Bromate-reducing capability of nitrate/nitrite-dependent methane driven membrane biofilm reactors

Area of Science:

• Environmental Science and Engineering
• Water Treatment Technologies
• Microbial Ecology

Background:

• Bromate contamination is a significant environmental and health concern, often found with nitrate in water.
• Methane-driven processes offer a sustainable, low-carbon approach for removing oxidized contaminants.
• The interaction between bromate and nitrate/nitrite reduction in these systems is not well understood.

Purpose of the Study:

• To investigate the simultaneous removal of bromate and nitrate/nitrite using methane-based membrane biofilm reactors (MBfRs).
• To understand the competitive dynamics and potential synergistic effects between bromate and nitrate/nitrite reduction.
• To elucidate the microbial communities and metabolic pathways involved in methane-driven contaminant removal.

Main Methods:

• Two methane-based membrane biofilm reactors (MBfRs) were operated, one enriched with nitrate (MBfR-W1) and the other with nitrite (MBfR-W2).
• Simultaneous monitoring of bromate, nitrate, and nitrite removal efficiencies and reduction rates.
• Microbial community analysis using 16S rRNA gene sequencing and identification of key metabolic intermediates like short-chain fatty acids (SCFAs).

Main Results:

• Both MBfRs achieved high bromate removal rates (up to 5.6 mg BrO₃⁻-Br L⁻¹·d⁻¹) alongside nitrate or nitrite elimination.
• Nitrate and nitrite were preferentially reduced over bromate, but nitrite pre-enrichment (MBfR-W2) improved resilience to operational changes and higher bromate loads.
• Unexpectedly, high nitrate/nitrite concentrations appeared to stimulate bromate reduction; heterotrophic denitrifiers, not methanotrophs, dominated, and SCFAs were key intermediates.

Conclusions:

• Methane-based MBfRs are effective for simultaneous bromate and nitrate/nitrite removal.
• Nitrite pre-enrichment can enhance system stability and performance under challenging conditions.
• Methane-derived SCFAs play a crucial role in facilitating multi-contaminant reduction via alternative microbial pathways.