Skip to main content
NCBI home page
Elsevier - PMC COVID-19 Collection logoLink to Elsevier - PMC COVID-19 Collection
. 2023 May 1;239:120020. doi: 10.1016/j.watres.2023.120020

Degradation of natural organic matter and disinfection byproducts formation by solar photolysis of free available chlorine

Chuze Chen 1, Xiating Zhao 1, Haoran Chen 1, Mengting Li 1, Liu Cao 1, Yuting Wang 1, Qiming Xian 1,⁎
PMCID: PMC10149525  PMID: 37167852

Abstract

Environment disinfection effectively curbs transmission of the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). However, elevated concentration of free available chlorine (FAC) in disinfectants can be discharged into surface water, generating toxic disinfection byproducts (DBPs). The impact of solar photolysis of FAC on natural organic matter (NOM) to form DBPs has not been well studied. In this work, solar photolysis of FAC was found to result in higher formation of DBPs, DBPs formation potential (DBPsFP), total organic chlorine (TOCl) and lower specific ultraviolet absorbance at 254 nm (SUVA254), compared to dark chlorination. In solar photolysis of FAC, formation of total DBPs was promoted by pH=8, but hindered by the addition of HCO3−, radical scavenger or deoxygenation, while addition of NO3−and NH4+both enhanced the formation of nitrogenous DBPs. Differences in the formation of DBPs in solar photolysis of FAC under various conditions were influenced by reactive species. The formation of trichloromethane (TCM) and haloacetic acids (HAAs) in solar photolysis of FAC positively correlated with the steady-state concentrations of ClO• and O3. The steady-state concentrations of •NO and •NH2 positively correlated with the formation of halonitromethanes (HNMs). HAAs and haloacetonitriles (HANs) mainly contributed to calculated cytotoxicity of DBPs. This study demonstrates that solar photolysis of FAC may significantly impact the formation of DBPs in surface water due to extensive use of disinfectants containing FAC during SARS-CoV-2 pandemic.

Keywords: Free available chlorine (FAC), Solar photolysis, Natural organic matter (NOM), Reactive species, Disinfection byproducts (DBPs)

Graphical abstract

Image, graphical abstract

Open in a new tab

1. Introduction

Free available chlorine (FAC) is the most widely used chemical disinfectant worldwide, considered as one of the most effective ways to curb the spread of harmful microorganisms and acute waterborne disease (WHO, 2017; Silverman and Boehm, 2020). Previous studies suggested that chlorination of NOM can lead to formation of more than 700 DBPs in disinfected source water, many of them reported to be carcinogenic, mutagenic, teratogenic (Kali et al., 2021; Plewa et al., 2017; Benson et al., 2017).

Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) has infected more than 600 million people (WHO, 2022). During SARS-CoV-2 pandemic, FAC is widely used in disinfectants to eliminate or deactivate SARS-CoV-2 in preventing its transmission (Li et al., 2021). Firstly, the usage of chlorine-containing disinfectants in wastewater treatment plants (WWTPs) are also increasing substantially during the pandemic. High chlorine levels in wastewater discharge will inevitably lead to elevated chlorine levels in the receiving water. Moreover, chlorine-containing disinfectants are also widely used in large quantities in public places (Li et al., 2021; Zhang et al., 2021). Li et al. (2021) reported that 14% of the 56 urban WWTPs in China used high chlorine disinfectant doses of more than 6 mg/L. Up to 0.4–1 mg/L of residual chlorine was detected in some lakes of China during pandemic (Yin et al., 2020). NOM in natural water may react with FAC to form DBPs. Chu et al. (2021) reported that the possible in situ formed chloramines facilitated the reaction with NOM in Yangtze River to produce nitrogenous and iodinated DBPs. Effluent from WWTPs with FAC up to 0.6 mg/L discharged during the epidemic was reported to increase concentrations of trichloromethane (TCM) and chlorinated acetic acid in the receiving waters (Chu et al., 2020). While most recent studies focused on how to effectively eliminate or deactivate SARS-CoV-2 virus, a few studies reported that elevated FAC discharged into surface water may react with NOM to form DBPs and reactions were affected by sunlight.

Currently, most studies focus on UV-driven FAC photolysis. There are several studies focusing on UV-driven photolysis of FAC to produce HO•, Cl•, and ClO•. These reactive species were reported to react with NOM or micropollutant in water to affect yields of DBPs (Guo et al., 2017; Li et al., 2016; Wang et al., 2017; Wu et al., 2016b) HO• was found to removal chromophoric groups of humic acid, while Cl• mainly reacted with humic acid and intermediates from humic acid degradation (Li et al., 2016). HO• and Cl• formed by UV/FAC at 254 nm increased the formation of TCM but decreased that of haloacetic acid (HAAs) from NOM. UV/FAC degraded high molecular weight (MW) fractions into low MW fractions. (Wang et al., 2017). It is also reported that solar photolysis of FAC enhanced the formation of DBPs from pharmaceutical and personal care products (PPCPs) or microcystin-LR (Hua et al., 2019; Zhang et al., 2019a). However, little information is available with respect to solar photolysis of FAC affecting the formation of DBPs from NOM. Young et al. (2018) applied solar photolysis of FAC in NOM solutions to increase yields of TCM and HAAs. Solar photolysis of FAC also enhanced depletion of DOM chromophores and fluorophores and removal of phenolic groups. But this work did not detect some nitrogenous DBPs (haloacetonitrile, halonitromethane) and consider the steady-state concentrations of reactive species formed by solar photolysis of FAC. Our study aims to address issues on the influencing factors and reactive species during solar photolysis of FAC, that are not considered in previous studies.

Solar irradiation alone eliminated the DBPs formation potential (DBPsFP) mainly because solar irradiation can degrade precursors of toxic DBPs (Chow et al., 2008; Wu et al., 2016a). Some studies reported that solar irradiation alone increased dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCAN) formation potential with increasing level of nitrite or nitrate (Xu et al., 2019a, 2019b). However, the impact of solar photolysis of FAC on NOM to form DBPsFP have not been fully studied yet. Moreover, there is little information regarding the roles of reactive species in driving the formation of DBPsFP from NOM in solar photolysis of FAC. There is an urgent need to study the effects of the solar photolysis of FAC and reactive species on NOM degradation and the potential risks of DBPs formation.

The objectives of this study are (1) to investigate the degradation of NOM by solar photolysis of FAC under various conditions (pH, HCO3 −, dissolved O2 (DO), radical scavenger, NO3 −, NH4 +) to form DBPs and DBPsFP as well as resulting change in specific ultraviolet absorbance (SUVA254), total organic chlorine (TOCl) and calculated cytotoxicity of DBPs in comparison to dark chlorination, (2) to understand roles of reactive species including HO•, Cl•, ClO•, O3, •NO, and •NH2 in driving the formation of DBPs from NOM. The research results will provide new information on the impact of solar photolysis of FAC in the formation of DBPs and support development of guidance for the use of disinfectants in the future.

2. Experimental section

2.1. Chemicals and materials

Suwannee River natural organic matter (SRNOM) was purchased from the International Humic Substance Society (Batch number 2R101N). More details of the chemical standards and regents used in this study are provided in the Text S1.

