A bacterium capable of degrading microcystin (MC), strain CH, was isolated from the sediment of Lake Chaohu, China. Strain CH was tentatively identified as Paucibacter sp. based on the analysis of 16S rRNA gene sequences. Paucibacter sp. strain CH can use microcystin LR (MCLR) as the sole carbon and energy sources, and 11.6 microg x mL(-1) of MCLR was degraded to below the detection limit within 10 hours with the first-order reaction rate constant of 0.242 h(-1). The optimum temperature and initial pH for MC degradation were 25-30 degrees C and pH 6-9, respectively. A novel intermediate product containing the Adda residue was detected during the degradation of MCLR, which is different from those produced by strain ACM-3962, and Adda was recognized as the final product of the degradation process. Furthermore, no homologue to any of the four genes, mlrA, mlrB, mlrC and mlrD previously associated with the degradation of MCLR by strain ACM-3962 was found in strain CH. These findings suggest that Paucibacter sp. strain CH mighe degrade MC through a different pathway from that of strain ACM-3962.
Abstract Grouting has become an important and effective means of prevention and treatment to mine water disaster. Explore the rapid and efficient mechanism and grouting technology for coal mine water control work has great significance. This paper proposed directional drainage grouting based on Grouting mechanism and practice experience. It could be used for tunnel closure, collapse column water inrush and “four-fuzziness” (measurements are not allowed, water inrush source uncertainty, water inrush location is unknown and leading water channels is unclear) mines. And the water grouting mechanism and key techniques are discussed in detail. The water disasters treatment of Renlou coal mine and Tianhe coal mine showed that directional drainage grouting have high efficiency, save materials, large safety factor and so on. It has broad application prospects.
Abstract Microcystins (MCs) are a family of related cyclic hepatotoxic heptapeptides, of which more than 70 types have been identified. The chemically unique nature of the C20 β‐amino acid, (2S,3S,8S,9S)‐3‐amino‐9‐methoxy‐2,6,8‐trimethyl‐10‐phenyldeca‐4,6‐dienoic acid (Adda), portion of the MCs has been exploited to develop a strategy to analyze the entirety. Oxidation of MCs causes the cleavage of MC Adda to form 2‐methyl‐3‐methoxy‐4‐phenylbutanoic acid (MMPB). In the present study, we investigated the kinetics of MMPB produced by oxidation of the most‐often‐studied MC variant, MC‐LR (L = leucine, R = arginine), with permanganate‐periodate. This investigation allowed insight regarding the influence of the reaction conditions (concentration of the reactants, temperature, and pH) on the conversion rate. The results indicated that the reaction was second order overall and first order with respect to both permanganate and MC‐LR. The second‐order rate constant ranged from 0.66 to 1.35 M/s at temperatures from 10 to 30°C, and the activation energy was 24.44 kJ/mol. The rates of MMPB production can be accelerated through increasing reaction temperature and oxidant concentration, and sufficient periodate is necessary forthe formation of MMPB. The initial reaction rate under alkaline and neutral conditions is higher than that under acidic conditions, but the former decreases faster than the latter except under weakly acidic conditions. These results provided new insight concerning selection of the permanganate‐periodate concentration, pH, and temperature needed for the oxidation of MCs with a high and stable yield of MMPB.
Nanosized Bi3NbxTa1−xO7 photocatalysts were prepared by a facile and low-cost sol−gel method using stable, less toxic Ta2O5, Nb2O5, and Bi(NO3)3·5H2O as the raw materials. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy, and UV−vis diffuse reflectance spectroscopy. The Bi3NbxTa1−xO7 nanoparticles exhibited an efficient photocatalytic activity in the decomposition of acid red G (ARG) dye solution under visible light irradiation. Besides decoloring, the typical sample Bi3Nb0.6Ta0.4O7 also showed an excellent photocatalytic property for the removal of the cyanotoxin, microcystin-LR (MC-LR, an emerging contaminant from the Contaminant Candidate Lists (CCLs 1-3) of the USEPA). The excellent visible light photocatalytic activity of the samples was mainly attributed to their narrow band gaps, small particle size, and the oxygen vacancies on the surface of the catalysts. According to experimental results, a possible mechanism of the photocatalysis over Bi3NbxTa1−xO7 was proposed.
During toxic Microcystis aeruginosa blooms, large amounts of cells can enter sediment through natural settlement, and coagulation treatment used to control water blooms can enhance the accumulation of cells. However, the current understanding of the fates of these cells and associated microcystins (MCs), as well as the effect of coagulation treatment on these factors, is limited. The results of the present study show that Microcystis aeruginosa cells in sediment were steadily decomposed under experimental conditions, and that they completely disappeared within 28 days. The major MCs released from settled cells were immediately degraded in sediment, and microbial degradation may be the main mechanism involved in this process. Coagulation treatment with PAC (polyaluminium chloride) + sepiolite can efficiently remove Microcystis aeruginosa cells from the water column and prevent their re-invasion. Furthermore, coagulation treatment with PAC + sepiolite had no significant effect on the release and decomposition of MCs and, thus, will not enhance the MCs pollution. However, coagulation treatment can accelerate the nutrient cycle by enhancing the settlement of cells. More attention should be paid to the effect on nutrient cycle when coagulation treatment is used for restoration of aquatic ecosystems.
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