Chlorinated Disinfection Byproducts Research Articles

Efficacy of activated persulfate in pathogen inactivation: A further exploration

Activated persulfate, a relatively new advanced oxidation process, has gained attention for its potential to ensure fresh produce safety. One of the major advantages is to avoid the formation of toxic chlorinated disinfection byproducts which are concerns for chlorine-based sanitizers. This study was aimed to investigate the efficacy of ferrous and alkaline activated persulfate in inactivating Escherichia coli O157:H7 and Listeria monocytogenes, with the primary focus on the effect of initial persulfate concentration, the effect of gradual addition of ferrous ion, and the stability of activated persulfate. The prepared 5-strain pathogen cocktails were treated by activated persulfate for 60 or 120 s. Sodium thiosulfate combined with phosphate buffer was used to quench the reaction. Both pathogens were plated onto non-selective agars for colony enumeration. The steady-state concentrations of sulfate and hydroxyl radicals were quantified in each activation conditions. The results showed higher initial persulfate concentration can lead to more pathogen reductions. About 8.50 log CFU/mL reduction was observed in 120 s after the initial persulfate concentration was increased to 80 mmol/L (ferrous activation on both pathogens) or 600 mmol/L (alkaline activation on L. monocytogenes). Gradual addition of ferrous ion into persulfate solution achieved more pathogen reductions than adding all ferrous ion at once. However, only the increases of reductions achieved by four sequential addition were significant (P < 0.05). In addition, the steady-state concentrations of both sulfate and hydroxyl radicals were found to be positively correlated with microbial reductions at all conditions. Furthermore, the pathogen inactivation efficacy of both ferrous and alkaline activated persulfate can be maintained for a relatively long period (up to 3 h).

Degradation of metronidazole by UV/chlorine treatment: Efficiency, mechanism, pathways and DBPs formation

Metronidazole (MET) is a widely used antibiotic but is recalcitrant in aquatic environment. This study investigated elimination of MET by UV/chlorine process systematically. The degradation of MET in the process well fitted pseudo first-order kinetics. Decreasing pH from 9 to 5 raised the rate constant from 0.0199 min-1 to 0.1485 min-1, possibly ascribed to change in species distribution and apparent quantum yields of radicals. Scavenging experiments indicated that both HO and Cl contributed to the degradation of MET, and that HO was the dominant species in the pH range studied. The second-order rate constant between Cl and MET was determined to be (5.64 ± 0.1) × 109 M-1 s-1. Three products were identified by UPLC-Q-TOF MS and degradation pathway was thus proposed. Significant amounts of chlorinated disinfection by-products (DBPs) were produced and 1,1,1-TCP was the dominant (83.6%-92.3%) in the UV/chlorine process. The kinetic model developed fitted well with experimental results, and was used to examine the effects of typical water parameters, such as chorine dosage, pH, inorganic anions, NOM and real water matrix. Furthermore, removal efficiency of MET by the UV/chlorine process were assessed in terms of electrical energy per order (EE/O). The efficiency was about 0.43 kWh m-3 order-1, 0.54 kWh m-3 order-1, 0.57 kWh m-3 order-1, respectively, for the removal of MET in ultrapure water (UPW) and two types of real water samples, indicating that UV/chorine was a practical method for authentic drinking water treatment practices.

Application of UVOX Redox® for swimming pool water treatment: Microbial inactivation, disinfection byproduct formation and micropollutant removal

Alternative disinfection technologies may overcome some of the limitations of conventional treatment applied in swimming pools: chlorine-resistant pathogens (e.g. Cryptosporidium oocysts and Giardia cysts) and the formation of chlorinated disinfection byproducts. In this paper, results of full scale validation of an alternative disinfection technology UVOX Redox® (hereinafter referred to as UVOX) that combines ozonation and UV irradiation are presented. The performance was assessed in terms of microbial inactivation, disinfection byproduct formation and micropollutant removal. UVOX was able to achieve 1.4–2.7 log inactivation of Bacillus subtilis spores at water flows between 20 and 76 m³/h. Lower formation of trichloromethane and dichloroacetic acid was observed with UVOX followed by chlorination when compared to chlorination alone. However, due to the use of ozone and the presence of bromide in the pool water, the formation of trihalomethanes and haloacetic acids shifted to more brominated byproducts. Chlorine alone was able to remove the target micropollutants: acetaminophen, atenolol, caffeine, carbamazepine, estrone, estradiol, and venlafaxine (>97% removal) after 24 h, with the exception of ibuprofen (60% removal). The application of UVOX in chlorinated water enhanced the removal of ibuprofen. The application of UVOX could lower the usage of chlorine to the level that provides an adequate residual disinfection effect.

