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Effect of Air On-Off Cycles on Activated-Sludge Denitrification

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The effect of alternating aerobic and anoxic conditions on denitrification by activated sludge was investigated in bench-scale sequencing batch reactors with a total of 10.5 hours of reaction time. After 2 to 5 hours of anoxic denitrification, mixed liquor was aerated for 36, 94, or 174 minutes and then returned to anoxic mixing. Acetate was added during both the denitrification and aerated reaction periods, except for one experiment with aeration without substrate. The specific denitrification rate was reduced by 26% from the totally anoxic rate of 0.023 mg nitrate/mg mixed liquor volatile suspended solids•h when the activatcd sludge received 36 minutes aeration and by 61% for both 94 and 174 minutes of aeration. However, aeration did not seem to cause the reduction directly. Rather, the addition of acetate with oxygen caused aerobic growth of bacteria, indicated by the significant increase in the specific oxygen uptake rate of the activated sludge consuming substrate under aerobic conditions.


Document Type: Research Article


Publication date: 1999-11-01

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  • Water Environment Research® (WER®) publishes peer-reviewed research papers, research notes, state-of-the-art and critical reviews on original, fundamental and applied research in all scientific and technical areas related to water quality, pollution control, and management. An annual Literature Review provides a review of published books and articles on water quality topics from the previous year.

    Published as: Sewage Works Journal, 1928 - 1949; Sewage and Industrial Wastes, 1950 - 1959; Journal Water Pollution Control Federation, 1959 - Oct 1989; Research Journal Water Pollution Control Federation, Nov 1989 - 1991; Water Environment Research, 1992 - present.
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