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pH as a Key Factor in the Competition Between Glycogen-Accumulating Organisms and Phosphorus-Accumulating Organisms

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The effects of pH on the anaerobic metabolism of glycogen-accumulating organisms (GAOs) and phosphorus-accumulating organisms (PAOs) were compared using models for the kinetics of acetate uptake. The comparison revealed that GAOs take up acetate faster than PAOs when the pH of the anaerobic zone is less than 7.25, but that PAOs remove acetate faster than GAOs at pHs greater than 7.5. It was also found that the growth efficiencies of the two organisms are similar. Furthermore, the amount of polyhydroxy-alkanoates available after replenishment of the polymers used during acetate uptake under anaerobic conditions is similar for the two organisms, making GAOs highly competitive in nutrient removal systems. The effects of pH on the competition between the two organisms were demonstrated during the operation of a laboratory-scale sequencing batch reactor. When the overall pH of the system was low, poor phosphate removal was observed. When the pH of the system was allowed to increase to a maximum of 7.5, phosphate removal improved, but was still incomplete. Total removal was only achieved when the pH of the system was never allowed to drop lower than 7.25. After the minimum pH in the system was increased, total removal of phosphate was achieved in 14 days. The results showed that pH control is a promising strategy for minimizing the accumulation of GAOs and increasing the reliability of biological excess phosphorus removal systems.


Document Type: Research Article


Publication date: March 1, 2001

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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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