Effects of chlorine dose on the composition and characteristics of chlorinated disinfection byproducts in reclaimed water

During chlorination of reclaimed water, the dose of chlorine used can influence the formation of chlorinated disinfection by-products (Cl-DBPs). We used non-targeted screening by Orbitrap mass spectrometry to identify Cl-DBPs in samples of chlorinated reclaimed water, and found that chlorination was likely to form slightly oxidized unsaturated aliphatic compounds and polycyclic aromatic compounds. Increasing the chlorine dose increased the proportion of polycyclic aromatic Cl-DBPs containing one chlorine atom (Cl₁-DBPs) and highly oxidized unsaturated aliphatic Cl-DBPs containing two chlorine atoms (Cl₂-DBPs). In addition, increasing the chlorine dose first decreased and then increased the proportion of Cl₁-DBPs with aromatic index values >0.5 and increased the proportion of Cl₂-DBPs with aromatic index values <0.5. Increasing the chlorine dose increased double bond equivalent minus oxygen values of Cl₁-DBPs and decreased the double bond equivalent minus oxygen values of Cl₂-DBPs, while the nominal oxidant state of carbon decreased for Cl₁-DBPs and increased for Cl₂-DBPs. In considering the possible precursors of Cl-DBPs and their reaction pathways, substitution reactions occurred more readily with aliphatic compounds and addition reactions occurred more readily with aromatic precursors. When the chlorine dose is increased, more Cl₂-DBPs may be formed by substitution. Overall, the chlorine dose influences Cl-DBP formation and composition and should be taken into account during water treatment.

Characteristics of the formation and toxicity index of nine newly identified brominated disinfection byproducts during wastewater ozonation

Ozonation plays an important role in wastewater treatment for reuse. However, the toxicity of wastewater treated with ozone considerably increases with bromide (Br^-) concentration >100 μg/L. Nine newly identified brominated disinfection byproducts (Br-DBPs) that are highly toxic in ozonated Br^--containing wastewater were found in our recent work, including 2-bromostyrene, 1-bromo-1-phenylethylene, 2-bromobenzaldehyde, 3-bromobenzaldehyde, 4-bromobenzaldehyde, 2-bromophenylacetonitrile, 3-bromophenylacetonitrile, 4-bromophenylacetonitrile, and 2,4,6-tribromophenol. In the present study, the formation and calculated toxicity index of the nine newly identified Br-DBPs were evaluated. The correlations between the water quality index and the formation of nine Br-DBPs were also analyzed. With the increase of ozone dosage, the concentrations of bromostyrenes, 3-bromobenzaldehyde, 4-bromobenzaldehyde, 2-bromophenylacetonitrile, and 2,4,6-tribromophenyl in the ozonated samples gradually increased. With the increase of Br^- concentration, the concentrations of bromostyrene, 2-bromobenzaldehyde, and 2,4,6-tribromophenol gradually increased. With the increase of NH₄⁺ concentration, the concentrations of bromophenylacetonitriles gradually increased. Among the nine Br-DBPs, the bromophenylacetonitriles and 2,4,6-tribromophenol contributed the most to the cytotoxicity index, 2,4,6-tribromophenol and bromostyrenes contributed the most to the genotoxicity index, and bromophenylacetonitriles and bromostyrenes contributed the most to the oxidative damage index. The dissolved organic carbon levels strongly correlated with the formation of 3-bromophenylacetonitrile and 4-bromophenylacetonitrile, and the fluorescence I-V region intensity integral was correlated with the formation of 4-bromobenzaldehyde and 2,4,6-tribromophenol. The results of the present study clarified the formation potential of the nine widely existing newly identified Br-DBPs, confirmed the high calculated toxicity indices, and are of great value for future research on Br-DBPs.

Promotive effects of vacuum-UV/UV (185/254 nm) light on elimination of recalcitrant trace organic contaminants by UV-AOPs during wastewater treatment and reclamation: A review

