| At present,chromium pollution has become a global environmental issue.Remediation of chromium pollution by anaerobic sludge was considered to be one of the most efficient and low-cost method.Anaerobic sludge,which possess high potential to repair high-concentration Cr(VI)pollution,was selected from environment in the present study.The technological parameters were optimized to increase its remediation ability of Cr(VI)pollution.Meanwhile,the mechanisms of anaerobic sludge bioremediation of chromium pollution were systematically discussed both from macroscale analysis and microscale analysis.The results could provide scientific basis and key guidance for the application of anaerobic sludge in engineering remediation of chromium pollution.Anaerobic sludge,which was taken from Shanghai Xujing Wastewater Treatment Plant,Qingdao Beer Second Plant and Qingdao Lvyin Kitchen Waste Treatment Plant,was chosen to explore their potential for repairing Cr(VI)pollution at high-concentration.The influence of carbon source,sulfate and temperature on high-concentration Cr(VI)remediation by anaerobic sludge were investigated by single factor method and orthogonal method.The results showed that the anaerobic sludge from Qingdao Lvyin Kitchen Waste Treatment Plant possessed the strongest potential to repair high-concentration Cr(VI)pollution among them.Carbon source,moderate amount of sulfate and higher culture temperature could improve the remediation ability.The optimum condition of repairing 500 mg/L Cr(VI)by anaerobic sludge is adding 3 g glucose and 2 g sulfate to the system when the temperature is 35?.The mechanisms of indirect bio-reduction of Cr(VI)by anaerobic sludge were studied by analyzing the sulfur cycle,the microbial community,the morphological structure of sludge and the formation of chromium.The results showed that Cr(VI)was reduced by sulfide to produce more elemental sulfur than sulfate in the indirect bioreduction system.As an electron acceptor,elemental sulfur was reduced to sulfide by Sulfurospirillum,which made both Desulfovibrio and Sulfurospirillum growing better at the same time.Sulfate,elemental sulfur and sulfide formed a favourable positive cycle in the Cr(?)indirect bio-reduction system to maintain a more stable Cr(?)reduction stream.The morphological and structural of sludge was obviously changed,which made it possessed higher reducibility as and stronger adsorption ability Less intracellular and intercellular Cr(?)indicated that most of Cr(?)was chemically reduced by sulfide,produced from the biological sulfate reductionThe physicochemical environment of Cr(?)bio-reduction systems was detected,and the relevant functional genes were quantified by fluorescence.The relationship between Cr(?)removal rate and the related functional genes in Cr(?)bio-reduction system was analyzed by SPSS software.The results showed that the process of biological reduction of Cr(?)by anaerobic sludge was tended to single electron transfer.The efficiency of anaerobic sludge in direct Cr(?)bio-reduction system was not only related to the physical and chemical environment,but also related to the copy number of the chromate reductase genes,which including ChrR and YieF.However,the efficiency of anaerobic sludge in indirect Cr(?)bio-reduction system was only related to the copy number of the sulfite reductase gene DsrA.At the same time,the coexistence of Cr(?)and sulfate promoted the increase of the copy number of DsrA,thus promoting the sulfate cycle. |
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