Research progress of disinfection and disinfection by-products in China

Evaluation of the killing effects of UV254 light on common airborne porcine viruses

UV exposure is a common method of disinfection and sterilization. In the present study, the parallel beam test was performed to collect fluids containing infectious viruses using a parallel beam apparatus after UV254 irradiation (0, 0.5, 1, 3, 5, 7, 10, or 20 mJ/cm2). The air sterilization test was performed by irradiating the air in the ducts with UV254 light (0, 1, 2, 3, 4, or 6 mJ/cm2) to collect airborne particles containing viruses through the air sterilization equipment. Furthermore, viral inactivation was assessed based on cytopathic effect (CPE) detection and immunofluorescent assays (IFA). Both the CPE and immunofluorescence signal intensity decreased as the UV254 dose increased. The UV254 doses required to inactivate ASFV (107.75 copies/mL), PRRSV (106.29 copies/mL), and PEDV (107.71 copies/mL) in the water were 3, 1, and 1 mJ/cm2, respectively. The UV254 dose required to inactivate ASFV (104.06 copies/mL), PRRSV (103.06 copies/mL), and PEDV (104.68 copies/mL) in the air was 1 mJ/cm2. This study provides data required for biosecurity prevention and control in swine farms.

Antimicrobial activity and nanoremediation of heavy metals using biosynthesized CS/GO/ZnO nanocomposite by Bacillus subtilis ATCC 6633 alone or immobilized in a macroporous cryogel

BACKGROUND

The world society is still suffering greatly from waterborne infections, with developing countries bearing most of the morbidity and death burden, especially concerning young children. Moreover, microbial resistance is one of the most prevalent global problems that extends the need for self-medication and the healing period, or it may be linked to treatment failure that results in further hospitalization, higher healthcare expenses, and higher mortality rates. Thus, innovative synthesis of new antimicrobial materials is required to preserve the environment and enhance human health.

RESULTS

The present study highlighted a simple and cost-effective approach to biosynthesize a chitosan/graphene oxide/zinc oxide nanocomposite (CS/GO/ZnO) alone and immobilized in a macroporous cryogel as a new antimicrobial agent. Bacillus subtilis ATCC 6633 was used as a safe and efficient bio-nano-factory during biosynthesis. The formation of CS/GO/ZnO was confirmed and characterized using different analyses including ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), selective area diffraction pattern (SADP), Zeta analyses, scanning electron microscope (SEM) and transmission electron microscopy (TEM). GO combined with ZnO NPs successfully and displayed an adsorption peak at 358 nm. The XRD results showed the crystalline composition of the loaded ZnO NPs on GO sheets. FTIR spectrum confirmed the presence of proteins during the synthesis which act as stabilizing and capping agents. The nanocomposite has a high negative surface charge (-32.8 ± 5.7 mV) which increases its stability. SEM and TEM showing the size of biosynthesized ZnO-NPs was in the range of 40-50 nm. The CS/GO/ZnO alone or immobilized in cryogel revealed good antimicrobial activities against B. cereus ATCC 14,579, Escherichia coli ATCC 25,922, and Candida albicans ATCC 10,231 in a dose-dependent manner. The CS/GO/ZnO cryogel revealed higher antimicrobial activity than GO/ZnO nanocomposite and standard antibiotics (amoxicillin and miconazole) with inhibition zones averages of 24.33 ± 0.12, 15.67 ± 0.03, and 17.5 ± 0.49 mm, respectively. The MIC values of the prepared nanocomposite against B. cereus, E. coli, and C. albicans were 80, 80, and 90 µg/ml compared to standard drugs (90, 120 and 150 µg/ml, respectively). According to the TEM ultrastructure studies of nanocomposite-treated microbes, treated cells had severe deformities and morphological alterations compared to the untreated cells including cell wall distortion, the separation between the cell wall and plasma membrane, vacuoles formation moreover complete cell lyses were also noted. In the cytotoxicity test of CS/GO/ZnO alone and its cryogel, there was a significant reduction (p˂0.05) in cell viability of WI-38 normal lung cell line after the concentration of 209 and 164 µg/ml, respectively. It showed the low toxic effect of the nanocomposite and its cryogel on the WI-38 line which implies its safety. In addition, water treatment with the CS/GO/ZnO cryogel decreased turbidity (0.58 NTU), total coliform (2 CFU/100 ml), fecal coliform (1 CFU/100 ml), fecal Streptococcus (2 CFU/100 ml), and heterotrophic plate counts (53 CFU/1 ml) not only in comparison with the chlorine-treated samples (1.69 NTU, 4 CFU/100 ml, 6 CFU/100 ml, 57 CFU/100 ml, and 140 CFU/1 ml, respectively) but also with the raw water samples (6.9 NTU, 10800 CFU/100 ml, 660 CFU/100 ml, 800 CFU/100 ml, and 4400 CFU/1 ml, respectively). Moreover, cryogel significantly decreased the concentration of different heavy metals, especially cobalt compared to chlorine (0.004 ppm, 0.002 ppm, and 0.001 ppm for raw water, chlorine-treated, and cryogel-treated groups, respectively) which helped in the reduction of their toxic effects.

CONCLUSION

This study provides an effective, promising, safe, and alternative nanocomposite to treat different human and animal pathogenic microbes that might be used in different environmental, industrial, and medical applications.

Effects of UV light on physicochemical changes in thermoplastic polyurethanes: Mechanism and disinfection byproduct formation

The presence of microplastics (MPs) products and particles in the environment can significantly impact the human body. Most MPs that enter the environment also enter the water cycle. During sunlight light irradiation (especially ultraviolet (UV) part) or UV disinfection, many of these MPs, particularly those rich in surface functional groups like thermoplastic polyurethanes (TPU), undergo physicochemical changes that can affect the formation of disinfection byproducts (DBPs). This study investigates the physicochemical changes of TPU in water after exposure to UV irradiation and incubation in the dark, as well as the formation of DBPs after chlorination. The results show that TPU undergo chain breakage, oxidation, and cross-linking when exposed to UV irradiation in an aqueous system. This leads to fragmentation into smaller particles, which facilitates the synthesis of DBPs. Subsequent research has demonstrated that the TPU leaching solution produces a significantly higher DBP content than the chlorination of TPU MPs, particularly at high concentrations of CHCl3. Therefore, it is important to give greater consideration to the soluble DBP precursors released by TPU.

Research progress on the generation of NDMA by typical PPCPs in disinfection treatment of water environment in China: A review

The drugs and personal care products in water sources are potential threats to the ecological environment and drinking water quality. In recent years, the presence of PPCPs has been detected in multiple drinking water sources in China. PPCPs are usually stable and resistant to degradation in aquatic environments. During chlorination, chloramination, and ozonation disinfection processes, PPCPs can act as precursor substances to generate N-nitrosodimethylamine (NDMA) which is the most widely detected nitrosamine byproduct in drinking water. This review provides a comprehensive overview of the impact of PPCPs in China's water environment on the generation of NDMA during disinfection processes to better understand the correlation between PPCPs and NDMA generation. Chloramine is the most likely to form NDMA with different disinfection methods, so chloramine disinfection may be the main pathway for NDMA generation. Activated carbon adsorption and UV photolysis are widely used in the removal of NDMA and its precursor PPCPs, and biological treatment is found to be a low-cost and high removal rate method for controlling the generation of NDMA. However, there are still certain regional limitations in the investigation and research on PPCPs, and other nitrosamine by-products such as NMEA, NDEA and NDBA should also be studied to investigate the formation mechanism and removal methods.

Sulfonamide disinfection byproducts exhibited severe toxicity to human commensal bacteria

Many antibiotic disinfection byproducts have been detected but their toxicity has not been evaluated adequately. In this report, the chlorination reaction kinetics of five common sulfamides (SAs), reaction intermediates and their toxicity were investigated. Chlorination of sulfapyridine (SPD), sulfamethazine (SMT), sulfathiazole (STZ), and sulfisoxazole (SIZ) followed the second-order kinetics, and were degraded completely within 10 min. A large number of reaction intermediates were deteced by LC-MS, among which a total of 16 intermediates were detected for the first time. Toxicity of the five SAs chlorination solutions was evaluated separately by examining their effects on the growth rate of S. salivarius K12, a commensal bacterium in the human digestive system. After 30 min chlorination, solutions of SMT, STZ and sulfadiazine (SDZ) each exhibited severe toxicity by inhibiting the bacteria growth completely, whereas the inhibition was only 50 % and 20  % by SIZ and SPD respectively. Based on the comparison between toxicity test results and mass spectra, three SA chlorination intermediates, m/z 187.2 (C10H10N4), m/z 287.2 (C9H7N3O4S2) and m/z 215 (C7H10N4O2S/C12H14N4) were proposed to be the primary toxicants in the chlorination products. Our study demonstrated the power of combined approach of chemical analysis and toxicity testing in identifying toxic disinfection byproducts, and highlighted the ne ed for more research on the toxicity evaluation and risk assessment of antibiotic disinfection byproducts.

