Chlorinated Disinfection Byproducts Research Articles

Comparison of Peracetic Acid and Chlorine Effectiveness during Fresh-Cut Vegetable Processing at Industrial Scale

This study was conducted to compare the efficacy of two sanitizing agents, chlorine and peracetic acid (PAA), in reducing spoilage and pathogenic microorganisms and disinfection by-products in the washing stage of three types of minimally processed vegetables: iceberg lettuce, carrots, and baby leaves. These fresh-cut products are consumed uncooked; thus, proper sanitation is essential in preventing foodborne illness outbreaks. The comparison was done at industrial scale with equipment already used in the fresh-cut industry and with washers designed and manufactured for this purpose. Results showed that for washing water hygiene and final product microbial quality, the use of PAA or chlorine had similar efficacy. Different scenarios combining PAA, chlorine, and water were tested, simulating the current industrial processes for each of the tested vegetables. Overall, results confirmed that the use of a sanitizer, PAA or chlorine, in the washing water is effective for the prevention of cross-contamination during the washing process and hence for produce food safety. For final product microbiological quality and shelf life, the use of chlorine or PAA showed no significant differences in lettuce or baby leaves. Chlorinated disinfection by-products in processing water were not formed in significant amounts when washing water was treated with PAA in all scenarios and for all tested vegetables, whereas washing with chlorine (80 mg/L) generated important amounts of trihalomethanes, chlorates, and chlorites. Although chlorates and chlorites were always below the recommended levels or legal limits established for drinking water, trihalomethanes exceeded the legal limits. For perchlorates, values were below the quantification limit in all scenarios. Our results show that PAA is a reliable alternative to chlorine disinfection strategies in the fresh-cut industry.

Mechanistic Study on Oxidative DNA Damage and Modifications by Haloquinoid Carcinogenic Intermediates and Disinfection Byproducts.

Haloquinones (XQs) are a group of carcinogenic intermediates of the haloaromatic environmental pollutants and newly identified chlorination disinfection byproducts (DBPs) in drinking water. The highly reactive hydroxyl radicals/alkoxyl radicals and quinone enoxy/ketoxy radicals were found to arise in XQs and H2O2 or organic hydroperoxides system, independent of transition-metal ions. However, it was not clear whether these haloquinoid carcinogens and hydroperoxides can cause oxidative DNA damage and modifications, and if so, what are the underlying molecular mechanisms. We found that 8-oxodeoxyguanosine (8-oxodG), DNA strand breaks, and three methyl oxidation products could arise when DNA was treated with tetrachloro-1,4-benzoquinone and H2O2 via a metal-independent and intercalation-enhanced oxidation mechanism. Similar effects were observed with other XQs, which are generally more efficient than the typical Fenton system. We further extended our studies from isolated DNA to genomic DNA in living cells. We also found that potent oxidation of DNA to the more mutagenic imidazolone dIz could be induced by XQs and organic hydroperoxides such as t-butylhydroperoxide or the physiologically relevant hydroperoxide 13S-hydroperoxy-9Z,11E-octadecadienoic acid via an unprecedented quinone-enoxy radical-mediated mechanism. These findings should provide new perspectives to explain the potential genotoxicity, mutagenesis, and carcinogenicity for the ubiquitous haloquinoid carcinogenic intermediates and DBPs.

Deactivation of Caenorhabditis elegans nematodes in drinking water by PMS/UV-C: efficiency and mechanisms.

The occurrence and infestations of chlorine-resistant invertebrates in drinking water distributions have attracted concerns on water quality in China, making effective deactivation imperative. This study presents a novel strategy for nematode (Caenorhabditis elegans) deactivation using peroxymonosulfate (PMS)/UV-C. The results indicated that 100% deactivation efficiency was obtained under optimal conditions. An acidic pH and 0.25 mg/L Fe(II) were beneficial to the PMS/UV-C-triggered deactivation of nematodes. A mechanism study demonstrated that [Formula: see text] was activated by UV-C to produce ·OH and [Formula: see text], which resulted in oxidative stress and stimulated the occurrence of cell apoptosis, leading to nematode deactivation. The results reveal PMS/UV-C as an alternative to chlorination in water treatment plants (WTP) or an emergency application when chlorine-resistant invertebrates breed in a second-supply water tank is a promising strategy for disinfection. This approach possessed the advantages of avoiding the production of chlorine disinfection by-products (DBP) and greater efficacy of nematode deactivation. This work will provide ideas for on-going research efforts into chlorine-resistant invertebrate deactivation and eventually achieve the direct drinking of municipal tap water.

