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Effect of turbulence, light and turbidity on the standard BOD test Morissette, Denis G.

Abstract

The currently used BOD test attempts to predict oxygen level depletion in a given environment, e.g. a moving stream, and is also a parameter for the design and operation of biological processes. It is run under conditions similar to those occurring in nature, but it has been reported that the oxidation rate in a stream is higher than the corresponding rate obtained from the laboratory BOD test. This study was undertaken to observe the effect of turbulence, light and turbidity, separately and in combinations, on the standard BOD test, using raw sewage samples. Mixing was found to increase the BOD, by an average of 15$. reduce the lag period and increase the ultimate BOD value. Light did not show any appreciable change on the standard BOD test, since only an average 4% increase in BOD^ was found. However, turbidity demonstrated an average reduction of 25% on BOD,, values. When the above physical changes were observed in combinations, the results were not additive. As an example, light and turbidity, in combination, did not reduce the BOD,-decrease to 21% (25%-k%). Instead, the decrease in BOD^ value was 5%. This clearly points out that physical changes to the BOD test should not only be studied separately, but also in combinations. Therefore, this study appears to expose the inade quacy of the present BOD test for actual stream conditions. It has also shown that without further research, extrapolating from the existing standard BOD test,yields questionable results. Inclusion in the BOD test, of the physical characteristics of the stream, is a possible solution to obtaining reliable results.

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