Biochar-supported Nanoscale Zero-valent Iron And Anaerobic Microorganisms For The Removal Of Trichloroethylene From Groundwater

As an important industrial materials and organic solvents,chlorinated hydrocarbons has become the most common pollutants in groundwater due to improper disposal,leakage during storage transport,which poses pose a serious threat to the environment and human health.Nanoscale valent iron(nZVI)has become the most popular chlorinated hydrocarbons remediation materials because of their strong reduction activity.This study aimed to use wheat straw biochar as carrier for nZVI to address its aggregation tendency and poor mobility in subsurface and biochar-supported nanoscale valent iron was prepared via in situ precipitation method.The performance of trichloroethylene removal was studied and the effects of pH,coexisting ions(Cl-,SO42-,HCO3-and NO3-)and humic acid were also investigated.Anaerobic sludge with Fe(Ⅲ)reduction function was acclimated by using an UASB reactor,the strengthen effect of anaerobic sludge on TCE removal by BC-nZVI which had been reused several times was studied.Three different biochars were prepared under different pyrolysis temperature(400 ℃,500 ℃ and 600 ℃),the biochar pyrolyzed at 600℃ possessed the richest pore structure and surface functional groups(C = C,C = O),showed the best adsorption performance of TCE and conformed the Freundlich adsorption model.The best weight ratio for biochar and nZVI was 1:1 and the best dosage was determined as 1g/L.BC-nZVI composite has good performance for TCE removal,and was in line with the pseudo-first order kinetics model.Weakly acidic condition(pH 5.7-6.8)could enhance the dechlorination efficiency.Cl-enhanced the removal of TCE due to its acceleration effect of electron transfer,while SO42-,HCO3-and NO3-all showed inhibitive effect.Humic acid inhibited the reactivity of BC-nZVI significantly.However,the inhibition weakened gradually as the concentration of humic acid increased from 40mg/L to 80mg/L.Biochar adsorption and nano-iron reductive dechlorination occurred almost simultaneously during reaction,and the reductive dechlorination of TCE by nZVI was the rate-determining step.When coupled with anaerobic sludge,the TCE removal efficiencies of BC-nZVI for 5th and 7th reusable were 1.22 and 1.47 times higher than BC-nZVI used alone,respectively.In summary,wheat straw biochar was an ideal material to support nZVI,which could slow down the agglomeration of nZVI effectively and improve its reactivity;Anaerobic sludge with Fe(Ⅲ)reduction function showed significant synergistic effect on the BC-nZVI which had been used several times,enhanced the lifetime of BC-nZVI composites for TCE removal.