Scaling up membrane aerated biofilm reactors (MABR) for sustainable wastewater treatment.

Membrane aerated biofilm reactors (MABR) have attracted increasing attention as a potential platform for low carbon wastewater treatment, owing to their high oxygen transfer efficiency, biofilm-based process intensification, and reported potential for reducing nitrous oxide (N2O) emissions under specific configurations. However, successful full-scale implementation requires careful management of scale dependent variations in gas transfer, liquid-side mass transfer, hydrodynamics and biofilm stratification. This review critically examines these bottlenecks and the engineering principles required to manage them. Key challenges include membrane wetting, boundary layer resistance, lumen pressure loss and condensate accumulation in longer fibres, flow maldistribution at high packing density, excessive biofilm growth and matrix specific competition for oxygen. Emerging strategies, including intermittent scouring, redox regulation, spatially differentiated aeration, model informed module design and hybrid nitrogen removal configurations, provide potential scaling pathways, but their performance remains configuration and wastewater dependent. Reliable full-scale deployment therefore requires treating MABR as an integrated platform combining module design, gas-water regulation, biofilm control and greenhouse-gas management. Plant wide models and data driven soft sensors may support adaptive operation, although real-time closed-loop control remains to be demonstrated. By synthesizing material evolution, hydrodynamic regulation and operation emission interactions, this review identifies the engineering conditions that may influence the long term operational and environmental performance of MABR.