For the first time, we demonstrate chromate (Cr(VI)) bioreduction using methane (CH4) 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)-reducing 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 11%-21% of the total bacterial DNA in the biofilm. Synergy within a microbial consortia likely was responsible for Cr(VI) reduction based on CH4 oxidation. In the synergy, methanotrophs fermented CH4 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.

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Three-dimensional (3D) flowerlike calcium citrate microspheres assembled from nanosheets were successfully synthesized through a soft chemical method. The phase structure, morphology and microstructure of the synthesized products were characterized by the SEM, XRD, infrared and Raman spectroscopy. The characterization results indicated that the well-organized products with the diameter ranging from 10 to 30μm were composed of nanosheet precursors (50~500nm-50~200nm-8~30nm). The (200) crystal plane was the preferential growth face in the self-assembly process and the sheet precursors could be progressively transformed into consecutive strip with continuous heating treatment. The novel flowerlike calcium citrate microspheres with controllable morphology shows potential application prospect in biomaterials or other fields.

We studied the effect of electron competition on chromate (Cr(VI)) reduction in a methane (CH)-based membrane biofilm reactor (MBfR), since the reduction rate was usually limited by electron supply. A low surface loading of SO promoted Cr(VI) reduction. The Cr(VI) removal percentage increased from 60 to 70% when the SO loading increased from 0 to 4.7 mg SO/m-d. After the SO loading decreased back to zero, the Cr(VI) removal further increased to 90%, suggesting that some sulfate-reducing bacteria (SRB) stayed in the reactor to reduce Cr(VI). However, a high surface loading of SO (26.6 mg SO/m-d) significantly slowed down the Cr(VI) reduction to 40% removal, which was probably due to competition between Cr(VI) and SO reduction. Similarly, when 0.5 mg/L of Se(VI) was introduced into the MBfR, Cr(VI) removal percentage slightly decreased to 60% and then increased to 80% when input Se(VI) was removed again. The microbial community strongly depended on the loadings of Cr(VI) and SO. In the sulfate effect experiment, three genera were dominant. Based on the correlation between the abundances of the three genera and the loadings of Cr(VI) and SO, we conclude that Methylocystis, a type II methanotroph, reduced both Cr(VI) and sulfate, Meiothermus only reduced Cr(VI), and Ferruginibacter only reduced SO.

A novel chitosan-based composite nanofibers which was composited poly (vinylpyrrolidone) (PVP) and poly (vinylalcohol) (PVA) was prepared by electrospinning, and the spinnability and morphology of CS-based composite nanofibers were investigated. The result of SEM showed that with the introduction of PVP to composite fibers the spinnability of the system was improved. And the CS/PVA/PVP composite fibers displayed mean diameter of 71 nm and narrower diameter distribution than CS/PVA composite fibers. IR demonstrated that there were intermolecular hydrogen bonds in CS/PVA/PVP fibers. XRD showed that the crystalline microstructure of the fibers was not well developed.