Study On The Application Of Iron-based Materials In The Autotrophic Bio-reduction Of Heavy Metals In Groundwater

Groundwater is an important part of the water cycle and water resources in nature,and it is also a valuable source of water for human beings.However,the mining,smelting of mineral resources,and the widespread application of nuclear energy have made the pollution of groundwater heavy metals(chromium,uranium,etc.)increasingly serious.Especially heavy metal pollution such as hexavalent chromium [Cr(?)] and hexavalent uranium [U(?)] have attracted widespread attention from scholars at home and abroad.Using domesticated microorganisms to resolve Cr(?)and U(?)pollution in groundwater is an efficient,economical,and environmentally friendly technology.Autotrophic microorganisms can combine with solid electron donors to effectively repair groundwater contaminated by heavy metals and avoid secondary pollution.In this study,natural Fe(?)-bearing minerals were first used as inorganic electron donors for Cr(?)autotrophic biological reduction.The removal efficiency of mackinawite was the best,reaching 98.1 ± 1.21% within 96 h.Then,a continuous flow column experiment was performed using mackinawite as an electron donor and shell as an inorganic carbon source,and the contribution of biotic and abiotic processes to the removal of Cr(?)was 76.0 ± 1.12% and 24.1 ± 1.43%,respectively.the mackinawite was gradually evolved into pyrite.High-throughput 16 S rRNA gene sequencing showed that the mackinawite-driven Cr(?)reduction is mediated through the cooperative interaction of microorganisms.Then,the feasibility of bioreduction of U(?)by different solid-state electron donors was studied through batch experiments,and the zerovalent iron [Fe(0)] removal effect was the best,the removal efficiency within 240 h was 95.9 ± 1.22%.Then the process of reducing U(?)with Fe(0)as an electron donor in the continuous flow column experimental system was studied,the effects of initial U(?)concentration,Hydraulic retention time change and nitrate addition on U(?)removal were investigated.U(?)was reduced to U(IV),and Fe(0)is finally oxidized to Fe(?I).The main functional bacteria are Simplicispira,Delftia,Anaerolinea,Clostridium.Finally,the remediation of mixed pollution of Cr(?)and U(?)using Fe(0)as an electron donor was investigated under the action of microorganisms.160 d continuous flow experiment showed that Cr(?)removal efficiency was high and it was removed before U(?).The 16 S rRNA technology showed that the microbial community in the column experiment reactor had changed significantly.Functional bacteria such as Desulfomicrobium,Acinetobacter,Bacillus,Pseudomonas were discovered.This study confirmed that natural Fe(?)-bearing minerals and zerovalent iron as electron donors can effectively support the reduction and fixation of Cr(?)and U(?)in groundwater mediated by autotrophs.It provides a new idea for in-situ remediation of Cr(?)and U(?)contaminated groundwater.