Removal Mechanism Of Thiacloprid From Environment By Biochar Loaded With Zero Valent Iron And Influence Of Environmental Factors

Neonicotinic pesticides are the most widely used pesticides in the world in recent years.mainly including 12 types of pesticides such as imidacloprid(IMI),thiamethoxam(THIA),thiacloprid(THI),etc.In particular,thiacloprid has significant carcinogenicity and reproductive toxicity to organisms,and its residues in water and soil will cause serious harm to the ecological environment.The adsorption of porous materials and the degradation of active materials are the main ways to remove thiacloprid.Zero-valent iron(ZVI)has a high surface area and reaction activity,which can remove THI from water by adsorption and reduction.However,ZVI tends to agglomerate,which reduces its overall effectiveness in removing pollutants.Biochar is a low-cost material with high specific surface area and porosity.The rich functional groups on biochar can promote electron transfer.Loading ZVI onto biochar can effectively reduce the agglomeration of ZVI and promote its electron transfer.This article aims to improve the utilization of ZVI by loading it onto biochar,thereby enhancing its removal capacity for THI.Therefore,commonly available pine biomass was selected as the precursor for biochar,and pine biochar(PBC)was prepared by hightemperature pyrolysis.ZVI-loaded biochar material(ZVI/PBC)was then prepared using sodium borohydride reduction method.Organic carbon,water conditions,and microorganisms play an important role in the process of ZVI reduction and dechlorination.They will affect the electron transfer between the material and THI,as well as the morphology of iron oxides.Therefore,combined with soil experiments,the effects of water management,exogenous organic carbon,and microorganisms on the remediation of THI-contaminated soil by ZVI/PBC were investigated.The main research content and results are as follows:(1)To investigate the synergistic effect of PBC and ZVI on the removal of THI,pinewood biomass was selected as the precursor material and PBC was prepared by pyrolysis at 500℃,ZVI and ZVI/PBC were prepared by the reduction of borohydride sodium,and their ability to remove THI from water was studied.The results showed that the removal efficiency of THI by ZVI/PBC was higher than the sum of PBC and ZVI removal rates.This indicates that PBC and ZVI can promote the removal of THI through synergistic effects.The kinetic results show that the addition of HA and OA can promote the removal of THI by the material.But the addition of OA has a more significant improvement effect.XPS analysis confirmed that FeCOO bonds were formed in ZVI and ZVI/PBC after the addition of HA and OA,indicating that iron ions formed chelating compounds with organic carbon during the reaction,which reduced the production of iron oxides and enhanced the electron transfer capacity of ZVI and ZVI/PBC.The electrochemical results showed that the electron transfer was the main pathway for THI degradation,and the electron transfer ability of ZVI was improved after being loaded onto PBC.The It curve shows that the current intensity increases after the addition of HA and OA,especially after the addition of OA,the promotion effect is more obvious.These results suggested that organic carbon can enhance the removal of THI by promoting electron transfer,and small molecular organic carbon has better promoting electron transfer ability.(2)ZVI/PBC material was used for the degradation of THI in soil,and the effect of exogenous organic carbon on the degradation of THI by ZVI/PBC was investigated by adding HA and OA.The results showed that the degradation amount of ZVI/PBC to THI was 6.15 mg/g,which increased to 6.40 mg/g and 8.01 mg/g when HA and OA were added,respectively.This indicated that HA had a small improvement effect on the degradation of THI by ZVI/PBC,while OA can significantly promote the degradation of THI by ZVI/PBC.The determination of iron ions and iron oxides in soil showed that organic carbon can promote the oxidation of ZVI/PBC to generate Fe(Ⅱ).This indicates that organic carbon can oxidize ZVI/PBC to promote the generation of Fe(Ⅱ),thereby enhancing the reduction and degradation of THI.OA can better promote the oxidation of ZVI/PBC and reduced the generation of crystalline iron oxide,while HA,due to its high molecular weight,covered the active sites of ZVI/PBC,weakening the transformation of amorphous iron oxide.Microbial analysis showed that the presence of organic carbon can promote the growth of Proteobacteria phylum,and increased the abundance of Methylobacterium and Microvirga,which can degrade THI,and thus enhanced the degradation of THI.Moreover,with the addition of HA and OA,the differences between microbial communities gradually widened.(3)Two water management regimes,including soil moisture(soil water content of 40%)and flooded(FB,soil water content of 200%),were set up to investigate the effects of water management on the remediation of THI-contaminated soil with ZVI/PBC,the blank treatment increased the degradation of THI by 1.08 mg/g,while ZVI/PBC increased the degradation of THI by 0.37 mg/g,indicating that flooded conditions favored the degradation of THI by ZVI/PBC.Flooded conditions promoted the degradation of weakly and moderately adsorbed THI by ZVI/PBC.The determination of iron oxides and iron ions in the soil showed that flooded conditions were conducive to the increase of Fe(Ⅱ)and the decrease of crystalline iron oxide,thus further enhancing the degradation of THI by ZVI/PBC.Microbial analysis also showed that since Microvirga proliferated under flooded conditions due to its anaerobic nature,which improved the degradation of THI.The inhibitory effect of ZVI/PBC on microbial growth did not significantly increase the degradation of THI under flooded conditions,which resulted in less proliferation of Microvirga.(4)To investigate the role of microbes in the degradation of THI,the soil microbes were sterilized using a high-pressure steam sterilizer(ST).The results showed that after sterilization,the blank treatment reduced the degradation of THI by 0.41 mg/g,while the ZVI/PBC treatment decreased the degradation of THI by 0.88 mg/g.This indicated that microbes played a certain role in the degradation of THI.The determination of the adsorbed state of THI in the soil showed that microbes mainly decompose and utilize weak and moderately adsorbed THI,with almost no degradation of strongly adsorbed THI.In addition,after sterilization,the content of crystalline iron oxide increased and Fe(Ⅱ)decreased in the ZVI/PBC treatment,which to some extent reduced the reduction and degradation of THI by ZVI/PBC.Through analysis of microbial community characteristics,it was determined that sterilization treatment would inactivate most bacterial genera.CK and PBC sterilization treatment showed some proliferation of Microvirga genus after 20 days of static storage,while there was no significant change in the ZVI/PBC treatment.The inhibition of Microvirga activity recovery by ZVI was the main reason for the decrease in THI degradation in the ZVI/PBC treatment after sterilization.