Analysis of the seasonal water quality variation at the hydraulic junction of a dual-source water distribution system

The implementation of a dual-source water supply system offers an increased level of reliability in water provision; however, intricate hydraulic dynamics introduce apprehensions regarding water safety at the hydraulic junction. In this study, we gathered data of the water quality at the hydraulic junction of a dual-source water supply system (plant A and plant B, sampling site A10 was near plant A, and sampling site A12 was near plant B) for one year in Suzhou Industrial Park. Our findings indicated that seasonal variations and water temperature exerted significant influence on the composition and formation of disinfection byproducts (DBPs). Notably, during the warmer months spanning from June to September, the concentration of trihalomethanes was the highest at the hydraulic junction, whereas the concentration of residual chloride was the lowest. The analysis on DBPs revealed that more Br-containing precursors in water in plant A resulted in the accumulation of more Br-containing DBPs at A10, whereas the highest concentration of Cl-containing DBPs accumulated at A12. The analysis of the dissolved organic matter (DOM) composition indicated an increase in concentration at A10 and A12 compared with that in plant A and plant B. The highest concentration of humic acids was observed at A10, whereas A12 accumulated the highest concentration of aromatic proteins and microbial metabolites. Owing to the fluctuations in water consumption patterns at the hydraulic junction, the water quality was susceptible to variability, thereby posing an elevated risk. Consequently, extensive efforts are warranted to ensure the maintenance of water safety and quality at this critical interface.

Effect of exposure to disinfection by-products during swimming exercise on asthma-related immune responses

Swimming is a widely practiced exercise in modern society, where there is a heightened interest in health. The exceptional benefits of swimming are well-known, yet the issue of water quality management inevitably arises due to its nature as an aquatic exercise. Several studies reported that chlorine disinfectants commonly used in swimming pool water disinfection could degrade into toxic disinfection by-products (DBPs) and suggested that the DBPs might induce respiratory disorders, including asthma. Conversely, there were also reports that the DBPs had no significant effects on respiratory conditions. In this study, we investigated the influence of swimming exercise and DBPs on asthma. The decomposition products had little effect on the number of T cells in various immune organs. However, swimming exercise was found to increase the cell count in proportion to the exercise duration. Nevertheless, there were no significant changes in other immune cells and the secretion of asthma-related cytokines. These findings indicate that the effects of swimming pool DBPs on respiratory conditions during swimming exercise are either negligible or absent, and instead, the immunological benefits gained through consistent swimming exercise outweigh any potential drawbacks.

Removal of N-nitrosopyrrolidine from GAC by a three-dimensional electrochemical reactor: degradation mechanism and degradation path

Nitrogen-containing disinfection by-products (N-DBPs) produced in the process of drinking water disinfection are widely concerning due to the high cytotoxicity and genotoxicity. It is due to the difficulty of natural degradation of N-DBPs in water and the fact that conventional treatment systems do not effectively treat N-DBPs in drinking water. In this study, N-nitrosopyrrolidine (NPYR) in water was electrocatalytically degraded by a three-dimensional electrode reactor (3DER). This system applied graphite plates as anode and cathode. The granular activated carbon (GAC) was used as third electrode. The degradation of NPYR using a continuous flow three-dimensional electrode reactor was investigated by examining the effects of flow rate, current density, electrolyte concentration, and pollutant concentration on the degradation efficiency, energy consumption, and reaction kinetics of GAC particle electrodes. The results showed that the optimal operating conditions were flow rate = 0.45 mL/min, current density = 6 mA/cm2, Na2SO4 concentration = 0.28 mol/L, and NPYR concentration = 20 mg/L. Under optimal conditions, the degradation of NPYR exceeded 58.84%. The main contributor of indirect oxidation was deduced from free radical quenching experiments. NPYR concentration was measured by GC-MS with DB-5 capillary column, operating in full scan monitoring mode for appropriate quantification of NPYR and intermediates. Based on the identification of reaction intermediates, a possible pathway for the electrochemical oxidation of NPYR on GAC particle electrodes was proposed.

Effects of ozone dose on brominated DBPs in subsequent chlor(am)ination: A comprehensive study of aliphatic, alicyclic and aromatic DBPs

Ozone‒chlor(am)ine is a commonly used combination of disinfectants in drinking water treatment. Although there are quite a few studies on the formation of some individual DBPs in the ozone‒chlor(am)ine disinfection, an overall picture of the DBP formation in the combined disinfection is largely unavailable. In this study, the effects of ozone dose on the formation and speciation of organic brominated disinfection byproducts (DBPs) in subsequent chlorination, chloramination, or chlorination‒chloramination of simulated drinking water were investigated. High-molecular-weight, aliphatic, alicyclic and aromatic brominated DBPs were selectively detected and studied using a powerful precursor ion scan method with ultra performance liquid chromatography/electrospray ionization triple quadrupole mass spectrometry (UPLC/ESI-tqMS). Two groups of unregulated yet relatively toxic DBPs, dihalonitromethanes and dihaloacetaldehydes, were detected by the UPLC/ESI-tqMS for the first time. With increasing ozone dose, the levels of high-molecular-weight (m/z 300-500) and alicyclic and aromatic brominated DBPs generally decreased, the levels of brominated aliphatic acids were slightly affected, and the levels of dihalonitromethanes and dihaloacetaldehydes generally increased in the subsequent disinfection processes. Despite different molecular compositions of the detected DBPs, increasing ozone dose generally shifted the formation of DBPs from chlorinated ones to brominated analogues in the subsequent disinfection processes. This study provided a comprehensive analysis of the impact of ozone dose on the DBP formation and speciation in subsequent chlor(am)ine disinfection.

Residence time and the concentration of microorganism in the ozone contactor: a CFD simulation on chamber deflectors

Disinfection is an important step in deep drinking water treatment technology. This study applies computational fluid dynamics to investigate and optimize the hydrodynamics inside the ozone contactor. ANSYS Fluent was used to solve all the control equations. A step method is used to simulate the residence time distribution. The mean residence time is simulated under the Eulerian framework. The deflectors are installed in chambers to direct flow. The deflectors allow for a more uniform flow and a longer mean residence time within the contactor. The baffling factor showed that the deflectors could reduce the short-circuit effect in the contactor and improve the disinfection efficiency by 34.6% compared to the original reactor. The Morrill factor coefficient is improved by 22.8% compared to the original reactor. According to the Aral-Demirel index, contactors with deflectors are significantly better than other baffle-type contactors. The presence of the deflectors increased the microbial inactivation efficiency from 95.3 to 96.5%. The optimal deflector height should be controlled between 30 and 60 mm.

Traditional methods and biosensors for detecting disinfection by-products in water: A review

In recent years, pollution caused by disinfection by-products (DBPs) has become a global concern. Initially, there were fewer contaminants, and the mechanism of their generation was unclear; however, the number of contaminants has increased exponentially as a result of rapid industrialization and numerous economic activities (e.q., during the outbreak of COVID-19 a surge in the use of chlorinated disinfectants was observed). DBP toxicity results in various adverse health effects and organ failure in humans. In addition, it profoundly affects other forms of life, including animals, plants, and microorganisms. This review comprehensively discusses the pre-treatment methods of traditional and emerging DBPs and the technologies applied for their detection. Additionally, this paper provides a detailed discussion of the principles, applicability, and characteristics of traditional large-scale instrumentation methods (such as gas/liquid/ion chromatography coupled with mass spectrometry) for detecting DBPs based on their respective detection techniques. At the same time, the design, functionality, classification, and characteristics of rapid detection technologies (such as biosensors) are also detailed and analyzed.

