A novel solar-activated chlorine dioxide process for atrazine degradation in drinking water

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Water Research

Volume 239, 1 July 2023, 120056
Water Research

A novel solar-activated chlorine dioxide process for atrazine degradation in drinking water

https://doi.org/10.1016/j.watres.2023.120056Get rights and content


New technologies using advanced oxidation processes (AOPs) with low energy-input to address the presence of micro-contaminants and the formation of disinfection byproducts (DBPs) are required for drinking water safety. In this work, the activation of chlorine dioxide with solar (solar/ClO2 process), a type of renewable and inexhaustible energy, was developed to degrade atrazine (ATZ) and control the formation of DBPs. Results revealed that solar/ClO2 process was effective in degrading ATZ. Hydroxyl radicals (•OH) and chlorine radicals (Cl•) produced in solar/ClO2 process were found to be the predominant agents for ATZ degradation with contribution rates of 55.9% and 44.1%, respectively, based on radical quenching tests and competition kinetics. Reaction pH did not affect the total amount of Cl• and •OH (i.e., [•OH]exp) and [Cl•]exp), while the conversion of Cl• to •OH was responsible for the depressed ATZ degradation efficiency with the increasing pH in solar/ClO2 process. The presence of bicarbonate (HCO3), chloride (Cl) and humic acid (HA) retarded the ATZ degradation mainly due to they decreased [•OH]exp) and [Cl•]exp. Using the UPLC-MS/MS analysis, six degradation intermediates of ATZ were tentatively identified, and the three-stage degradation pathway as well as the stepwise detoxification of ATZ were confirmed by the condensed Fukui function (CFF) calculation and ECOSAR prediction. Applying solar/ClO2 as a pretreatment of HA-containing water, the formation of DBPs during post-chlorination was significantly reduced. However, the presence of ATZ during solar/ClO2 pretreatment of HA significantly lowered the control efficiency of DBPs. The major degradation intermediate, i.e., deethyldeisopropylhydroxyatrazine (DEIHA), of ATZ could incorporate into HA and therefore providing more precursors for DBPs. The acute toxicity recorded by the behavior of zebrafish larvae revealed that using chloramine instead of chlorine downstream the solar/ClO2 pretreatment of ATZ and HA could significantly reduce the acute toxicity by decreasing the formation of total DBPs. This study demonstrated the great potential of applying solar/ClO2 process followed by chloramination to simultaneously degrade micro-contaminants and reduce DBPs formation as well as toxic risk in practical applications.



Advanced oxidation process (AOPs) combining chlorine-based disinfectants are promising treatment strategies to be integrated into conventional water treatment plants to degrade micro-contaminants. Chlorine-based AOPs degrade micro-contaminants mainly by producing powerful reactive species such as hydroxyl radicals (•OH) and reactive chlorine species (RCS) (Fan et al., 2022; Qin et al., 2022; Zhang et al., 2022). The common strategy in practical applications to produce these powerful reactive species is by the ultraviolet light (UV) with chlorine, chloramine, and more recently with chlorine dioxide (ClO2) (Kong et al., 2021; Wu et al., 2021; Zhang et al., 2019b). Compared with chlorine-based AOPs and chloramine-based AOPs, ClO2-based AOPs has some advantages such as considerable biocidal efficiency of ClO2 and less DBPs formation potential (Pang et al., 2023). Therefore, ClO2-based AOPs have been rising great attention.

Attempts have been made to investigate the degradation of micro-contaminants by UV/ClO2 AOP at a UV wavelength of 254 nm (i.e., UVC254/ClO2 process). The UVC254/ClO2 process was demonstrated to produce reactive species (e.g., chlorine oxide radicals (ClO•), chlorine radicals (Cl•), hydroxyl radicals (•OH), and ozone) to facilitate the degradation of micro-contaminants including sulfamethoxazole, triclosan and ciprofloxacin (Sichel et al., 2011). However, the degradation efficiency of micro-contaminants by UVC254/ClO2 process was lower than the well documented UVC254/chlorine and UVC254/chloramine process (Kong et al., 2021; Tian et al., 2020). Besides, the low absorption coefficients (60.7 M−1cm−1) of ClO2 at UVC254 resulting in less production of reactive species and high input of energy limited the application of UVC254/ClO2 process in micro-contaminants elimination (Xu et al., 2022; Ye et al., 2022). To conquer these limitations, activation of ClO2 in UVA range (320 nm to 400 nm), at wavelength of 360 nm (i.e., UVA/ClO2 process) was performed in literatures (Chuang et al., 2022, Kong et al., 2021). The high absorption coefficients (619.1 to 1284.2 M−1cm−1) of ClO2 in the UVA range which are over 1 magnitude higher than that at UVC254 enable the production of more reactive species in UVA/ClO2 process than in UVC254/ClO2 process (Firak et al., 2022). Although UVA/ClO2 process showed good degradation efficiency towards micro-contaminants, the energy conversion efficiency of UVA lower than 70% from electrical power into optical power was still deemed not energy-efficient (Peng et al., 2022). Overall, the UV-based /ClO2 AOP require additional energy input, which is detrimental to economic-savings.

