Ethane-driven chromate and nitrate bioreductions in a membrane biofilm reactor

Chromium (Cr(VI)) and co-contaminating nitrate (NO3-) pose major threats to human health. Hydrogen-and methane-driven Cr(VI) and NO3- bioreductions have been documented, but unknown is whether or not non -methane short-chain gaseous alkanes (SCGAs), such as ethane (C2H6), also can drive Cr(VI) and NO3- re-ductions. This study demonstrated simultaneous Cr(VI) and NO3- bioreductions driven by C2H6 oxidation in a membrane biofilm reactor (MBfR) that delivered C2H6 directly to a biofilm by its diffusion through non-porous membranes. Scanning electron microscopy and X-ray photoelectron spectroscopy showed that the biofilm was mainly composed of cocci and bacillus and that a Cr(III) precipitate was the major product of microbial Cr(VI) reduction. Microbial community analysis showed that the C2H6-oxidizing bacterium Mycobacterium oxidized C2H6 and delivered organic intermediates to Cr(VI)-reducing bacteria TM7a, Sediminibacterium, and Deinococcus. Because the first step of ethane catabolism is a monooxygenation, the influent had to have dissolved oxygen, and the dominant respiratory process was O2 reduction. By providing insights into how Cr(VI) and NO3- bioreductions can be driven by C2H6 oxidation, these finding support the application of SCGAs for ex-situ bioremediation of waters contaminated with Cr(VI) and NO3-.

Automated summary

This study demonstrated simultaneous Cr(VI) and NO3- bioreductions driven by C2H6 oxidation in a membrane biofilm reactor (MBfR). The biofilm was mainly composed of cocci and bacillus, and a Cr(III) precipitate was the major product of microbial Cr(VI) reduction.