. test are of particular interest. 

 They are: (a) the effect of illumination, (b) quan- 

 tity of algae, and (c) the influence of dead as op- 

 posed to living algae. Water from the Ohio River 

 containing limited quantities of phytoplankton was 

 incubated in an uncovered water bath at 20°C at an 

 east window. Half the bottles were exposed to 

 daily fluctuations in natural light; the others were 

 covered with opaque material. At the same hour 

 each day, duplicate bottles of each group were 

 processed for B.O.D. concentration. The 13-day 

 record is shown in Figure 10. The five-day B.O.D., 

 after more closely simulating natural conditions, is 

 only about half that derived by closer adherence to 

 the standard procedure. The fluctuation in B.O.D. 

 that occurred during the first five days resulted 

 from intermittent sunny and cloudy weather . With 

 continuous illumination, there was generally an ex- 

 cess of dissolved oxygen in the sample. In another 

 test, when replicates were incubated in the dark 

 for 19 hours, the B.O.D. was 2.77 ppm. , but with 

 natural light it was only 1 .15 ppm. Furthermore, 

 as shown in Figure 11, the mean B.O.D. of sam- 

 ples processed only at noon would have been, for 



those illuminated, 0.55 ppm., but for those in the 

 dark, 2.10 ppm. - a difference of 400%! It is ap- 

 parent that incubation in neither continuous light 

 nor continuous darkness can effectively adjust for 

 the photosynthetic and oxidation reactions related 

 to algae . 



To explore the influence of plankton quantity, 

 B.O.D. samples were prepared so that one con- 

 tained the phytoplankton removed from 20 volumes 

 of Ohio River water, the other the quantity from 40 

 volumes. Three samples are referenced "X algae" 

 and "2X algae" in Figure 12, which shows increas- 

 ing amounts of algae result also in increasing 

 B.O.D. 



In the standard B.O.D. test with its five-day 

 incubation in the dark , respiratory oxygen demand 

 of living algae gradually is replaced by an oxygen- 

 consuming attack by bacteria , protozoa , and other 

 organisms as the algae die. The extent and rapid- 

 ity of such transition in bottled samples is not 

 known although, as pointed out, the same situation 

 in principle has been observed repeatedly in natu- 

 ral waters . 



Chlorella variegata and sewage were added 

 to standard dilution water to give a fixed sewage 

 concentration of 0.5% and an algal density of 1 .22 



67 



