Uranium removal and microbial community in a H2-based membrane biofilm reactor

• The H2-based Membrane Biofilm Reactor (MBfR) achieved ∼95% U removal.
• Nanocrystalline UO2 and amorphous U precipitates were present in the biofilm.
• The biofilm microbial community shifted drastically when sulfate was present.
• When stimulated by SO42−SO42− and −HCO3HCO3−, Clostridiaceae spores appeared to reduce U.

We evaluated a hydrogen-based membrane biofilm reactor (MBfR) for its capacity to reduce and remove hexavalent uranium [U(VI)] from water. After a startup period that allowed slow-growing U(VI) reducers to form biofilms, the MBfR successfully achieved and maintained 94–95% U(VI) removal over 8 months when the U surface loading was 6–11 e− mEq/m2-day. The MBfR biofilm was capable of self-recovery after a disturbance due to oxygen exposure. Nanocrystalline UO2 aggregates and amorphous U precipitates were associated with vegetative cells and apparently mature spores that accumulated in the biofilm matrix. Despite inoculation with a concentrated suspension of Desulfovibrio vulgaris, this bacterium was not present in the U(VI)-reducing biofilm. Instead, the most abundant group in the biofilm community contained U(VI) reducers in the Rhodocyclaceae family when U(VI) was the only electron acceptor. When sulfate was present, the community dramatically shifted to the Clostridiaceae family, which included spores that were potentially involved in U(VI) reduction.

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