The use of vacuum-UV/UV (185/254 nm) for trace organic contaminants (TOrCs) elimination during wastewater treatments has attracted much attention. Advanced oxidation processes which combine VUV/UV and additional oxidants (vacuum-UV/UV-based advanced oxidation processes, VUV/UV-AOPs) provide a promising method for eliminating recalcitrant and toxic TOrCs for wastewater reclamation. Researches in this area are increasing but the promoting effects, mechanisms, and influencing factors have not been well summarized. A comprehensive discussion of the limitations of this technique and future research directions is needed. VUV/UV-AOPs have considerable synergistic effects by increasing usage of VUV/UV photons and the oxidant, which increases radical generation. In terms of elimination kinetics, VUV/UV-AOPs outperform conventional UV-AOPs and VUV/UV processes in most cases; a 1.2-87.7-fold increase of the fluence-based kinetic constant is achieved. In terms of energy efficiency per order (EE/O) of TOrCs elimination, the EE/O of VUV/UV-AOPs only accounts for 4% of UV-AOPs and 63% of VUV/UV. However, VUV/UV-AOPs still need to be further investigated. Firstly, although VUV and UV processes have similar radical formation pathways, limited information is available on the quantum yields of photolysis and radical formation of oxidants under VUV irradiation. Secondly, optimization of VUV/UV-AOPs operating conditions, especially oxidant dosage and water-flow patterns, is needed. Thirdly, VUV/UV-AOPs are significantly inhibited by organic and inorganic matters, but the mechanisms of inhibition on VUV/UV scattering, radical quenching, and radical conversion are not well understood. Such inhibition suggests that the use of VUV/UV-AOPs would be limited to relatively clear water treatment, e.g., reverse osmosis effluent for potable water reuse and ultrapure water production. Related research is needed to establish a clearer scheme for VUV/UV-AOPs in terms of the spatial distribution of radical species in the VUV/UV irradiation system and the relevant optimization method for promoting oxidation performance.

Novel chlorinated disinfection byproducts from tannic acid: nontargeted identification, formation pathways, and computationally predicted toxicity

Tannic acid is ubiquitously present in various simulated and real water sources and in wastewater. Various chlorinated disinfection byproducts (Cl-DBPs) are generated via reactions with tannic acid during disinfection with chlorine. We used high-resolution mass spectrometry in combination with our self-developed halogen extraction code to selectively identify Cl-DBPs. Our strategy enabled successful detection of 35 Cl-DBP formulas formed by chlorination of tannic acid, and we identified 26 of these structures. The structures of 17 novel Cl-DBPs are firstly reported here. The reaction pathways of these Cl-DBPs were tentatively proposed. These Cl-DBPs are likely to be generated during chlorination at various chlorine doses, from 0.0 to 10.0 mg-Cl₂/L, and 14 of the 26 Cl-DBPs were detected in simulated drinking water, which implies a relatively high probability of incidence. Quantitative structure-activity relationship toxicity analyses predicted that most of these Cl-DBPs would exhibit much higher acute toxicity than the common DBPs trichloromethane and monochloroacetic acid and that some of these compounds would induce developmental toxicity and be mutagenic, which further emphasizes that these Cl-DBPs should raise concerns. This study broadens our understanding of the Cl-DBPs formed from tannic acid and should prompt wider application of our analytical strategy in environmental matrices.

Elimination of amino trimethylene phosphonic acid (ATMP) antiscalant in reverse osmosis concentrate using ozone: Anti-precipitation property changes and phosphorus removal

Amino trimethylene phosphonic acid (ATMP) was widely used as an antiscalant in reverse osmosis (RO) systems to prevent membrane scaling, and entered RO concentrate at elevated levels. However, phosphonate antiscalants in RO concentrate might aggravate phosphorus pollution, remobilize heavy metals, and adversely affect the sedimentation treatment of RO concentrate. Ozonation was found an efficient method for ATMP treatment. The ATMP removal efficiencies with 8 mg/L ozone were 100% and 86.5% for ultrapure water and RO concentrate, respectively. The ATMP mineralization efficiency reached 46.5% with 8 mg/L ozone. The rate constant for the reaction between ATMP and ozone was 1.92 × 10⁶ M^-1 s^-1. Increasing the pH from 3 to 9 decreased the ATMP removal efficiency from 90% to 30.9% but increased the orthophosphate formation to ATMP removal ratio from 0.11 to 0.48. The ATMP intermediates generated with low ozone dosages exhibited moderate chelation and anti-precipitation capacity, and their chelation and anti-precipitation capacity could be further attenuated by increasing the ozone dosage. Ozonation alone enhanced the growth potential for microalgae in RO concentrate because orthophosphate formed. Combining ozonation and coagulation effectively removed 83.0% of the total phosphorus from RO concentrate. The maximum algal density of Scenedesmus sp. LX1 decreased by 78.7% by ozonation and coagulation.