Chlorinated disinfection byproducts of diazepam perturb cell metabolism and induce behavioral toxicity in zebrafish larvae

Numerous byproducts resulting from chlorinated disinfection are constantly being generated during water treatment processes. The potential risks of these new emerging pollutions remain largely unknown. Here, we determined the risks of chlorinated disinfection byproducts of diazepam (DZP) in the cellular and zebrafish exposure experiments. The cytotoxicity of disinfection byproducts (MACB and MBCC) was greater than DZP in macrophage raw 264.7 cells at 10 mg/L. We further found that the effects of MBCC on the metabolism of glycine, serine, threonine and riboflavin were far greater than DZP by the targeted metabolomics methods. Moreover, MBCC significantly decreased the peak amplitude of neuronal action potential in primary embryonic rat (Spragu-Dawley SD) hippocampal neurons. We finally determined behavioral toxicity of DZP and byproducts in zebrafish larvae. MBCC significantly decreased the maximal swim-activity and peak duration of zebrafish after 72 h exposure. Altogether, these findings indicate the MBCC pose serious pressures on public health.

Nontargeted identification of chlorinated disinfection byproducts formed from natural organic matter using Orbitrap mass spectrometry and a halogen extraction code

Natural organic matter is a major source of precursors of hazardous chlorinated disinfection byproducts (Cl-DBPs) formed during water treatment, but the majority of Cl-DBPs are still unidentified. In this study, we used a self-written halogen extraction code to identify halogen isotopic patterns in combination with the R package MFAssignR, to identify Cl-DBPs from Orbitrap mass spectra. One hundred and eighty-nine Cl-DBPs were detected during chlorination of a Suwannee River natural organic matter solution, and the structures of 20 of these compounds are reported for the first time. Kendrick mass defect analysis and structural identification confirmed that chlorinated carboxylic acids are common and likely to form during chlorination. A toxicity prediction using quantitative structure-activity relationship models indicated that most of the chlorinated carboxylic acids may be highly toxic. Our analytical strategy can identify Cl-DBPs accurately from complex mixtures and may also be applicable to the identification of other halogenated disinfection byproducts formed during water treatment.

Toxicity of disinfection byproducts formed during the chlorination of sulfamethoxazole, norfloxacin, and 17β-estradiol in the presence of bromide.

Brominated disinfection byproducts (Br-DBPs) are formed during the disinfection process of water containing bromine ions, such as marine aquaculture water. Little attention has been paid to Br-DBPs with anthropogenic chemicals as precursors. This study summarized the sodium hypochlorite (NaClO) oxidation of three frequently used pharmaceuticals, including two antibiotics, norfloxacin (NOR) and sulfamethoxazole (SMX), and the growth hormone estrogen 17β-estradiol (E2). Transformations of the pharmaceuticals were found to be faster in marine aquaculture water than in distilled water. Several Br-DBPs and Cl-DBPs were identified for NOR, SMX, and E2. It was shown that the carboxyl group, piperazine ring, C3, and C8 atoms were the primary reaction sites on NOR. The aniline moiety and S-N bond were identified to be the reaction sites on SMX. The C2, C4, C9, and C16 atoms were the potential reaction centers on E2. Preliminary calculation by QSAR model indicated that the value of logKow significantly increased with an increase in the number of bromine atoms in the Br-DBPs. The results of the bioconcentration factors (BCF) analysis suggested that the bioaccumulation of Br-DBPs were greater than that chlorinated DBPs (Cl-DBPs) in distilled water.

The Efficiency of Multi-Media Filtration in Drinking Water Treatment Plants for the Removal of Natural Organic Matter