A new detoxification mechanism for aldoxime therapeutic antidotes for chemical warfare nerve-agents

Pyridinium aldoximes are best-known as therapeutic antidotes for organophosphorus chemical warfare nerve-agents and pesticides. Polyhalogenated quinones are a class of carcinogenic intermediates and newly identified chlorination disinfection byproducts in drinking water. However, it is not clear what is the exact chemical mechanism underlying such detoxication. Here we showed that pralidoxime, one of the representatives of pyridinium aldoximes, can markedly enhance the dechlorination and hydroxylation of the highly reactive and toxic tetrachloro-1,4-benzoquinone (also called chloranil) in two-consecutive steps to produce the much less toxic 2,5-dichloro-3,6-dihydroxy-1,4-benzoquonine (chloranilic acid), with rate acceleration of up to 180000-times. In contrast, no enhancing effect was observed when the hydroxylamine group was blocked via methylation to form O -methylated pralidoxime. The major reaction product from pralidoxime was characterized as its corresponding nitrile (2-cyano-1-methylpyridinium chloride). Along with oxygen-18 isotope-labeling studies, we proposed that nucleophilic substitution coupled with an unprecedented double Beckmann fragmentation reaction was responsible for this dramatic enhancement of the detoxification reaction. This paper reviewed the unprecedented double Beckmann fragmentation reaction. Our findings may have broad biological and environmental implications for future research on the aldoxime therapeutic agents and carcinogenic polyhalogenated quinones, which are two important classes of compounds of major biomedical and environmental interest.

Exposure to disinfection by-products during gestation and newborns' small for gestational age

Objective: To explore the associations between exposure to chlorination disinfection by-products (CDBPs) during gestation and newborns' small for gestational age (SGA). Methods: During April 2010 to July 2012, a total of 3 903 pregnant women who lived in a district with the same water treatment plant in Wuhan, China were recruited to this perspective study. Information about demographic characteristics of pregnant women and their newborns was collected. The tap water samples were monthly collected for 28 months in 3 different sites, with 84 samples, and 4 kinds of trihalomethanes (THMs)(chloroform (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and bromoform (TBM)) and 2 kinds of chlorohaloacetic acids (HAAs) (trichloroacetic acid (TCAA), dichloroacetic acid (DCAA)) were determined. The pregnant women were divided into 4 groups(Q1 to Q4) by quartile method according to their exposure level of CDBPs. Binary Logistic regression models were used to assess the associations between exposure to CDBPs during gestation and newborns' small for gestational age. Results: The average weight of all the newborns was (3 310.19±389.91) g, of which 169 (4.33%) were SGA. The median concentrations of TCM, BDCM, bromo-THMs, total THMs, TCAA, and DCAA during the whole pregnancy were 18.07, 4.93, 8.51, 26.74, 10.65, and 13.77 μg/L, respectively. Binary Logistic regression analysis showed dose-response relationships between elevated TCM and total THMs during the whole gestation and compared with Q1 group, while there was a increased risk of SGA in Q4 group, and OR(95%CI) was 1.87 (1.01-3.49) , 2.30 (1.22-4.35) , respectively (P for trend equaled to 0.044, 0.015). Compare with Q1 group, there also be positive associations between exposure to TCAA (Q4 group) during first-trimester and the whole gestation and SGA, while OR(95%CI) was 2.16 (1.19-3.91) (P for trend equaled to 0.015). Conclusion: Exposure to CDBPs during gestation might increase the risk of newborns' SGA.

Water Distribution System Failure Risks with Increasing Temperatures.