Synergistic effects of ozone/peroxymonosulfate for isothiazolinone biocides degradation: Kinetics, synergistic performance and influencing factors

Synergistic effects of ozone (O₃) and peroxymonosulfate (PMS, HSO₅^-) for isothiazolinone biocides degradation was studied. The synergistic ozonation process (O₃/PMS) increased the efficiency of methyl-isothiazolinone (MIT) and chloro-methyl-isothiazolinone (CMIT) degradation to 91.0% and 81.8%, respectively, within 90 s at pH 7.0. This is 30.6% and 62.5% higher than the corresponding ozonation efficiency, respectively. Total radical formation value (R_ct,R) for the O₃/PMS process was 24.6 times that of ozonation alone. Calculated second-order rate constants for the reactions between isothiazolinone biocides and (k_SO4-,MIT and k_SO4-,CMIT) were 8.15 × 10⁹ and 4.49 × 10⁹ M^-1 s^-1, respectively. Relative contributions of O₃, hydroxyl radical (OH) and oxidation to MIT and CMIT removal were estimated, which were 15%, 45%, and 40% for O₃, OH and oxidation to MIT, and 1%, 67%, and 32% for O₃, OH and oxidation to CMIT at pH 7.0, respectively. Factors influencing the O₃/PMS process, namely the solution pH, chloride ions (Cl^-), and bicarbonate (HCO₃^-), were evaluated. Increasing the solution pH markedly accelerated O₃ decay and OH and formation, thus weakening the relative contribution of O₃ oxidation while enhancing that of OH and . Cl^- had a negligible effect on MIT and CMIT degradation. Under the dual effect of bicarbonate (HCO₃^-) as inhibitor and promoter, low concentrations (1-2 mM) of bicarbonate weakly promoted MIT and CMIT degradation, while high concentrations (10-20 mM) induced strong inhibition. Lastly, oxidation performance of O₃ and O₃/PMS processes for MIT and CMIT degradation in different water matrices was compared.

Photolysis of free chlorine and production of reactive radicals in the UV/chlorine system using polychromatic spectrum LEDs as UV sources

Recently, ultraviolet light-emitting diodes (UV-LEDs) and chlorine combined system has been employed as an emerging advanced oxidation process. However, UV-LEDs were commonly considered as monochromatic UV sources. In this study, the obvious quantum yields of chlorine photolysis under 265 nm and 280 nm LEDs irradiations were investigated with treating LEDs as polychromatic UV sources. Particularly, Φ_obs-poly of HOCl and OCl⁻ for 265 nm LED were found to be 1.50 and 0.70 mol E^-1, respectively, whereas Φ_obs-poly of HOCl and OCl⁻ for 280 nm LED were 1.28 and 0.64 mol E^-1, respectively. It was identified that Φ_obs-poly were 5.66-14.63 % lower than Φ_obs-mono. This suggests that obvious quantum yield using peak emission wavelength would overestimate the true quantum yield. The production of radical species in LED UV/chlorine systems were determined by the degradation of BA, and illustrated by a mathematical model. Different trends were observed for 265 nm and 280 nm LED UV/chlorine systems as pH increased from 5.0 to 10.0. As pH increased, the formation of OH continuously decreased in both 265 nm and 280 nm LED systems. The formation of Cl increased at neutral pH and more Cl and OH were formed due to the higher molar absorbance coefficient at 280 nm. The chlorine dose-dependent effects on radical productions at pH of 5.0, 7.5 and 10.0 were also assessed. At pH of 5.0, OH was the main radical product and had linear correlation with chlorine dose. At pH of 7.5, the productions of OH and Cl showed similar profiles that increased rapidly at low chlorine dosage and then slowed down.

Understanding the influence of pre-ozonation on the formation of disinfection byproducts and cytotoxicity during post-chlorination of natural organic matter: UV absorbance and electron-donating-moiety of molecular weight fractions

Pre-ozonation can reduce the formation of disinfection byproducts (DBPs) and related adverse effects during subsequent chlorination, but the change of each molecular weight (MW) fraction during each step of combined pre-ozonation and post-chlorination has not been well illustrated. In this study, it was investigated in terms of electron-donating-moieties (EDMs) and UVA₂₅₄ for a representative natural organic matter from Suwanee river (SRNOM). Pre-ozonation suppressed the post-chlorination of SRNOM through oxidation of almost all EDMs (>85%) and UVA₂₅₄ (>90%) in high MW fractions (HMW, >3.2 kDa) and moderate EDMs (43%) and UVA₂₅₄ (72%) in medium MW fractions (MMW, 1.0-3.2 kDa). Furthermore, pre-ozonation led to comparable abatements of EDMs and UVA₂₅₄ for HMW fractions, but lower abatement of EDMs than UVA₂₅₄ for MMW fractions. However, when t-BuOH was used as an ^•OH-quencher, pre-ozonation led to a few instances in which there were higher abatements of EDMs than UVA₂₅₄ for the MMW fraction. These findings suggested that the HMW fraction dominantly underwent ring-cleavage of phenols via O₃- or ^•OH-oxidation. Differently, the MMW fraction underwent ring-cleavage of phenols and quinones-formation via O₃-oxidation, but occasionally underwent hydroxylation and hydro-phenol formation via ^•OH-oxidation. Because of forehand elimination of reactive moieties (e.g. EDMs), pre-ozonation obviously inhibited the formation of representative DBPs (67%-84% inhibition), total organic chloride (51% inhibition) and cytotoxicity (31% inhibition), but may have promoted the formation of carbonyl-DBPs (trichloroacetone and chloral hydrate). When compared with UVA₂₅₄, EDMs would better for surrogate of DBPs formation. EDM abatement surrogated the formation of total organic chlorine (TOCl) and cytotoxicity following a two-stage phase, possibly because the speciation of DBPs and transformation products varied with the abatement of EDMs.