Recent progress in identification of water disinfection byproducts and opportunities for future research

Numerous disinfection by-products (DBPs) are formed from reactions between disinfectants and organic/inorganic matter during water disinfection. More than seven hundred DBPs that have been identified in disinfected water, only a fraction of which are regulated by drinking water guidelines, including trihalomethanes, haloacetic acids, bromate, and chlorite. Toxicity assessments have demonstrated that the identified DBPs cannot fully explain the overall toxicity of disinfected water; therefore, the identification of unknown DBPs is an important prerequisite to obtain insights for understanding the adverse effects of drinking water disinfection. Herein, we review the progress in identification of unknown DBPs in the recent five years with classifications of halogenated or nonhalogenated, aliphatic or aromatic, followed by specific halogen groups. The concentration and toxicity data of newly identified DBPs are also included. According to the current advances and existing shortcomings, we envisioned future perspectives in this field.

Effects of disinfection by-products in swimming pool environments on the immunological mechanisms of respiratory diseases

Swimming in pools is a popular and healthy recreational activity. However, potential adverse health effects from disinfection byproduct (DBP) exposure in pool water are concerning. This study evaluated how such DBP exposure affects the respiratory system. DBP exposure was simulated with an animal-specific pool environment model. Experimental animals were exposed to DBPs for a specified duration and frequency over 4 weeks. The wet and dry weights of murine lungs were measured, with no significant differences observed. There were no significant differences in interkeukin (IL)-2/4/10, and interferon-γ levels. However, IL-6 expression decreased in the experimental group. To investigate the effects of DBP exposure on immune cell response, various samples, such as bronchoalveolar lavage fluid, lymph nodes, spleen, and thymus, were collected for T-cell isolation and fluorescence-activated cell sorting. Asthma-related blood cell distribution was analyzed using a complete blood count test; no significant differences were found. Thus, DBP exposure through this model did not induce substantial lung tissue damage, major alterations in cytokine expression (besides IL-6), significant immune cell responses, or changes in asthma-associated blood cell distribution. However, considering earlier results, future studies should focus on specific types, intensity, and duration of exercise that could affect DBP exposure-related immune-inflammatory responses.

Disinfection by-product precursors introduced by sandstorm events: Composition, formation characteristics and potential risks

Sandstorms, a natural meteorological event, occur repeatedly during the dry season and can accumulate large amounts of natural/anthropogenic pollutants during the deposition process, potentially introducing disinfection by-product (DBP) precursors into surface waters. In this study, the characteristics of sandstorm-derived dissolved organic matter (DOM) and its DBP formation potential were elucidated. Overall, sandstorm-derived DOM mainly consisted of low-molecular-weight, low-aromaticity, high-nitrogen organic matter, with a dissolved organic carbon (DOC) release yield of 14.4 mg-DOC/g. The halogenated DBP formation potential (calculated as total organic halogen) of sandstorm-derived DOM was comparable to that of surface water, while the normalized DBP-associated toxicity was 1.96 times higher. Similar to DOM introduced by other depositional pathways, sandstorm-derived DOM also had higher yields of highly cytotoxic DBPs (haloacetaldehydes [HALs], haloacetonitriles [HANs] and halonitromethanes [HNMs]). The average atmospheric deposition flux for DOM during the sandstorm event (50.4 ± 2.1 kg km-2 day-1) was 6.95 times higher than that of dry deposition, indicating a higher probability of contaminant input. Simultaneously, the estimation revealed that the sandstorm will increase the formation potential of toxicity forcing agents, such as HALs, HANs and HNMs, in surface water by 3.87%, 2.39% and 9.04%, respectively. Considering the high frequency of sandstorm events and the sorption of other organic pollutants by sand and dust, the impact of sandstorms on surface water quality should be of concern.

Health risk assessment of heavy metals and disinfection by-products in drinking water in megacities in China: A study based on age groups and Monte Carlo simulations

Heavy metal(loid)s (HMs) and disinfection by-products (DBPs) in drinking water pose risks to human health and jeopardize drinking water. Water-related behaviors vary significantly among different age groups and regions. In this study, the carcinogenic and non-carcinogenic risks of HMs (As, Cd, Cr6+, Cu, Pb, and Zn) and DBPs (bromodichloromethane (BDCM), bromoform, chloroform, dibromochloromethane (DBCM), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA)) in drinking water in two Chinese megacities (Beijing in North China and Guangzhou in South China) via multiple exposure pathways were assessed. The results showed that children aged 9 months to 2 years had a total carcinogenic risk (TCR) and hazard index (HI) above acceptable levels, indicating that despite the drinking water quality in the selected megacities meeting the current Chinese national standards (GB 5749-2022), the health risks of exposure to HMs and DBPs in drinking water for local young children should not be neglected. Specifically, the carcinogenic risk (CR) of exposure to As in drinking water for children < 18-years-old, who were divided into different age groups, was 1.5-2.0- and 4.5-5.9-times higher than the TCR of exposure to DBPs in Beijing and Guangzhou, respectively. Regarding children aged 9 months to 2 years, the exposure to TCAA accounted for the largest proportion (35.6 %) of the TCR of exposure to DBPs in Beijing drinking water, 5.4-times higher than that in Guangzhou; whereas, the TCR of exposure to DBPs in Guangzhou drinking water was predominantly caused by exposure to chloroform, accounting for 40.6 % of the TCR and 1.5-times higher than that in Beijing. In addition, the CR of exposure to DCAA in drinking water in both megacities accounted for a large proportion of the TCR for children aged 9 months to 2 years. Monte Carlo simulations showed that 62.2 % and 42.6 % of the TCR of simultaneous exposure to As and DBPs in drinking water exceeded the acceptable level for sensitive populations, that is, children aged 1-2 years in Beijing (95th percentile = 4.2 × 10-4) and children aged 9-12 months in Guangzhou (95th percentile = 5.2 × 10-4), respectively. This elaborate health risk assessment sheds light on improving the water quality indices to guarantee drinking water safety in China.

Catalytic activity of H2O2 by goethite and lepidocrocite: Insight from 5-bromosalicylic acid removal mechanism and density functional theory calculation (ID:CHEM114760)

We have compared the elimination of 5-bromosalicylic acid (BSA) in the systems of goethite (α-FeOOH)/H₂O₂ and lepidocrocite (γ-FeOOH)/H₂O₂. The results demonstrated that BSA (10 mg L^-1) could be successfully adsorbed on α- and γ-FeOOH (0.5 g L^-1) and then effectively degraded after the addition of H₂O₂ (14.7 mM). BSA adsorption on both α- and γ-FeOOH followed pseudo-second order adsorption kinetic models, with γ-FeOOH having greater adsorption ability than α-FeOOH. In the α-FeOOH/H₂O₂ system, BSA degradation was well fitted with the pseudo-second order kinetics, whereas the oxidation in γ-FeOOH/H₂O₂ system had a two-stage pseudo-first order kinetics. Electron paramagnetic resonance (EPR) results for these two systems revealed the presence of •OH and •OOH, and further tests with radical captures demonstrated their dominance in degrading BSA. Based on the electronic structure analysis, electrons were more easily transferred from the H₂O₂ molecule to the Fe atoms of α-FeOOH, explaining the density functional theory (DFT) calculation results, which showed that α-FeOOH performed better in catalyzing the decomposition of H₂O₂. However, the free radicals are more likely to desorb from γ-FeOOH, which made the γ-FeOOH/H₂O₂ system more efficient in degrading BSA.

Reduction of byproduct formation and cytotoxicity to mammalian cells during post-chlorination by the combined pretreatment of ferrate(VI) and biochar

Ferrate [Fe(VI)] can efficiently degrade various pollutants in wastewater. Biochar application can reduce resource use and waste emission. This study investigated the performance of Fe(VI)/biochar pretreatment to reduce disinfection byproducts (DBPs) and cytotoxicity to mammalian cells of wastewater during post-chlorination. Fe(VI)/biochar was more effective at inhibiting the cytotoxicity formation than Fe(VI) alone, reducing the cytotoxicity from 12.7 to 7.6 mg-phenol/L. The concentrations of total organic chlorine and total organic bromine decreased from 277 to 130 μg/L and from 51 to 39 μg/L, compared to the samples without pretreatment. Orbitrap ultra-high resolution mass spectrometry revealed that the number of molecules of DBPs decreased substantially from 517 to 229 by Fe(VI)/biochar, with the greatest reduction for phenols and highly unsaturated aliphatic compounds. In combination with the substantial reduction of 1Cl-DBPs and 2Cl-DBPs, 1Br-DBPs and 2Br-DBPs were also reduced. Fluorescence excitation-emission matrix coupled with parallel factor analysis suggested that fulvic acid-like substances and aromatic amino acid was obviously reduce likely due to the enhanced oxidation of Fe(IV)/Fe(V) produced by Fe(VI)/biochar and adsorption of biochar. Furthermore, the DBPs generated by electrophilic addition and electrophilic substitution of precursors were reduced. This study shows that Fe(VI)/biochar pretreatment can effectively reduce cytotoxicity formation during post-chlorination by transforming DBPs and their precursors.

