Research On The Removal Of Antimony And Chromium From Wastewater Based On Electrosorption And Bioelectrochemistry

The contamination of heavy metals antimony(Sb)and chromium(Cr)in wastewater poses significant risks to human health and the ecological environment,making it one of the challenging issues in the field of environmental protection.With the improvement of environmental governance standards and the demand for new technologies,continuous research and development of novel treatment techniques for heavy metal wastewater is of great significance,building upon the foundation of traditional heavy metal treatment technologies.In recent years,electrochemical methods have attracted considerable attention in the field of removing heavy metal ions from wastewater due to their advantages of simple operation and stable performance,such as electrosorption and bioelectrochemical methods.However,the development of electrochemical technologies is hindered by challenges such as difficulties in electrode material preparation and a lack of research on the bioelectrochemical mechanisms.Therefore,in this study,we established an investigation of the effects and mechanisms of nitric acid-modified activated carbon-based electrosorption for the removal of Sb(Ⅴ)and Cr(Ⅵ)from wastewater,along with the introduction of microbial action based on electrosorption,constructing a bioelectrochemical method for the study of the effects and mechanisms of Sb(Ⅴ)and Cr(Ⅵ)removal from sulfate-containing and sulfate-free wastewater.The main research conclusions are as follows:(1)In the study of nitric acid-modified activated carbon electrosorption,the optimum operating voltage for electrosorption was determined to be 1.4 V,and the optimal hydraulic retention time was 4 hours.When the influent concentrations of Sb(Ⅴ)and Cr(Ⅵ)were both 5 mg L-1,the maximum removal efficiencies of Sb(Ⅴ)and Cr(Ⅵ)under electroadsorption were increased by 47.4%and 37.1%,respectively,compared to adsorption removal rates.This improvement can be attributed to the increase in specific surface area by 39%and the rise in maximum pore volume by 21%after the activated carbon particles were modified with nitric acid.The total amount of oxygencontaining functional groups on the surface increased,and additional functional groups such as hydroxyl and carboxyl groups were introduced.Additionally,the electrochemical performance of the nitric acid-modified activated carbon electrode was enhanced,with a 46%increase in specific capacitance compared to the unmodified state.On the other hand,the results of adsorption kinetics analysis showed that the adsorption kinetics of Sb(Ⅴ)and Cr(Ⅵ)by nitric acid-modified activated carbon electrosorption followed a pseudo-first-order kinetic model.The presence of a double-layer effect on the activated carbon surface was observed,and the adsorption rate was directly proportional to the double-layer residual capacitance.Furthermore,chemical adsorption occurred on the surface of the nitric acid-modified activated carbon,where the oxygen-containing functional groups combined with the ions to achieve the removal effect.(2)Under neutral conditions,the bioelectrochemical reactors enhanced the removal efficiency of Cr(Ⅵ)in wastewater,but the removal rate of Sb(Ⅴ)decreased due to high sulfide concentration or weakened antimony reducing bacteria.When the sulfide concentration in the bioelectrochemical reactor was higher than 8.5 mg L-1,the removal rate of Sb(Ⅴ)decreased.When gradually reducing the sulfide concentration to below 6 mg L-1,the removal rate of S(Ⅴ)increased again.In addition,when using bioelectrochemical method to remove Sb(Ⅴ)and Cr(Ⅵ)in sulfate-containing and sulfate-free acidic wastewater,it was found that the electric field could stimulate microbial activity and significantly improve the removal efficiency of Sb(Ⅴ)and Cr(Ⅵ).In sulfate containing acidic wastewater,when the inflow concentrations of Sb(Ⅴ)and Cr(Ⅵ)were both 1 mg L-1,the removal rate of Cr(Ⅵ)by the bioelectrochemical reactor was about 60%,and the removal rate of Sb(Ⅴ)was close to 100%,while the removal rates of Sb(Ⅴ)and Cr(Ⅵ)in the control reactors were less than 3%.The microbial community analysis showed that the electric field stimulated the diversity and richness of microbial community,with the proliferation of electrochemically active bacteria,such as Desulfobulbus,Desulfovibrio,and chromium reducing bacteria,such as Pseudomonas.However,the relative abundance of antimony reducing bacteria(Propionivibrio)decreased.This study further explored the mechanism of bioelectrochemistry removal of Sb(Ⅴ)and Cr(Ⅵ),which mainly included direct reduction by metal reducing bacteria,indirect reduction by electrochemically active bacteria,and sulfide reduction in sulfate-containing wastewater.