In the coming decades, ambient temperature increase from climate change threatens to reduce not only the availability of water but also the operational reliability of engineered water systems. Relatively little is known about how temperature stress can increasingly cause hardware components to fail, quality to be affected, and service outages to occur. Changes to the estimated-time-to-failure of major water system hardware and the probability of quality noncompliance were estimated for a modern potable water system that experiences hot summer temperatures, similar to Phoenix, AZ, and Las Vegas, NV. A fault tree model was developed to estimate the probability that consequential service outages in quantity and quality will occur. Component failures are projected to have a percent increase of 10-101% in scenarios where peak summer temperature has increased from 36 to 44 °C, which create the conditions for service outages to have a percent increase of 7-91%. Increased service outages due to multiple pumping unit failures and water quality noncompliances are the most notable concerns for water utilities. The most effective strategies to prevent temperature-related failures should focus on monitoring and correcting chlorine residual and disinfection byproduct concentration, and on cooling pumping unit motors and electronics.

Impact of Methylobacterium in the drinking water microbiome on removal of trihalomethanes

A major class of chlorine disinfection by-products in water treatment and distribution systems is the trihalomethanes. When they occur at high concentration in drinking water they may cause serious problems to human health. Little is known about the capacity of bacterial species that are endemic to drinking water to affect the fate of those chlorination by-products. Methylobacterium species have been previously found to play an important role in the degradation of another major group of chlorine disinfection by-products: the haloacetic acids. Thus, the role that Methylobacterium might play in the concentration of trihalomethanes in drinking water was explored in this study. Concentrations of trihalomethanes were measured in drinking water for different concentrations of Methylobacterium and under different organic matter and chlorine concentrations. The results revealed that when the Methylobacterium DSM 18358 is present in drinking water, even at a low relative abundance of 1%, it plays a key role in decreasing the concentration of trihalomethanes up to 48% from the initial one after 24 h.

Chlorotyrosines versus Volatile Byproducts from Chlorine Disinfection during Washing of Spinach and Lettuce.

Following the Food Safety Modernization Act of 2011 in the U.S., guidelines for disinfection washes in food packaging facilities are under consideration to control pathogen risks. However, disinfectant exposures may need optimization because the high concentrations of chlorine disinfectant promote the formation of high levels of disinfection byproducts (DBPs). When chlorine doses up through the 200 mg/L as Cl2 range relevant to the current practice were applied to spinach and lettuce, significant DBP formation was observed, even within 5 min at 7 °C. Concentrations of volatile chlorinated DBPs in washwater were far higher than typically observed in disinfected drinking water (e.g., 350 μg/L 1,1-dichloropropanone). However, these DBPs partitioned to the aqueous phase and so represent a greater concern for the disposal or reuse of washwater than for consumer exposure via food. The volatile DBPs represent the low-yield, final products of chlorination reactions with multiple biomolecular precursors. The initial, high-yield transformation products of such reactions may represent a greater concern for consumer exposure because they remain bound within the biopolymers in food and would be liberated during digestion. Using protein-bound tyrosine as an example precursor, the concentrations of the initial 3-chlorotyrosine and 3,5-dichlorotyrosine transformation products from this one precursor in the leaf phase were comparable to, and, in the case of some lettuces, exceeded, the aggregate aqueous concentration of volatile DBPs formed from multiple precursors. Chlorotyrosine formation increased when spinach was shredded due to the greater accessibility of chlorine to proteins in the leaf interiors. The cytotoxicity of chlorotyrosines to Chinese hamster ovary cells was higher than any of the trihalomethanes regulated in drinking water.

Impact of ozonation and biologically enhanced activated carbon filtration on the composition of micropollutants in drinking water.

A pilot-scale drinking water treatment process for Songhua River, including conventional treatment (coagulation-settlement and rapid sand filtration), ozonation, biological enhanced activated carbon (BEAC) filtration, and chlorination disinfection, was carried out in this study. To investigate the impact of ozonation and BEAC filtration on removing the composition of micropollutants in drinking water, we detected the micropollutant composition from each stage of the treatment process by non-targeted analysis using a GC-MS technique and compared the results between effluents of single BEAC and O3-BEAC processes. Aromatic compounds and esters could be abated efficiently during single BEAC filtration via biodegradation and adsorption; however, possible metabolic products (i.e., alkenes) were formed by biodegradation. Comparatively, O3-BEAC process could reduce micropollutants much more significantly than single BEAC process especially for aromatic compounds including substituted benzenes and polycyclic aromatic hydrocarbons (PAHs) without the formation of metabolic products through the coupling effect of oxidation, biodegradation, and adsorption, suggesting that ozonation improved the removal potential of micropollutants in the BEAC process. In addition, conventional and novel chlorinated disinfection by-products were also measured during post-chlorination.

