Study On The Removal Of Antimonate And Nitrate From Water By Sulfur Autotrophic Internal Recirculation Bioreactor

China is the largest country for the reserve and production of antimony in the word.Due to the disorderly mining and processing of antimony-containing minerals caused serious antimony pollution in the water.There are relatively few studies on removing antimonate in water.It is particularly important to explore an efficient,economical and stable process to achieve efficient removal of antimonate.Biological method has the advantages of high efficiency and low cost,which is the most promising treatment method.The current biological method mainly focuses on reducing Sb（Ⅴ）to Sb（III）by heterotrophic,which is easy to cause secondary pollution of organic matter and cannot easily achieve the purpose of removing the total antimony in the water.At the same time,due to the massive application of agricultural nitrogen fertilizers and the disorderly discharge of industrial nitrogen-containing sewage,nitrate has become a common groundwater and surface water pollutant.Therefore,the combined pollution of antimonate and nitrate in water has become an important research topic in water purification.In response to the above problems,a sulfur autotrophic bioreactor was established in this study,and used internal recirculation rate to improve the mass transfer efficiency to achieve high-efficiency removal of antimonate.The main research contents are as follows:1.A sulfur autotrophic internal recirculation rate bioreactor was established for antimonate removal.The effect of hydraulic retention time（HRT）and internal recirculation rate on the removal efficiency was investigated.The result shows that under all experimental conditions（HRT was 1.5-8 h,internal recirculation rate was0-5）,the removal efficiency of total antimony（TSb）was only 67.68%,and the removal efficiency of Sb（Ⅴ）was 82.37%.Longer HRT and larger internal recirculation rate can achieve efficient removal of TSb.When HRT was 8 h,the TSb removal efficiency was higher than 95.69%,the removal efficiency of Sb（Ⅴ）was higher than97.60%,and when HRT was 4 h（internal recirculation rate was 5）,the removal efficiency of TSb was 97.28±0.19%,the removal efficiency of Sb（Ⅴ）was92.80±1.69%.Both HRT and internal recirculation rate had great impact on SO₄^2-concentration and alkalinity consumption.Longer HRT and larger internal recirculation rate led to greater SO₄^2-concentration and consumption of alkalinity in the effluent.The Scanning electron microscope-energy dispersive X-ray spectroscopy（SEM-EDS）,Raman,X-ray diffraction spectrum（XRD）and X-ray photoelectron spectroscopy（XPS）were used to characterize the precipitated product in the reactor during the experimental process,which proved that it was Sb₂S₃.The high-throughput sequencing was used to analyze the microbial community structure,which shows that the diversity of microorganisms decreases with the increase of time.Proteobacteria was the dominant bacteria in the reactor,and the community abundance increases with the height of the reactor.Increasingly,although the abundance of Bacteroidetes and Acidobacteriar was low,they were often found in antimony polluted water,which might be related to antimonate reduction.2.A sulfur autotrophic internal recirculation rate bioreactor was established to deal with the combined pollution of antimonate and nitrate.The effect of hydraulic retention time（HRT,which was 8 h,4 h and 1.5 h）and internal recirculation rate（which was 0,2.5 and 5）on the removal efficiency was investigated.The result shows that compared with single antimonate pollution,co-existing nitrate under the same conditions inhibited the removal efficiency of Sb（Ⅴ）and TSb,shortening HRT and larger internal recirculation rate also both reduce the removal efficiency of Sb（Ⅴ）and TSb.When HRT was 4 h.The removal efficiency of TSb was less than 66.13%,the removal efficiency of Sb（Ⅴ）was less than 84.77%.When the HRT was 1.5 h（internal recirculation rate was 5）,the removal efficiency of TSb was the lowest,which was4.72±1.36%,and the removal efficiency of Sb（Ⅴ）was 4.76±1.11%.HRT and internal recirculation rate had a smaller effect on the removal of NO₃^-,which the effluent nitrate concentrations was less than 0.59 mg-N/L during the entire experimental operation period.Both longer HRT and larger internal recirculation rate will lead to a more violent sulfur disproportionation reaction,resulting the effluent SO₄^2-concentrations and alkalinity consumption increasing.SEM-EDS,Raman,XRD and XPS were used to characterize the precipitated products in the reactor,which proved that it was Sb₂S₃.The High-throughput sequencing analysis results of the microorganisms in the reactor showed that as the reaction time increased,theα-diversity diversity of the microbial community decreased.Proteobacteria was the dominant phylum in the reactor,and Sulfuriferula and Thiovirga might be involved in the reduction progress of nitrate and antimonate.Sulfuricurvum might be the sulfur disproportionation reaction bacteria.