2.2. Simulated solar irradiation and chlorination

The radiation light spectrum and illustration of experiment setup were provided in Fig. S1 and Fig. S2, respectively. Photon fluence rate entering the solution in the range of 300−400 nm for simulated solar irradiation was determined by method of p-nitroanisole/pyridine actinometry (Text S2).

During simulated solar irradiation, SRNOM solutions were placed in a quartz beaker and exposed to 500 W xenon lamp (Niubite Electromechanical Plant, China) with the solutions temperature kept at 25.0 ℃. Experiments were performed in duplicate in buffered solution (10 mM phosphate, unless otherwise specified at pH 7.0 ± 0.1.). SRNOM solutions (2 mg/L as C, 300 mL each) were treated according to 5 different procedures. (1): exposure to FAC and simulated solar irradiation (FAC+light); (2): exposure to FAC alone in dark condition (FAC only); (3): exposure to FAC+light under various conditions including HCO3 − (2 mM, 8 mM), t-BuOH (50 mM), without O2, NO3 − (5 mg/L, 10 mg/L), NH4 + (1 mg/L, 2 mg/L); (4): exposure to FAC only under various conditions in dark condition including HCO3 − (2 mM, 8 mM), t-BuOH (50 mM), without O2, NO3 − (5 mg/L, 10 mg/L), NH4 + (1 mg/L, 2 mg/L); (5): exposure to simulated solar irradiation alone (light only). Without O2 was achieved by purging N2 of high purity (99.999%) into reacting solutions for 30 min to ensure the concentration of DO less than 0.1 mg L−1 (Hua et al., 2019). After each treatment, 100 mL of solution was quenched by sodium thiosulfate (Na2S2O3) at a dose about 1.5 times that of the chlorine dosage and was analyzed for DBPs. The remaining solution (200 mL) was not added Na2S2O3 and used to analyze DBPsFP. The determination of DBPsFP was used in previous studies of DBPsFP in solar irradiation of reclaimed water or effluent (Wu et al., 2016a; Xu et al., 2019a, 2019b). Disinfectant dosage for DBPsFP was calculated by the equation of, Cl2 (mg/L) = 3×DOC (mg/L as C) + 8×NH4 + (mg/L as N) + 10 mg/L with temperature maintained at 25℃ in dark condition for 48 h. After chlorination, Na2S2O3 was also used as quenching agent, and DBPs were determined immediately to prevent decomposition of DBPs. DBPsFP (μg/mg C) was calculated by following Eqs 1.

DBPsFP=Caftertest−Cbeforetest (1)

Where Cafter test (μg/mg C) and Cbefore test (μg/mg C) are DBPs concentrations measured after and before the DBPsFP test, respectively after being normalized by DOC.

2.3. Determination of HO•, Cl•, and ClO•

Nitrobenzene (NB), benzoate (BA) and 1,4-dimethoxybenzene (DMOB) were used as probes of HO•, Cl•, and ClO• respectively. NB reacts with HO• but inert to O3 and reactive chlorinated species (RCS). BA reacts with HO• and Cl• but inert to O3 and ClO•. DMOB reacts with HO•, Cl•, and ClO• in the absence of O2 Hua et al., 2019; Mvula et al., 2009; Fang et al., 2014). Steady-state concentrations of HO•, Cl•, and ClO• were calculated by Eqs. ((2)−(4).

kNB′=kHO•·NB[HO•]SS (2)
kBA′=kHO•·BA[HO•]SS+kCl•·BA[Cl•]SS (3)
kDMOB′=kHO•·DMOB[HO•]SS+kCl•·DMOB[Cl•]SS+kClO•·DMOB[ClO•]SS (4)

Where kNB′, kBA′ and kDMOB′ represent pseudo first order constants of NB, BA, DMOB in FAC+light respectively. kHO•·NB(3.9×109 M−1s−1) is the rate constant between NB and HO•. kHO•·BA(5.9×109 M−1s−1) and kCl•·BA(1.8×1010 M−1s−1) are the rate constants between BA and HO• and Cl• respectively.kHO•·DMOB(7.0×109M−1s−1),kCl•·DMOB(1.8×1010M−1s−1) and kClO•·DMOB(2.1×109 M−1s−1) are the rate constants between DMOB and HO•, Cl•, and ClO• respectively.

The kintecus model (version 5.55) contained 147 reactions obtained from literatures (Table S1) (Ianni et al., 2018), which was used to predict the steady−state concentrations of reactive species in solar photolysis of FAC. This model has been used in advanced oxidation process or simulated solar photolysis (Guo et al., 2018; Zhang et al., 2019a).

2.4. Analytical methods

pH was measured by pH-meter (Thermo, USA). DO was determined by DO meter (Thermo, USA). TOCl was measured using active carbon absorption-combustion-ion chromatography (Text S4). Change in UV–Visible absorbance spectra was recorded from 190 to 800 nm (UV254 specifically) by UV-vis spectrophotometer (UV-1800, Shimadzu, Japan) using in 0.5 nm increments in a 1 cm length quartz cuvette. Analysis of NB, BA, DMOB were conducted using high-performance liquid chromatography (Agilent 1260 USA) (Text S5). Quantitative analysis of 35 halogenated DBPs comprise 9 HAAs determined using liquid-liquid-extraction, derivation and GC-ECD analysis based on EPA Methods 552.3 (Domino et al., 2003) and other 26 halogenated DBPs including 6 trihalomethane (THMs), 9 haloacetonitriles (HANs), 9 halonitromethane (HNMs), and 2 haloketones (HKs) determined using liquid-liquid extraction and GC-ECD analysis following EPA Methods 551.1 (Much and Hautman, 1995). More details can be found in Text S6 and analytical recoveries for DBPs are shown in Table S2.

2.5. DBPs-associated additive cytotoxicity

The cytotoxicity contribution of a single DBP was calculated by dividing measured DBP concentration by its LC50 value. It is assumed that the cytotoxicity of individual DBPs can be additive (Eq. (5)).

CDBPscyto=∑CDBPLC50 (5)

Where LC50 (M) of DBPs are the concentrations that introduced a 50% reduction in growth of Chinese Hamster Ovary (CHO) cells compared to the control groups (Table S3). The cytotoxicity contribution of the two HKs (1,1-dichloropropanone (1,1-DCP) and 1,1,1-trichloropropanone (1, 1, 1-TCP)) were not included because both LC50 values were not available.CDBP (M) was the measured concentration of individual DBP and CDBPscyto is the sum of calculated cytotoxicity from all measured DBPs.

2.6. Data analysis

All data analyses were performed by SPSS version 20.0 and Origin 2023a software. Under various conditions, correlation analysis was built between DBPs or DBPsFP and radical concentration. PCA analysis was used to cluster the concentration of DBPs and DBPsFP during solar photolysis of FAC under various conditions. DBPs and DBPsFP concentrations were the data after 15, 30, 45, 60, 120 min treatment and radical concentrations were obtained by Kintecus model prediction after the same time interval.