Enhanced formation of chlorinated disinfection byproducts in the UV/chlorine process in the presence of benzophenone-4

Benzophenone-4 (BP4) is UV-filter that is widely in sunscreens and cosmetics to prevent skin damage from sunlight exposure. Washing off of BP4 from the human body in swimming pools represents a direct source of BP4 in the environment. In this study, we investigated the transformation of BP4 by free chlorine, chloramine, and UV/chlorine, which can be found in swimming pool water. It was found that BP4 can be rapidly removed by both chlorine and chloramine treatment, but only chlorination led to appreciable formation of chlorinated disinfection by-products (DBPs), such as dichloroacetic acid and trichloroacetic acid. However, chloramination of BP4 resulted in higher levels of chlorinated intermediates, which were relatively recalcitrant to further chlorination. The UV/chlorine process was significantly more efficient than the chlorine treatment alone for BP4 removal and resulted in trace chlorinated intermediates and formation of DBPs. Radical scavenger tests revealed that the removal of BP4 in the UV/chlorine process was mostly ascribed to reactions with the Cl and OH generated from HClO photolysis. The presence of methanol as a radical scavenger resulted in incomplete removal of BP4 in the UV/chlorine process and enhanced the formation of DBPs. The increase in DBP formation was because the residual BP4 can be exited to a triplet state (3BP4∗) upon UV irradiation. 3BP4∗ subsequently reacted with O2 to form 1O2, a reactive oxygen species that generated DBPs by reacting with chlorinated intermediates in water. All benzophenone-type UV-filters may have similar photochemical activity and thus influence the transformation of other organics in sunlit surface water environments.

Susceptibility of the Algal Toxin Microcystin-LR to UV/Chlorine Process: Comparison with Chlorination.

Microcystin-LR (MC-LR), an algal toxin (cyanotoxin) common in sources of drinking water, poses a major human health hazard due to its high toxicity. In this study, UV/chlorine was evaluated as a potentially practical and effective process for the degradation of MC-LR. Via mass spectrometry analysis, fewer chlorinated-MC-LR products were detected with UV/chlorine treatment than with chlorination, and a transformation pathway for MC-LR by UV/chlorine was proposed. Different degrees of rapid degradation of MC-LR were observed with varying pH (6-10.4), oxidant dosage (0.5-3 mg L-1), natural organic matter (0-7 mg L-1), and natural water sources. In contrast to the formation of primarily chloroform and dichloroacetic acid in deionized water where MC-LR serves as the only carbon source, additional chlorinated disinfection byproducts were produced when sand filtered natural water was used as a background matrix. The UV/chlorine treated samples also showed quantitatively less cytotoxicity in vitro in HepaRG human liver cell line tests than chlorination treated samples. Following 16 min (96 mJ cm-2) of UV irradiation combined with 1.5 mg L-1 chlorine treatment, the cell viability of the samples increased from 80% after exposure to 1 mg L-1 MC-LR to 90%, while chlorination treatment evidenced no reduction in cytotoxicity with the same reaction time.

PPCP Degradation by Chlorine-UV Processes in Ammoniacal Water: New Reaction Insights, Kinetic Modeling, and DBP Formation.

The combination of chlorine and UV (i.e., chlorine-UV process) has been attracting more attention in recent years due to its ready incorporation into existing water treatment facilities to remove PPCPs. However, limited information is available on the impact of total ammonia nitrogen (TAN). This study investigated two model PPCPs, N,N-diethyl-3-toluamide (DEET) and caffeine (CAF), in the two stages of the chlorine-UV process (i.e., chlorination and UV/chlor(am)ine) to elucidate the impact of TAN. During chlorination, the degradation of DEET and CAF was positively correlated with the overall consumption of total chlorine by TAN. Reactive nitrogen intermediates, including HNO/NO- and ONOOH/ONOO-, along with •OH were identified as major contributors to the removal of DEET and CAF. During UV irradiation, DEET and CAF were degraded under UV/chlorine or UV/NH2Cl conditions. •OH and •Cl were the major reactive species to degrade DEET and CAF under UV/NH2Cl conditions, whereas •OCl played a major role for degrading CAF under UV/chlorine conditions. Numerical models were developed to predict the removal of DEET and CAF under chlorination-UV process. Chlorinated disinfection byproducts were detected. Overall, this study presented kinetic features and mechanistic insights on the degradation of PPCPs under the chlorine-UV process in ammoniacal water.

