A Simulation Study Of Influence Of Black Carbon On PCB1 Degradation By Nanoscale Zero-valent Iron/palladium In Sediments

Nanoscale zero-valent iron?nZVI?reduction is a promising technique for the remediation of sediment polychlorinated biphenyls?PCBs?contamination.The impact of black carbon,an important organic matter in sediments,on the remediation process has not been studied systematically.On one hand,the strong adsorption of black carbon will hinder the mass transfer of PCBs and inhibit its degradation;on the other hand,recent studies have found that black carbon is a good electron transfer medium which can accept and donate electrons,and it may accelerate the reduction activity of nZVI.Therefore,in this paper,bamboo chips were used to prepare biomass-derived black carbon at different pyrolysis temperatures,and 2-chlorobiphenyl?PCB1?was selected as the target pollutant.On the basis of studying the adsorption-desorption characteristics of PCB1 on black carbon,the experiment of the effect of black carbon on the reduction of PCB1 by nanoscale zero-valent iron/palladium?nZVI/Pd?in aqueous solution and sediments was simulated.Combined with the analysis of PCB1 degradation products and the form of residual PCB1,the mechanism of black carbon adsorption-desorption and electron transfer on the reduction of PCB1 by nZVI/Pd was explored.The main conclusions are as follows:?1?With the increasing of pyrolysis temperature,the adsorption capacity of black carbon,the nonlinear adsorption proportion increased,and the desorption ratios decreased.Among them,the adsorption of 400?black carbon on PCB1 was worst,the the adsorption capacity,the adsorption strength and the fast and slow desorption ratios of which were only 3642.04 mg·kg^-1,2029.12(mg·kg^-1)/(mg·L^-1)ⁿ,0.228 and0.223,respectively.The adsorption of 900?black carbon on PCB1 was best,the the adsorption capacity,the adsorption strength and the fast and slow desorption ratios of which were only 93742.5 mg·kg^-1,77853.31(mg·kg^-1)/(mg·L^-1)ⁿ,0.111 and 0.154,respectively.Besides,releasing of PCB1 adsorbed by partitioning?based on"similar compatibility"?was throughout the whole desorption process.However,PCB1adsorbed by surface adsorption?based on pore filling and?-?electron donor acceptor?was difficult to desorb and released only a small amount.?2?The degradation of PCB1 adsorbed on black carbon by nZVI/Pd in aqueous solution showed that,black carbon at different pyrolysis temperatures had different effects on the degradation of PCB1 by nZVI/Pd.The degradation rate of PCB1increased with pyrolysis temperature of black carbon.Among them,the degradation rate?48h?of PCB1 on 900?black carbon reached 95.25%,similar to the free PCB1?99.20%?.After 48 hours of degradation,most of PCB1 remaining on the low-temperature black carbon was at the irreversible desorption state,and the ratios of the fast and slow desorption were between 5.5%?7.1%and 9.7%?12.7%,while almost all PCB1 remaining on the high-temperature black carbon was at the irreversible desorption state.On the one hand,the adsorption of PCB1 on the black carbon inhibited the degradation of PCB1,which led to the degradation rate of PCB1 adsorbed on black carbon was smaller than free PCB1.On the other hand,the electron transfer capability of black carbon increased with pyrolysis temperature,and thus H⁺could obtain electrons more easily.Therefore,PCB1 adsorbed on black carbon could also obtain more[H]and electrons and it was degraded faster.?3?The degradation of PCB1 adsorbed in black carbon-sediment system by nZVI/Pd showed that,the degradation rate?15d?of PCB1 was 58.11%in single sediment system.400?black carbon inhibited the degradation of PCB1 in sediments,and the inhibitory effect enhanced with the increament of addition of 400?black carbon,and the degradation rate?15d?of PCB1 was 47.82%in 1%400?black carbon-sediment system.Appropriate amount of 900?black carbon could promote the degradation of PCB1 in the sediment.The degradation rate?15d?of PCB1 reached75.29%in 2%900?black carbon-sediment system.The mechanisms were as follows:400?black carbon enhanced the adsorption of PCB1 in sediments,although its electron transfer had a weakly promoting effect,it inhibited the degradation of PCB1generally;Although 900?black carbon had a stronger adsorption effect on PCB1 than400?black carbon,its electron transfer was faster,and it played a role in promoting the degradation of PCB1 generally.In summary,in sediments,black carbon at different pyrolysis temperatures had different effects on the degradation of PCBs by nZVI.Low-temperature black carbon inhibited the degradation of PCBs mainly by adsorption,while high-temperature black carbon promoted the degradation of PCBs mainly by electron transfer.This study provided a theoretical basis for the remediation of PCBs contaminated sediments by nZVI.