3. Results and discussion

3.1. Formation of DBPs

Since solutions did not contain Br and I, none of brominated and iodinated DBPs were detected. Among chlorinated DBPs, 12 of them: TCM, 3 HANs including monochloroacetonitrile (MCAN), DCAN, TCAN, 3 HNMs including monochloronitromethane (MCNM), dichloronitromethane (DCNM), trichloronitromethane (TCNM), 2 HKs including 1, 1-DCP, 1, 1, 1-TCP, 3 HAAs including monochloroacetic acid (MCAA), dichloroacetic acid (DCAA), trichloroacetic acid (TCAA) were detected.

Fig. 1 shows the comparison of concentrations of these 12 chlorinated DBPs between during FAC+light and FAC only experiments at three different pH values: pH=6 (Fig. 1a), pH=7 (Fig. 1b) and pH=8 (Fig. 1c). Two general trends can be observed in Fig. 1: total DBPs concentrations increased with reaction times and the concentrations were higher in FAC+light than in FAC only. Increased DBPs formation in FAC+light could be largely due to presence of the reactive species such as HO•, Cl•, ClO•, and O3, which are generated by solar photolysis of FAC (Hua et al., 2019; Young et al., 2018). Reactive species can affect the formation of DBPs from NOM (Li et al., 2016; Young et al., 2018; Wang et al., 2017) or micropollutants (Hua et al., 2019; Zhang et al., 2019b; Wu et al., 2017). FAC itself cannot directly produces reactive species but in FAC+light, FAC not only oxidizes NOM but also generates reactive species to produce or degrades DBPs precursors. Past works showed that both HO• and Cl• generated by solar photolysis of FAC, contributed to generating HAAs precursors but not TCM precursors from NOM (Young et al., 2018). However, in this study, reactive species also mainly promoted the formation of HKs and HAAs.

Fig. 1.

Fig. 1

Open in a new tab

DBPs concentrations and UTOCl/TOCl in FAC+light (left bar) and FAC only (right shadow bar) at (a) pH=6, (b) pH=7 and (c) pH=8. Other conditions: [FAC]0=4 mg/L (as Cl2), 2 mg/L SRNOM (as C), 25 ℃.

3.1.1. Effect of pH

The concentrations of DBPs in FAC only at pH=7 was selected as the reference, to which ratios of DBPs under other conditions were plotted in Fig. S3. In FAC only, at pH=6,7 or 8, none of DCNM and TCNM was formed and ratios of other DBPs were in range of 1.10−0.95 from 15 min to 120 min, indicating little impact of pH on the formation of DBPs. Therefore, increased formation of DBPs in FAC+light was mainly due to reactive species generated by solar photolysis of FAC not FAC itself. Concentrations of total DBPs at pH=6 or pH=8 in FAC+light were 1.85−1.43 and 2.32−1.72 times higher than that in FAC only, respectively (Fig. 1a, 1c). At pH from 6 to 8 in FAC+light, concentrations of total DBPs from 15 min to 120 min were 54.96−72.87 μg/L, 48.01−64.95 μg/L, 70.64−87.27 μg/L, respectively. Although the concentrations of total DBPs followed the order of pH=8>pH=6>pH=7, effect of pH on the formation of individual DBPs in FAC+light could be different. As shown in Fig. S4, the formation of TCM, 1, 1, 1-TCP, MCAA and DCAA followed pH=8>pH=6≈pH=7 while that of 1, 1-DCP and TCAA followed pH=6>pH=8>pH=7. The formation of HANs and MCNM remained steady and no DCNM and TCNM formed at different pH. The differences in the formation of DBPs in FAC+light may be ascribed to yields of radical species, since pH can change the distribution of HOCl and OCl− (pKa=7.5) (Hua et al., 2019; Young et al., 2018). During FAC+light, lower concentrations of HO• and Cl• but a higher concentration of ClO• at pH=8 compared with pH=6. Higher concentration of ClO• might be positively correlated with formation of DBPs.

3.1.2. Effect of HCO3−

In FAC+light, with increased HCO3 −from 2 mM (122 mg/L) to 8 mM (488 mg/L), the concentrations of total DBPs were 41.61−60.28 μg/L and 33.49−55.23 μg/L, respectively (Fig. 2 a, 2b), which were both lower than that at pH=7 without HCO3 − (48.01−64.95 μg/L, Fig. 1b). Further, addition of HCO3 −in FAC only from 2 mM to 8 mM also did not cause significant difference in the formation of DBPs (Fig. S3). HCO3 − can quench HO• and Cl• with rate constant of 3.90×108 M − 1s−1 and 2.20×108 M − 1s−1, respectively and produce CO3 •−, considered as the selective oxidant for micropollutants with electron-donating group (Huang et al., 2018; Wu et al., 2017; Zhou et al., 2020b). In FAC+light with addition of HCO3 −, HO• and Cl• were quenched by HCO3 −, resulting in decreased formation of HAAs and increased formation of TCM, HKs compared with that at pH=7 (Fig. S5). An explanation is that HO• and Cl• may produce TCM and HAAs precursors, and the role of CO3 •− is not negligible and it may compensate for the quenched HO• and Cl• to generate precursors of TCM and HKs but not HAAs.

Fig. 2.

Fig. 2

Open in a new tab

DBPs concentrations and UTOCl/TOCl in FAC+light (left bar) and FAC only (right shadow bar) under various conditions. (a) 2 mM HCO3−, (b) 8 mM HCO3−, (c) without O2, (d) 50 mM t-BuOH. Other conditions: [FAC]0=4 mg/L (as Cl2), 2 mg/L SRNOM (as C), 25 ℃, pH=7.

3.1.3. Effect of DO and HO•, Cl•, O(3p)

In FAC+light, concentrations of total DBPs were decreased by 58−51% (20.01−31.97 μg/L, Fig. 2c) in the absence of O2 compared with that at pH=7 (48.01−64.95 μg/L, Fig. 1b). Deoxygenation had significant effects on decreasing the formation of TCM (62−10%), TCAN (99–98%), 1, 1, 1-TCP (50–30%), MCAA (61–57%), DCAA (66–61%) and TCAA (63−52%) in FAC+light compared with that at pH=7 (Fig. S6). In this study, deoxygenation mainly inhibited formation of O3, and O3 may contribute to producing precursors of TCM, TCAN, 1, 1, 1-TCP, and HAAs. At the same time, however, deoxygenation in FAC only also did not cause significant difference in the formation of DBPs compared with that at pH=7 (Fig. S3). To further confirm the roles of reactive species, t-BuOH was used to eliminate 97% of HO•, 95% of Cl•, and 53% of O(3p). Elimination of O(3p) further inhibited the formation of O3. (Young et al., 2018; Zhang et al., 2019a). As shown in Fig. 2d, addition of 50 mM t-BuOH in FAC+light resulted in 33.10−43.69 μg/L of total DBPs, decreasing by 31−33% compared with that at pH=7 (48.01−64.95 μg/L, Fig. 1b). In FAC+light without the involvement of HO•, Cl•, and O(3p), formation of TCM, MCAN, TCAN, MCNM, 1, 1, 1-TCP, MCAA, DCAA and TCAA were 21−33%, 100−10%, 10−15%, 20−25%, 27−31%, 51−48%, 64−80%, 61−79% of that at pH=7, respectively (Fig. S6). In this study, HO•, Cl•,and O3 may contribute to generating precursors of these decreased DBPs. Further work needed to be done to distinguish direct effects of O3 and radical species on DBPs precursor.

