Membrane Bioreactors for Nitrogen Removal from Wastewater: A Review

The application of membrane bioreactor (MBR) processes for conventional, municipal and industrial wastewater treatment [e.g., biological oxygen demand (BOD) reduction] is well established. The research and development of MBR processes for nitrogen removal is more recent. To date, no thorough review of MBR technology for nitrogen removal from wastewater has been carried out. The review presented here provides an overview of MBR process configurations for the removal of nitrogen based on conventional nitrogen-removal pathways (i.e., nitrification/denitrification) as well as alternative nitrogen-removal pathways, such as anaerobic ammonium oxidation (ANAMMOX). A wide range of system configurations have been explored for the application of MBR for nitrogen removal, including immersed or side-stream membrane configurations, single or multichamber processes, and the application of fixed and moving bed biofilms. Operating variables play an important role in controlling nitrogen removal and fouling, especially feed composition (particularly the carbon∶nitrogen ratio), membrane characteristics, solids retention time, and hydraulic retention time. Modeling approaches for predicting nitrogen removal using MBR are evolving and are better able to represent key process differences in MBRs compared to conventional activated sludge. Although several challenges remain (e.g., membrane fouling, cost, and energy consumption), a number of opportunities exist (such as new reactor configurations, new microbial pathways, and development of a better understanding of process function through metaomic approaches) that may lead to the broader application of MBR processes for nitrogen removal from municipal wastewater in the future.