Full-scale hybrid membrane aerated biofilm reactor (MABR) upgrade enhances the removal of organic micropollutants

Abstract

Hybrid membrane aerated biofilm reactors (MABRs) integrate a range of redox conditions with increased biomass residence times in biofilms to create conditions that are expected to enhance the removal of organic micropollutants (OMPs). However, the removal of OMPs with MABRs remains unexplored. This study monitored the behavior of 20 OMPs over multiple seasons, both before and after the upgrade of a full-scale conventional activated sludge (CAS) facility to a hybrid MABR. More than half of the target compounds (13 out of 20) were present at lower concentrations in the effluent after MABR addition when compared to pre-upgrade operation. Plantwide removal efficiencies of highly removable compounds (>75%) (acetaminophen, ibuprofen, naproxen, triclosan, triclocarban, and norfluoxetine) and the recalcitrant carbamazepine were not impacted by the addition of the MABR process. However, the removal of three endocrine disruptors (bisphenol A, estrone, and estradiol) improved from a moderate removal (25 to 75%) to a high removal. Further, removal of an additional seven pharmaceuticals (gemfibrozil, sulfamethoxazole, trimethoprim, diclofenac, atorvastatin, and its ortho-hydroxy metabolites) improved from poor (<25%) to high or moderate removal with the hybrid MABR/CAS configuration. After the MABR upgrade, it was found that six OMPs exhibited higher removal rates under warm weather conditions (19.3 ± 1.6 °C) compared to cold weather conditions (13 ± 1.2 °C). Mass balance analysis on the MABR alone revealed a broad range of compound-specific responses, such as complete biotransformation (acetaminophen), partial removal (naproxen), and potential transformation from conjugates (sulfamethoxazole, carbamazepine). Overall, the three-year monitoring of the full-scale facility before and after the upgrade revealed that upgrading the CAS to a hybrid MABR configuration can enhance the removal of some OMPs that are poorly removed by the CAS process alone.