3.1.4. Effect of nitrogen species

In FAC+light, with increased NO3 − from 5 mg/L to 10 mg/L, concentrations of total DBPs increased to 72.87−92.15 μg/L (Fig. 3 a), 73.89−106.46 μg/L (Fig. 3b), and were 1.51−1.41 and 1.53−1.63 times of that at pH=7 (48.01−64.95 μg/L, Fig. 1b), respectively. For individual DBPs, addition of 10 mg/L NO3 − in FAC+light resulted in the increase of a number of nitrogenous DBPs including TCAN (220−230%), DCAN (220−370%), MCNM (50−70%) and chlorinated DBPs including 1, 1-DCP (224−367%), 1, 1, 1-TCP (66−78%), MCAA (18−48%), DCAA (18−63%), TCAA (45−67%), respectively in comparison to that at pH=7 (Fig. S7). In addition, DCNM and TCNM were found with addition of NO3 −in FAC+light (Fig. S9), but were not observed at pH=7 without addition of NO3 −. Moreover, in FAC only, NO3 − also did not greatly affect formation of DBPs compared with that at pH=7 (Fig. S3) and did not generate DCNM and TCNM (Fig. S9). This result showed that solar photolysis of NO3 − resulted in higher level of HANs and HNMs. Nitrogenous DBPs exhibit relatively higher cytotoxicity than carbonous DBPs which may pose great concern for organism (Zhou et al., 2020a; Chen et al., 2021). NO3 − can be photolyzed to form •NO2 and •NO but does not greatly change profile of RCS. It is reported that •NO2 and •NO result in the formation of nitrated and nitrosated products that tend to be more toxic and persistent than their parent compounds (Huang et al., 2018; Scholes et al., 2019). Addition of NO3 − in FAC+light also promoted the formation of HAAs, HKs from NOM, which were not observed in previous studies.

Fig. 3.

Fig. 3

Open in a new tab

DBPs concentrations and UTOCl/TOCl in FAC+light (left bar) and FAC only (right shadow bar) under various conditions, (a) 5 mg/L NO3−, (b) 10 mg/L NO3−, (c) 1 mg/L NH4+, (d) 2 mg/L NH4+. Other conditions:[FAC]0=4 mg/L (as Cl2), 2 mg/L SRNOM (as C), 25 ℃, pH=7.

At pH=7, 1 mg/L NH4 + exactly reacts with 4 mg/L HOCl (as Cl2) to mainly form 56 μM NH2Cl. With increased NH4 + from 1 mg/L to 2 mg/L, solar photolysis of NH2Cl increased concentrations of total DBPs by 28−135%, 75−164%, respectively compared with that by dark chloramination of SRNOM (Fig. 3c, 3d). In FAC+light with 1 mg/L and 2 mg/L NH4 +, concentrations of total DBPs were 17.54−40.58 μg/L (Fig. 3c) and 21.39−39.37 μg/L (Fig. 3d), decreasing by 63−37% and 55−39% in comparison to that at pH=7 without NH4 + (48.01−64.95 μg/L, Fig. 1b). Addition of NH4 + in FAC+light reduced formation of TCM, HANs, HKs, MCNM, HAAs (Fig. S8) but significantly increased formation of DCNM, TCNM compared with that at pH=7 (Fig. S9). Solar photolysis of NH2Cl can produce •NO, •NH2, and Cl• but cannot produce ClO• (Chen et al., 2021; Wu et al., 2019). It is reported that •NO can degrade NOM to form nitrophenol, as an important DCNM and TCNM precursors (Zhou et al., 2020b).

3.2. SUVA254 transformation

SUVA254 is a widely used surrogate parameter to characterize NOM and provides a quantitative measure of aromatic contents, which are generally thought as precursors for TCM, HAAs by dark chlorination (Wang et al., 2017; Hua et al., 2015). In this study, solar photolysis of SRNOM did not lead to a large reduction of DOC during the 120 min experiments (Fig. S10). As shown in Table S4, in FAC only, except for addition of NH4 +, little differences in SUVA254 were observed under various conditions, meaning the capacity of FAC to degrade SUVA254 was not significantly affected under various conditions. Addition of NH4 + in FAC only led to higher SUVA254 mainly because of weak oxidation capacity of NH2Cl. As shown in Fig. S11, NOM treated with FAC+light had substantially lower SUVA254 compared with that in FAC only. Similar results have already been reported. For example, bleaching of UV254 were enhanced by UV-driven photolysis of FAC or solar photolysis (Wang et al., 2017; Young et al., 2018), which indicated that reactive species formed by solar photolysis of FAC greatly contributed to the destruction of aromatic compound in NOM. Table S4 suggested that in FAC+light, in comparison to that at pH=7, several conditions (pH=6, 5 mg/L NO3 −, 10 mg/L NO3 −) enhanced SUVA254 degradation, but other conditions (pH=8, 2 mM HCO3 −, 8 mM HCO3 −, 1 mg/L NH4 +, 2 mg/L NH4 +, without O2, 50 mM t-BuOH) showed opposite trends. FAC+light under various conditions produced different profiles of reactive species and the degradation of SUVA254 reflected the extent to which the aromatics were destructed by reactive species.

3.3. TOCl transformation

TOCl reflects total concentration of chlorinated organic matter formed by reaction among FAC, reactive species and NOM. Unknown total organic chlorine (UTOCl) was obtained by subtracting measured DBPs from TOCl. As shown in Table S5, in FAC only, ratios of TOCl concentrations formed under various conditions to that at pH=7 were in the range from 0.90 to 1.10 except for addition of NH4 +, indicating TOCl formed in FAC only were not significantly changed among various conditions. Weak oxidation capacity of NH2Cl resulted in lower TOCl concentration in FAC only with addition of NH4 +. In FAC+light at pH=7, TOCl reached 445.1 μg/L after 15 min treatment and gradually decreased to 222.9 μg/L at 120 min (Fig. S12 a). However, measured total DBPs gradually increased at the same time, resulting in ratios of UTOCl to TOCl (UTOCl/TOCl) to be decreased from 0.93 to 0.82 (Fig. 1a). Declining UTOCl/TOCl can also be observed under various conditions in FAC+light (Figs. 1−3), which indicated ratios of unknown DBPs keeping decrease during FAC+light. Previous studies suggested that TOCl can be photo-cleaved by natural sunlight and halophenolic analogs underwent photo-nucleophilic substitutions or the hydroxyphenolic analogs were decomposed to aliphatic compounds (Ibrahim and Hua, 2016a; Liu et al., 2017). In this study, unknown DBPs may also be photodegraded into aliphatic compounds. Moreover, degradation of TOCl was affected by various conditions. For example, Ibrahim and Hua (2016b) reported degradation of TOCl by natural sunlight in the order of pH=8>pH=7>pH=6. In this study, degradation rates of TOCl in FAC+light also followed the same order of pH=8>pH=7>pH=6 (Fig. S12 a−c). With increased NO3 − from 5 mg/L to 10 mg/L in FAC+light, formation of TOCl were 314.1 μg/L and 289.7 μg/L, respectively, after 15 min, decreasing by 29%, 35% compared with that at pH=7 at same time (445.1 μg/L), respectively (Fig. S12 h, i). NO3 − could transfer energy to other pollutants and induce indirect photolysis and NO3 −induced photodegradation accounted for 25% of direct photolysis (Ibrahim and Hua, 2016a, 2016b). Generally, TOCl profiles in FAC+light experiments under different conditions depend on its formation rates and degradation rates. Photodegradation of TOCl by solar photolysis of FAC requires further investigations as there are few studies focusing on it so far (Ibrahim and Hua, 2016a, 2016b).