Combining high resolution mass spectrometry with a halogen extraction code to characterize and identify brominated disinfection byproducts formed during ozonation

Ozonation is widely used during water treatment but can generate a variety of toxic disinfection byproducts, especially in the presence of bromide. In the present study, our halogen extraction code was extended and modified to identify bromine isotopic patterns and combined with the R package MFAssignR in selectively identifying brominated disinfection byproducts (Br-DBPs) from high resolution mass spectra. In total, 127 Br-DBPs formed from a Suwannee River natural organic matter (SRNOM) solution were successfully detected from tens of thousands of mass spectrometry peaks. Kendrick mass defect analysis and structural characterization identified 17 structures, 15 of which were identified as brominated carboxylic acids and firstly reported here. Computational model predictions indicated that these brominated carboxylic acids may possess high toxic potencies and raise valid concerns. The adapted halogen extraction code described in this study is a powerful tool for a wider application of analyzing Br-DBPs in complex water matrices and provides an effective technique to characterize and identify these compounds in future studies.

Reduction of cytotoxicity and DNA double-strand break effects of wastewater by ferrate(VI): Roles of oxidation and coagulation

Ferrate(VI) (Fe(VI)) can oxidize individual pollutants, but the pollutant oxidation does not necessarily result in toxicity reduction. Besides, Fe(VI) resultant Fe(III) particles has previously been used to remove heavy metals, but its influence on organic matter and toxicity of wastewater is unknown. This study investigated influence of Fe(VI) on the cytotoxicity and DNA double-strand break (DSB) effects of secondary effluents from wastewater treatment plants to Chinese hamster ovary cells. Adding 5.0 mg/L Fe(VI) as Fe reduced the cytotoxicity and genotoxicity of secondary effluents by 44%-71% and 40%-59%, respectively. The toxicity reduction could be explained by the alleviation of oxidative stress in cells when they were exposed to the Fe(VI)-treated organic matter. Oxidation and coagulation accounted for 60 and 40% of the reductions in cytotoxicity and genotoxicity, demonstrating that both oxidation and coagulation processes can play important roles in reducing toxicity. Molecular weight (MW)-distribution analysis showed that the oxidation process was favored for removing ultraviolet absorbance and fluorescence intensity of organic matter, while the coagulation process removed more dissolved organic carbon (DOC), especially the DOC of fractions with MW < 500 Da. Compared with ferric chloride, the Fe(VI) resultant Fe(III) showed better coagulation performance on organic matter, cytotoxicity and genotoxicity removal, because of the different particle sizes and crystalline structures. This study highlights the benefit of using Fe(VI) in advanced treatment as Fe(VI) reduced the overall toxicity of secondary effluents.

The promotions on radical formation and micropollutant degradation by the synergies between ozone and chemical reagents (synergistic ozonation): A review

The combination of ozone (O₃) and chemical reagents (such as H₂O₂) shows synergies on the radical formation and micropollutant degradation. The promoting performance was associated with various parameters including chemical reagents, micropollutants, solution pH, and the water matrix. In this review, we summarized existing knowledge on radical formation pathways, radical yields, and radical oxidation for different synergistic ozonation processes in various water matrices (such as groundwater, surface water, and wastewater). The increase of radical yields by synergistic ozonation processes was positively related to the increase of O₃-decay, with the increase being 1.1-4.4 folds than ozonation alone (0.2). Thus, synergistic ozonation can promote the degradation rate and efficiency of O₃-resistant micropollutants (second order rate constant, k_P,O3 < 200 M^-1 s^-1), but only slightly affects or even minorly inhibits the degradation of O₃-reactive micropollutants (k_P,O3 > 200 M^-1 s^-1). The water matrices^, such as the dissolved organic matters, negatively suppressed the degradation of micropollutant by quenching O₃-oxidation and radical oxidation (i.e. maximum promoting was decreased by 1.3 times), but may positively extend the promoting effects of synergistic ozonation to micropollutants that are more reactive to O₃ (i.e. k_P,O3 was extended from <200 to <2000 M^-1 s^-1). The formation of bromate would be increased through increasing radical oxidation by synergistic ozonation, but can be depressed by relative higher H₂O₂ as the reducing agent of HOBr/OBr^- intermediate. The increase in bromate formation by O₃/permononsulfate is a considerable concern due to permononsulfate cannot reduce the HOBr/OBr^- intermediate.