Background: Filtration is a processing unit in a Drinking Water Treatment Plant (DWTP) that is used to remove particles from the water. This study is the result of pilot-scale research on Gravity Rapid Sand Filter (GRSF). The purpose of this paper was to evaluate the performance of the Triple Media Filter (TMF) (Granular Activated Carbon (GAC) + anthracite + garnet) and Dual-Media Filter (DMF) (anthracite + sand) in the removal of Natural Organic Matter (NOM) as a precursor of Trihalomethanes (THMs) and chlorination Disinfection by-Products (DBPs). Methods: Filtration rate was performed at conventional (120 m/d) and a high rate (240 m/d) and compared with full-sized Single Media Filter (SMF) with a sand media. The removal efficiency of turbidity, color, and UV absorption at a wavelength of 254 nm (UV254) and Dissolved Organic Carbon (DOC) parameters were investigated. Besides, the Specific Ultraviolet Absorbance (SUVA) was calculated from the ratio of UV254 to DOC. Results: The results showed that the Multimedia Filter (MMF) at 120 and 240 m/d filtration rate had higher removal efficiency compared with a control SMF in removing measured parameters (p<0.05). Also, similar filters have shown the same efficiency relative to each other in different loading rates and there was an insignificant difference. Conclusion: MMF can significantly remove organic pollutants and control the formation of DBPs during water treatment. The study suggests that SMF should be replaced with MMF to improve water quality.

Occurrence, influencing factors, toxicity, regulations, and abatement approaches for disinfection by-products in chlorinated drinking water: A comprehensive review.

Disinfection is considered as a vital step to ensure the supply of clean and safe drinking water. Various approaches are adopted for this purpose; however, chlorination is highly preferred all over the world. This method is opted owing to its several advantages. However, it leads to the formation of certain by-products. These chlorination disinfection by-products (DBPs) are genotoxic, carcinogenic and mutagenic. Still chlorination is being practiced worldwide. Present review gives insights into the occurrence, toxicity and factors affecting the formation of regulated (THMs, HAAs) and emerging DBPs (N-DBPs, HKs, HAs and aromatic DBPs) found in drinking water. Furthermore, remediation techniques used to control DBPs have also been summarized here. Key findings are: (i) concentration of regulated DBPs surpassed the permissible limit in most of the regions, (ii) high chlorine dose, high NOM, more reaction time (up to 3h) and high temperature (up to 30°C) enhance the formation of THMs and HAAs, (iii) high pH favors the formation of THMs while low pH is suitable of the formation of HAAs, (iv) high NOM, low temperature, low chlorine dose and moderate pH favors the formation of unstable DBPs (N-DBPs, HKs and HAs), (v) DBPs are toxic not only for humans but for aquatic fauna as well, (vi) membrane technologies, enhanced coagulation and AOPs remove NOM, (vii) adsorption, air stripping and other physical and chemical methods are post-formation approaches (viii) step-wise chlorination is assumed to be an efficient method to reduce DBPs formation without any treatment. Toxicity data revealed that N-DBPs are found to be more toxic than C-DBPs and aromatic DBPs than aliphatic DBPs. In majority of the studies, merely THMs and HAAs have been studied and USEPA has regulated just these two groups. Future studies should focus on emerging DBPs and provide information regarding their regulation.

Sucralose, a persistent artificial sweetener in the urban water cycle: insights into occurrence, chlorinated byproducts formation, and human exposure

As a globally important artificial sweetener, sucralose (SUC) is a persistent emerging contaminant in global aquatic environments. This research comprehensively track the fate and transport of SUC throughout an urban water cycle; to perform laboratory experiments to determine chlorinated disinfection by-products (DBPs) of SUC sebsequent to advanced oxidation with ozone; and to perform a risk evaluation of SUC related DBPs.; The results demonstrated that SUC was consistently present throughout the urban water cycle, including consumer's tap water. The inluent to the municipal wastewater treatment plant contained 1033.4-2626.3 ng/L SUC, and as expected for this non-biodegradable artificial sweetener, the concentration in the effluent was slightly reduced to 917.6-2031.2 ng/L. The concentration of SUC varied in surface waters with a peak value of 2070.0 ng/L. In finished drinking water 288.1–505.3 ng/L SUC was found, and values of 177.7–409.7 ng/L were present in the distribution system. Up to 16.3% of SUC concentration discharged as municipal wastewater was delivered to residents in their drinking water. While conventional treatment little removed SUC, the mean removal efficiency of SUC with ozonation followed by activated carbon filtration was 39.6% at a full-scale drinking water treatment plant. The fate and transformation of SUC in drinking water treated by ozonation and chlorination were investigated in laboratory experiments. Ozonation partially degraded SUC; however, intermediates reacted with chlorine to generate DBPs, including trichloromethane (TCM), dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA). Peak 7-days potential formation of TCM, DCAA and TCAA were 0.016, 0.51 and 23.34 μg/mg SUC, respectively. DBP yields increased with increasing chlorine dosage, chlorination time, temperature, and solution pH. The presence of ammonia nitrogen in water facilitated dichloroacetonitrile (DCAN) production up to 0.78 μg/mg SUC, while simultaneously reducing the yield of TCM, DCAA and TCAA. Human exposure analysis revealed that carcinogenic risks of DBPs caused only by SUC ozonation were in the range of 1.86 × 10−12-6.12 × 10−9, while non-carcinogenic risks were in the range of 6.0 × 10−9-4.37 × 10−6. The pervasive occurrence of SUC in an urban water cycle, couple to its resistance to biological and chemical treatment, confirms that SUC is a persistent contaminant in the aquatic system, including tap water.