A Review of Ozone Systems Costs for Municipal Applications. Report by the Municipal Committee – IOA Pan American Group

ABSTRACTOzone has proven effective in improving water treatment plant performance, increasing customer satisfaction, and meeting increasingly stringent regulatory requirements. The benefits include disinfection; reducing chlorine disinfection by-products; micro-coagulation; enhanced filter performance; biological filtration; oxidation of iron, manganese, sulfide, taste- and odor-causing compounds, pharmaceuticals and personal care products (PPCPs), and endocrine disrupting compounds (EDCs). Despite the effectiveness of ozone in water treatment, a perception remains that ozone may be too expensive for consideration at many water treatment facilities. This paper presents an evaluation by the Municipal Committee of the International Ozone Association (IOA-MC) that aims to provide a realistic assessment of the current capital and operating costs of ozone in the North American water treatment practice. A general strategy is proposed for developing preliminary estimates of ozone capital and operating costs that could be used by engineers and/or owners for planning purposes. The information presented may benefit utilities, managers, and engineers engaged in the evaluation of treatment options.

17β-estradiol as precursors of Cl/Br-DBPs in the disinfection process of different water samples

During chlorine disinfection process, reactions between the disinfectant and 17β-estradiol (E2) lead to the formation of halogenated disinfection byproducts (DBPs) which can be a risk to both ecosystem and human health. The degradation and transformation products of E2 in sodium hypochlorite (NaClO) disinfection processes of different water samples were investigated. The reaction kinetics research showed that the degradation rates of E2 were considerably dependent on the initial pH value and the types of water samples. In fresh water, synthetic marine aquaculture water and seawater, the reaction rate constant was 0.133 min−1, 2.067 min−1 and 2.592 min−1, respectively. The reasons for the above phenomena may be due to the different concentrations of bromide ions (Br−) in these three water samples which could promote the reaction between NaClO and E2. Furthermore, Br− could also cause the formation of brominated DBPs (Br-DBPs). The main DBPs, reaction centers and conceivable reaction pathways were explored. Seven halogenated DBPs have been observed including three chlorinated DBPs (Cl-DBPs) and four Br-DBPs. The active sites of E2 were found to be the pentabasic cyclic ring and the ortho position of the phenol moiety as well as C9-C10 position. The identified Cl/Br-DBPs were also confirmed in actual marine aquaculture water from a shrimp pond. The comparison of bio-concentration factors (BCF) values based on calculation of EPI-suite showed that the toxicities of the Br-DBPs were stronger than that of their chloride analogues. The absorbable organic halogens (AOX) analysis also suggested that the DBPs produced in the marine aquaculture water were more toxic than that in the fresh water system.

The dependence of chlorine decay and DBP formation kinetics on pipe flow properties in drinking water distribution

Simultaneous chlorine decay and disinfection byproduct (DBP) formation have been discussed extensively because of their regulatory and operational significance. This study further examines chemical reaction variability in the water quality changes under various hydrodynamic conditions in drinking water distribution. The variations of kinetic constant for overall chlorine decay (kE) and trihalomethane (THM) formation were determined under stagnant to turbulent flows using three devices of different wall demand and two types of natural organic matters (NOM) in water. The results from the comparative experiments and modeling analyses show the relative importance of wall demand (kw), DBP-forming chlorine decay (kD), and other bulk demand (kb') for pipe flows of Re = 0–52500. It is found that chlorine reactivity of virgin NOM is the overriding factor. Secondly, for tap water NOM of lower reactivity, pipe flow properties (Re or u) can significantly affect kE, the THM yield (T), formation potential (Y), and the time to reach the maximum THM concentration (tmax) through their influence on kinetic ratio kD(kb'+kw). These observations, corroborating with turbidity variations during experiments, cannot be explained alone by chlorine dispersion to and from the pipe wall. Mass exchanges through deposition and scale detachment, most likely being flow-dependent, may have contributed to the overall chlorine decay and DBP formation rates. Thus for the simultaneous occurrence of chlorine decay and DBP formation, model considerations of NOM reactivity, pipe types (wall demand), flow hydraulics, and their interactions are essential.

