Biological Bromate Reduction Driven by Methane in a Membrane Biofilm Reactor

As a potent greenhouse gas with a greenhouse warming potential 28 times that of carbon dioxide over a time scale of 100 years, methane has been proven to be useful as an electron donor for the removal of various contaminants, e.g., nitrate, nitrite, perchlorate, and chromate, from contaminated water. However, microbial bromate reduction supported by methane has not been reported so far. Here, a lab-scale membrane biofilm reactor (MBfR) was set up to explore the feasibility of bromate reduction driven by methane under oxygen-limiting conditions. Long-term operational performance demonstrated that a complete reduction of bromate (BrO₃^-) to bromide (Br^-) could be achieved, with 100% bromate removal efficiency under a volume loading of 1 mg of Br L^-1 day^-1. Volatile fatty acids (VFAs) were produced in the reactor (concentrations ranging from 1.81 to 27.9 mg/L) under oxygen-limiting conditions. High-throughput 16S rRNA gene sequencing indicated that Methanosarcina became the only dominate methane-oxidizing microorganism, and the abundance of Dechloromonas increased from 0.9 to 18.0% after they had been fed bromate. It is hypothesized that under oxygen-limiting conditions methane is oxidized into VFAs, which might be used to reduce bromate by dissimilatory bromate-reducing bacteria (likely Dechloromonas). This study offers a potential technology for bromate removal using a methane-based MBfR. © 2017 American Chemical Society.