Hydroxylation of some emerging disinfection byproducts (DBPs) in water environment: Halogenation induced strong pH-dependency

In this work, the hydroxylation mechanisms and kinetics of some emerging disinfection byproducts (DBPs) have been systematically investigated through theoretical calculation methods. Five chlorophenols and eleven halogenated pyridinols were chosen as the model compounds to study their pH-dependent reaction laws in UV/H₂O₂ system. For the reactions of HO^• with 37 different dissociation forms, radical adduct formation (RAF) was the main reaction pathway, and the reactivity decreased with the increase of halogenation degree. The k_app values (at 298 K) increased with the increase of pH from 0 to 10, and decreased with the increase of pH from 10 to 14. Compared with phenol, the larger the chlorination degree in chlorophenols was, the stronger the pH sensitivity of the k_app values; compared with chlorophenols, the pH sensitivity in halogenated pyridinols was further enhanced. As the pH increased from 2 to 10.5, the degradation efficiency increased at first and then decreased. With the increase of halogenation degree, the degradation efficiency range increased, the pH sensitivity increased, the optimal degradation efficiency slightly increased, and the optimal degradation pH value decreased. The ecotoxicity and bioaccumulation of most hydroxylated products were lower than their parental compounds. These findings provided meaningful insights into the strong pH-dependent hydroxylation of emerging DBPs on molecular level.

Chlorinated nucleotides and analogs as potential disinfection byproducts in drinking water

Identification of emerging disinfection byproducts (DBPs) of health relevance is important to uncover the health risk of drinking water observed in epidemiology studies. In this study, mutagenic chlorinated nucleotides were proposed as potential DBPs in drinking water, and the formation and transformation pathways of these DBPs in chlorination of nucleotides were carefully investigated. A total of eleven chlorinated nucleotides and analogs were provisionally identified as potential DBPs, such as monochloro uridine/cytidine/adenosine acid and dichloro cytidine acid, and the formation mechanisms involved chlorination, decarbonization, hydrolysis, oxidation and decarboxylation. The active sites of nucleotides that reacted with chlorine were on the aromatic heterocyclic rings of nucleobases, and the carbon among the two nitrogen atoms in the nucleobases tended to be transformed into carboxyl group or be eliminated, further forming ring-opening or reorganization products. Approximately 0.2-4.0 % (mol/mol) of these chlorinated nucleotides and analogs finally decomposed to small-molecule aliphatic DBPs, primarily including haloacetic acids, trichloromethane, and trichloroacetaldehyde. Eight intermediates, particularly chlorinated imino-D-ribose and imino-D-ribose, were tentatively identified in chlorination of uridine. This study provides the first set of preliminary evidence for indicating the promising occurrence of chlorinated nucleotides and analogs as potential toxicological-relevant DBPs after disinfection of drinking water.

Removal and transformation of disinfection by-products in water during boiling treatment

Disinfection by-products (DBPs) remain an ongoing issue because of their widespread occurrence and toxicity. Boiling is the most popular household water treatment method and can effectively remove some DBPs. However, the transformation behavior of DBPs during boiling is still unclear, and the key contributors to toxicity have not been identified. In this study, the changes in the concentrations of DBPs in the single-DBP systems and the multi-DBP systems during boiling were monitored, and in-depth discussions on the removal and transformation of DBPs in both systems were carried out. The results showed that boiling was effective in removing volatile DBPs (over 90% for TCAL, TCAN, and DCAN, and over 60% for TCM), but ineffective for non-volatile DBPs (around 20% for TCAA and below 10% for DCAA and MCAA). By hydrolysis and decarboxylation, the transformation occurred among DBPs, i.e., 55% TCAL to TCM, followed by 23% DCAN to DCAA, 22% TCAN to TCAA, and 10% TCAA to TCM. The transformations were found to be significantly influenced by other co-existing DBPs. In multi-DBP systems, the transformations of DCAN to DCAA and TCAN to TCAA were both promoted, while the transformation of TCAN to TCAA was inhibited. Transformation and volatilization are the two processes responsible for DBP removal. Toxicity estimates indicated that boiling was effective in reducing the toxicity of DBPs and improving the safety of the water, despite the interconversion of DBPs in drinking water during boiling. This study emphasized the importance of studying the interconversion behaviors of DBPs in drinking water during boiling and provided practical information for end-use drinking water safety.

Experiments and machine learning-based modeling for haloacetic acids rejection by nanofiltration: Influence of solute properties and operating conditions

Because of potential risks to public health, the presence of haloacetic acids (HAAs) in drinking water is a major concern. Nanofiltration (NF) has shown potential for HAAs rejection, and several factors, namely, membrane properties, solute properties, and operating conditions, have been revealed key roles. However, knowledge of NF separation mechanism by quantifying these factors is limited. This study investigated and modeled NF performance on HAAs rejection. NF performance was experimentally investigated under various transmembrane pressure (TMP), cross-flow velocity (CV), temperature, pH, ionic strength (IS), and HAAs initial feed concentration (C_in). We used machine learning (ML) to understand the mechanism from the perspective of HAAs properties and operating conditions. Multiple linear regression (MLR), support vector machine (SVM), multsilayer perceptron (MLP), extreme gradient boosting (XGBoost), and random forest (RF) models were used. The MLP, XGBoost and RF models achieved significant performance with high R² (0.970, 0.973, and 0.980) and low RMSE (4.71, 4.41, and 3.84). These three models were analyzed using the Shapley Additive explanation (SHAP) to quantify relative contributions of HAAs properties and operating conditions. XGBoost-SHAP produced the most logical results and was the best-performing model for selecting optimal input variables combinations. The results showed that Stokes radius (r_s), logarithmic octanol-water partitioning coefficient (logK_ow), molecular weight (MW), pH, TMP, and temperature are key variables for interpreting NF process. The effects of HAAs properties were ranked as r_s > logK_ow > MW, suggesting significance of size exclusion and hydrophobic interaction. The impact of the operational conditions followed the order pH > TMP > temperature, illustrating that pH was the major influencing operating condition. This study demonstrated significant capacity of ML, which reduced amount of experimental work. In addition, the main operating conditions can be evaluated in terms of their contributions, making ML an efficient tool for risk management and process optimization.

The occurrence, formation and transformation of disinfection byproducts in the water distribution system: A review

Disinfection is an effective process to inactivate pathogens in drinking water treatment. However, disinfection byproducts (DBPs) will inevitably form and may cause severe health concerns. Previous research has mainly focused on DBPs formation during the disinfection in water treatment plants. But few studies paid attention to the formation and transformation of DBPs in the water distribution system (WDS). The complex environment in WDS will affect the reaction between residual chlorine and organic matter to form new DBPs. This paper provides an overall review of DBPs formation and transformation in the WDS. Firstly, the occurrence of DBPs in the WDS around the world was cataloged. Secondly, the primary factors affecting the formation of DBPs in WDS have also been summarized, including secondary chlorination, pipe materials, biofilm, deposits and coexisting anions. Secondary chlorination and biofilm increased the concentration of regular DBPs (e.g., trihalomethanes (THMs) and haloacetic acids (HAAs)) in the WDS, while Br^- and I^- increased the formation of brominated DBPs (Br-DBPs) and iodinated DBPs (I-DBPs), respectively. The mechanism of DBPs formation and transformation in the WDS was systematically described. Aromatic DBPs could be directly or indirectly converted to aliphatic DBPs, including ring opening, side chain breaking, chlorination, etc. Finally, the toxicity of drinking water in the WDS caused by DBPs transformation was examined. This review is conducive to improving the knowledge gap about DBPs formation and transformation in WDS to better solve water supply security problems in the future.

Efficient degradation of N-nitrosopyrrolidine using CoFe-LDH/AC particle electrode via heterogeneous Fenton-like reaction

With the rapid development of drinking water disinfection technology, extensive attentions are paid to the nitrogenous disinfection by-products (N-DBPs) that has strong carcinogenicity, thus their degradation becomes important for the health of human beings. In this work, for the first time, CoFe-LDH material used as particle electrode is proposed to treat trace N-nitrosopyrrolidine (NPYR) in a three-dimensional aeration electrocatalysis reactor (3DAER). The factors on the degradation efficiency and energy consumption of NPYR are systematically investigated, and the results of radical quenching experiments show that the degradation of NPYR is completed by combining with ·OH, ·O₂and direct oxidation together. CoFe-LDH particle electrode plays a vital role in generating ·OH via heterogeneous ‾Fenton-like reaction. Moreover, the adsorbed saturated CoFe-LDH particle electrode can be regenerated by electrochemical action to induce further recycle adsorption and form in-situ electrocatalysis. This work pave a way for the removal of NPYR with high efficiency, low energy conservation and environmental protection.

