Effects of dilution on dissolved oxygen depletion and microbial populations in the biochemical oxygen demand determination |
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Authors: | Kyo Seong Seo Ho Nam Chang Joong Kon Park Kwang-Ho Choo |
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Institution: | (1) Department of Chemical Engineering, Kyungpook National University, 1370 Sankyeok-Dong, Buk-Gu, Daegu, 702-01, South Korea;(2) Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, Daejeon, 305-701, South Korea;(3) Department of Environmental Engineering, Kyungpook National University, 1370 Sankyeok-Dong, Buk-Gu, Daegu, 702-01, South Korea |
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Abstract: | The biochemical oxygen demand (BOD) value is still a key parameter that can determine the level of organics, particularly
the content of biodegradable organics in water. In this work, the effects of sample dilution, which should be done inevitably
to get appropriate dissolved oxygen (DO) depletion, on the measurement of 5-day BOD (BOD5), was investigated with and without seeding using natural and synthetic water. The dilution effects were also evaluated for
water samples taken in different seasons such as summer and winter because water temperature can cause a change in the types
of microbial species, thus leading to different oxygen depletion profiles during BOD testing. The predation phenomenon between
microbial cells was found to be dependent on the inorganic nutrients and carbon sources, showing a change in cell populations
according to cell size after 5-day incubation. The dilution of water samples for BOD determination was linked to changes in
the environment for microbial growth such as nutrition. The predation phenomenon between microbial cells was more important
with less dilution. BOD5 increased with the specific amount of inorganic nutrient per microbial mass when the natural water was diluted. When seeding
was done for synthetic water samples, the seed volume also affected BOD due to the rate of organic uptake by microbes. BOD5 increased with the specific bacterial population per organic source supplied at the beginning of BOD measurement. For more
accurate BOD measurements, specific guidelines on dilution should be established. |
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Keywords: | Biochemical oxygen demand Dilution Microbial population Nutrient Predation |
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