Abstract
This study examined the reaction mechanism, influencing factors and toxicity of diclofenac sodium (DS) degradation by ultraviolet (UV)/chlorine process. The UV/chlorine was capable of eliminating DS from water. The DS degradation during the UV/chlorine process followed a pseudo-first-order kinetic model that was influenced by chlorine dosage, solution pH, humic acid and bicarbonate concentrations. The free chlorine affects not only DS elimination, but the contribution of various active species as well. Increasing free chlorine dosage from 1 to 7 mg·L−1 increased the first-order rate constant of NaClO, ·OH and reactive chlorine species (RCS) from 0.00063, 0.00328 and 0.002030 min−1 to 0.00233, 0.01010 and 0.09740 min−1, respectively, and increased the contribution of RCS from 8.20% to 75.71%, while the contributions of UV, NaClO, and ·OH were declined from 76.02%, 2.54% and 13.24% to 14.63%, 1.81%, and 7.85%, respectively. The contribution of RCS became increasing prominence with the increment of free chlorine dosage. The kobs,UV/chlorine,DS value decreased from 0.07970 to 0.04450 min−1 as pH increased from 5.0 to 8.0. The presence of bicarbonate and natural organic matter both exerted an inhibitory effect on DS degradation. Eleven intermediate products were identified and the degradation pathway involved C-N cleavage, condensation, hydroxylation, and decarboxylation was proposed. The UV/chlorine process effectively reduced acute toxicity and was superior to chlorination. The genotoxicity induced by a chlorinated solution treated by the UV/chlorine process exhibited negative genotoxicity. These results show that the UV/chlorine process is capable for the degradation and detoxification of DS.
Highlights
Pharmaceuticals and personal care products (PPCPs) are notable emerging organic contaminants in the aquatic environment due to their frequently occurrence and potential adverse impact on ecosystems and human health (Baalbaki et al 2016; Deng et al 2020; Kosma et al.2014; Padhye et al 2014; Richardson and Ternes 2014)
The diclofenac sodium (DS) degradation kinetics were conducted at different free chlorine dosages ( 0, 1, 3, 5 and 7 mg·L−1) during the UV/chlorine treatment
The degradation of DS followed pseudo-first-order kinetics during the UV/chlorine process, which can be expressed as Eq (3)
Summary
Pharmaceuticals and personal care products (PPCPs) are notable emerging organic contaminants in the aquatic environment due to their frequently occurrence and potential adverse impact on ecosystems and human health (Baalbaki et al 2016; Deng et al 2020; Kosma et al.2014; Padhye et al 2014; Richardson and Ternes 2014). Conventional water and wastewater treatment technologies (e.g., coagulation and sedimentation) cannot effectively destruct DS (Carballa et al 2004; Joss et al 2006; Kimura et al.2007; Stülten et al 2008; Ternes et al 2002, 2004; Vieno et al 2007; Zhang et al 2008). Effective technologies must be developed to eliminate DS from water. Many methods such as activated carbon adsorption (Westerhoff et al 2005), chlorine disinfection (Westerhoff et al 2005), ultrasonic irradiation (Hartmann et al 2008), ozonation (O3) (Rosal et al 2009; Westerhoff et al 2005), UV/O3 (Justoa et al 2013), Fenton oxidation (Ravina et al 2002), UV/Fenton (Bae et al 2013), UV/TiO2 (Rizzo et al 2009), and UV/H2O2 (Kim et al 2014) have been investigated for DS removal. UV disinfection is a promising treatment technology for drinking water because it can provide a high level of disinfection without chemical addition
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