3.4. DBPsFP in FAC+light

DBPsFP can be used to understand quality and quantity of DBP precursors from NOM. When Surface water polluted by FAC, and NOM containing in natural river maybe degraded by solar photolysis of FAC as they travel from the discharge points to downstream water intakes. Combined effects of FAC+light can alter DBPs precursors in NOM (Wang et al., 2017; Wu et al., 2016a). Fig. 4 depicted the DBPsFP under various conditions after 15 min treatment. TCM and HAAs accounted for most DBPsFP. Compared with untreated SRNOM, light only slightly increased DBPsFP, mainly due to the enhanced formation of TCM and 1, 1, 1-TCP. Wu et al. reported that solar irradiation induced the formation of more TCM, chloral hydrate (CH) and TCNM (Wu et al., 2018). Solar irradiation of NOM leads to the formation of excited triplet sates of NOM (3NOM*), and reactive oxygen species (ROS). These reactive species convert macromolecular organic acids to small organic acids, as precursors of TCM (Wan et al., 2021; Bodhipaksha et al., 2015). Fig. 4 showed that DBPsFP under various conditions in FAC+light was generally higher than that in FAC only, except for without O2. The higher DBPsFP in FAC+light was likely due to differences in radical chemistry under various conditions, changing profile of DBPs precursor in NOM. DBPsFP at different pH in FAC+light followed the order of pH=8>pH=6>pH=7. pH=8 may promote the formation of ClO• and O3 while pH=6 may promote the formation of Cl• and HO•, both may produce more TCM and HAAs precursors. In FAC+light without O2 led to lowest DBPsFP, indicating O3 may play an important role in generating DBPs precursors. When HO•, Cl•, and O(3P) were quenched by t-BuOH, DBPsFP were similar with that in FAC only. Even though addition of HCO3 − inhibited the formation of DBPs in FAC+light, its DBPsFP were still higher than that in FAC only, which may be ascribed to CO3 •−in forming DBPs precursors. Addition of either NO3 −or NH4 + in FAC+light both enhanced formation of nitrated and nitrosated products and then promoted HANs and HNMs formation potentials

Fig. 4.

Fig. 4

Open in a new tab

DBPsFP under various conditions in FAC+light (left bar) and FAC only (right shadow bar) and light only after 15 min treatment. Other conditions:[FAC]0=4 mg/L (as Cl2) (except for light only), 2 mg/L SRNOM (as C), 25 ℃.

3.5. Reactive species in driving the formation of DBPs

As shown in Table S6, the Kintecus model predicted radical concentrations matched well with the measured ones for HO•, Cl•, and ClO•. Kintecus model can be used as a tool to predict radicals' concentrations in this study. Beside HO•, Cl•, and ClO•, Kintecus model further predicts steady state concentration of O3, CO3 •−, •NO2, •NO, •NH2. Formation of HO•, Cl•, and O3 mainly derives from solar photolysis of HOCl. Increased O3 exposure with increased pH was attributable to a higher proportion of OCl−, which enhanced the production of O(3P) and subsequently reacted with O2 to generate O3 (Hua et al., 2019; Bulman et al., 2019). Addition of HCO3 − can react with HO• and Cl• to form CO3 •−through, leading to higher concentration of CO3 •− (Huang et al., 2018; Liu et al., 2018). Solar photolysis of NO3 − produce reactive nitrogen species (RNS) through two main reactions to form •NO2 and HO• or NO2 − and O(3P) (Benedict et al., 2017; Huang et al., 2018; Scholes et al., 2019). Solar photolysis of NH2Cl produces •NH2, Cl•, and •NH2 can react with O2 to form •NO (Zhou et al., 2020a; Wu et al., 2019).

Aquatic NOM is a complexed heterogeneous mixture of macromolecules, mainly containing humic acid (HA) and fulvic acid (FA) (Guo et al., 2022; Yang et al., 2022).Young et al. reported that degradation of NOM treated by solar photolysis of FAC leads to break down of larger humic substances to smaller molecular weight compounds. Similar results were also reported for NOM degraded by UV/Cl2, RCS and O3 played an important role in producing small molecule compounds, acting as DBPs precursors (Wang et al., 2017). By multiplying the concentrations of reactive species (HClO, HO•, Cl•, ClO•, O3, CO3 •−) modeled by Kinetcus model with its known rate constants with NOM. ClO• and O3 accounted for over 90% of the contribution to the degradation of NOM since ClO• and O3 were formed at relatively higher concentrations and their higher rate constants with NOM. ClO• and O3 may react with NOM first to produce small molecules and facilitate subsequent reactions. In this study, [ClO•]SS positively correlated with the formation of TCM, HANs, 1, 1, 1-TCP and HAAs (Fig. 5 a). As shown in Fig. 1b, 1c, in FAC+light, these DBPs was higher at pH=8 than that at pH=7 since concentration of ClO• is higher at pH=8 (Table S6). ClO• was reported to form organic radicals and facilitate subsequent hydroxylation or chlorination to form hydroxylated or chlorinated aromatic rings products (Guo et al., 2022). Nonetheless, [ClO•]SS negatively correlated with the TCM-FP, TCNM-FP, HKs-FP. ClO• may consume precursors of halogenated DBPs in NOM through electron transfer and thus inhibit these DBPsFP during post-chlorination. Moreover, in FAC+light at pH=8, increased TCM-FP was mainly ascribed to enhanced formation of O3.

Fig. 5.

Fig. 5

Open in a new tab

(a) Pearson's correlation heat map between measured DBPs, DBPsFP and modeled concentrations of reactive species (FP: formation potential), (b) PCA analysis of measured DBP and DBPsFP under various conditions in FAC+light.

There are several studies focusing on O3 formed by solar photolysis of FAC to degrade pollutants such as carbamazepine, microcystin-LR through addition on unsaturated C-bonds or hydroxylation on aromatic rings (Young et al., 2018). O(3P) was only generated by photolysis of FAC under irradiation wavelengths of 320−400 nm, therefore O3 was mainly formed in solar photolysis of FAC not UV-driven process (Benedict et al., 2017). [O3]SS positively correlated with the formation of MCAN, DCAN, DCNM, TCNM, HAAs and TCM-FP, HAAs-FP etc. O3 may produce more non halogenated precursors and then react with excessive FAC in post chlorination (Fig. 5a). As shown in Fig. 2c, without O2 in FAC+light, deoxygenation mainly inhibited formation of O3 and the formation of MCAN, DCAN and HAAs were lower than that at pH=7 and also caused reduction of TCM-FP and HAAs-FP. Fig. 5b also showed that DBPs and DBPsFP without O2 in FAC+light separated in different clusters with that at pH=7 due to lower formation of DBPs and DBPsFP.

