Degradation Of Polychlorinated Biphenyls (PCBs) By Nanoscale Zero-valent Iron (NZVI) Under Aerobic Conditions

Polychlorinated biphenyls(PCBs)are one group of persistent organic pollutants(POPs)that are of international concern.In the past,the degradation of PCBs using Nanoscale Zero-valent Iron(NZVI)mainly focused on its reductive dechlorination effect.However,the field environment is difficult to be controlled under anaerobic conditions completely.The main objective of this work was to evaluate the effect of the degradation processes of PCBs and the extracted PCBs from the field PCBs-contaminated soil in this system with an automatic pH control system under aerobic conditions.Electron Paramagnetic Resonance(EPR)technique was used to identify the radical species generated in this process.The effects of environmental factors on the degradation of PCBs and generation of radical species were also investigated in details.(1)This study examined the effect of three low weight molecule organic acids on the dechlorination and degradation efficiency of 4-ClBP by NZVI.After 96 h reaction,the dechlorination efficiency of 4-ClBP by NZVI was 65%,and the degradation efficiency was 74%.The dechlorination and degradation efficiency of 4-ClBP with salicylic acid(SA)were 54.0%and 69.9%,with tannic acid(TA)were 61.2%and 70.8%,and with galic acid(GA)were 54.6%and 69.5%,respectively.The enhancing effect of these three low weight molecule organic acids was found at the initial of the reaction.And in these four reaction system,pH showed a rapid rise and then reached equilibrium quickly.(2)The reaction solution pH was controlled by an automatic pH control system under aerobic conditions,in which the dechlorination of 2-ClBP by NZVI was investigated.The reaction solution pH was controlled in 5.0 with an automatic pH control system.After 4 h reaction,the degradation efficiency of 2-ClBP by NZVI under aerobic conditions was 59.4%,lower than the 65.5%in anaerobic conditions.When solution pH was controlled in 5.0,the degradation efficiency was 74.5%significantly higher than pH 3.0,7.0 and 11.0,respectively.When the concentration of NZVI was 1 g/L,2 g/L,5 g/L and 10 g/L,the degradation efficiency were 64.4%,69.5%,74.5%and 81.6%,respectively.Increasing NZVI concentration accelerated the degradation efficiency.Existing of humic acid(HA),SA,TA and GA(as the influencing factors)promoted the degradation efficiency,which were 64.6%,68.5%,63.9%and 61.4%,respectively.In the reaction system by NZVI,we found the hydroxy1 by EPR.(3)The reaction solution pH was controlled in 5.0 with an automatic pH control system,the degradation of 2,4,4'-CB and extracted PCBs solution from PCBs-contaminated soil by NZVI under aerobic conditions was investigated.After 4 h reaction,the degradation efficiency of 2,4,4'-CB by NZVI under aerobic conditions was 64.2%,lower than the 65.1%in anaerobic conditions.Adding HA to the system,the dechlorination efficiency of 2,4,4'-CB decreased to 54.3%.The degradation efficiency of extracted PCBs from contaminated soil by NZVI were 35.2%in the condition of solutio pH keeping 5.0 and with oxygen.This study has a certain theoretical significance and practical value for the repair of PCBs contaminated soils.