Synergistic effect of humic substances and bicarbonate on diclofenac degradation by Cu(Ⅱ)/peracetic acid

Abstract

Bicarbonate (HCO3-) and humic substances (HS), two common water matrix components, were found to exhibit synergistic effect on diclofenac (DCF) degradation by Cu(Ⅱ)/peracetic acid (PAA) process in this work. The mechanism of their impacts on the performance of Cu(Ⅱ)/PAA system was systematically investigated and the reactive species generated in this system was identified. The results revealed that organic radicals (CH3C(O)OO• and CH3C(O)O•) and Cu(Ⅲ) were both generated in HCO3--Cu(Ⅱ)-fulvic acid (FA)/PAA system, and the presence of FA induced Cu(Ⅲ) to become the dominant reactive species for DCF degradation. In comparison with humic acid (HA), FA showed a stronger enhancement effect on DCF removal in HCO3--Cu(Ⅱ)/PAA system, which might be due to its stronger electron transfer capability. However, DCF degradation in HCO3--Cu(Ⅱ)-HS/PAA system with HA-FA mixture was similar to that with HA alone, because Cu(Ⅱ) was prior to be coordinated with HA in HA-FA mixture. The operating parameters (i.e., HCO3-, Cu(Ⅱ) and PAA concentrations) were optimized for DCF degradation. Finally, the efficient DCF degradation in real waters proved that the presence of HS and HCO3- in real waters also strongly enhanced DCF elimination by Cu(Ⅱ)/PAA process. The findings of this work suggested that HCO3- and HS, which are extensively distributed in aquatic environment, can significantly improve the performance of Cu(Ⅱ)/PAA system and this system may be an efficient technology for the removal of refractory pollutants in real waters.