Impact of High Flow on Phosphorus Treatment Performance

Abstract

This thesis assesses the impact of high flow conditions on the performance of five wastewater treatment plants (WWTPs) in Sweden in terms of phosphorus (P) removal, focusing specifically on effluent P mass flow. Predictive models were developed for each WWTP using actual flow and effluent P concentration data to estimate the effluent P mass flow outcomes under varying flow rates. These estimates provide stakeholders with valuable insights into current performance and potential opportunities for optimisation. The research involved the collection and analysis of three years of flow, influent, and effluent P concentration data for each plant. Statistical analyses were conducted to identify flow rate patterns, and regression models were developed to predict effluent P concentration which is then used to estimate effluent P mass flow under different flow conditions. Key findings indicate that as flow increases, effluent P mass flow also rises. When a WWTP’s capacity is exceeded, bypass scenarios occur, resulting in a significant increase in effluent P mass flow. The effectiveness of P removal at each WWTP is closely related to the plant's overall treatment capacity and the inflow it receives. The study also examined the performance of WWTPs under two scenarios: swapping of catchments and swapping of WWTPs within municipalities, revealing additional opportunities for optimisation. For most municipalities, improving catchment area management could help reduce inflow peaks, and for all of them, upgrading design capacities, techniques, or WWTP operations could significantly enhance P removal performance. In conclusion, this thesis provides important insights for optimising WWTP performance in P treatment under high flow conditions, contributing to improved environmental protection and regulatory compliance in Sweden.