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

ABSTRACT

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, K_m, and explore biofilm development. The silicone membrane had a measured K_m of 2.6 m/d, and the micromembrane cord had an apparent K_m 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.

GRAPHICAL ABSTRACT

KEYWORDS:

• MABR
• nitrification
• biofilms
• hollow fibre membranes
• apparent K_m

Acknowledgments

We thank Al Greek and the City of South Bend for allowing us to operate the field bundle MABR at the South Bend WTTP, and for providing analytical data for the field studies. We acknowledge Karl Cronberger and the Analytical Science and Engineering at Notre Dame (ASEND) Core Facility for assistance with the ESEM imaging.

The ‘bundle’ reactors, both with micromembrane cords and with silicone membranes, were provided by SUEZ as an in-kind contribution to WERF project U2R14, along with approximately 10% of the total project budget. SUEZ also provided individual micromembrane cords and individual micromembranes for the individual membrane studies. Oxymem provided silicone membranes, which were used for the individual membrane studies. Neither SUEZ or Oxymem influenced the way we conducted the studies, interpreted the results, or wrote this publication.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author, RN, upon reasonable request.

Additional information

Funding

This work was supported by SUEZ; Water Environment Research Foundation: [Grant Number WERF project U2R14].