HO• (E0=2.7 V) is a nonselective oxidant and attacks aromatic rings via addition and reacts with aliphatic via addition or H-abstraction (Yang et al., 2022) with rate constants in the range of 108−1010 M−1s−1. Cl• (E0=2.4 V) is produced together with HO• simultaneously by solar photolysis of FAC. Compared with HO•, Cl• is selectively reactive with substituted aromatics such as phenols, benzoic acid, toluene and aniline (Wu et al., 2017; Yang et al., 2022). HO• and Cl• are the important reasons that solar photolysis of FAC produces more DBPs than that FAC only dose. Fig. 5b showed that DBPs and DBPsFP in FAC+light with addition of t-BuOH distinctly separated from that at pH=7. When HO•, Cl•, and O(3p) is quenched by t-BuOH, TCM, MCAN, TCAN, MCNM, 1, 1, 1-TCP, HAAs were all inhibited, indicating that HO•, Cl•, and O(3p) may contribute to formation of these DBPs (Fig. 2d). However, [HO•]ss and [Cl•]ss are not significantly correlated with measured DBPs since HO• and Cl• may widely react with small molecules but not selectively produce DBPs precursors (Fig. 5a). When HO• and Cl• are quenched by HCO3 − to form CO3 •− (E0 = 1.78 V). Pathway for CO3 •−to degrade pollutant such as oxcarbazepine, are mainly electron transfer and oxidation (Liu et al., 2018; Zhou et al., 2020b). Fig. 5b showed that DBPs and DBPsFP with addition of HCO3 − in FAC+light could be clustered with that at pH=7. In FAC+light with addition of HCO3 −, DBPsFP was lower than that at pH=7, but it was still higher than that at pH=7 in FAC only (Fig. 4), which may be ascribed to lower oxidant capacity of CO3 •− compared with HO• and Cl•.

Contribution of RNS to degrade contaminants is important in the photolysis of NO3 − or NH2Cl. Rate constants of RNS with most pollutants are not available. Pathways for ibuprofen, naproxen, triclosan degraded by •NO were mainly nitrosation and hydroxylation, especially nitro- or nitroso-transformation products tend to exhibit increased toxicity. (Huang et al., 2018; Scholes et al., 2019; Wu et al., 2019). •NH2 is relatively unreactive to organic compounds but it may form amination products and then be oxidized. It is reported that UV-driven NH4 + and NO3 −photolysis produce more nitro(so)products through addition into aromatic rings in NOM, acting as important DCNM and TCNM precursors (Zhou et al., 2020a). In this study, concentrations of [•NO]ss and [•NH2]ss are significantly positively correlated with the formation of several nitrogenous DBPs including DCNM, TCNM and DCNM-FP, TCNM-FP. Fig. 3 also showed in FAC+light, higher concentrations of DCNM and TCNM were formed with addition of NH4 + than that with addition of NO3 −, which may be ascribed to higher [•NO]ss and [•NH2]ss (Table S6). Formation of HANs was not positively correlated with [•NO]ss or [•NH2]ss. Fig. 5b showed that DBPs and DBPsFP in FAC+light with addition of NO3 −were clustered in different group from that with addition of NH4 + mainly due to higher formation of HANs and HAAs. One possible explanation is that some other RNS in FAC+light with addition of NO3 − may contribute to the formation of HANs.

3.6. Calculated cytotoxicity

The calculated cytotoxicity of DBPs under various conditions are presented in Fig. 6 . HANs and HAAs dominated the DBP-associated calculated cytotoxicity, accounting for 62−98% of the additive toxicity. The highest calculated cytotoxicity was produced by FAC+light with addition of NO3 − since the highest concentrations of HANs was formed. FAC+light at pH=8 also showed relatively higher calculated cytotoxicity because of higher formation of HAAs.

Fig. 6.

Fig. 6

Open in a new tab

Calculated cytotoxicity of DBPs under various conditions in FAC+light. Other conditions: [FAC]0=4 mg/L (as Cl2), 2 mg/L SRNOM (as C), 25 ℃, pH=7 except for pH=6 or pH=8.

4. Conclusions and environmental implications

Under the SARS-CoV-2 pandemic, FAC is used as an effective strategy to inactivate the virus in various settings, including households, workplaces, and public facilities. However, elevated concentration of FAC is discharged into surface water and reacts with NOM to form toxic DBPs. The results showed that solar photolysis of FAC may increase DBPs, DBPsFP, TOCl and decrease SUVA254. In this process, solar photolysis of FAC plays an important role in driving the formation of DBPs by producing reactive species (HO•, Cl•, ClO•, O3, •NO, •NH2). ClO• and O3 positively correlated with formation of TCM and HAAs. •NO and •NH2 positively correlated with the formation of HNMs. Especially, in FAC+light with addition of NO3 − enhanced formation of HANs and HAAs was observed, contributing to most calculated cytotoxicity. The study results provide insight into the NOM degraded by solar photolysis of FAC under various conditions and identify some important reactive species driving the formation of DBPs. Theses knowledge may advance our understanding on reaction mechanism of solar photolysis of FAC and contribute to the development of guidance for the use of disinfectants in the future.

Appendix A. Supplementary data

Additional details of materials and chemicals, analysis methods, instrumental parameters, reactive species kinetic model and data of detected concentrations of DBPs, TOCl, SUV254 (PDF).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (Grant number: 21876078, 42177356), the Fundamental Research Funds for the Central Universities (2022300301).

Footnotes

Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.watres.2023.120020.

Appendix. Supplementary materials

mmc1.docx (7.4MB, docx)

Data availability

  • The data that has been used is confidential.

