Degradation Kinetics and Disinfection By-Product Formation of Iopromide during UV/Chlorination and UV/Persulfate Oxidation

Abstract

As the detection of micropollutants in various water resources is commonly reported, developing an efficient technology to remove them to maintain water safety has become a major focus in recent years. The degradation kinetics of iopromide, one of a group of iodinated X-ray contrast media (ICM), using advanced oxidation processes of ultraviolet/chlorination (UV/Cl2) and UV/persulfate (UV/PS) oxidation were investigated in this research. The results show that iopromide degradation fitted pseudo-first-order kinetics, and the rate constants were calculated as 2.20 (± 0.01) × 10−1 min−1 and 6.08 (± 0.10) × 10−2 min−1 in UV/Cl2 and UV/PS, respectively. In the two systems, the degradation rates were positively correlated with the initial concentrations of HOCl and PS, respectively. In the UV/Cl2 system, the degradation rate of iopromide reached a maximum at pH 7, while in the UV/PS system, pH had only a slight effect on the degradation rate. Chloride in water had a negligible effect on iopromide degradation, whereas bromide inhibited iopromide degradation in the UV/Cl2 system. The contributions of UV irradiation, •OH, and RCS to iopromide degradation during UV/Cl2 treatment were calculated as 20.8%, 54.1%, and 25.1%, respectively. One carbonated and three nitrogenated disinfection by-products (C-DBP (chloroform) and N-DBPs (dichloroacetonitrile, trichloronitromethane, and trichloroacetone)) were detected at relatively high levels, along with three emerging iodinated DBPs (dichloroiodomethane, monochlorodiiodomethane, and triiodomethane). More C- and N-DBPs were generated in the UV/Cl2 and UV/PS systems than in UV irradiation, while considerably higher I-DBPs were generated in UV irradiation than in the other two systems. Thus, it is essential to pay attention to DBP formation when UV/Cl2 or UV/PS is used to treat iopromide in water. In order to better control the generation of carcinogenic and toxic I-DBPs, Cl2 or PS combined with UV should be adopted for iopromide degradation, instead of UV alone, for providing safe drinking water to the public.

Degradation of metribuzin in the UV/chlorine process: kinetic model, degradation by-products and transformation pathways

“…5 by using eqn (11)–(14). 44,45 Although Cl• with a standard electrode potential of 2.2–2.6 V is also a strong oxidant, 42 its contribution to metribuzin degradation was negligible during UV/chlorination based on the experimental findings in this investigation. r UV = ( k obs,UV / k obs,UV/chlorine ) × 100% r Chlorine = ( k obs,chlorine / k obs,UV/chlorine ) × 100% r HO• = ( k obs,UV/chlorine − k obs,HO• )/ k obs,UV/chlorine × 100% r RCS = (1 − r UV − r Chlorine − r HO• ) × 100%where r UV , r Chlorine , r HO• , and r RCS are the contribution percentages of UV, chlorine, and HO• to metribuzin degradation, respectively.…”

A review of recent studies on nano zero-valent iron activated persulfate advanced oxidation technology for the degradation of organic pollutants

“…The wavelength and UV dose are two critical factors influencing the activation of persulfate by UV light. 22–24 In theory, a higher UV intensity results in a faster generation rate of sulfate radicals. 25 However, the generation of UV radiation is often expensive, limiting the practical application of UV technologies.…”

A comparative study on the degradation of iohexol and diatrizoate during UV/persulfate process: kinetics, degradation pathways and iodinated disinfection by-products

“…The techniques that have been reported for ICM removal include biodegradation 7 and advanced oxidation processes (AOPs) such as electrochemical, 8 ozone, 9 UV/O 3 , 10 Fenton, 11 UV/H 2 O 2 , 12 UV/Cl 2 , 1 UV/NH 2 Cl, 13 UV/ClO 2 , 14 and Co(II)/ peracetic acid 15 processes, which are mainly based on the formation of hydroxyl radicals (HO•), reactive chlorine species (RCS, e.g., Cl•, ClO•, and Cl 2 •−), and carbon-centric radicals. Recently, AOPs based on sulfate radicals (SO 4 •−) have received increasing attention in the field of water treatment, 16 and the activating methods of PS include transition metal, UV irradiation, heat, ultrasonic, microwave, and base-activated methods.…”

“…Iodinated X-ray contrast media (ICM) are widely used for imaging soft tissues such as organs, veins, and arteries because of their imaging properties that distinguish them from other tissues. 1 ICM contain inert substances that do not bind to other tissues in the body and can be excreted out with urination and excretion after 24 h. 2 Although ICM do not cause direct harm to the human body, their indirect effects should not be ignored. For example, the high stability and low biodegradability of ICM make them not easy to remove by water treatment processes, so ICM are commonly detected in wastewater effluents, rivers, surface waters, and drinking water.…”

“…The techniques that have been reported for ICM removal include biodegradation 7 and advanced oxidation processes (AOPs) such as electrochemical, 8 ozone, 9 UV/O 3 , 10 Fenton, 11 UV/H 2 O 2 , 12 UV/Cl 2 , 1 UV/NH 2 Cl, 13 UV/ClO 2 , 14 and Co( ii )/peracetic acid 15 processes, which are mainly based on the formation of hydroxyl radicals (HO·), reactive chlorine species (RCS, e.g. , Cl·, ClO·, and Cl 2 · − ), and carbon-centric radicals.…”