Biological Reduction Of Bromate And Tellurite Driven By Elemental Sulfur / Zero Valent Iron

With the rapid development of my country’s modern industry,the pollution of oxidized substances in groundwater is becoming more serious,posing a serious threat to humans and the ecological environment.Seawater intrusion and wastewater discharge from steel,glass and other manufacturing industries make bromate and tellurite potential pollutants in groundwater,.In this study,autotrophic biological reduction of bromate and tellurite in groundwater was studied by using solid electron donors（elemental sulfur and zero valent iron）,which are low-cost,easy to operate and more in line with the oligotrophic characteristics of groundwater.It laid a theoretical and practical foundation for the scale application of autotrophic reduction technology of oxidized substances in groundwater.The effect and mechanism of reducing bromate by autotrophic organisms were studied by batch experiments.The initial bromate concentration was 40 mg L^-1.After 48 h and 16 h,91.0±2.1%and 91.0±4.0%bromate reduction was achieved in sulfur autotrophic system and iron autotrophic system,respectively.The reduction rates were 0.77±0.01 mg L^-1h^-1and1.16±0.11 mg L^-1h^-1,respectively.The removal rates of bromate were much higher than that of methane electron donor system,which was equivalent to that of acetate electron donor system.Bromine is the main product of bromate reduction,SO₄^2-and Fe（Ⅲ）are the main oxidation products of S（0）and Fe（0）,respectively.The results of 16S r RNA high-throughput sequencing showed that thiomonas,ferrovibrio,pseudoxanthomonas and Clostridium sp.were the main functional microorganisms.In the process of bromate reduction,the concentration of HCO₃^-decreased and the formation of VFAs was detected in the two autotrophic systems.Combined with the analysis of functional microorganisms,the potential mechanism was speculated as follows:S（0）or Fe（0）oxidizing bacteria（thiomonas or ferrovibrio）first used inorganic carbon source（HCO₃^-）to synthesize VFAs,and then heterotrophic bromate reducing bacteria（pseudoxanthomonas or Clostridium）The reduction of bromate was further realized by using volatile fatty acids.In a typical batch cycle of 48 hours,the removal rates of sulfur autotrophic and iron autotrophic bio reduced tellurite were 91.2±0.8%and 80.3±0.8%,respectively.Elemental tellurium is the main product of tellurite reduction,and SO₃^2-,SO₄^2-and Fe（Ⅲ）are the oxidation products of elemental sulfur and zero valent iron,respectively.Volatile fatty acids were also detected in the typical operation cycle,and the initial tellurite concentration increased from 20 mg L^-1to 80 mg L^-1.The reduction rate of tellurite in sulfur autotrophic system and iron autotrophic system decreased from 98.3%±0.2%and 97.7±0.8%to 82.1±1.6%and 72.7±1.4%,respectively.With the increase of initial p H from 5.5 to 10.0,the reduction rate of tellurite in sulfur autotrophic system decreased from 98.3±0.6%to 32.2±0.8%,and the highest reduction rate of tellurite in iron autotrophic system was 80.7±0.9%in neutral environment.High throughput sequencing showed that Thiobacillus,ferrovibrio and Rhodobacter were the main microorganisms in the two systems.