Effects of Chlorine Dose on the Composition and Characteristics of Chlorinated Disinfection Byproducts in Reclaimed Water

Effects of Chlorine Dose on the Composition and Characteristics of Chlorinated Disinfection Byproducts in Reclaimed Water

Potential of biologically activated carbon to improve chlorine stability from biodegradation in surface waters

We report that biological activated carbon (BAC) has the significant potential to improve chlorine stability in the drinking water and dissolved organic carbon (DOC) is not a good indicator of chlorine stability. The BAC followed by enhanced coagulation (EC) could be beneficial for improving chlorine stability. BAC granules obtained from an aged (>26,000-bed volume over a year) BAC column was incubated in the same surface water. The prolonged (58 days) incubation achieved a DOC removal (up to 47%) and improvement of chlorine stability (up to 93% of chlorine reactive agents) with time. Surprisingly, a smaller initial biological removal in DOC (12% or 0.61 mg/L) by BAC substantially improved chlorine stability (64% of chlorine reactive agents), but a further improvement per mg-DOC removal is small. BAC process removes non-coagulable compounds that are chlorine reactive, but at the same time increases the coagulable compounds that are chlorine reactive, implying coagulation after BAC (BAC/EC) is beneficial in stabilising the chlorine and DOC removal. Over the incubation period, a shift in the microbial community is less significant except for the abundance of Nitrospira increasing with the removal in biodegradable organic carbon. BAC treatment followed by coagulation is a good strategy, but the evaluation should be based on chlorine stability and disinfection by-products (DBPs) formation rather than the DOC.

Combination of high resolution mass spectrometry and a halogen extraction code to identify chlorinated disinfection byproducts formed from aromatic amino acids

Chlorination can lead to the formation of hazardous chlorinated disinfection byproducts (Cl-DBPs). We identified tyrosine (Tyr) and tryptophan (Trp) as precursors of toxic Cl-DBPs and developed a halogen extraction code to complement ultra performance liquid chromatography in tandem with high resolution mass spectrometry (UPLC-HRMS) in detecting and identifying Cl-DBPs. We detected 20 and 11 Cl-DBPs formed from chlorination of Tyr and Trp, respectively, and identified the structures of 15 Cl-DBPs. Fourteen structures were previously unreported. We also proposed the tentative formation pathways of these newly identified Cl-DBPs. Their incidence in real water sources demonstrated that these Cl-DBPs are likely to form during chlorination of reclaimed water. We computationally predicted the toxicity of these Cl-DBPs, which was relatively high, indicating that these Cl-DBPs could be hazardous and were of valid concern. Combining analytical data with the halogen extraction code can identify Cl-DBPs accurately from complex compounds. This analytical method can be used to identify Cl-DBPs of water treatment procedures in further studies.

The multiple roles of chlorite on the concentrations of radicals and ozone and formation of chlorate during UV photolysis of free chlorine

