Dynamic mechanistic model for biological nutrient (nitrogen and phosphorus) removal activated sludge systems

The objective of this research was to develop and calibrate a dynamic mechanistic model for biological nutrient (nitrogen and phosphorus) removal activated sludge systems treating municipal wastewater. The IAWPRC (ASM1) model for non-polyP heterotrophic and autotrophic organisms and the Wentzel et al. (1989b) model for polyP organisms were merged to form a general activated sludge model. After a number of initial modifications the model was tested against literature data from laboratory-scale nitrification denitrification biological excess phosphorus removal (NDBEPR) systems. Specific areas were identified which required further study. These included (1) accounting for sludge production and oxygen utilization in BEPR systems; (2) denitrification behaviour in BEPR systems; and (3) other issues such as hydrolysis under unaerated conditions.; The main body of this thesis is a series of five papers. The first paper presents a study of COD and nitrogen balances in activated sludge systems. The results suggest that systems incorporating anaerobic zones exhibit low COD balances compared to aerobic and anoxic-aerobic systems. Possible mechanisms for this "loss" of COD are discussed, including the possibility that the COD loss is related to fermentation processes occurring under anaerobic conditions.; The second paper presents a study of denitrification behaviour in BEPR activated sludge systems. Results of a review of microbiological studies and many continuous and batch reactor experimental studies indicate that a significant fraction of the polyP organisms can use nitrate as an electron acceptor in the absence of oxygen for oxidation of stored PHB and simultaneous uptake of phosphorus.; The development of a general activated sludge model for biological nutrient removal activated sludge systems is discussed in the third paper. Several modifications were made to both the ASM1 and Wentzel et al. model components. A fermentation process has been included for the conversion of readily biodegradable COD to short chain fatty acids (assuming a loss of COD). Hydrolysis of enmeshed slowly biodegradable COD under anaerobic conditions has been incorporated, as well as anoxic growth of polyP organisms. The matrix representation and a description of the model processes are also presented, as well as a brief outline of influent wastewater characterization.; The application of the general model is demonstrated in the fourth paper for aerobic and anoxic-aerobic systems, as well as a number of nutrient removal (NDBEPR) systems for both steady state and dynamic conditions. Simulations show the model is capable of predicting sludge production and oxygen utilization for a range of system types and configurations, as well as tracking changes in a number of parameters including soluble phosphorus and nitrate concentrations.; In the final paper the consequences of the COD loss assumptions incorporated in the model are demonstrated for a number of experimental anoxic-aerobic and anaerobic-anoxic-aerobic systems. Simulations indicate that without the assumption of COD loss, predictions of oxygen consumptions and volatile suspended solids production are significantly over-estimated for NDBEPR systems (and to a lesser extent anoxic-aerobic systems). These systems apparently consume less oxygen and produce less volatile solids than aerobic systems for the same amount of COD removal. (Abstract shortened by UMI.)...