Modelling of Granular Sludge Bioreactor to Study the Influence of Dissolved Oxygen Concentration and Loading Rates on Simultaneous COD, N and P-removal

Recently, aerobic granular sludge reactors have been extensively studied as a new technology for wastewater treatment. In this study, a mathematical model has been developed and compared with the experimental results to study the microbial distribution and overall conversions performance of the reactor at different conditions such as dissolved oxygen concentrations and COD, nitrogen and phosphorus loading rates. A laboratory reactor with working volume of 3 L was operated in sequencing batch mode. A model was developed using Aquasim software to investigate the structure and performance of the reactor at different dissolved oxygen concentrations and COD, nitrogen and phosphorus loading rates. The model results showed that the majority of the microorganisms inside the biofilm are phosphate accumulating organisms. Total COD and P-removal under the laboratory conditions at a dissolved oxygen (DO) concentration of 100% was reached, but the obtained N-removal was not sufficient. Therefore, the N-removal at lower oxygen concentrations was studied. The optimum value for nitrogen removal was obtained (more than 98%) with a DO concentration of 40-45% and 35% by simulation and in the laboratory reactor, respectively. The model describes the experimental data at different COD, nitrogen and phosphorus loading rates, sufficiently well. The results of the experimental data and model were in a good agreement. Therefore, the model can be used for process understanding and optimization of this complex system.