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 Ozonated Wastewater to HepG2 Cells: Taking Full Account of Nonvolatile, Volatile, and Inorganic Byproducts

Wastewater ozonation forms various toxic byproducts, such as aldehydes, bromate, and organic bromine. However, there is currently no clear understanding of the overall toxicity changes in ozonated wastewater because pretreatment with solid phase extraction cannot retain inorganic bromate and volatile aldehydes, yet contributions of known ozonation byproducts to toxicity are unknown. Moreover, compared with bromate, organic bromine did not receive widespread attention. This study evaluated the toxicity of ozonated wastewater by taking aldehydes, bromate, and organic bromine into consideration. In the absence of bromide, formaldehyde contributed 96-97% cytotoxicity and 92-95% genotoxicity to HepG2 cells among the detected known byproducts, while acetaldehyde, propionaldehyde, and glyoxal had little toxicity. Both formaldehyde and dibromoacetonitrile drove toxicity among the known byproducts when bromide was present. Toxicity assays in HepG2 cells showed that when secondary effluents contained no bromide, the cytotoxicity of the nonvolatile organic fraction (NVOF) was reduced by 56-70%, and genotoxicity was completely removed after ozonation. However, the formed aldehydes (volatile organic fraction, VOF) led to increased overall toxicity. In the presence of bromide, compared with the secondary effluent, ozonation increased the cytotoxicity of the NVOF_Br from 3.4-4.0 mg phenol/L to 10.3-13.9 mg phenol/L, possibly due to the formation of organic bromine. In addition, considering the toxicity of VOF_Br (VOF in the presence of bromide, including aldehydes, tribromomethane, etc.), the overall cytotoxicity and genotoxicity became much higher than those of the secondary effluent. Although bromate had a limited impact on cytotoxicity and genotoxicity, it caused an increase in oxidative stress in HepG2 cells. Therefore, when taking full account of nonvolatile, volatile, and inorganic fractions, ozonation generally increases the toxicity of wastewater.

[Key Problems and Novel Strategy of Controlling Emerging Trace Organic Contaminants During Municipal Wastewater Reclamation]

Emerging trace organic contaminants (TOrCs) have been ubiquitously detected in municipal wastewater. TOrCs show low concentrations but are usually harmful to aquatic biota and recalcitrant to treatments. The advanced treatment of TOrCs is challenged by four main aspects. First, it is hard to qualify the chemical structure and concentrations of TOrCs, which are typically very low. Second, risk assessment results vary with the selection of target-species and toxicity-endpoints, which makes it hard to regulate priority lists and concentration limits. Third, TOrCs account for less than 0.01% of the total organics in wastewater. Thus, TOrCs cannot be selectively and efficiently removed by conventional treatments. Fourth, it is hard to optimize and manage the treatment trains of TOrCs. In this manuscript, a new strategy combing non-targeting TOrC screening and TOrC "fingerprinting" are proposed to overcome the difficulties of quantification and treatment optimization. Based on this, the standards and regulations to control the TOrCs in reclaimed water should be developed on the basis of elimination efficiency rather than concentration.

Applications of UV/H2O2, UV/persulfate, and UV/persulfate/Cu2+ for the elimination of reverse osmosis concentrate generated from municipal wastewater reclamation treatment plant: Toxicity, transformation products, and disinfection byproducts

Reverse osmosis concentrate (ROC) resulting from treatment of municipal wastewater reclamation involves high concentrations of recalcitrant pollutants. This study evaluated the toxicity of an ROC containing harmful biocides during representative UV synergistic oxidation processes (SOPs) (e.g., UV/hydrogen peroxide (H₂O₂), UV/persulfate (PS), and UV/PS/Cu²⁺). Treated ROC exhibited up to 1.3-2.3 times higher toxicity than the parent compounds such as dodecyl trimethyl ammonium chloride (DTAC) and dodecyl dimethyl benzyl ammonium chloride (DDBAC). Based on the intermediates identification, the major toxic intermediates were screened through silico assessment using the quantitative Ecological Structure-Activity Relationship (ECOSAR) tool. The transformation products (TPs) of hydroxylation and ketonization were the major formed reactions from the UV/PS/Cu²⁺. Also, some cytotoxic TPs were accumulated during the UV/H₂O₂ and UV/PS oxidations, where the carbonaceous-disinfection byproducts were more than the nitrogenous-disinfection byproducts. In the presence of chloride and bromide, chlorate and bromate could be formed during the UV-SOP; they were influenced by the different water matrix in comparison with the different ROC. Also, the formation of the total organic halogen species (TOX) was found to follow this order: UV/PS/Cu²⁺ < UV/H₂O₂ < UV/PS. In this study, the predicted cytotoxicity using the correlation between the TOX and the cytotoxicity was more acceptable than that of the cytotoxicity index method. Further, the R-square of the correlation between the TOX and the cytotoxicity for the UV/H₂O₂ and UV/PS was 0.82 and 0.79, respectively. The predicted cytotoxicity using the TOX correlation method in the ROC could also be used to monitor and prevent the application of different oxidations in municipal wastewater reclamation treatment plants.

