Simultaneous Bio-autotrophic Reduction Of Antimonate And Nitrate From Aqueous Solution In A Sulfur Packed Bed Reactor

China is the largest country in the world for the production and consumption of antimony.The mining,smelting and processing of antimony have caused the problem of antimony pollution in the water environment.At the same time,nitrate has become a common groundwater and surface water pollutant due to the large amount of nitrogen fertilizers applied in modern agriculture and the emergence of artificial nitrogen fixation activities.Therefore,the combined pollution of antimonate and nitrate in water has become an important research topic in water purification.Biological method is the most promising method due to its low cost,high efficiency and simple operation.At present,sulfur autotrophic denitrification has been widely developed,while sulfur autotrophic reduction for antimonate?Sb?V??to a less stable antimonite?Sb?III??is rarely reported.In this study,sulfur autotrophic method was used to explore the removal mechanism of combined nitrate and antimonate from water,and the formation of related products and by-products were investigated and the characteristics of microbial community structure were revealed.The main research contents are as follows:1.An up-flow sulfur autotrophic fixed-bed bioreactor was established for Sb?V?removal.The effect of hydraulic retention time?HRT?on the removal efficiency was investigated,and the results showed that when the HRT decreased from 5.42 h to 4.90 h,2.70 h,and 1.50 h,the sulfur autotrophic fixed-bed bioreactors were effective for Sb?V?removal.The removal efficiency of Sb?V?is higher than 92.1±1.1%,and the total antimony removal efficiency is higher than 63.2±1.9%.An excessive amount of sulfate was generated during the reaction,and it was speculated that an S disproportionation reaction occurred,and the S disproportionation reaction was performed simultaneously with the removal of Sb?V?.Scanning electron microscope-energy dispersive X-ray spectroscopy?SEM-EDS?,X-ray diffraction spectrum?XRD?analysis and Raman spectroscopy were used to characterize the precipitated product in the reactor during the experimental process,which proved that it was a mixture of Sb₂S₃ and S⁰.It is speculated that the reaction path is that Sb?V?is reduced to form Sb?III?.After sulfur autotrophy,Sb?III?react with S^2-which is produced by the S disproportionation reaction to form precipitate Sb2S3,hence the total antimony was reduced.The high-throughput sequencing technology was used to analyze the microbial community structure,and it was found that the microbial community structure in the reactor showed regularity.As the reactor height increased,the community abundance gradually decreased on the condition of long HRT,and the dominant bacteria in the reactor were Sulfuricurvum,Microbacter,Melioribacter,Thiomonas,Ignavibacterium and Sulfurimonas,among which Sulfuricurvum may be involved in the degradation of antimonate,Microbacter,Melioribacter and Thiomonas may be related to sulfur disproportionation.2.An up-flow sulfur autotrophic fixed-bed bioreactor was established to deal with the combined pollution of antimonate and nitrate.The effect of hydraulic retention time on the removal efficiency was investigated,and the results showed that the sulfur autotrophic fixed-bed bioreactor can effectively remove Sb?V?and NO3^-when the HRT decreases from 5.42 h to 4.90 h,2.70 h,and 1.00 h.Sb?V?removal efficiency is greater than 88.2±1%,total antimony removal efficiency is greater than 66.9±2.1%,and the removal of NO3^-is not affected by the adjustment of HRT,which is always greater than 98.5%.And compared with reducing antimonate,the reduction of NO₃^-reached the steady state more easily,and the intermediate product NO2^-was always less than 0.08 mg/L,and no accumulation occurred.An excessive amount of sulfate is generated during the reaction,which is generated by the S disproportionation reaction.The S disproportionation reaction is carried out together with the removal of Sb?V?and NO₃^-.The SEM-EDS analysis,XRD analysis and Raman spectroscopy were used to characterize the precipitates produced during the experiment.It was proved that the precipitate was a mixture of Sb2S3 and sulfur,and the presence of nitrate had no effect on the morphology of the precipitate.Using high-throughput sequencing technology to analyze the microbial community structure,it was found that the microbial community structure in the reactor was regular,and the community abundance gradually decreased with the increase of the reactor height on the condition of long HRT.In addition,Ferritrophicum is closely related to nitrate reduction.Sulfurimonas is responsible for the reduction of antimonate and nitrate in this reaction,Microbacter and Thiomonas participate in the sulfur disproportionation reaction.