Degradation of clofibric acid in UV/chlorine disinfection process: kinetics, reactive species contribution and pathways

Abstract

As a potential endocrine disruptor, clofibric acid (CA) was investigated in this study for its degradation kinetics and pathways in UV/chlorine process. The results showed that CA in both UV photolysis and UV/chlorine processes could be degraded via pseudo-first-order kinetics, while it almost could not be degraded in the dark chlorination process. The observed rate constant (kobs) in UV photolysis was 0.0078 min−1, and increased to 0.0107 min−1 combining with 0.1 mM chlorine. The kobs increased to 0.0447 min−1 with further increasing the chlorine dosage from 0.1 to 1.0 mM, and reached a plateau at higher dosage (greater than 1.0 mM). The higher kobs was obtained at acid solution rather than basic solution. Moreover, the calculated contributions of radical species to kobs indicated that the HO• contributed significantly to CA degradation in acidic conditions, while the reactive chlorine species and UV direct photolysis dominated in neutral and basic solution. The degradation of CA was slightly inhibited in the presence of HCO3− (1 ∼ 50 mM), barely affected by the presence of Cl− (1 ∼ 200 mM) and greatly suppressed by humic acid (0 ∼ 5 mg l−1). Thirteen main degradation intermediates and three degradation pathways of CA were identified during UV/chlorine process.

Aquatic photodegradation of clofibric acid under simulated sunlight irradiation: kinetics and mechanism analysis

“…This route has been reported in the degradation pathways of CA in the UV/chlorine process. 60 4-Chlorophenolate has also been detected during the photocatalytic and ozonation degradation of CA. 61,62 Simultaneously, coexisting methacrylate and 4-chlorophenolate may react with P 5 through acylation reaction.…”

New Evidence of the Enhanced Elimination of a Persistent Drug Used as a Lipid Absorption Inhibitor by Advanced Oxidation with UV-A and Nanosized Catalysts

“…For the removal of pharmaceuticals and acidic drugs such as CA metabolites, several physicochemical water treatment procedures were investigated, e.g., coagulation, adsorption through granular activated carbon [12,13], sedimentation, or filtration [14]. However, the main disadvantage of these techniques is that they transfer the pollutant from one phase to another but do not completely remove it through a mineralization mechanism.…”

Degradation of Paracetamol by an UV/Chlorine Advanced Oxidation Process: Influencing Factors, Factorial Design, and Intermediates Identification

“…During the UV/chlorine process, HOCl and OCl − are activated by the UV photolysis to simultaneously produce the main • OH and • Cl radicals (Equations (6)–(8)). The formed • Cl radicals can react with the chloride ions (derived from the HOCl or OCl − solution) to form Cl 2 •− (Equation (9)) [24,26,31]. Those radicals can induce the PRC oxidation and sequentially generate some specific by-products.…”

“…Therefore, the combination of UV irradiation and chlorination (UV/chlorine) turns into the advanced oxidation process (AOP). This combination can enhance the degradation efficiency of diffident kinds of organic pollutants, such as atrazine [20], ibuprofen [21], diuron [22], trimethoprim [23], phenacetin [15], benzoic acid [24], and clofibric acid [25,26]. It is also expected that such combination can remarkably enhance the degradation efficacy of paracetamol in water solutions.…”

“…Notably, depending on the target organic compounds, some transformative products, which are generated during the chlorination process, can be more toxic than the target parent compounds. As reported by many researchers, the • OH and • Cl radical groups played an important role in the decomposition pathways of organic compounds [15,20,22,23,25,26]. The existence of by-products generated from the degradation process of parent organic compounds through the UV/chlorine system has been thoroughly identified by the gas chromatography–mass spectrometry (GC-MS) or liquid chromatography–mass spectrometry (LC-MS).…”