References

  1. Benedict K.B., McFall A.S., Anastasion C. Quantum yield of nitrite from the photolysis of aqueous nitrate above 300nm. Environ. Sci. Technol. 2017;51:4387–4395. doi: 10.1021/acs.est.6b06370. [DOI] [PubMed] [Google Scholar]
  2. Benson N.U., Akintokun O.A., Adedapo A.E. Disinfection byproducts in drinking water and evaluation of potential health risks of long-term exposure in Nigeria. J. Environ. Public Health. 2017;7535797 doi: 10.1155/2017/7535797. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Bodhipaksha L.C., Sharpless C.M., Chin Y., Sander M., Langston W.K., Mackay A.A. Triplet photochemistry of effluent and natural organic matter in whole water and isolates from effluent-receiving rivers. Environ. Sci. Technol. 2015;49:3453–3463. doi: 10.1021/es505081w. [DOI] [PubMed] [Google Scholar]
  4. Bulman D.M., Mezyk S.P., Remucal C.K. The impact of pH and irradiation wavelength on the production of reactive oxidants during chlorine photolysis. Environ. Sci. Technol. 2019;53:4450–4459. doi: 10.1021/acs.est.8b07225. [DOI] [PubMed] [Google Scholar]
  5. Chen C., Du Y., Zhou Y., Wu Q., Zheng S., Fang J. A formation of nitro(so) and chlorinated products and toxicity alteration during the UV/monochloramine treatment of phenol. Water Res. 2021;194 doi: 10.1016/j.watres.2021.116914. [DOI] [PubMed] [Google Scholar]
  6. Chow A.T., Leech D.M., Boyer T.H., Singer P.C. Impact of simulated solar irradiation on disinfection byproduct precursors. Environ. Sci. Technol. 2008;42:5586–5593. doi: 10.1021/es800206h. [DOI] [PubMed] [Google Scholar]
  7. Chu W., Fang C., Deng Y., Xu Z. Intensified disinfection amid COVID-19 pandemic poses potential risks to water quality and safety. Environ. Sci. Technol. 2021;55(7):4084–4086. doi: 10.1021/acs.est.0c04394. [DOI] [PubMed] [Google Scholar]
  8. Chu W., Shen J., Luan X., Xiao R., Xu Z. Study on secondary risk of water environment under enhanced disinfection of wastewater treatment plant during epidemic prevention and control. Water Wastewater Eng. 2020;46(6):1–14. [Google Scholar]
  9. Domino, M.M., Pepich, B.V., Munch, D.J., Fair, P.S., Xie, Y., 2003. Determination of haloacetic acids and dalapon in drinking water by liquid–liquid microextraction, derivatization, and gas chromatography with electron capture detection. US Environmental Protection Agency, USA. EPA Method 552.3 Revision 1.0.
  10. Fang J., Fu Y., Shang C. The roles of reactive species in micropollutant degradation in the UV/free chlorine system. Environ. Sci. Technol. 2014;48:1859–1868. doi: 10.1021/es4036094. [DOI] [PubMed] [Google Scholar]
  11. Guo K., Wu Z., Chen C., Fang J. UV/Chlorine process: an efficient advanced oxidation process with multiple radicals and functions in water treatment. Acc. Chem. Res. 2022;55:286–297. doi: 10.1021/acs.accounts.1c00269. [DOI] [PubMed] [Google Scholar]
  12. Guo K., Wu Z., Shang C., Yao B., Hou S., Yang X., Song W., Fang J. Radical chemistry and structural relationships of PPCP degradation by UV/chlorine treatment in simulated drinking water. Environ. Sci. Technol. 2017;51:10431–10439. doi: 10.1021/acs.est.7b02059. [DOI] [PubMed] [Google Scholar]
  13. Guo K., Wu Z., Yan S., Yao B., Song W., Hua Z., Zhang X., Kong X., Li X., Fang J. Comparison of the UV/chlorine and UV/H2O2 processes in the degradation of PPCPs in simulated drinking water and wastewater: kinetics, radical mechanism and energy requirements. Water Res. 2018;147:184–194. doi: 10.1016/j.watres.2018.08.048. [DOI] [PubMed] [Google Scholar]
  14. Hua G., Reckhow D.A., Abusallout I. Correlation between SUVA and DBP formation during chlorination and chloramination of NOM fractions from different sources. Chemosphere. 2015;130:82–89. doi: 10.1016/j.chemosphere.2015.03.039. [DOI] [PubMed] [Google Scholar]
  15. Hua Z., Guo K., Kong X., Lin S., Wu Z., Wang L., Huang H., Fang J. PPCP degradation and DBP formation in the solar/free chlorine system: effects of pH and dissolved oxygen. Water Res. 2019;150:77–85. doi: 10.1016/j.watres.2018.11.041. [DOI] [PubMed] [Google Scholar]
  16. Huang Y., Kong M., Westerman D., Xu E.G., Coffin S., Cochran K.H., Liu Y., Richardson S.D., Schlenk D., Dionysios D.D. Effects of HCO3− on degradation of toxic contaminants of emerging concern by UV/NO3−. Environ. Sci. Technol. 2018;52:12697–12707. doi: 10.1021/acs.est.8b04383. [DOI] [PubMed] [Google Scholar]
  17. Ianni, J.C.Kintecus, Windows version 5.50, 2018.
  18. Ibrahim A., Hua G. Natural solar photolysis of total organic chlorine, bromine and iodine in water. Water Res. 2016;92:69–77. doi: 10.1016/j.watres.2016.01.047. [DOI] [PubMed] [Google Scholar]
  19. Ibrahim A., Hua G. Photolytic dehalogenation of disinfection byproducts in water by natural sunlight irradiation. Chemosphere. 2016;159:184–192. doi: 10.1016/j.chemosphere.2016.05.090. [DOI] [PubMed] [Google Scholar]
  20. Kali S., Marina K., Ghaffar M.S., Rasheed S., Waseem A., Lqbal M.M., Niazi M.B., Zafar M.L. Occurrence, influencing factors, toxicity, regulations, and abatement approaches for disinfection byproducts in chlorinated drinking water: a comprehensive review. Environ. Pollut. 2021 doi: 10.1016/j.envpol.2021.116950. [DOI] [PubMed] [Google Scholar]
  21. Li T., Jiang Y., An X., Liu H., Hu C., Qu J. Transformation of humic acid and halogenated byproduct formation in UV-chlorine processes. Water Res. 2016;102:421–427. doi: 10.1016/j.watres.2016.06.051. [DOI] [PubMed] [Google Scholar]
  22. Li Z., Song G., Bi Y., Gao W., He A., Lu Y., Wang Y., Jiang G. Occurrence and distribution of disinfection byproducts in domestic wastewater effluent, tap water, and surface water during the SARS-CoV‑2 pandemic in China. Environ. Sci. Technol. 2021;55(7):4103–4114. doi: 10.1021/acs.est.0c06856. [DOI] [PubMed] [Google Scholar]
  23. Liu J., Zhang X., Li Y. Photoconversion of chlorinated saline wastewater DBPs in receiving seawater is overall a detoxification process. Environ. Sci. Technol. 2017;51:58–67. doi: 10.1021/acs.est.6b04232. [DOI] [PubMed] [Google Scholar]
  24. Liu T., Yin K., Liu C., Luo J., Crittenden J., Zhang W., Luo S., He Q., Deng Y., Liu H., Zhang D. The role of reactive oxygen species and carbonate radical in oxcarbazepine degradation via UV, UV/H2O2: kinetics, mechanisms and toxicity evaluation. Water Res. 2018;147:204–213. doi: 10.1016/j.watres.2018.10.007. [DOI] [PubMed] [Google Scholar]
