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

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 ( SO4•- ), 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), SO4•- , superoxide radical anions ( O2-• ), hydroperoxyl radicals (HO2•), hydrogen peroxide (H2O2), and singlet oxygen (O2). Among these oxidants, •OH play a key role in the degradation of PE. However, SO4•- are more effective and efficient than •OH since SO4•- 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.