Pilotförsök för utökad nitrifikation med en biofilmsprocess

Sammanfattning

This study investigated the potential of a moving bed biofilm reactor (MBBR) process as a post-nitrification step to reduce ammonium nitrogen concentrations in treated wastewater. The study was conducted in a pilot plant at Ellinge wastewater treatment plant, where two parallel reactors with different operating strategies were compared, one of which was periodically subjected to higher loading through intermittent addition of primary settled wastewater. The work combined experimental studies in the pilot plant, laboratory analyses, and modelling based on BSM2 to evaluate the performance of the MBBR process and key parameters to con-sider for full-scale implementation of post-nitrification. To replicate real operating conditions, biologically treated wastewater was continuously supplied from Ellinge wastewater treatment plant at a flow rate proportional to the plant's flow, and the temperature was adjusted to match that of the plant's incoming water. The results showed that the MBBR process as a post-nitrification step was capable of achieving low ammonium concentrations under stable conditions with steady loading, but that variations in loading and short-term peak flows negatively affected ammonium conversion efficiency. The operating strategy involving addition of primary settled wastewater promoted faster develop-ment of higher nitrification rates in the biofilm but appeared to make the process more sensitive to larger load variations and very high flow rates. The formation of nitrous oxide presents a challenge for the process, as nitrite accumulation can lead to increased emissions. For the implementation of a full-scale MBBR process, a balance between efficient nitrogen removal and potential climate impact from the process must be con-sidered. Modelling based on BSM2 confirmed the pilot results, demonstrating effective ammonium con-version and an area-efficient process that can serve as a compact complement to existing treat-ment systems. The results indicate that the process has the potential to contribute to meeting future stricter discharge requirements for ammonium, provided that operating strategies are op-timized with respect to both treatment performance and nitrous oxide emissions.