Effects of phosphate-enhanced ozone/biofiltration on formation of disinfection byproducts and occurrence of opportunistic pathogens in drinking water distribution systems

The effects of ozone-biologically activated carbon (O3-BAC) treatment with various phosphate doses (0, 0.3 or 0.6 mg/L) were investigated on the formation of disinfection by-products (DBPs) and occurrence of opportunistic pathogens (OPs) in drinking water distribution systems (DWDSs) simulated by annular reactors (ARs). It was found that the lowest DBPs and the highest inactivation of OPs such as Mycobacterium spp., Mycobacterium avium, Aeromonas spp., Pseudomonas aeruginosa and Hartmanella vermiformis, occurred in the effluent of the AR with 0.6 mg/L phosphate addition. Based on the results of different characterization techniques, for the AR with 0.6 mg/L phosphate-enhanced O3-BAC treatment, dissolved organic carbon in the influent exhibited the lowest concentration and most stable fraction due to the improved biodegradation effect. Moreover, the total amount of suspended extracellular polymeric substances (EPS) in the bulk water of the AR decreased greatly, resulting in the lowest chlorine consumption and DBPs formation in the AR. In Fourier transform infrared spectra of the suspended EPS, the amide II band (1600-1500 cm−1) disappeared and the protein/polysaccharide ratio decreased remarkably, indicating the destruction of protein and a decrease in hydrophobicity. Moreover, β-sheets and α-helices in the protein secondary structures were degraded while the random coils increased sharply as phosphate addition increased to 0.6 mg/L, inhibiting microbial aggregation and hence weakening the chlorine-resistance capability. Thus, most of the OPs in suspended biofilms were more easily inactivated by residual chlorine, resulting in the lowest OPs occurrence in the effluent of the AR. Our findings indicated that enhancing the efficiency of the BAC filter by adding phosphate is a promising method for improving water quality in DWDSs.

Effect of disinfectant residual on the interaction between bacterial growth and assimilable organic carbon in a drinking water distribution system

Public health is threatened by deteriorated water quality due to bacterial regrowth and uncontrolled growth-related problems in drinking water distribution systems (DWDSs). To investigate the scope of this problem, a two-year field study was conducted in south China. The amount of assimilable organic carbon (AOC), total cell concentrations (TCC), and intact cell concentrations (ICC) of water samples were determined by flow cytometry. The results indicated that ICC was significantly correlated to AOC concentration when the chlorine concentration was less than 0.15 mg/L, and ICC was lower at chlorine concentrations greater than 0.15 mg/L, suggesting that free chlorine level had effect on AOC and ICC. To further analyze the effect of disinfectant on AOC and bacterial growth, we designed an orthogonal experiment with different dosages of two commonly used disinfectants, chlorine and chloramine. The results demonstrated that high concentrations of free chlorine (＞0.15 mg/L) and chloramine (＞0.4 mg/L) were associated with relatively low proportions of intact cells and cultivable bacteria. Compared with chlorine, chloramine tended to cause lower AOC level and intact cells, likely because the chlorinated disinfection byproducts (DBPs) were more easily absorbed by bacteria than the chloraminated DBPs. Based on the statistical analysis of 240 water samples, ICC was limited when AOC concentration was less than 135 μg/L, while temperature and the number of small-size particles showed positive effects on ICC (P＜0.05). We conclude that the use of chloramine and controlling particle numbers should be suitable strategies to limit bacterial regrowth.