Fluorescence Detection of Trace Disinfection Byproducts by Ag Nanoprism-Modulated Lanthanide MOFs

Disinfection byproducts (DBPs), as an emerging water pollutant, present increasing concern and risk in public health and water safety. Due to their low concentration levels and inherent similarity in molecular structures, sensitive and accurate determination of DBPs is still a challenge especially for onsite or online detection. Herein, a self-regulated fluorescent probe based on the Ag nanoprism-modified lanthanide metal-organic framework (AgNPR@EuMOF) is designed for trichloroacetic acid (TCAA) detection. The EuMOF is constructed with Eu as the metal node and 5-boronoisophthalic acid as the ligand. By introducing sulfhydryl groups into EuMOF, AgNPR can be anchored on the EuMOF surface through Ag-S bonds, enabling the synthesis of stable AgNPR@EuMOF composites. During the sensing process, the triangle AgNPR will react with the organic halogen molecule, accomplished with the blue shift of surface plasmon resonance absorption peak and the significant change in the fluorescence of EuMOF. This probe can detect TCAA in a wide concentration range (0.1-40 μM) with high sensitivity and specificity. The density functional theory calculation on binding energies between DBPs and AgNPR suggests that TCAA has the largest interaction ability with AgNPR than other DBPs. Moreover, the detection of TCAA in real tap water and swimming pool water is also demonstrated with high accuracy. The reported AgNPR@EuMOF represents one of the pioneer fluorescence probes in DBP detection, which holds great promise for onsite or online analysis of trace DBPs in water.

Bromoacetic acid causes oxidative stress and uric acid metabolism dysfunction via disturbing mitochondrial function and Nrf2 pathway in chicken kidney

Since the outbreak of COVID-19, widespread utilization of disinfectants has led to a tremendous increase in the generation of disinfection byproducts worldwide. Bromoacetic acid (BAA), one of the common disinfection byproducts in the environment, has triggered public concern because of its adverse effects on urinary system in mammals. Nevertheless, the BAA-induced nephrotoxicity and potential mechanism in birds still remains obscure. According to the detected content in the Taihu Lake Basin, the model of BAA exposure in chicken was established at doses of 0, 3, 300, 3000 μg/L for 4 weeks. Our results indicated that BAA exposure caused kidney swelling and structural disarrangement. BAA led to disorder in renal function (CRE, BUN, UA) and increased apoptosis (Bax, Bcl-2, caspase3). BAA suppressed the expression of mitochondrial biogenesis genes (PGC-1α, Nrf1, TFAM) and OXPHOS complex I genes (ND1, ND2, ND3, ND4, ND4L, ND5, ND6). Subsequently, BAA destroyed the expression of Nrf2 antioxidant reaction genes (Nrf2, Keap1, HO-1, NQO1, GCLM, GCLC). Furthermore, renal oxidative damage led to disorder in uric acid metabolism genes (Mrp2, Mrp4, Bcrp, OAT1, OAT2, OAT3) and exacerbated destruction in renal function. Overall, our study provided insights into the potential mechanism of BAA-induced nephrotoxicity, which were important for the clinical monitoring and prevention of BAA.

Current understanding on antibacterial mechanisms and research progress of tea polyphenols as a supplementary disinfectant for drinking water

Disinfection by-products (DBPs) generated during the disinfection of drinking water have become an urgent problem. So, tea polyphenol, a natural green disinfectant, has attracted widespread attention in recent years. This review summarizes the antibacterial mechanism of tea polyphenols and the recent findings on tea polyphenols as disinfectants for drinking water. These studies show that tea polyphenol is an antibacterial agent that works through different mechanisms and can be used as a supplementary disinfectant because of its higher lasting effect and economical cost. The dosage of tea polyphenols as a disinfectant of ultrafiltration effluent is the lowest among all the tea polyphenols disinfection methods, which can ensure the microbial safety of drinking water. This application of tea polyphenols is deemed a practical solution to solving the issue of disinfecting drinking water and reducing DBPs. However, it is necessary to further explore the influence of factors such as pipeline materials on the disinfection process and efficacy to expand the application scope of tea polyphenols. The large-scale application of tea polyphenols still needs to be fine-tuned but with new developments in tea polyphenol purification technology and the long-term need for drinking water that is safe for human consumption, tea polyphenols have good prospects for further development.

Study on the Disinfection Efficiency of the Combined Process of Ultraviolet and Sodium Hypochlorite on the Secondary Effluent of the Sewage Treatment Plant

The combined disinfection process of ultraviolet and sodium hypochlorite has more advantages than the single disinfection method in reducing the disinfectant dosage, shortening the reaction time, and resisting the impact of water quality changes and inhibiting the light reactivation of microorganisms. Given this, using the secondary effluent of a sewage plant as the research object, the disinfection efficiency of the combined process of ultraviolet and sodium hypochlorite was investigated. The experimental results showed that the inactivation effect of UV followed by sodium hypochlorite on fecal coliform and the inhibition of microbial photoreactivation was more significant than that of simultaneous disinfection of UV and sodium hypochlorite disinfection. When the UV dose was 24 mJ/cm2, after disinfection with UV followed by sodium hypochlorite, only 1 mg/L of sodium hypochlorite was required to be added, and a contact reaction time of 1 min for the fecal coliform index to meet the first-Class A emission standard. After disinfection, the effluent’s maximum reactivation rate of fecal coliform was 26.96%. However, the simultaneous disinfection of ultraviolet and sodium hypochlorite required the addition of 3 mg/L of sodium hypochlorite. After disinfection, the maximum reactivation rate of the fecal coliform group reached 30.81%.

Synergistic cytotoxicity of binary combinations of inorganic and organic disinfection byproducts assessed by real-time cell analysis

Chlorine, chlorine dioxide, and ozone are widely used as disinfectants in drinking water treatments. However, the combined use of different disinfectants can result in the formation of various organic and inorganic disinfection byproducts (DBPs). The toxic interactions, including synergism, addition, and antagonism, among the complex DBPs are still unclear. In this study, we established and verified a real-time cell analysis (RTCA) method for cytotoxicity measurement on Chinese hamster ovary (CHO) cell. Using this convenient and accurate method, we assessed the cytotoxicity of a series of binary combinations consisting of one of the 3 inorganic DBPs (chlorite, chlorate, and bromate) and one of the 32 regulated and emerging organic DBPs. The combination index (CI) of each combination was calculated and evaluated by isobolographic analysis to reflect the toxic interactions. The results confirmed the synergistic effect on cytotoxicity in the binary combinations consisting of chlorite and one of the 5 organic DBPs (2 iodinated DBPs (I-DBPs) and 3 brominated DBPs (Br-DBPs)), chlorate and one of the 4 organic DBPs (3 aromatic DBPs and dibromoacetonitrile), and bromate and one of the 3 organic DBPs (2 I-DBPs and dibromoacetic acid). The possible synergism mechanism of organic DBPs on the inorganic ones may be attributed to the influence of organic DBPs on cell membrane and cell antioxidant system. This study revealed the toxic interactions among organic and inorganic DBPs, and emphasized the latent adverse outcomes in the combined use of different disinfectants.

Assessing microbial and chemical exposure risks of Giardia in indoor swimming pool water disinfected by chlorine

Swimming pools adopt chlorination to ensure microbial safety. Giardia has attracted attention in swimming pool water because of its occurrence, pathogenicity, and chlorine resistance. To control Giardia concentrations in pool water and reduce the microbial risk, higher chlorine doses are required during disinfection. Unfortunately, this process produces carcinogenic disinfection byproducts that increase the risk of chemical exposure. Therefore, quantitatively evaluating the comparative microbial vs. chemical exposure risks that stem from chlorination inactivation of Giardia in swimming pool water is an issue that demands attention. We simulated an indoor swimming pool disinfection scenario that followed common real-world disinfection practices. A quantitative microbial risk assessment coupled with a chemical exposure risk assessment was employed to compare the Giardia microbial exposure risk (MER) and the trihalomethane chemical exposure risk (CER) to humans. The results demonstrated a 22% decrease in MER- and CER-induced health exposure risk, from 8.45E-5 at 8:00 to 6.60E-5 at 19:00. Both the MER and CER decreased gradually, dropping to 3.26E-5 and 3.35E-5 at 19:00, respectively. However, the CER exceeded the MER after 18:30 and became the dominant factor affecting the total exposure risk. Past the 18 hr mark, the contribution of trihalomethane CER far exceeded the risk aversion from microbial inactivation, leading to a net increase in total exposure risk despite the declining MER. Swimmers may consider swimming after 19:00, when the total exposure risk is the lowest. Lowering water temperature and/or pH were identified as the most sensitive factors to minimize the overall health exposure risk.

