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

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 & BULL; and CH3C(O)O & BULL;) 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.