[Long-term outcome of 48 unoperated adult patients with Ebstein's anomaly]

Objective: To analyze the long-term outcome of unoperated Ebstein's anomaly (EA) patients aged over 18 years, and to evaluate the related factor of outcomes. Methods: The data of 48 unoperated EA patients from March 2004 to December 2008 in the First Hospital of Tsinghua University, were analyzed. The clinical data of the patients were collected, and patients received regular echocardiography, ECG and chest X-ray examinations. Septal leaflet attachment ratio (SLAr) was calculated based on transthoracic echocardiography imagines. The patients were divided into 3 groups according to SLAr: SLAr<0.45 (n=18), 0.45≤SLAr≤0.60 (n=21) and SLAr>0.60 (n=9). Chest X-ray was used for measurement of cardiothoracic ratio (CTR). Kaplan Meier survival curve was used to calculate the long-term survival rate. Cox proportional hazards regression model was used to analyze the influencing factors of death. Results: There were 19 males, and the mean age at diagnosis was (21.3±11.1) years. Forty-two patients (87.5%) were complicated with arrhythmia, including W-P-W syndrome (n=4), supraventricular tachycardia (n=16), right bundle branch block (n=37), and atrial fibrillation (n=2). The mean duration of follow-up was (148.8±16.8) months, the follow-up rate was 100% with no loss-to-follow up. Nine cases (18.8%) died during follow-up: 6 cases (12.5%) died of cardiac origin, including 3 cases of heart failure, 1 case of arrhythmia, and 2 cases of sudden death; 1 case died of accident; 2 cases died from unknown causes. During the follow-up period, the survival rates were 17/18, 19/21 (90.5%) and 3/9 in the SLAr<0.45, 0.45≤SLAr≤0.60 and SLAr>0.60 group, respectively. According to Kaplan-Meier survival curve, the 5-year survival rates among the three groups were 100%, 100% and 78%, respectively. The 10-year survival rates among the three groups were 94%, 95% and 44%, respectively. Decreased activity tolerance and heart failure were found in 7 patients (6 patients in SLAr>0.60 group and 1 patient in 0.45≤SLAr≤0.60 group). Two patients had cerebrovascular embolism. There were 3 cases with tachyarrhythmia lasting more than 24 hours. Cox regression analysis showed that the risk of death was higher in patients with SLAr>0.60 than in patients with SLAr<0.45 (HR=12.375, 95%CI 1.692-22.146, P=0.015); the risk of death in patients with CTR≥0.65 was 1.306 times higher than that in patients with CTR<0.65 (HR=1.306, 95%CI 0.417-12.754, P=0.038). Conclusions: EA patients often combines with arrhythmia. For unoperated EA patients, SLAr>0.60 and CTR≥0.65 are risk factors of death. EA patients with arrhythmia should be actively treated with drugs or radiofrequency ablation.

Surrogates for on-line monitoring of the attenuation of trace organic contaminants during advanced oxidation processes for water reuse

The large number of trace organic contaminants (TrOCs) in wastewater has resulted in severe concerns to human health. Ozonation and UV/H₂O₂ are widely used to remove TrOCs in wastewater treatment process. Owing to the trace concentrations of TrOCs in wastewater, real-time monitoring of the abatement efficiency of TrOCs through ozonation and UV/H₂O₂ is quite challenging. Instead of a direct measurement of all the TrOCs, the research community has begun to use different surrogates to monitor the attenuation of TrOCs during AOPs. Various surrogates have been developed over the past few decades. In this review, the different types of surrogates are summarized, including ultraviolet spectroscopy and fluorescence spectroscopy. Strong linear correlations have been found for the removal of TrOCs using AOPs, and the abatement of UV absorption spectroscopy at 254 nm or total fluorescence (TF). Moreover, a two-phase linear correlation can better describe the ozone-resistant TrOCs compared with a single linear correlation. Two different kinds of predictive models exist that use surrogates as the input for ozonation: the regression model and kinetic model. The development of the models requires a further understanding of the impacts of water quality, seasonal variations, and storm events on the kinetic parameters. For the in situ monitoring system, the light-emitting diode (LED) is one of the most promising light sources, although the sensitivity and accuracy still need to be improved.