Regrowth potential of chlorine-resistant bacteria in drinking water under chloramination

The regrowth of chlorine-resistant bacteria in drinking water can deteriorate water quality. The study evaluated the relationship between organic carbon and the regrowth potential of chlorine-resistant bacteria remaining in chloraminated water samples. The results showed that the community structure of bacteria changed with the increase of chloramine dosage. The order in which organic carbon utilized by bacteria was affected by the composition of bacterial community. The biodegradable dissolved organic carbon (BDOC), assimilable organic carbon (AOC), bacterial regrowth potential (BRP) and total cell concentration (TCC) in cultivated water sample after disinfection with 1.8 mg/L chloramine increased form 0.22 mg/L, 33.68 µg/L, 2.70 × 10⁵ cells/mL and 3.48 × 10⁴ cells/mL before cultivation to 1.20 mg/L, 193.90 µg/L, 4.74 × 10⁵ cells/mL and 1.46 × 10⁵ cells/mL, respectively. The increase of TCC did not result in the decrease of BDOC, AOC and BRP in the cultivated water samples. The results showed that other biodegradable organic carbon in chloraminated water samples assimilated by residual chlorine-resistant bacteria besides AOC, BDOC, and organic carbon assimilated by indigenous bacteria. AOC, BDOC, and BRP indicators used to characterize the biostability of drinking water were not enough to accurately assess the regrowth potential of chlorine-resistant bacteria remaining in drinking water. It is suggested to supplement the index of TCC in cultivated water samples, which might be able to more accurately evaluate the regrowth potential of chlorine-resistant bacteria remaining in drinking water.

The Supervision and Management Mode of Disinfection Supply Center Improves the Standardization of Sterile Goods Management in Clinical Departments

Background. In daily inspection, the nonstandard management of sterile articles in clinical departments of hospitals often leads to the destruction of the sterilization effectiveness of sterile articles. Therefore, it is necessary to strengthen governance and improve this phenomenon. This study intends to investigate the mode in which the disinfection supply center participates in the supervision and management of the management of sterile items in clinical departments. It played a role in improving the standardization of the management of sterile articles in clinical departments and ensured the closed-loop management of the sterilization effectiveness of sterile articles. Methods. Every quarter, the disinfection supply center of our hospital will inspect the standardized management of sterile articles in all clinical departments of the hospital, mainly including the storage environment and facilities of sterile articles, the cleanliness of storage cabinets, placement principles, whether they are stored by category, and the quality and validity management of sterile articles. The quarterly inspection results were summarized and analyzed to find the existing problems and the causes. The disinfection supply center shall supervise the improvement. After the disinfection supply center inspected the standardized management of sterile articles in all clinical departments of the hospital for the first time according to the inspection contents, under the guidance and assistance of the nursing department and the hospital infection department, it improved the sterile article management system, conducted knowledge training for the whole hospital, and incorporated the standardized management of clinical sterile articles into the quality control inspection of the nursing department. In the later stage, the disinfection supply center is responsible for conducting routine inspection and supervision on the standardized management of sterile articles in all clinical departments of the hospital every quarter according to the inspection contents, including summarizing, analyzing, and urging the clinical departments to achieve the improvement of the management of sterile articles in clinical departments. Results. The standardization of aseptic articles after improvement was significantly higher than before and during improvement, and the qualified rate was significantly different (99.4% vs 97.9% vs 89.5%, $P<0.05$ ). The average number of lost packages caused by nonstandard management in the department was significantly reduced. The average rate of lost sterile packages during and after the improvement was significantly lower than that before the improvement (10.5% vs 97.9% vs 89.5%, $P<0.05$ ). It also effectively reduced the cost caused by the loss of sterile packages. Conclusion. The disinfection supply center participates in the quality control and management of sterile articles in the nursing department and regularly inspects and supervises the management of sterile articles in clinical departments. It can effectively improve the standardized management of sterile articles in clinical departments, ensure the safety of sterile articles, and form a closed loop of sterilization effectiveness.

Insights into metal-organic frameworks HKUST-1 adsorption performance for natural organic matter removal from aqueous solution

Natural organic matter (NOM) has rich halogenation reactive sites, therefore acts as the main precursor of disinfection byproducts (DBPs) in the chlorine disinfection process during drinking water treatment. In this research, high-quality metal-organic framework HKUST-1 is rapidly synthesized by a solvothermal method, and we are the first to report adsorption of aqueous humic acid (HA), representing NOM, and its adsorption behavior, influencing factors, and recycling capability. The crystalline HKUST-1 possessed a microporous framework with a high 1385 m²/g specific surface area, and three-dimensional structure as characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM). 99% removal of 5 mg/L HA was observed at pH 5.8, room temperature, and 0.6 g/L HKUST-1. The maximum capacity was 14.42 mg HA/g HKUST-1 at room temperature. The Langmuir adsorption isotherm, quasi-second-order kinetic model, and thermodynamic parameters accurately describe the spontaneous and disorderly endothermic adsorption of HA by HKUST-1. The desorption regeneration process was accomplished by washing HKUST-1 with NaOH and calcination; it showed that HKUST-1 was viable in three regeneration cycles. The mechanism of HA adsorption by HKUST-1 is electrostatic and synergistic interaction between π-π bonding, and hydrogen bonding. HKUST-1 is a potential treatment strategy to remove NOM.

Strategies for mitigating chlorinated disinfection byproducts in wastewater treatment plants

A case study of 15 wastewater treatment plants (WWTPs) at a full-scale was assessed for the risks of disinfection byproduct (DBP) formation, mainly the regulated trihalomethanes (THMs) and haloacetic acids (HAAs) and chlorate as an inorganic byproduct regulated recently in the EU. Raw wastewater from large, medium/small urban areas were treated with single or combined disinfection processes (i.e., chlorine, peracetic acid (PAA) and ultraviolet (UV) radiation). Sampling was executed once a month over seven months for the medium/small WWTPs and twice a month for the large ones. Due to the potential risk of SARS-CoV-2 contaminated wastewater, several inactivation methods were examined before the DBP analysis. Due to the inactivation step, the stability of THM4 and HAA9 suffered reductions, monitoring their presence only in the effluents after the disinfection treatments. In contrast, chlorate levels remained unchanged after the inactivation treatment; thus both raw wastewater and effluents were examined for their occurrence before disinfection treatments. Results showed that chlorate residues in the raw wastewater varied greatly from undetected levels to as high as 42.2 mg L^-1. As the continuous monitoring of DBPs was performed, a positive correlation with chlorine or chlorine/UV was found. Changes in the physicochemical parameters indicated that the quality of the raw wastewater varied considerably depending on the WWTPs, and it influenced byproduct formation. In all WWTPs, chlorine alone or combined with UV significantly increased the presence of THMs, HAAs, and chlorate levels in the treated effluents. When the same WWTPs changed to PAA or PAA/UV, DBPs were diminished completely. This study highlights the risk of chlorate residues in raw wastewater during the pandemic. It also showed how the chemical risks of DBP formation could be reduced by changing the chlorinated disinfection technologies to PAA or PAA/UV, particularly if reclaimed water is intended for agricultural irrigation to minimize DBP residues.

Formula Assignment Algorithm for Deuterium-Labeled Ultrahigh-Resolution Mass Spectrometry: Implications of the Formation Mechanism of Halogenated Disinfection Byproducts

Ultrahigh-resolution mass spectrometry (UHR-MS) coupled with isotope labeling has attracted significant attention in elucidating the mechanisms of the transformation of dissolved organic matter (DOM). Herein, we developed a novel formula assignment algorithm based on deuterium (D)-labeled UHR-MS, namely, FTMSDeu, for the first time. This algorithm was employed to determine the precursor molecules of halogenated disinfection byproducts (X_n-DBPs) and to evaluate the relative contribution of electrophilic addition and substitution reactions in X_n-DBP formation according to the H/D exchange of DOM molecules. Further, tandem mass spectrometry with homologous-based network analysis was used to validate the formula assignment accuracy of FTMSDeu in the identification of iodinated disinfection byproducts. Electrophilic substitution accounted for 82-98, 71-89, and 43-45% of the formation for Cl-, Br-, and I-containing X_n-DBPs, respectively, indicating the dominant role of the electrophilic substitution in chlorinated disinfection byproducts with low Br and I concentrations. The absence of putative precursors in some X_n-DBPs also suggests that X_n-DBP formation includes secondary reactions (e.g., oxidation and hydrolysis) in addition to the electrophilic addition and/or substitution of halogens. These findings highlight the significance of isotopically labeled UHR-MS techniques in revealing the transformation of DOM in natural and engineered systems.

