Study On Cr(Ⅵ) Removal Performance By Shewanella Putrefaciens CN32 Immobilized With Biochar

Cr（Ⅵ）pollution has characteristics of wide range,long duration and high concealment of transmission.It has caused serious harm to the environment and human health,and has become one of the urgent environmental problems to be solved.Microbial immobilization technology can effectively reduce and fix heavy metals without damaging the environment and causing secondary pollution,which is one of the most promising strategies for controlling heavy metal pollution.In this study,goethite-modified biochar（GMB）was prepared by hydrolytic co-precipitation method,and the adsorption effect and mechanism of GMB on Cr（Ⅵ）were carried out.The best-modified biochar material was used as the carrier,and the typical soil microorganism S.putrefaciens CN32 was immobilized by adsorption and embedding method.The bacteria were applied to the remediation for Cr（Ⅵ）polluted water and soil.The main results include:The modification of goethite greatly improves the adsorption efficiency of biochar.The best goethite-modified biochar GMB600-12 was selected by comparison.The theoretical adsorption capacity of Cr（Ⅵ）was 20.67 mg/g,which was 82.68 times that of the original biochar.The preparation conditions were as follows:pyrolysis temperature was 600℃,mass ratio of biochar to Fe（NO₃）₃·9H₂O was 1:12.FTIR analysis showed that iron hydroxyl oxide（Fe OOH）and other substances were formed on the surface of the modified biochar,and the functional groups of-OH/Fe-OH were enhanced.XPS analysis showed that after 90 min of adsorption,about 3/4 of Cr（Ⅵ）fixed on the surface of biochar was reduced to Cr（III）.The relative content of Fe（II）decreased from 50.26%to 48.73%,and the content of C-O and C=O on the surface of biochar decreased.Therefore,it is speculated that Cr（Ⅵ）can be removed on the GMB600-12 surface mainly through REDOX reaction.GMB600-12 was used as a carrier to adsorb Shewanella Putrefaciens CN32,and immobilized with sodium alginate to obtain S.putrefaciens CN32/GMB-SA.After 36 h of reaction,the removal rates of Cr（Ⅵ）and total Cr in the liquid phase reached 79.94%and80.06%,respectively.The results showed that Cr（Ⅵ）was reduced to Cr（III）and all of them were adsorbed in the bacteria to avoid the risk of reoxidation.Secondly,the immobilized bacteria maintained a stable removal efficiency in the p H range of 5.0～9.0,overcoming the sensitivity of S.putrefaciens CN32 to p H changes.S.putrefaciens CN32/GMB-SA was applied to the remediation of Cr-contaminated soil,and it was found that Cr（Ⅵ）could be rapidly adsorbed and stabilized in the soil to avoid further pollution.For the soil with Cr content of 170.98,209.81 and 302.04 mg/kg,the total exchangeable chromium in the soil decreased by 89.66%,91.75%and 93.48%after adding 30 bacteria/g and 10 days of stabilization,respectively.While the total Fe/Mn oxides combined chromium increased by55.31%,63.23%and 61.65%,respectively.The total chromium in residue increased by10.57%,23.10%and 43.34%,respectively.This indicates that the immobilized bacteria can transform most of the chromium into a more stable form and reduce the migration and diffusion of chromium in the soil.The remediation of Cr-contaminated soil by S.putrefaciens CN32/GMB-SA mainly consists of three parts:adsorption of sodium alginate;REDOX,adsorption and complexation of biochar;and microbial reduction removal.