ClO2 has high absorption coefficients of 50 ∼ 100 M−1cm−1 and 619.1 ∼ 1284.2 M−1cm−1 in the wavelength range of 220 to 240 nm and 300 to 420 nm, respectively (Kong et al., 2021; Peng et al., 2022). This suggests the potential activation ability of solar irradiation at wavelength of 300 ∼ 420 nm towards ClO2. Solar is a cost-effective and bebign energy consisting of ∼ 3% UV light, 44% visible light and 53% infeared, and features enormous advantages such as clean, obtainable, renewable and inexhaustible (Yang et al., 2021). Recently, the common applied chlorine, persulfate and sulfite have been proved well cooperated with solar in degrading micro-contaminants (Chen et al., 2023; Sanchez-Montes et al., 2022; Tan et al., 2022). For example, chlorine can absorb energy at the solar emission of 300 ∼ 400 nm to produce ClO•, Cl•, and •OH et al., to effectively degrade micro-contaminants (Sanchez-Montes et al., 2022). While for the ClO2 with a wider adaption to the solar irradiation spectrum, whether solar irradiation can activate ClO2 to produce the powerful reactive species and thus promote to the degradation of micro-contaminants have never been reported.

Generally, AOPs applying in water treatment would have significant effect on the formation of disinfection byproducts (DBPs) during the following disinfection process (Chen et al., 2022; Ding et al., 2019; Zhang et al., 2019a; Zhou et al., 2020). It was found that UV/sulfite treatment of amino acids could generate precursors more prone to form haloacetonitrile during post-chlorination (Chen et al., 2022). While UV/persulfate degradation of chloramphenicol could convert the amino groups into nitro groups, and therefore greatly alleviate the formation of haloacetonitrile (Chu et al., 2016a). This demonstrated that the degradation intermediates during the degradation of micro-contaminants in AOPs played predominant role in the DBPs formation. Effect of UV/ClO2 pretreatment on the DBPs formation showed that UV/ClO2 process could enhance the formation of DBPs, while the authors did not offer corresponding explanations and effective coping strategies (Kong et al., 2021; Peng et al., 2022). For the potential solar/ClO2 process, its effect on and underlying mechanism of the DBPs formation during following disinfection step as well as the control strategies need to be comprehensively addressed.

Herein, the solar/ClO2 process was constructed for the first time to degrade micro-contaminants. Atrazine (ATZ) was selected as a target micro-contaminant. As a common herbicide, ATZ has caused significant environmental contamination, and it is frequently detected in surface water and ground water with concentrations ranging from 0.07 to 3.00 ug/L (Joseph et al., 2022; Urseler et al., 2022). Firstly, the removal efficiency and reactive species-mediated mechanisms of ATZ degradation in solar/ClO2 process was investigated. Secondly, the effects of different operation conditions (e.g., pH and ClO2 dose) and water matrices (e.g., bicarbonate (HCO3), chloride (Cl), humic acid (HA) and real waters) on ATZ degradation were evaluated. Thirdly, the ATZ degradation pathway in solar/ClO2 process and the formation of DBPs during following chlorination were addressed. Finally, the toxic risk of DBPs was determined and the risk control strategy was proposed.


Section snippets

Materials and reagents

The information of the materials and reagents used in this study is provided in Text S1. All of the chemicals with reagent grade were used without further purification. Chlorine dioxide (ClO2) stock solutions were freshly prepared by the reaction of sulfuric acid and sodium chlorite, and standardized with a UV–visible spectrophotometer at 359 nm according to the previous literature (Peng et al., 2022). Real waters were collected from Taihu lake and Yangtze river, with basic water qualities

Degradation efficiency of ATZ by solar/chlorine dioxide process

The degradation kinetics of ATZ by solar alone, ClO2 alone, and solar/ClO2 process in neutral aquatic solution were shown in Fig. 1a. ATZ hardly underwent directly photolysis by solar irradiation. The degradation percentage of ATZ was less than 5% after treatment by ClO2 alone for 30 min, indicating that ClO2 oxidation can't remove ATZ. By contrast, ATZ could be degraded during solar/ClO2 process with a reduction rate of 86.3% within 30 min. The degradation of ATZ by solar/ClO2 process could be 


This study elucidated the degradation of ATZ in solar/ClO2 process and the strategies for controlling DBPs during the subsequent disinfection step. Results revealed that •OH and Cl• were the dominant radicals that responsible for the efficient degradation of ATZ in solar/ClO2 process. Increasing pH could induce the conversion of Cl• to •OH, hence retard the ATZ degradation in solar/ClO2 process. HCO3, Cl and HA mainly induced depletion of •OH and Cl•, and therefore decreased the degradation

Declaration of Competing Interest

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled, “A novel solar-activated chlorine dioxide process for atrazine degradation in drinking water”


Financial support was received from the National Natural Science Foundation of China (Project 52200012), the Jiangsu Funding Program for Excellent Postdoctoral Talent (2022ZB150), the Fundamental Research Funds for the Central Universities (B220201047), the Anhui Provincial Key Laboratory of Environmental Pollution Control and Resource Reuse (2022EPC05), the Science and Technology Development Plans of Ministry of Housing and Urban-Rural Development (2021-K-131), the Six Talent Peaks Project in


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