ABSTRACT
93An integrated activated sludge model was used to describe removal of organic matter, nitrogen and phosphorus in a full-scale wastewater treatment plant Haarlem Waarderpolder in The Netherlands. The plant consists of a conventional anoxic/aerobic activated sludge line, side-stream combined biochemical phosphorus removal line and sludge treatment line. In this integrated model., the “Delft model” for biological phosphorus removal (BPR) replaced the module for P removal of Activated Sludge Model No.2 (ASM2). With the adjustment of only three model parameters (fermentation rate constant, glycogen formation rate constant and the percentage of denitrifying activity of phosphorus accumulating organisms) the model proved well capable of describing the performance of the treatment plant (for both liquid phase and biomass). The model was validated using batch tests with the activated sludge and showed satisfactory results in describing the anaerobic P release and aerobic and anoxic P uptake processes. The model was to a lower extend capable of well predicting nitrification, endogenous P release and especially denitrification processes. Both model simulations and results of the sampling program suggested that the acetate dosage to the system could be reduced up to 30%. It was also shown that pH strongly affects observed phosphate/acetate ratio and possibly fermentation rate in the side-stream BPR process. Simulation of three alternative plant configurations showed that: (1) plant effluent quality would strongly deteriorate if the side-stream process is skipped and the rest of the plant is retained in its original state, (2) good effluent quality would be achieved in a main-stream process (modified UCT system) where an additional anaerobic tank is added in front of the activated sludge unit, however, the required acetate addition would be sevenfold higher in comparison with a present side-stream configuration.
