Study On The Sulfur-based Mixotrophic Microbial Remediation Of Heavy Metals In Groundwater

Water is one of the most important components of nature and an indispensable part of the human body.It is a resource that human beings cannot live without.The groundwater volume is stable,and the water quality is good.It is one of the important water sources for agriculture,cities and industry.However,with the development of the economy and the exploration and utilization of resources by humans have caused part of groundwater to be polluted by heavy metals such as vanadium(V(?))and chromate(Cr(?)).Microbial remediation of heavy metal contaminated groundwater is a highly efficient,economical and environmentally friendly technology.Mixotrophic microbial reduction technology combines autotrophic and heterotrophic microbial reduction to improve the efficiency of microbial remediation of heavy metal contaminated groundwater and reduce the risk of secondary pollution of groundwater.Firstly,elemental sulfur and acetate were used as electron donors to realize the mixotrophic microbial restoration of V(?)contaminated groundwater.In a typical experimental cycle(48 h),the removal efficiency of V(?)reached 83.9 ± 3.84%.the 16 S rRNA technology was employed to explore the microbial community changes in the bioreactors and the enrichment of Geobacter? Spirochaeta? Syntrophobacter was observed.Subsequently,elemental sulfur was used as the inorganic electron donor and acetate as the organic electron donor for microbial remediation of Cr(?)contaminated groundwater.The removal efficiency of Cr(?)was 95.5 ± 0.74% within 48 h.After experimental analysis,it was confirmed that the reduced product of Cr(?)was Cr(III).The microbial community in the reactor was analyzed,the obvious changes of the community and the presence of functional microorganisms such as Mesotoga,Geobacter and Desulfovibrio were found.Finally,solid wood chips,elemental sulfur and oyster shell were used as fillers to simulate the in-situ microbial remediation of Cr(?)contaminated groundwater using a continuous flow mode column reactor.The reactor was operated for 228 days and the results showed that the shortening of the hydraulic retention time(HRT)and the increase of the initial Cr(?)concentration would reduce the removal efficiency of the Cr(?)in the reactor.Nitrate was added to the column bioreactor to observe its operation effect,and the results showed that it has an electronic competition with Cr(?)and is more susceptible to electronics transported by bacteria.Significant microbial community changes were observed,such as the abundance increasing of microbial communities in the bioreactor and proportion increasing of bacteria in the phylum of Bacteroidetes.This study validated the feasibility of mixotrophic microbial remediation of V(?)and Cr(?)contaminated groundwater,and provided new ideas for in situ remediation of groundwater contaminated by V(?)and Cr(?).