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.

Tracing nitrogenous byproducts during ozonation in the presence of bromide and ammonia using stable isotope labeling and high resolution mass spectrometry

Ammonia has been widely used to inhibit bromate formation during ozonation. However, our recent study found that during ozonation in the presence of bromide and ammonia, toxicity increased under certain conditions that might be attributed to the formation of nitrogenous byproducts. Herein, a typical structural moiety of natural organic matter (NOM), hydroquinone, was evaluated for its potential to form nitrogenous byproducts. During ozonation of the hydroquinone solution containing bromide and ammonia, toxicity of organic byproducts increased significantly. As organic bromine was hardly detected, organic nitrogen was responsible for the increased toxicity. An effective method combining ultra-performance liquid chromatography in tandem with high resolution mass spectrometry (UPLC-HRMS) with an isotope labeling strategy was used to trace nitrogenous byproducts. Four newly formed nitrogenous byproducts were detected, two of which were also detected in Suwannee River natural organic matter (SRNOM) solution treated under the same ozonation condition. Furthermore, the molecular structures and formation pathways of these nitrogenous byproducts were proposed. This study highlights that, despite the widespread use, adding ammonia to inhibit bromate formation during ozonation might increase the toxicity posed by nitrogenous byproducts. During ozonation in the presence of bromide and ammonia, particular attention should be paid to nitrogenous byproducts.

Comprehensive GC×GC-qMS with a mass-to-charge ratio difference extraction method to identify new brominated byproducts during ozonation and their toxicity assessment

Ozonation might increase the risk of wastewater due to byproduct formation, especially in the presence of bromide. In this study, a new analytical method was developed to identify new brominated disinfection byproducts (Br-DBPs) during ozonation, using comprehensive two-dimensional gas chromatography-single quadrupole mass spectrometry (GC×GC-qMS) connected with an electron capture detector in parallel. The obtained data were analyzed using a mass-to-charge ratio (m/z) difference extraction method. Over 1304 DBPs were detected in an ozonated phenylalanine solution. Further screening of 635 DBPs was conducted using the m/z difference extraction method. Finally, the structures for 12 Br-DBPs were confirmed and for 4 Br-DBPs were tentatively proposed by comparison with the NIST library and standard compounds. Eight of the confirmed Br-DBPs are first reported and identified: 2-bromostyrene, 1-bromo-1-phenylethylene, 2-bromobenzaldehyde, 3-bromobenzaldehyde, 4-bromobenzaldehyde, 2-bromophenylacetonitrile, 3-bromophenylacetonitrile and 4-bromophenylacetonitrile. These DBPs and 2,4,6-tribromophenol were detected at nanogram- to microgram-per-liter concentrations during ozonation of authentic water samples like algal bloom waters, wastewater treatment plant effluents, and surface water. The toxicities of these compounds were generally higher than that of bromate. The developed analytical method is a powerful technique for analyzing complex compounds and provides a novel way of identifying byproducts in future studies.

Study on synergistic effect of ozone and monochloramine on the degradation of chloromethylisothiazolinone biocide

In this study, it was found that monochloramine induced the formation of reactive species during ozonation of chloromethylisothiazolinone (CMIT). CMIT was found recalcitrant to chloramine. However, chloramine promoted the degradation of CMIT by ozonation significantly. Hydroxyl radicals contributed most to CMIT degradation (87%) during ozone/chloramine synergistic oxidation process (SOP). The hydroxyl radical exposure during ozone/chloramine SOP was around 7.9 times higher than that of ozonation process. The hydroxyl radical yield of ozone/chloramine SOP was estimated to be 32%. The reaction mechanisms between ozone and chloramine were postulated to include the oxygen transfer reaction to form singlet oxygen, and the formation of hydroxyl radical by the insertion pathway or electron transfer pathway. Chloramine dosage and pH are essential influencing factors. The degradation of CMIT increased from 41% to 74% with increasing chloramine dosage (0-20 μM), and then decreased to 65% when chloramine dosage continually increased to 40 μM. Ozone/chloramine SOP showed better performance at acidic or neutral conditions than basic condition. Based on the intermediates identified, the degradation pathway of CMIT during ozone/chloramine SOP included the oxidation of sulfur atom and the substitution of chlorine group by hydroxyl group. The oxidation of sulfur atom induced lower toxicities of transformation products. The toxicities of hydroxylation products were lower to fish and algae, but higher to daphnia. Based on the GC-ECD results, only trichloromethane (1.94 μg/L) was detected after ozone/chloramine SOP, accounting for 0.17% (μM/μM) of the CMIT removal.