Chlorine dioxide (ClO2) has emerged as a promising alternative to free chlorine for water disinfection and/or pre-oxidation due to its reduced yields of chlorinated disinfection byproducts. ClO2 decomposes to form chlorite (ClO2−), which influences the following advanced oxidation processes (AOPs) for micropollutant abatement in drinking water. This study aims at investigating the effects of ClO2− on the concentrations of reactive species (e.g., radicals and ozone) and on the formation of chlorate in the UV/chlorine AOP. Results showed that the concentration of ClO· in the UV/chlorine process remarkably decreased by 98.20–100.00% in the presence of ClO2− at concentration of 0.1–1.0 mg·L−1 as NaClO2. The concentrations of HO· and ozone decreased by 42.71–65.42% and by 22.02–64.31%, respectively, while the concentration of Cl· was less affected (i.e., 31.00–36.21% reduction). The overall concentrations of the reactive species were differentially impacted by ClO2−’s multiple roles in the process. UV photolysis of ClO2− generated HO· but not Cl·, ClO· or ozone under the drinking water relevant conditions. ClO2− also competed with chlorine for UV photons but this effect was minor (< 1.0%). The radicals/ozone scavenging by ClO2− outcompeted the above two to lead to the overall decreasing concentrations of the reactive species, in consistency with the kinetic model predicted trends. ClO2− reacted with radicals and ozone to form chlorate (ClO3−) but not perchlorate (ClO4−). HO· played a dominant role in ClO3− formation. The findings improved the fundamental understanding on micropollutant abatement and inorganic byproduct formation by the UV/chlorine process and other AOPs in ClO2−-containing water.

Photooxidation of atrazine and its influence on disinfection byproducts formation during post-chlorination: effect of solution pH and mechanism

Partial photooxidation of micropollutants may lead to various degradation intermediates, obviously affecting disinfection byproducts (DBPs) formation during the post-chlorination process. The photooxidation of atrazine (ATZ) in aqueous solutions with low-pressure mercury UV lamps in UV, UV/H2O2 and UV/TiO2 treatment system and the formation of chlorinated disinfection byproducts (DBPs) during subsequent chlorination processes including dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), 1,1,1-trichloro-2-propanone (TCP), trichloromethane (TCM) and chloropicrin (CHP) were investigated in this study. The effect of solution pH on the oxidation pathway of ATZ in three UV photooxidation treatment process and the impact of photooxidation on the DBPs formations were assessed. Based on UPLC-ESI–MS/MS analyses, identification of main oxidation intermediates was performed and the plausible degradation pathways of ATZ in photooxidation system were proposed, indicating that photooxidation of ATZ in UV/H2O2 and UV/TiO2 process system was significantly pH-dependent processes. Dichloroacetic acid (DCAA), trichloroacetic acid (TCAA), 1,1,1-trichloro-2-propanone (TCP), trichloromethane (TCM) and chloropicrin (CHP) were detected in photooxidized ATZ solutions. Compared to the other three DBPs, TCM and TCP were the main DBPs formed. The DBPs formations were greatly promoted in oxidized ATZ solutions. Solution pH and UV irradiation time exhibited obvious impact on the DBPs formation on the basis of DBP species. The variation tendency of DBPs observed relates to the combustion of ATZ in photooxidation system and the production oxidation intermediates.

Chlorinated wash water and pH regulators affect chlorine gas emission and disinfection by-products

In the washing operations of fruit and vegetables, the maintenance of an appropriate range of pH in the water when using chlorine is crucial to ensure the maximum concentration of hypochlorous acid (HOCl), the form of chlorine with the highest antimicrobial activity. In this study, the effect of two inorganic acids (phosphoric and sulfuric) and two organic acids (carbonic and citric) as pH regulators was evaluated. Chlorinated wash water was generated using sodium hypochlorite as a chlorine source. The results showed that the optimal pH range with >90% of chlorine as HOCl was between 5.0 and 6.0 for all pH regulators. Phosphoric acid and sulfuric acid provided a wider pH range (3.0–6.0) for the maximum HOCl concentration than citric acid and carbonic acid (4.5–6.0 and 5.0–6.0, respectively). When citric acid was used as a pH regulator, a reduction of available chlorine was observed at pH < 4.5, decreasing 50% the concentration at pH 4.0. The implication of citric acid on chlorine gas emission was studied by the changes in free chlorine, comparing citric and phosphoric acids at pH 3.5 and 5.0. These analyses confirmed the emission of gaseous chlorine as after 15 min free chlorine decreased at pH 3.5, while the level was maintained at pH 5.0. Further experiments were conducted to assess the effect of these pH regulators on the generation of disinfection by-products (DBPs), including chlorates, haloacetic acids (HAAs), and trihalomethanes (THMs). Chlorine (25 mg L−1 free chlorine) and different pH regulators were added to adjust the pH to 5.5 in lettuce wash water. The pH regulators tested neither affected the antimicrobial activity measured as the total mesophilic aerobic bacteria (0.32 log cfu 100 mL−1) nor the accumulation of chlorates (28 mg L−1), as mean values reached. However, pH regulators significantly affected the formation of chlorine halogenated DBPs. Citric acid, as the pH regulator most widely used in some sectors of the food industry, promoted the highest accumulation of THMs (710 μg L−1), although the lowest HAAs (618 mg L−1) at the maximum content of organic matter (600–700 mg L−1). Among the pH regulators, phosphoric acid was identified as the best pH regulator for chlorine-based sanitizers because of the wide range of pH to generate HOCl (as compared to carbonic acid), its inorganic nature avoiding THM formation (as compared to citric acid), and less corrosive action to industrial equipment (as compared to sulfuric acid).

