Modeling long term nutrient removal in a sequencing batch reactor

A modified version of IAWQ activated sludge model 2 (ASM 2) was developed t o address the long-term dynamic behavior of nutrients in a sequencing batch reactor (SBR) activated sludge process. Experimental data was obtained fro m a long-term experimental work carried out in a 100-1 bench scale SBR. Cha nges in TOC, NH4-N, NO3-N, NO2-N and PO4-P could be reliably predicted afte r the model parameters were adapted to the SBR conditions. Better phosphoru s dynamics were achieved by considering the sub-model of denitrification by phosphorus accumulating organisms (PAO). Long-term simulations were carrie d out with the calibrated model to investigate the behavior of N and PO4-P under disturbed loading conditions. After attaining sufficient biological p hosphorus removal activities in the sludge, influent TOC concentration was stepwise decreased and increased for 5 weeks, nle decrease in organic loadi ng caused the deterioration of biological phosphorus removal with simultane ous increase in effluent NO3-N concentration Subsequently increasing the or ganic loading restored the original effluent conditions. The model simulati on predictions well match with the experimental results under disturbed org anic loading conditions. The simulated results implied that the deteriorati ng phenomena of phosphorus removal can be explained by two mechanisms: poor P-uptake by PAO and washout of PAO itself. (C) 1999 Elsevier Science Ltd. All rights reserved.