MABR... How Does It Work, Where Does It Fit, and Why Is It Compelling? Lessons from 4 Full-scale Systems

The performance of four membrane-aerated biofilm reactors (MABR) located in different geographies and configured with pure biofilm and IFAS systems are evaluated. Oxygen transfer rates between 12 to 19 gO2/m2d were achieved with silicone (PDMS) membranes. Nitrification rates between 1.0 and 2.9 gN/m2.d were achieved. On all sites there was competition for oxygen between autotrophic nitrifiers and heterotrophic bacteria. The percentage of oxygen utilized for nitrification can be influenced by the location of the MABR modules within a treatment system. Installing the modules in the anoxic zone resulted in the highest nitrifications rated 5.8 gN/m2.d and the highest percentage of oxygen utilized for nitrification 90%. Installing the MABR modules in an anaerobic zone is not advisable – the produced nitrate consumes VFA and therefore limits bio-P removal. In addition, if the tank is deeply anaerobic with low redox potential, sulfur and iron compounds will be reduced and the produced hydrogen sulfide will inhibit nitrification and the reduced iron and sulfur compounds will be re-oxidized. MABR modules can potentially be installed in plug flow aerobic reactor close to the head of the aerobic zone. It is not advisable to install the MABR modules in a CSTR type aerobic tank or at the end of a plug flow reactor; there will be insufficient substrate to support a biofilm and red worms and leaches may prevent a healthy biofilm forming.