Glycogen plays an important role in biological phosphorus removal from wastewaters. Existing measurement techniques often overestimate the glycogen content of the biomass due to the presence of glucose and/or other carbohydrates than glycogen in the cell material. As an alternative to conventional methods a bioassay for glycogen determination in biological phosphorus removal systems was developed. The bioassay is based on the strict stoichiometric coupling between anaerobic acetate uptake and glycogen consumption. In other words, the glycogen concentration of the sludge was determined indirectly by measuring the maximal total acetate uptake by the activated sludge in anaerobic batch tests. The bioassay was successfully tested for the determination of glycogen content of the sludge taken from the lab-scale, acetate-fed, anaerobic-aerobic-settling sequencing batch reactor operating at pH 7±0.1 and temperature of 20°C. This determination of glycogen requires that glycogen (not poly-P) is the limiting factor for anaerobic acetate uptake. A method to verify this assumption based on the effect of pH on phosphate/acetate ratio is proposed and used. The bioassay is easy to apply and gives a direct measure of the glycogen content of bio-P bacteria, but its reliability still needs to be verified at full-scale biological P-removal plants.

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