Disinfection by-product (DBP) research in China: Are we on the track?

Disinfection by-products (DBPs) formed during water disinfection has drawn significant public concern due to its toxicity. Since the first discovery of the trihalomethanes in 1974, continued effort has been devoted on DBPs worldwide to investigate the formation mechanism, levels, toxicity and control measures in drinking water. This review summarizes the main achievements on DBP research in China, which included: (1) the investigation of known DBP occurrence in drinking water of China; (2) the enhanced removal of DBP precursor by water treatment process; (3) the disinfection optimization to minimize DBP formation; and (4) the identification of unknown DBPs in drinking water. Although the research of DBPs in China cover the whole formation process of DBPs, there is still a challenge in effectively controlling the drinking water quality risk induced by DBPs, an integrated research framework including chemistry, toxicology, engineering, and epidemiology is especially crucial.

Efficient synergistic disinfection by ozone, ultraviolet irradiation and chlorine in secondary effluents

Disinfection of secondary effluents is vital to provide a sustainable aquatic environment, minimize microbial risks and guarantee public and environmental safety. This study investigated the effectiveness of six treatment trains including single and combined disinfection processes (i.e., ozone alone, ultraviolet (UV) irradiation alone, chlorine alone, sequential ozone-UV, sequential ozone-chlorine and sequential ozone-UV-chlorine) on bacterial inactivation, as well as bulk water quality parameters such as color, turbidity, absorbance at 254 nm (UV₂₅₄), dissolved organic carbon (DOC) and fluorescence based on samples collected from an actual water reclamation plant (WRP). For the single disinfection processes, when the ozone, UV and chlorine doses reached 5 mg/L, 15 mJ/cm² and 4 mg/L, respectively, the log removal of Escherichia coli (E. coli) reached 5 log. A trailing phenomenon was observed with further increases in the disinfectant dosage. Under the combined treatment scenarios, ozone pretreatment resulted in substantial removal of color, turbidity, UV₂₅₄, fluorescence excitation-emission matrix (FEEM) and chlorine consuming organics, thus enhancing the efficiency of subsequent UV irradiation or chlorine treatments. In the sequential ozone-UV-chlorine experiments, E. coli inactivation reached 7 log with ozone, UV and available chlorine of 3 mg/L, 5 or 10 mJ/cm² and 2.5 mg/L, respectively. On the basis of the results from the actual WRP, the estimated operating cost per unit for the disinfection systems is 0.065 CNY/t, which is economical for long-term operation.

Generation of hydroxyl radicals during photodegradation of chloroacetic acids by 254 nm ultraviolet: A special degradation process revealed by a holistic radical determination methodology

Upon ultraviolet (UV) irradiation, aqueous contaminants may undergo direct and/or indirect photolysis. Direct photolysis refers to transformation of contaminants by UV photon, and indirect photolysis refers to degradation of contaminants by UV-induced reactive species in the presence of photosensitizers. Because hydroxyl radical (•OH) was unexpectedly observed during chloroacetic acids photolysis without using photosensitizer, a question arises regarding whether direct photolysis-induced indirect photolysis (DPIP) was present and how it originated and evolved along the process. To answer these questions, this study employed multiple different yet complementary •OH detection approaches (i.e., probe, scavenger, electron paramagnetic resonance, and hydroxylation products) to prove the presence and role of •OH. Given that hydrogen peroxide (H₂O₂) was produced only in oxygenated water but not in deoxygenated water, we revealed that •OH was mainly generated by reduced oxygen. Meanwhile, several photolysis products like formate, glycolic acid, and glyoxylic acid were able to yield H₂O₂ too, suggesting that they can all trigger formation of •OH under 254 nm UV. In addition to evidences of DPIP phenomenon, this study is also novel in demonstrating a holistic methodology to prove and identify the presence and sources of radicals, which might help enhance understandings of UV processes.

Facile synthesis of MgAl layered double hydroxides by a co-precipitation method for efficient nitrate removal from water: kinetics and mechanisms

A series of MgAl-LDH as highly efficient adsorbents for removing low concentrations of NO₃⁻ were synthesized. The mechanism of NO₃⁻ removal has been comprehensively discussed in terms of its characterization, adsorption kinetics and thermodynamics.

Free available chlorine initiated Baeyer-Villiger oxidation: A key mechanism for chloroform formation during aqueous chlorination of benzophenone UV filters

Chloroform, a regulated disinfection by-product in water, is often generated during chlorination disinfection treatment. However, the formation of chloroform is heavily dependent on the molecular structures of precursors. Moreover, compounds containing ketone moiety are ubiquitous in water environments. However, it is unclear if they can generate chloroform during chlorination. In this study, 14 benzophenones (BPs), efficient and widely used UV filters, with different substituents were selected to explore chloroform formation during chlorination. All 14 BPs generated chloroform, with yields dependent on their molecular structures and operational conditions. Compounds 2,2',4,4'-tetrahydroxy-BP and benzophenone produced the highest and lowest chloroform of 0.313 and 0.013 g/g, respectively, corresponding to the fastest and slowest formation rate constants of 1.41 × 10^-1 and 2.71 × 10^-2 min^-1. Alkaline conditions and high chlorine dosages were favorable to chloroform formation. Three reactions played key roles in chloroform formation from BPs: (1) chlorine initiated Baeyer-Villiger oxidation converted ketone moieties of BP molecules into esters; (2) the esters further underwent hydrolysis and formed phenolic and benzoic products; and (3) benzoic acids underwent decarboxylation and hydrolysis to form phenolic products. Subsequently, these phenolic products could further generate chloroform in the chlorination system. More importantly, BPs could generate chloroform in the ambient water matrices during practical chlorination treatment. This work emphasized the critical role of Baeyer-Villiger oxidation for chloroform formation, implying that pollutants containing aromatic ketone moieties generate chloroform during chlorination disinfection, and their potential risk should therefore be reviewed.

Comparative cytotoxicity studies of halophenolic disinfection byproducts using human extended pluripotent stem cells

2,4,6-trichlorophenol (TCP), 2,4,6-tribromophenol (TBP) and 2,4,6-triiodophenol (TIP) are a new class of halophenolic disinfection byproducts (DBPs) which have been widely detected in drinking water. In recent years, their developmental toxicity has got increasing public attention due to their potential toxic effects on embryo development towards lower organisms. Nonetheless, the application of human embryos for embryonic toxicologic studies is rendered by ethical and moral considerations, as well as the technical barrier to sustaining normal development beyond a few days. Human extended pluripotent stem (EPS) cells (novel totipotent-like stem cells) represent a much more appropriate cellular model for studying human embryo development. In this study, we utilized human EPS cells to study the developmental toxicity of TCP, TBP and TIP, respectively. All three halophenolic DBPs showed cytotoxicity against human EPS cells in an obvious dose-dependent manner, among which TIP was the most cytotoxic one. Notably, the expression of pluripotent genes in human EPS cells significantly declined after 2,4,6-trihalophenol exposure. Meanwhile, 2,4,6-trihalophenol exposure promoted ectodermal differentiation of human EPS cells in an embryoid bodies (EBs) differentiation assay, while both endodermal and mesodermal differentiation were impaired. These results implied that phenolic halogenated DBPs have specific effects on human embryo development even in the early stage of pregnancy. In summary, we applied human EPS cells as a novel research model for human embryo developmental toxicity study of environmental pollutants, and demonstrated the toxicity of phenolic halogenated DBPs on early embryo development of human beings.

