Coupled syngas fermentation to multiple oxidized contaminants reduction in a membrane biofilm reactor

Multiple oxidized contaminants (MOC) frequently coexist in water sources, posing significant human health risks. Major challenges in the biological reduction of MOC include the lack of effective carbon sources and competition for a sole electron donor. This study demonstrates the feasibility of using syngas fermentation in a lab-scale membrane biofilm reactor (MBfR) to provide dual electron donors, volatile fatty acids (VFAs) and H₂, to support simultaneous removal of nitrate, selenate, bromate, and perchlorate. MBfR was employed for efficient gas delivery, achieving complete MOC removal with non-toxic end products (N₂, Se⁰, Br^-, and Cl^-) generated over 200 days of operation. In situ batch tests revealed that MOC reduction was synergistically driven by H₂ and VFAs generated via gas fermentation. H₂ primarily facilitated bromate reduction, VFAs enhanced perchlorate reduction, while nitrate and selenate were reduced by both electron donors. Maximal removal rates reached 108.1 mg N/L/d, 6.9 mg Br/L/d, 5.5 mg Cl/L/d, and 5.4 mg Se/L/d when both H₂ and VFAs were utilized. High-throughput 16S rRNA gene amplicon sequencing suggested gas fermenters (Acetobacterium and Clostridium), autotrophic MOC-reducing taxa (e.g., Shewanella), and heterotrophic MOC-reducing taxa (e.g., Clostridium, Desulfovibrio) as the dominant community members, underscoring their roles in syngas conversion and contaminant reduction. These findings highlight the potential of integrating syngas fermentation in MBfRs as an efficient strategy for simultaneous MOC removal, providing a promising approach for water remediation.