Degradation of lipid regulators by the UV/chlorine process: Radical mechanisms, chlorine oxide radical (ClO•)-mediated transformation pathways and toxicity changes

Degradation of three lipid regulators, i.e., gemfibrozil, bezafibrate and clofibric acid, by a UV/chlorine treatment was systematically investigated. The chlorine oxide radical (ClO•) played an important role in the degradation of gemfibrozil and bezafibrate with second-order rate constants of 4.2 (±0.3) × 108 M−1 s−1 and 3.6 (±0.1) × 107 M−1 s−1, respectively, whereas UV photolysis and the hydroxyl radical (HO•) mainly contributed to the degradation of clofibric acid. The first-order rate constants (k′) for the degradation of gemfibrozil and bezafibrate increased linearly with increasing chlorine dosage, primarily due to the linear increase in the ClO• concentration. The k′ values for gemfibrozil, bezafibrate, and clofibric acid degradation decreased with increasing pH from 5.0 to 8.4; however, the contribution of the reactive chlorine species (RCS) increased. Degradation of gemfibrozil and bezafibrate was enhanced in the presence of Br−, whereas it was inhibited in the presence of natural organic matter (NOM). The presence of ammonia at a chlorine: ammonia molar ratio of 1:1 resulted in decreases in the k′ values for gemfibrozil and bezafibrate of 69.7% and 7%, respectively, but led to an increase in that for clofibric acid of 61.8%. Degradation of gemfibrozil by ClO• was initiated by hydroxylation and chlorine substitution on the benzene ring. Then, subsequent hydroxylation, bond cleavage and chlorination reactions led to the formation of more stable products. Three chlorinated intermediates were identified during ClO• oxidation process. Formation of the chlorinated disinfection by-products chloral hydrate and 1,1,1-trichloropropanone was enhanced relative to that of other by-products. The acute toxicity of gemfibrozil to Vibrio fischeri increased significantly when subjected to direct UV photolysis, whereas it decreased when oxidized by ClO•. This study is the first to report the transformation pathway of a micropollutant by ClO•.

Formation and speciation of disinfection byproducts in desalinated seawater blended with treated drinking water during chlorination

Desalinated seawater containing bromide ion (Br−) blended with drinking water may produce brominated disinfection byproducts (Br-DBPs) during chlorination, which would pose a potential threat to human health when incorporated into the municipal water supply system. This study investigated the formation and speciation of twenty-one DBPs during chlorination in two desalinated seawater blends, i.e., treated drinking water blended with reverse osmosis (RO) permeate and post-treatment (PT) product water. After chlorination, the number and concentrations of DBPs formed in the desalinated seawater obviously enhanced, with chlorinated DBPs (Cl-DBPs) dominating. Sixteen DBPs were found in both RO and PT blends samples during chlorination, in which haloacetic acids (HAAs) had the highest concentration, followed by trihalomethanes (THMs) and halogen acetonitriles (HANs). When the volume of desalinated seawater in the blends was increased, the transformation from Cl-DBPs to Br-DBPs was observed for THMs and HANs, indicating that Br− was more easily incorporated into THMs and HANs than HAAs. Additionally, more Br− participated in the DBPs formation per unit dissolved organic carbon and Br-DBPs/DBPs increased, when the blended ratio of the desalinated seawater increased. The DBP-associated toxicity in the blends was estimated based on the toxicity-weighted concentration with Br-HANs as the predominant contributor, followed by Cl-HAAs.

Characterization of brominated disinfection byproducts formed during chloramination of fulvic acid in the presence of bromide

To date, study on the speciation of brominated disinfection byproducts (Br-DBPs), which have higher cytotoxicity and genotoxicity than their analogous chlorinated DBPs (Cl-DBPs), formed in chloramination is still limited. In this study, the previous unknown Br-DBPs formed during chloramination of artificial drinking water were explored with electrospray ionization ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). In total, 193 formulae of one bromine containing Br-DBPs and 5 formulae of two bromine containing Br-DBPs were detected in the chloraminated artificial drinking water sample. Compared to Br-DBPs formed in chlorination, Br-DBPs formed in chloramination have relatively high O/C ratio for the same nominal molecular mass. More than 63% of the Br-DBPs formed during chloramination can be classified as aromatic molecules or polycyclic aromatic molecules, according to their modified aromaticity index (AImod). Further investigation on the change of precursor SRFA molecules during chloramination showed that SRFA molecules with high O/C ratio and low H/C ratio were more reactive and decreased significantly in relative abundance during chloramination. Precursor SRFA molecules with high degree of oxidation and high unsaturation were preferred to form Br-DBPs during chloramination. The results reported in this study provide valuable information on Br-DBPs formed during chloramination and may help us in minimizing DBPs during chloramination.