Pilot-Scale Nitrogen Recovery from Anaerobic Digester Centrate Utilizing Ultrafiltration and Membrane Contactors

Anaerobic digester centrate contains high concentrations of nitrogen, predominantly in the form of ammonium. Most wastewater treatment plants send the centrate back to their headworks, missing the opportunity to recover valuable products and overloading their energy-intensive nitrification–denitrification processes for nitrogen removal. Membrane contactors provide a promising, lower energy demand alternative for high-efficiency nitrogen recovery (>80%); however, previous studies have reported performance declines due to membrane fouling and inadequate pretreatment, limiting the practical application of this technology. In this study, we investigated ultrafiltration as a pretreatment strategy to mitigate fouling and enhance membrane contactor performance. A pilot-scale hybrid ultrafiltration–membrane contactor system was investigated and achieved 80% nitrogen recovery from centrate without noticeable performance decline at a feed pH as low as 8.5. These results demonstrate that ultrafiltration effectively removes foulants and improves nitrogen recovery efficiency, suggesting that membrane contactor systems with appropriate pretreatment represent a viable and energy-efficient approach for nitrogen recovery in wastewater treatment plants.