Effect of UV254 disinfection on the photoformation of reactive species from effluent organic matter of wastewater treatment plant

UV₂₅₄ is one of the main disinfection methods used in wastewater treatment plants (WWTPs) for the inactivation of pathogens in the effluents before being discharged into the receiving waters. The effluent organic matters (EfOM) are well-known photosensitizers for the generation of reactive species, mainly including the triplet states of EfOM (³EfOM*), singlet oxygen (¹O₂) and hydroxyl radical (^•OH), which contribute to the removal of trace pollutants in water. However, the effect of UV₂₅₄ disinfection on the photoreactivity of EfOM remains unclear. Here we investigated the photophysical and photochemical properties variation of EfOM after UV₂₅₄ disinfection, along with humic substances (HS) as comparison. The UV₂₅₄ disinfection caused a decrease of aromaticity, fluorescence intensity and molecular weight for all samples, while a reduction formation of triplet state of these dissolved organic matters (³DOM*), ¹O₂, hydrogen peroxide (H₂O₂), and superoxide anions (O₂^•-) under simulated sunlight was observed. In contrast, the generation of ^•OH was increased after UV₂₅₄ disinfection. The quantum yield of ¹O₂ was positively correlated with triplet quantum yield coefficient (f_TMP) in all cases. However, the quantum yield of ^•OH exhibited positive and negative correlations with f_TMP for EfOM and HS, respectively. The quantum yields showed positive correlations with E2/E3 (ratio of the absorbance at 254 to 365 nm) for untreated DOM samples, while for the first time we found the trends differ distinctly after UV₂₅₄ disinfection. These findings indicate that UV₂₅₄ disinfection in WWTPs significantly increases the potential of ^•OH photoproduction from effluents and the cost-effective solar irradiation after UV₂₅₄ disinfection is expected to be a novel technique for further removal of pathogen and trace organic pollutants in wastewater effluents and receiving waters.

Removal of trihalomethanes and haloacetamides from drinking water during tea brewing: Removal mechanism and kinetic analysis

Disinfection by-products (DBPs) are associated with various adverse health effects. Diversiform advanced treatment processes have been applied for the control of DBPs, but DBPs can still be frequently detected in tap water. Tea-leaves can be made into popular beverage and is itself a porous bio-adsorbent. By simulating tea brewing process, this study evaluated the removal of DBPs from drinking water during the tea brewing process. Removal of four trihalomethanes (THMs) and four haloacetamides (HAMs) by different fermentation degree tea-leaves was investigated. Little DBPs were removed by unfermented and semi-fermented tea-leaves (i.e., Meitan turquoise bud and Dahongpao tea) with less than 5% removal of HAMs, whereas 40% HAMs can be removed by fermented tea (i.e., Jinjunmei tea and Shuixian tea). Tea soup is neutral and slightly acidic, so little DBP hydrolysis was observed under typical tea-leaf brewing process. DBPs were mainly removed by volatilization and adsorption during tea brewing. Removal difference caused by DBP volatilization is very small. The DBP removal difference of four kinds of tea-leaves may be caused by fermentation degree. The surface of unfermented Meitan turquoise bud had a smooth and regular morphology, whereas a rough, irregular, hollow and spongy surface of fermented tea (i.e., Jinjunmei and Shuixian tea) was observed. Generally, the higher the degree of tea fermentation, the more adsorption sites, and the more removal of DBPs. Finally, the model, which takes the DBP initial concentration, tea-leaf dose and brewing time into account, was established under the experimental conditions to predict the variation of DBP concentration during tea brewing, and suggestions for DBP removal were provided to reduce DBP exposure risk. The integrated toxic risk during tea brewing was also investigated, and about 30% integrated cytotoxicity and 26% genotoxicity was reduced during Jinjunmei and Shuixian tea-leaf brewing.

Development and Application of a High-Precision Algorithm for Nontarget Identification of Organohalogens Based on Ultrahigh-Resolution Mass Spectrometry

Brominated and/or chlorinated organic compounds (referred to as organohalogens) are frequently detected in natural and engineered environments. However, ultrahigh-resolution mass spectrometry (UHR-MS)-based nontargeted identification of organohalogens remains challenging because of the coexistence of a vast number of halogenated and nonhalogenated organic molecules. In this study, a new algorithm, namely, the NOMDBP code, was developed to simultaneously identify organohalogens and non-organohalogens from the UHR-MS spectra of natural and engineered waters. In addition to isotopic patterns, for the first time, three optional filter rules [i.e., selection for minimum nonoxygen heteroatoms, inspection of the presence of newly formed halogenated disinfection byproducts (Xn-DBPs), and of their precursors] were incorporated into our code, which can accurately identify DBP-associated peaks and further elucidate Xn-DBP generation and transformation mechanisms. The formula assignment ratio against 2815 previously reported organohalogens, and their 11,583 isotopologues exceeded 97%. Application of our algorithm to disinfected natural organic matter indicated that oxygen-containing Xn-DBP species accounted for a majority of the Xn-DBPs. Furthermore, brominated Xn-DBPs (Br-DBPs) were characterized by a higher degree of unsaturation compared to chlorinated Xn-DBPs. In addition to electrophilic substitution and electrophilic addition reactions, the decomposition/transformation pathway was found to be another important mechanism in Br-DBP formation. The results of this study highlight the superior potential of our code for the efficient detection of yet unknown organohalogens (including organohalogens bearing nonoxygen heteroatoms) in a nontargeted manner and for the identification of their generation mechanism occurring during the disinfection process.

Effects of ascorbate and carbonate on the conversion and developmental toxicity of halogenated disinfection byproducts during boiling of tap water

Chlorine disinfection inactivates pathogens in drinking water, but meanwhile it causes the formation of halogenated disinfection byproducts (DBPs), which may induce adverse health effects. Humans are unavoidably exposed to halogenated DBPs via tap water ingestion. Boiling of tap water has been found to significantly reduce the concentrations of halogenated DBPs. In this study, we found that compared with boiling only, adding ascorbate (vitamin C) or carbonate (baking soda) to tap water and then boiling the water further reduced the level of total organic halogen (a collective parameter for all halogenated DBPs) by up to 36% or 28%, respectively. Adding ascorbate removed the chlorine residual in tap water and thus prevented the formation of more halogenated DBPs in the boiling process. Adding carbonate elevated pH of tap water and consequently enhanced the hydrolysis (dehalogenation) of halogenated DBPs or led to the formation of more trihalomethanes that might volatilize to air during the boiling process. The comparative developmental toxicity of the DBP mixtures in the water samples was also evaluated. The results showed that adding a tiny amount of sodium ascorbate or carbonate (2.5-5.0 mg/L) to tap water followed by boiling for 5 min reduced the developmental toxicity of tap water to a substantially lower level than boiling only. The addition of sodium ascorbate or carbonate to tap water in household could be realized by preparing them in tiny pills. This study suggests simple and effective methods to reduce the adverse effects of halogenated DBPs on humans through tap water ingestion.

Application of (LC/)MS/MS precursor ion scan for evaluating the occurrence, formation and control of polar halogenated DBPs in disinfected waters: A review

Water disinfection can result in the unintended formation of halogenated disinfection byproducts (DBPs), which have been the subject of intensive investigation over the past 40 years. Robust methods for evaluating and characterizing the formation of halogenated DBPs are prerequisites for ultimately controlling the formation of DBPs and ensuring quality and safe disinfected water. Only a fraction of the total organic halogen (TOX) formed during disinfection has been chemically identified or even well characterized by the classical (derivatization-)gas chromatography/mass spectrometry (GC/MS) method. Such a method may not be amenable to the detection of polar halogenated DBPs, which constitute a major portion of the TOX that is still unaccounted for. Accordingly, a novel precursor ion scan (PIS) method using (liquid chromatography/) electrospray ionization-triple quadrupole mass spectrometry was developed for the rapid selective detection of all polar halogenated DBPs-no matter whether the DBPs are known or unknown-in water. This article reviews recent literature on the application of the PIS method for evaluating the occurrence, formation and control of polar halogenated DBPs in disinfected waters. The challenges in developing the PIS method were briefly summarized. Application of the powerful method pinpointed >150 previously unknown DBPs and revealed the formation, speciation and transformation of halogenated DBPs in disinfected drinking water, wastewater effluents, and swimming pool water. For the same source water, positive correlations were found between the total ion intensity (TII) levels in the PIS spectra of m/z 35/79/126.9 and the total organic chlorine/bromine/iodine levels in the disinfected water sample, and a disinfected sample with a higher TII level generally showed a higher toxic potency. Accordingly, the TII value can be used as a surrogate to comparatively reflect the water quality and assess the efficiency of a DBP control approach. To achieve a more comprehensive and systematic understanding of the DBP compositions in different waters and thus better control the DBP formation and reduce their overall toxicity, topics for future work were discussed.