A systematic review of nitrogen removal pathways in membrane aerated biofilm reactor (MABR) systems

Membrane aerated biofilm reactor (MABR) offers enhanced wastewater treatment performance, energy efficiency, and environmental sustainability. Additionally, its counter-diffusional biofilm structure facilitates the formation of strata, which can support multiple pollutant removal pathways. In this paper, both conventional and emerging nitrogen removal pathways in MABR were reviewed including simultaneous nitrification and denitrification (SND), partial nitrification and denitrification (PND), and partial nitrification and anammox (PNA). To achieve high nitrogen removal efficiency through any of these pathways, operational parameters must be controlled. Nitrite oxidizing bacteria (NOB) inhibition to accumulate nitrite is a necessary condition to successfully achieve PND and PNA. Methods to suppress NOB (while retaining ammonia oxidizing bacteria – AOB) including inhibitor addition, limited oxygen supply, intermittent aeration, temperature control among others, have been used. Principal component analysis and CART® Regression were performed on the different operational parameters. The results indicate that the most important parameters that affect nitrogen removal efficiency via the SND pathway are pH, influent ammonia concentration, temperature, hydraulic retention time (HRT), and dissolved oxygen concentration. As MABR continues to be adopted more widely in wastewater treatment facilities globally, there is a need for further research on the effects of frequent temperature fluctuations and extreme weather conditions on SND, PND and PNA within MABR biofilm structure. • Zones in MABR biofilm can be optimized for partial nitrification and denitrification. • Partial nitrification in MABR biofilm is affected by NOB adaptability within the biofilm. • Intermittent aeration suppresses NOB in MABR biofilm, achieving partial nitrification. • There is limited study on the use of PND for nitrogen removal in MABR.