CALIBRATION OF AEROBIC ENDOGENOUS PROCESSES IN ACTIVATED SLUDGE MODELS FOR ENHANCED BIOLOGICAL PHOSPHORUS REMOVAL

Activated sludge systems operated for enhanced biological phosphorus removal (EBPR) are particularly sensitive to dynamic loading conditions. Increases in effluent phosphorus are often reported immediately after low loading conditions, such as weekends or rain events. Mathematical models for EBPR can be used to predict a system's response to low loading conditions. However, it is not clear to what extent do existing EBPR models represent the endogenous processes that dominate during low loading and/or starvation conditions. The purpose of this study is to evaluate the endogenous processes during aerobic starvation and determine whether current EBPR models are able to predict the response of an EBPR system to aerobic starvation. Activated sludge from a laboratory EBPR system was used to perform batch experiments. Phosphorus release and storage product utilization were monitored during aerobic starvation. Based on the observed results, we hypothesized that PAO preferentially use polyhydroxyalkanoates, then glycogen, and then polyphosphate during starvation. The Activated Sludge Model No. 2 and EAWAG models over predicted phosphorus release during aerobic starvation. Modifications to the EAWAG model were proposed to accurately describe the observed transformations of polyphosphate and glycogen. The modified model was in close agreement with the phosphorus release and glycogen oxidation observed during starvation. It is expected that the modified model can better predict the performance of systems exposed to low loading conditions, but further research is needed to further validate the proposed model modifications.