  25. Much, J.W., Hautman, D.P., 1995. Determination of chlorination disinfection by-products, chlorinated solvents, and halogenated pesticides/herbicides in drinking water by liquid–liquid extraction and gas chromatograph with electron-capture detection. US Environmental Protection Agency, USA. EPA Method 551.1 Revision 1.0.
  26. Mvula E., Naumov S., Von Sonntag C. Ozonolysis of lignin models in aqueous solution: anisole, 1,2-dimethoxybenzene, 1,4-dimethoxybenzene, and 1,3,5-trimethoxybenzene. Environ. Sci. Technol. 2009;43:6275–6282. doi: 10.1021/es900803p. [DOI] [PubMed] [Google Scholar]
  27. Plewa M.J., Wagner E.D., Richardson S.D. TIC-Tox: a preliminary discussion on identifying the forcing agents of DBP-mediated toxicity of disinfected water. Environ. Sci. Technol. 2017;58:208–216. doi: 10.1016/j.jes.2017.04.014. [DOI] [PubMed] [Google Scholar]
  28. Scholes R.C., Carsten P., Sedlak D.L. The role of reactive nitrogen species in sensitized photolysis of wastewater-derived trace organic contaminants. Environ. Sci. Technol. 2019;53:6483–6491. doi: 10.1021/acs.est.9b01386. [DOI] [PubMed] [Google Scholar]
  29. Silverman A.I., Boehm A.B. Systematic review and meta-analysis of the persistence and disinfection of human coronaviruses and their viral surrogates in water and wastewater. Environ. Sci. Technol. Lett. 2020;7:544–553. doi: 10.1021/acs.estlett.0c00313. [DOI] [PubMed] [Google Scholar]
  30. Wan D., Wang H., Sharma V.K., Selvinsimpson S., Dai H., Luo F., Wang C., Chen Y. Mechanistic investigation of enhanced photoreactivity of dissolved Organic matter after chlorination. Environ. Sci. Technol. 2021;55:8937–8946. doi: 10.1021/acs.est.1c02704. [DOI] [PubMed] [Google Scholar]
  31. Wang W., Zhang X., Wu Q., Du Y., Hu H. Degradation of natural organic matter by UV/chlorine oxidation: molecular decomposition, formation of oxidation byproducts and cytotoxicity. Water Res. 2017;124:251–258. doi: 10.1016/j.watres.2017.07.029. [DOI] [PubMed] [Google Scholar]
  32. WHO Coronavirus Disease (COVID-19) Dashboard data last updated: 2022/11/1, 13:00 pm CEST Overview Data Table, https://covid19.who.int/.
  33. WHO, 2017. Guidelines for drinking-water quality: fourth edition incorporating the first addendum. World Health Organization (WHO), Geneva. [PubMed]
  34. Wu Z., Chen C., Zhu B., Huang C., An T., Meng F., Fang J. Reactive nitrogen species are also involved in the transformation of micropollutants by the UV/Monochloramine process. Environ. Sci. Technol. 2019;53:11142–11152. doi: 10.1021/acs.est.9b01212. [DOI] [PubMed] [Google Scholar]
  35. Wu J., Ye J., Peng H., Wu M., Shi W., Liang Y., Liu W. Solar photolysis of soluble microbial products as precursors of disinfection by-products in surface water. Chemosphere. 2018;201:66–76. doi: 10.1016/j.chemosphere.2018.02.185. [DOI] [PubMed] [Google Scholar]
  36. Wu Q., Li C., Du Y., Wang W., Huang H., Hu H. Elimination of disinfection byproduct formation potential in reclaimed water during solar light irradiation. Water Res. 2016;95:260–267. doi: 10.1016/j.watres.2016.02.023. [DOI] [PubMed] [Google Scholar]
  37. Wu Z., Fang J., Xiang Y., Shang C., Li X., Meng F., Yang X. Roles of reactive chlorine species in trimethoprim degradation in the UV/chlorine process: kinetics and transformation pathways. Water Res. 2016;104:272–282. doi: 10.1016/j.watres.2016.08.011. 2016b. [DOI] [PubMed] [Google Scholar]
  38. Wu Z., Guo K., Fang J., Yang X., Hong X., Hou S., Kong X., Shang C., Yang X., Meng F., Chen L. Factors affecting the roles of reactive species in the degradation of micropollutants by the UV/chlorine process. Water Res. 2017;126:351–360. doi: 10.1016/j.watres.2017.09.028. [DOI] [PubMed] [Google Scholar]
  39. Xu J., Kralle Z.T., Hart C.H., Dai N. Effects of Sunlight on the Formation Potential of Dichloroacetonitrile and Bromochloroacetonitrile from wastewater effluent. Environ. Sci. Technol. 2019;53:4285–4294. doi: 10.1021/acs.est.9b06526. [DOI] [PubMed] [Google Scholar]
  40. Xu J., Kralles Z.T., Dai N. Effects of sunlight on the trichloronitromethane formation potential of wastewater effluents: dependence on nitrite concentration. Environ. Sci. Technol. 2019;53:4285–4294. doi: 10.1021/acs.est.9b00447. [DOI] [PubMed] [Google Scholar]
  41. Yang X., Rosario-Ortiz F.L., Lei Y., Pan Y., Lei X., Westerho P. Multiple roles of dissolved organic matter in advanced oxidation processes. Environ. Sci. Technol. 2022;56(16):11111–11131. doi: 10.1021/acs.est.2c01017. [DOI] [PubMed] [Google Scholar]
  42. Yin, W., Wang, C., Zhang, H., Lei, P., 2020. Impact of the use of disinfectants on water environment in Wuhan during COVID-19 pandemic. Yangtze River. 51(5), 29–33. DOI:10.16232/j.cnki.1001-4179.2020.05.005.
  43. Young T.R., Li W., Guo A., Korshin G.V., Dodd M.C. Characterization of disinfection byproduct formation and associated changes to dissolved organic matter during solar photolysis of free available chlorine. Water Res. 2018;146:318–327. doi: 10.1016/j.watres.2018.09.022. [DOI] [PubMed] [Google Scholar]
  44. Zhang X., He J., Lei Y., Qiu Z., Cheng S., Yang X. Combining solar irradiation with chlorination enhances the photochemical decomposition of microcystin-LR. Water Res. 2019;159:324–332. doi: 10.1016/j.watres.2019.05.030. [DOI] [PubMed] [Google Scholar]
  45. Zhang X., Zhai J., Zhong Y., Yang X. Degradation and DBP formations from pyrimidines and purines bases during sequential or simultaneous use of UV and chlorine. Water Res. 2019;165 doi: 10.1016/j.watres.2019.115023. [DOI] [PubMed] [Google Scholar]
  46. Zhang Z., Zhou Y., Han L., Guo X., Wu Z., Fang J., Hou B., Cai Y., Jiang J., Yang Z. Impacts of COVID pandemic on the aquatic environment associated with disinfection byproducts and pharmaceuticals. Water Res. 2021;15(6):150–169. doi: 10.1016/j.scitotenv.2021.151409. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Zhou S., Wu Y., Zhu S., Sun J., Bu L., Dionysios D.D. Nitrogen conversion from ammonia to trichloronitromethane: potential risk during UV/chlorine process. Water Res. 2020;172 doi: 10.1016/j.watres.2020.115508. [DOI] [PubMed] [Google Scholar]
  48. Zhou Y., Chen C., Guo K., Wu Z., Wang L., Hua Z., Fang J. Kinetics and pathways of the degradation of PPCPs by carbonate radicals in advanced oxidation processes. Water Res. 2020;185 doi: 10.1016/j.watres.2020.116231. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

mmc1.docx (7.4MB, docx)

Data Availability Statement

  • The data that has been used is confidential.

Articles from Water Research are provided here courtesy of Elsevier

RESOURCES