Kinetics, mechanistic, toxicological and economical investigations of para-chlorophenol degradation by UV/persulfate and UV/persulfate/Fe2+ processes

Abstract

Para-chlorophenol (4-chlorophenol, 4-CP) is a member of the toxic chlorinated phenolic compounds. It is broadly used in preservatives, and as a precursor for some herbicides and fungicides and has been detected in natural aquatic environments. This work examined the photochemical degradation of 4-CP by ultraviolet light (UV), UV/persulfate (UV/PS) and UV/persulfate/Fe²⁺ (UV/PS/Fe²⁺) methods. Under UV light irradiation (UV-C, 254 nm), the removal efficiency of 4-CP (20 mg/L) was 44.7, 58.8 and 66.8% at pH 3, 6 and 11, respectively, after 25 min of irradiation. The addition of 0.5 mM PS to UV enhanced the removal efficiency of 4-CP to 90.2% (at pH 3) and 100% (at pH 6 and 11), at the same treatment time. However, complete removal of 4-CP occurs in UV/persulfate/Fe²⁺ process, employing Fe²⁺ = 0.3 mg/L, PS = 0.5 mM and 4-CP = 20 mg/L, at pH 3, after 25 min of treatment. Additionally, the degradation efficacy was adversely affected by humic acid (HA) and inorganic ions. Similarly, the TOC removal was 65.8 and 86.1%, for UV/PS and UV/persulfate/Fe²⁺ techniques, after 120 min. Moreover, the contribution of SO₄^•− and HO^• was investigated by scavenging study. Additionally, GC-MS was used to detect the degradation products (DPs) of 4-CP. Finally, ECOSAR program was used to evaluate the toxicity of 4-CP and its DPs. Nonetheless, the present study suggests that UV/PS and UV/persulfate/Fe²⁺ techniques can effectively eliminate chlorophenols from aquatic environments.

Graphical Abstract