Ascorbic acid-enhanced Fe(III)/peracetic acid process for the degradation of diclofenac: Treatment efficiency, mechanism and influencing factors

To overcome the sluggish reduction from Fe(III) to Fe(II) and excessive iron sludge production in Fe(III)/peracetic acid (PAA) process, ascorbic acid (AA), an environmental-friendly and natural reductant, was proposed in this study to boost the oxidation ability of Fe(III)/PAA process by facilitating the cycling of Fe(III)/Fe(II). AA-enhanced Fe(III)/PAA process exhibited remarkable acceleration in the degradation of diclofenac (DCF), with the removal rate of DCF being around 51 times higher than that without AA. Multiple reactive species of (FeO2+)-O-IV, R-O-center dot, and (OH)-O-center dot were involved in the abatement of DCF in the AA/Fe(III)/PAA process. (FeO2+)-O-IV was confirmed as the predominant contributor for the elimination of DCF, whereas R-O-center dot and (OH)-O-center dot also participated in DCF abatement. In the AA-enhanced Fe(III)/PAA process, AA rapidly complexed with Fe(III) to produce the Fe(III)-AA complex, which was subsequently decayed to generate Fe(II), and then reactive species were generated by activating PAA with Fe(II) to degrade DCF through the pathways of dichlorination-cyclization, decarboxylation, and hydroxylation. The acute toxicity of the reaction solution employing BioFixlumi as a toxicity indicator decreased with the abatement of DCF. Common inorganic ions, including Cl-, SO42-, CO32-, and NO3-, had no adverse influence on DCF degradation, while humic acid and common cations (Zn2+, Ca2+, and Mg2+) inhibited DCF abatement. AA/Fe(III)/PAA process was highly effective for DCF removal in actual water samples, including surface water and underground water. AA/Fe(III)/PAA process was prone to degrading micropollutants with higher fractions of deprotonated species and lower ionization potentials, and performed with high selectivity towards micropollutants. Overall, the outstanding oxidation capacity and environmental friendliness of AA/Fe (III)/PAA process render it a potential technology to remove micropollutants in wastewater treatment.