Non-volatile disinfection byproducts are far more toxic to mammalian cells than volatile byproducts

Water is often chlorinated to protect public health, but chlorination causes harmful disinfection byproducts to form. Currently available in vitro assays generally determine non-volatile disinfection byproduct (NVDBP) toxicities because of the limitation of pretreatments used, but chemical analyses and regulations are focused on volatile disinfection byproducts (VDBPs) such as trihalomethanes. The gap of VDBP toxicities have been of concern for some time. In this study, we extracted VDBPs from two chlorinated effluent organic matters and one chlorinated natural organic matter, using a helium aeration-liquid nitrogen condensation system, and systematically assessed the VDBP and NVDBP toxicities to mammalian cells. VDBPs accounted for 10%-20% of the total organic halogen concentrations in three chlorinated water samples. VDBPs were much less cytotoxic, caused fewer DNA double-strand breaks, induced less reactive oxygen species and DNA/RNA oxidative damage marker of 8-hydroxyl(deoxy)guanosine in cells than did NVDBPs. Moreover, by collecting the VDBPs, toxicity measurement of the full range of DBPs was achieved. Cytotoxicity, reactive oxygen species and 8-hydroxyl(deoxy)guanosine levels were significantly higher for cells exposed to the mixture of VDBPs and NVDBPs than only NVDBPs, but not by large percentages (20%-30% for cytotoxicity), suggesting NVDBPs mainly contributed to the toxicity of chlorinated water. Our study suggested that future research should focus more on NVDBP toxicity and identifying toxicity drivers from NVDBPs.

[Adsorption of Sb(Ⅴ) in Water by Natural Pyrite: Performance and Mechanism]

The adsorption performance of three iron ores (pyrite, hematite, and magnetite) on Sb(Ⅴ) was compared and pyrite was shown to exhibit the highest adsorption performance. The effects of particle size, concentration, and pH on the adsorption performance were investigated with pyrite as the absorbent. The rejection of Sb(Ⅴ) was the highest (>80%) when pyrite (particle size <0.074 mm) was used as the absorbent with a concentration of 1 g ·L^-1 and pH=7. The ion competition experiment indicated that PO₄^3- can inhibit the adsorption of Sb(Ⅴ), while SO₄^2- and CO₃^2- have no significant effects on the adsorption of Sb(Ⅴ) because PO₄^3- can compete with Sb(Ⅴ) for active adsorption sites on the surface of pyrite. The results also showed that the quasi-second-order kinetic model and Langmuir model can better simulate the adsorption process, which shows a single-layer adsorption behavior and chemisorption plays a main role in the rejection of Sb(Ⅴ). FTIR analysis suggested that the removal of Sb(Ⅴ) by pyrite was a coordinated ion exchange reaction. EDS and XPS results further confirmed that Sb(Ⅴ) was adsorbed on the surface of pyrite and was not reduced to Sb(Ⅲ), which is more toxic.

Degradation of non-oxidizing biocide benzalkonium chloride and bulk dissolved organic matter in reverse osmosis concentrate by UV/chlorine oxidation

Non-oxidizing biocide that is used to inhibit the microorganism growth on RO membrane, are observed to be high concentration and toxic in RO concentrate. The synergistic oxidation process (SOP) of UV/chlorine was investigated to simultaneously reduced the content (60.2 %) and toxicity (57.0 %) of a representative biocide dodecylbenzyldimethylammonium chloride (DDBAC) in real RO concentrate, with a UV fluence 1080 mJ/cm² and chlorine dose 20 mg/L. Besides eliminating the DDBAC, UV/chlorine reduced the UVA₂₅₄ and fluorescence of the dissolved organic matters (DOM). The oxidation mechanism was verified to be the radical electrophilic addition rather than the chlorine-electrophilic substitution through the decay of electron-donation moiety and UVA₂₅₄. As results, high molecular weight fractions of DOM (>2k Da, 79.2 %) was cleaved into low molecular weight fractions (<0.4k Da, 18.4 %) and organic halide was formed. Parallel-factor analysis of the fluorescence components suggested that decomposition of the protein-like fluorophore is most likely to surrogate the biocide removal and organic halide formation compared to other fluorophore components and UVA₂₅₄. Accordingly, a portable fluorescence probe with 400 nm excitation and 410-600 nm emission wavelengths was developed as an online surrogate for the DDBAC removal and organic halide formation.