Study On Bio-reduction Of Heavy Metals In Groundwater Supported By Solid Electron Donors

With the rapid development of modern industry,heavy metal pollution in groundwater is becoming more and more serious,especially the pollution ofvanadium and chromium,which are widely used in industry,seriously threatens the groundwater ecosystem.The bioremediation of V(V)and Cr(Ⅵ)pollution in groundwateris a promising method of restoration.Due to the oligotrophic characteristics of groundwater,autotrophic bioremediation is particularly important,butmicrobialremediation of heavy metals supported bysolid electron donors is largely unknown.In this study,elemental sulfur(S(0))and zero-valent iron(Fe(0))were used as the sole electron donor for autotrophs to reduce V(V).The V(V)removal efficiencies reached 97.5 ±1.2% and 86.6 ± 2.5% in 120 hours,respectively.The reduction product of V(V)was V(IV)which can be precipitated in a neutral pH environment.S(0)was oxidized to sulfate and Fe(0)was oxidized to Fe(Ⅲ).Microbial community analysis revealed microorganisms related tosulfur oxidation,iron oxidation and V(V)reduction.Metagenomics analysis found related functional genes.Then,Cr(Ⅵ)was reduced using S(0)and Fe(0)as sole electron donor for autotrophs,respectively.Cr(Ⅵ)removal efficiency reached 93.7 ± 0.8% and 99.3 ± 1.0%,respectively,within 120 hours.Cr(Ⅵ)was reduced to Cr(Ⅲ),which spontaneously precipitates at neutral pH.The residual volatile fatty acids were observed after the experimental period.The effects of initial Cr(Ⅵ)concentration and bicarbonate concentration on the removal rate and reduction rate of Cr(Ⅵ)were studied.High-throughput sequencing results revealed the synergistic mechanism in this process.Finally,the reduced iron-bearing minerals were selected as electron donor for autotrophic organisms to reduce V(V).The experiments confirmed that the removal of V(V)could be achieved by using the selected iron-bearing minerals as electron donors.Among them,Magquinolite performed best.In 120 h,the V(V)removal efficiency was 95.9±1.1%.A continuous flow reactor was then used to study the performance of the reduction of V(V)by Magquinolite-basedautotrophic V(V)bio-recution during continuous operation for 140 days.16 S rDNA sequencing results showed that Proteiniphilum and Thiobacillus were the main functional genus of V(V)reduction in this system.This study confirms that solid electron donors can effectively support biological reduction of V(V)and Cr(Ⅵ)in groundwater,providing a new idea for the efficient remediation of V(V)and Cr(Ⅵ)contaminated aquifers.