Experimental Study and Mathematical Modeling of Enhanced Biological Phosphorus Removal Based on Aeration Effects: Operational and Metabolic Insights

Enhanced Biological Phosphorus Removal (EBPR), as a promising technology, has been implemented in many wastewater treatment plants (WWTP) worldwide, with high efficiency in phosphorus removal performance. In a well-operated EBPR, lower operational cost, reduced sludge production, and lower environmental impacts are achievable. Yet, with the proven capability of EBPR in efficient phosphorus removal, disturbance and periods of unexplained insufficient phosphorus removal have been detected in real WWTP in different cases due to loss of PAO biomass under presumed favorable conditions for EBPR. These complications may lead to process upset, system failure, and violation of discharge regulations. Disruption in process performance may originate from several external factors such as heavy rainfall, excessive nitrate loading to the anaerobic reactor, excessive aeration of activated sludge, or it may be a result of PAOs competition with other groups of microorganisms such as glycogen accumulating organisms (GAO). Therefore, the key in reaching low P-effluent levels is to optimize the operation and minimize the effect of inefficient factors. This Ph.D. study has focused on aeration as a crucial operational factor in the EBPR process in sequential batch reactor (SBR) systems. EBPR aerobic P-uptake, anaerobic P-release, and carbon storage of phosphorus accumulating organisms (PAOs) are closely related to oxygen mass transfer. The study is oriented to different aspects of aeration, addressing aeration concentration (dissolved oxygen (DO) concentration), aeration duration (aerobic hydraulic retention time (HRT)), and aeration pattern (continuous/intermittent). The performance of EBPR in SBRs under various aeration strategies was investigated for different DO concentrations (0.4-4 mg/L), HRT (120-320 minute), and aeration patterns of continuous and intermittent (25 to 50 minute on/off intermittent aeration/non-aeration intervals).

Moreover, this study investigated the effect of reaching micro-aeration with adaptation strategies on EBPR performance. The development of steady and instant-DO reduction in different aeration strategies was studied in batch tests with enriched PAOs at different DO levels. Subsequently, comparative modeling using calibrated BioWin software was implemented for SBRs to predict the nutrient removal performance by changing DO concentration and the aerobic-HRT and understanding the effect of parameters on treatment performance to improve operation and control.