Advanced oxidation processes for phthalate esters removal in aqueous solution: a systematic review

Abstract

This study addresses a systematic review of the scientific literature to evaluate the most common advanced oxidation processes (AOP) for the removal of phthalate esters (PE) in aqueous matrices. Six AOP were reviewed for PE degradation such as processes based on photolysis, Fenton, ozonation and sulfate radicals ( ${\text{SO}}_4^{•-}$ ), combined AOP and other processes. The PE degradation efficiencies by AOP processes ranged from 40.3 to 100%. In the reviewed literature, an initial PE concentration within 0.04-250 mg/L was applied. The H₂O₂ concentrations used in the UV/H₂O₂ process and O₃ concentrations in ozonation-based processes ranged between 0.85-1,360.6 mg/L and 2-4,971 mg/L, respectively. Based on the reported results, the PE oxidation data fit well to the pseudo-first order kinetic model. A review of the studies revealed that many oxidant species are produced in the AOP, including hydroxyl radicals (^•OH), ${\text{SO}}_4^{•-}$ , superoxide radical anions ( ${\text{O}}_2^{-•}$ ), hydroperoxyl radicals (HO₂ ^•), hydrogen peroxide (H₂O₂), and singlet oxygen (O₂). Among these oxidants, ^•OH play a key role in the degradation of PE. However, ${\text{SO}}_4^{•-}$ are more effective and efficient than ^•OH since ${\text{SO}}_4^{•-}$ has a higher oxidation power (E = 2.5-3.1 V) compared to ^•OH radicals (E = 1.8-2.7 V). In different AOP processes, the aromatic rings of PE are destroyed by ^•OH and produce intermediates such as phthalic acid (C₆H₄(CO₂H)₂), benzoic acid ethyl ester (C₉H₁₀O₂), 2, 5-dihydroxybenzoic acid (C₇H₆O₄), formic acid (CH₂O₂), acetic acid (CH₃COOH), and oxalic acid (C₂H₂O₄), among some others. Until now, limited data have been reported on PE toxicity assessment. The reviewed literature has shown that AOP can be used effectively to degrade PE from aqueous matrices. However, this systematic study suggests focusing more on the evaluation of the toxicity of the effluent resulting from AOP for the decomposition of PE in future studies.

Keywords: advanced oxidation process; aqueous solution; phthalate esters; removal; systematic review.