Effect of membrane type on the behavior of nitrifying membrane aerated biofilms: silicone membranes vs. micromembrane cords.

There is increasing interest in membrane-aerated biofilm reactors (MABRs), due to their energy efficiency and ability to intensify wastewater treatment. While MABR membranes play a key role, supporting biofilms and transferring O2, little research has addressed how membrane types impact MABR performance. This research compared two types of membranes used in commercial MABRs: a silicone hollow-fibre membrane and a 'micromembrane cord,' consisting of an inert cord surrounded by fine proprietary polymeric membranes. We used single-membrane MABRs to determine the oxygen mass transfer coefficient, Km, and explore biofilm development. The silicone membrane had a measured Km of 2.6 m/d, and the micromembrane cord had an apparent Km of 1 m/d. Pure MABR bundles (only biofilm) were operated with synthetic wastewater, and hybrid MABRs (suspended biomass and biofilm) with real wastewater, to explore behaviour for a wide range of conditions. The maximum ammonium oxidation fluxes with synthetic wastewater were 7.8 gN/m2d for the silicone membrane and 4.3 gN/m2d for the micromembrane cord. However, at bulk NH4+ concentrations below 5 mgN/L, the ammonium oxidation fluxes were similar. A previously published MABR model effectively captured the behaviour of each membrane. Nitrification fluxes with real wastewater were lower than synthetic wastewater, likely because of the presence of chemical oxygen demand (COD). Although the ammonium oxidation fluxes were higher for the silicone membranes for a given air supply pressure, the fluxes for the micromembrane cord could be increased using higher intramembrane air pressures. Overall, this research helped understand the impact of membrane types on nitrification fluxes.