Bioreduction of Chromate in a Methane-Based Membrane Biofilm Reactor

摘要

For the first time, we demonstrate chromate (Cr(Ⅵ)) bioreduction using methane (CH_4) as the sole electron donor in a membrane biofilm reactor (MBfR). The experiments were divided into five stages lasting a total of 90 days, and each stage achieved a steady state for at least 15 days. Due to continued acclimation of the microbial community, the Cr(Ⅵ)-redudng capacity of the biofilm kept increasing. Cr(Ⅵ) removal at the end of the 90-day test reached 95% at an influent Cr(Ⅵ) concentration of 3 mg Cr/L and a surface loading of 0.37g of Cr m~(-2) day~(-1). Meiothermus (Deinococci), a potential Cr(Ⅵ)-reducing bacterium, was negligible in the inoculum but dominated the MBfR biofilm after Cr(Ⅵ) was added to the reactor, while Methylosinus, a type Ⅱ methanotrophs, represented 1196-21% of the total bacterial DNA in the biofilm. Synergy within a microbial consortia likely was responsible for Cr(Ⅵ) reduction based on CH_4 oxidation. In the synergy, methanotrophs fermented CH_4 to produce metabolic intermediates that were used by the Cr(Ⅵ)-reducing bacteria as electron donors. Solid Cr(Ⅲ) was the main product, accounting for more than 88% of the reduced Cr in most cases. Transmission electron microscope (TEM) and energy dispersive X-ray (EDS) analysis showed that Cr(Ⅲ) accumulated inside and outside of some bacterial cells, implying that different Cr(Ⅵ)-reducing mechanisms were involved.