Characterization of lower Phong river dissolved organic matters and formations of unknown chlorine dioxide and chlorine disinfection by-products by Orbitrap mass spectrometry

Dissolved organic matter (DOM) have been reported as precursors of disinfection byproducts (DBPs) and its molecular characteristics are rarely investigated due to its complexity. In this study, changes in the characteristics of DOM were investigated in the lower Phong River in Thailand in dry season and after the first rain in rainy season, using a non-targeted analysis with Orbitrap mass spectrometry. The river was rich with CHO features dominated by lignin-like molecules, while lipid-like molecules increase after domestic wastewater discharges. Wastewater discharge released DOM with higher molecular weight (MW) that was less oxygenated (low O/C) and less oxidized (low carbon oxidation state [Cos]). A lake affected by anthropogenic activities contributed more oxidized DOM into the river, while surface runoff carried DOM that is more oxygenated (high O/C), less hydrogenated (low H/C), and more oxidized (high Cos) to the stream. Water treatment further modified DOM to be lower MW. Approximately three hundred Cl-containing features (CHOCl) detected upstream were also found downstream. Disinfection by chlorine (Cl2) or chlorine dioxide (ClO2) formed both CHO and CHOCl DBPs. Low chlorine dosage applied to upstream and downstream samples resulted in many common unknown DBPs while increasing chlorine dosage resulted in more unique DBPs. At the same dosage, Cl2 reacted with DOM more than ClO2, including more oxidized molecules that are refractory to ClO2. Both Cl2 and ClO2 produced chlorinated and non-chlorinated DBPs, and some DBPs were commonly found by both disinfections. Cl2-produced DBPs were more unsaturated (higher [DBE–O]/C) and oxidized (higher Cos) than ClO2-DBPs.

Molecular characterization of transformation and halogenation of natural organic matter during the UV/chlorine AOP using FT-ICR mass spectrometry

UV/chlorine process, as an emerging advanced oxidation process (AOP), was effective for removing micro-pollutants via various reactive radicals, but it also led to the changes of natural organic matter (NOM) and formation of disinfection byproducts (DBPs). By using negative ion electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS), the transformation of Suwannee River NOM (SRNOM) and the formation of chlorinated DBPs (Cl-DBPs) in the UV/chlorine AOP and subsequent post-chlorination were tracked and compared with dark chlorination. In comparison to dark chlorination, the involvement of ClO•, Cl•, and HO• in the UV/chlorine AOP promoted the transformation of NOM by removing the compounds owning higher aromaticity (AImod) value and DBE (double-bond equivalence)/C ratio and causing the decrease in the proportion of aromatic compounds. Meanwhile, more compounds which contained only C, H, O, N atoms (CHON) were observed after the UV/chlorine AOP compared with dark chlorination via photolysis of organic chloramines or radical reactions. A total of 833 compounds contained C, H, O, Cl atoms (CHOCl) were observed after the UV/chlorine AOP, higher than 789 CHOCl compounds in dark chlorination, and one-chlorine-containing components were the dominant species. The different products from chlorine substitution reactions (SR) and addition reactions (AR) suggested that SR often occurred in the precursors owning higher H/C ratio and AR often occurred in the precursors owning higher aromaticity. Post-chlorination further caused the cleavages of NOM structures into small molecular weight compounds, removed CHON compounds and enhanced the formation of Cl-DBPs. The results provide information about NOM transformation and Cl-DBPs formation at molecular levels in the UV/chlorine AOP.

Detection, transformation, and toxicity of indole-derivative nonsteroidal anti-inflammatory drugs during chlorine disinfection

As important emerging contaminants, nonsteroidal anti-inflammatory drugs (NSAIDs) are the most intensively prescribed pharmaceuticals introduced to drinking water due to their incomplete removal in wastewater treatment. While concentrations of NSAIDs in drinking water are generally low, they have been attracting increasing concern as a result of their disinfection byproducts (DBPs) generated in drinking water disinfection. In this work, detection methods were set up for four representative indole-derivative NSAIDs (indomethacin, acemetacin, sulindac, and etodolac) using ultra performance liquid chromatography/electrospray ionization-triple quadruple mass spectrometry (UPLC/ESI-tqMS). ESI+ was better for detection of indomethacin and sulindac, whereas ESI− was suitable to detection of acemetacin and etodolac. With optimized MS parameters, the instrument detection and quantitation limits of the four indole derivatives were achieved to be 1.1–24.6 ng/L and 3.7–41.0 ng/L, respectively. During chlorination, indomethacin and acemetacin could undergo five major reaction types (chlorine substitution, hydrolysis, decarboxylation, C–C coupling, and C–N cleavage) to form a series of DBPs, among which 19 were proposed/identified with structures. Based on the revealed structures of DBPs, transformation pathways of indomethacin and acemetacin in chlorination were partially elucidated. Notably, individual and mixture toxicity of indomethacin and acemetacin before/after chlorination were evaluated using a well-established acute toxicity assessment and a Hep G2 cell cytotoxicity assay, respectively. Results showed that the predicted acute toxicity of a few chlorination DBPs were higher than their precursors; chlorination substantially enhanced the mixture cytotoxicity of indomethacin by over 10 times and slightly increased the mixture cytotoxicity of acemetacin.

Molecular-level characterization of biodegradable organic matter causing microbial regrowth in drinking water by non-target screening using Orbitrap mass spectrometry

Biodegradable organic matter (BOM), which can be partially evaluated by assimilable organic carbon (AOC), can deteriorate the biological stability of drinking water, causing microbial regrowth in premise plumbing. However, little information is available about the compounds consisting of BOM or AOC. In this study, non-target screening analysis using high-resolution Orbitrap mass spectrometry (Orbitrap MS) was applied to resolve the BOM candidates in drinking water. The ozonated water was incubated with a microbial community in the effluent from biological activated carbon (BAC) filtration. Changes in the molecular-level composition of dissolved organic matter before and after incubation were assessed by Orbitrap MS. In the ozonated water, 14 components were extracted as BOM candidates. On the other hand, 22 BOM candidates were screened in the finished drinking water incubated with an indigenous microbial community proliferating in drinking water. Comparison of these candidates showed that the ozonated water and finished drinking water had different BOM compositions. A chlorine disinfection experiment demonstrated that most of the 22 BOM candidates in the finished drinking water were generated as chlorine disinfection byproducts. Although BAC filtration effectively removed BOM candidates generated by ozonation, different types of BOM were generated by the final chlorine disinfection. Chlorine disinfection is indispensable for microbial risk control, but it also influences the residual BOM composition in drinking water causing microbial regrowth.

Degradation of organic pollutants by ferrate/biochar: Enhanced formation of strong intermediate oxidative iron species

Biochar draws increasing attention as soil amendment, carbon sink, slow-release fertilizer, and adsorbent. Herein, it was interesting to find out that among 11 kinds of commercial biochar, 3 of them facilitated ferrate oxidation of sulfamethoxazole (SMX). With the addition of biochar, oxidation rates of 5 kinds of organic pollutants (including antibiotics, pharmaceuticals, and personal care product) increased by 3–14 times, and the total organic carbon (TOC) removal ratio increased by 2.4–8 times. Radical scavenging experiment, electron spin resonance (ESR) analysis, and probe compound (sulfoxide) oxidation experiment showed that no radical but intermediate iron species [Fe(IV) and Fe(V)] participated in the oxidation reactions. Redox-active moieties (phenolic hydroxyl) on biochar interact with ferrate as electron shuttle and enhance the formation of intermediate iron species through electron transfer. The intermediate iron species not only interacted with organic pollutants and accelerated their transformation, but also corrupted (oxidized) the physical structure of biochar and expanded its surface area and pore volume. Increase of surface area and pore volume of the spent biochar in turn resulted in the improved adsorption capacity. In addition to eliminating emerging organic pollutants, ferrate/biochar removed 8.7%–31.6% of TOC in authentic water and decreased the formation potential of 20 kinds of chlorinated disinfection by-products (DBPs) by 9.2%–23.9%.