Chlorine Dose Research Articles

Long Duration Forecasting and its Performance Capability for Seasonal Variation Modelling of Residual Chlorine Concentrations: A Comparative Evaluation of two Small-scale Water Distribution Systems in Japan

Chlorine dosing control is a critical task for health security, complying with drinking water quality standards while achieving customer satisfaction. In Japan, this became more difficult due to decreasing number of technical personnel as a result of declining population and huge retirement of veterans. As experienced-based dosing control still exists and is considered inefficient due to risks of inaccurate dosing and need of experienced manpower, streamlining of operations is needed. This study aims to address these concerns through the development and evaluation of a deep learning model for residual chlorine concentrations capable of forecasting long durations. In this paper, the model is investigated in seasonal timeframe analyzing trends and variations. Two water distributions systems of varying network—simple and complex, are also compared to further analyze model performance and versatility. The model utilizes the past 24 hours of flow rate, chlorine level at treatment plant, water temperature, and residual chlorine at private homes as input to predict the 12 hours ahead of residual chlorine at private homes evaluated at hourly training lengths of 0.5, 1, 1.5, 2 years. Results revealed that the model achieved high accuracy in predicting hourly residual chlorine with general increasing model error from winter, spring, autumn, and summer due to the progressing instabilities in chlorine concentrations from low to high temperatures. Moreover, smaller system tends to be more unstable incurring lower model performance relative to larger system. In terms of optimal training length, ≥1Y training models are found to have lesser chance of data drift occurrence prospectively reducing model retraining frequency in the future.

Reducing E. coli and Coliform in clean water using chlorine diffuser combined with white sand

Background: Water intended for hygiene, sanitation, and drinking must be free of physical, chemical, and microbiological pollutants. The most frequent microbiological contaminants in water are E. coli and Coliform bacteria. Chlorination, which uses chlorine compounds, is a widely used technique to eliminate germs from water. This process is regarded as effective and safe for sanitation, disinfection, and consumption. Purpose: To analyze differences in the reduction of E. coli and Coliform bacteria in water using the chlorine diffuser method combined with white sand. Method: A quasi-experimental method and a pretest posttest design, carried out at a boarding house x in Gonilan Kartasura village. The research sample was taken by purposive sampling. The sample criteria are water at the research location, namely Gonilan village which classified as densely populated. Research data was collected using observation techniques using observation sheets with three folds and three divisions of time span, namely 30 minutes, 45 minutes and 60 minutes. The data collected was then analyzed using the anova method to determine the average differences in group samples. Results: The application of a chlorine diffuser combined with white sand can reduce levels of E. coli bacteria. In the Anova test, the p-value scores were obtained at 0.045 and 0.031, thus the alternative hypothesis was accepted, namely that there was a decrease in E. coli and Coliform bacteria using the chlorine diffuser method combined with white sand. The research results in the 60th minute of the experiment went from 1 to 0. Meanwhile, there was no significant decrease in Coliform bacteria. Initially the Coliform level was 68.3, then after 60 minutes of experimentation it only decreased to 63.6. Conclusion: Based on the research carried out, it was concluded that there was a significant reduction in the levels of E. coli and Coliform bacteria using the chlorine diffuser combined with white sand with a higher dose of chlorine used.

Chlorine dosage management in drinking water systems: comparing Bayesian optimization to evolutionary algorithms

ABSTRACT To maintain a sufficient chlorine residual in water distribution systems (WDSs), chlorine dosage needs to be optimized. The majority of previous studies that aimed to optimize chlorine dosage in WDSs considered single-species water quality (WQ) models featuring chlorine decay with simple reaction kinetics. Recent efforts have proposed using multi-species water quality (MS-WQ) models to account for chlorine interactions with various chemical and microbiological species, thus providing a comprehensive and accurate evaluation of the WQ within WDSs. Nevertheless, the key challenge of implementing MS-WQ models within optimization frameworks is their high computational cost and poor scalability for larger WDSs. Furthermore, previous optimization studies generally relied on evolutionary algorithms (EAs), which require conducting a significant number of WQ simulations. Bayesian optimization (BO) has been recently suggested as an efficient alternative to EAs for the optimization of computationally expensive functions. This study aims to present a systematic comparison between BO and other widely used EAs for the optimization of MS-WQ in WDSs. A case study featuring a real-life, midsized benchmark WDS was implemented to comprehensively evaluate all three optimization techniques. The results revealed that BO is notably more computationally efficient and less sensitive to changes in the constraints than EAs.

Evaluation of the Safe Water Optimization Tool to Provide Evidence-Based Chlorination Targets in Surface Waters: Lessons from a Refugee Setting in Uganda.

The Safe Water Optimization Tool (SWOT) generates evidence-based point-of-distribution free residual chlorine (FRC) targets to adjust chlorine dosing by operators and ensure water quality at point-of-consumption. To investigate SWOT effectiveness in surface waters, we conducted two before-and-after mixed-method evaluations in a Uganda refugee settlement served by piped and trucked surface water systems. We surveyed 888 users on water knowledge, attitudes, and practices; collected 2768 water samples to evaluate FRC,Escherichia coli, and disinfection by-products (DBPs) concentrations; and conducted nine key-informant interviews with system operators about SWOT implementation. After baseline data collection, SWOT chlorination targets were generated, increasing point-of-distribution FRC targets from 0.2 to 0.7-0.8 mg/L and from 0.3 to 0.9 mg/L for piped and trucked systems, respectively. At endline, household point-of-consumption FRC ≥ 0.2 mg/L increased from 23 to 35% and from 8 to 42% in the two systems. With these increases, we did not observe increased chlorinated water rejection or DBPs concentrations exceeding international guidelines. Informants reported that SWOT implementation increased knowledge and capacity and improved operations. Overall, SWOT-generated chlorination targets increased chlorine dosage, which improved household water quality in surface waters although less than previously documented with groundwater sources. Additional operator support on prechlorination water treatment processes is needed to ensure maximally effective SWOT implementation for surface water sources.

Probing into the formation of brominated halonitromethanes from the intracellular organic matter of Anabaena during UV/chlorine disinfection

Eutrophication events in water bodies result in the release of algal organic matter, which is an essential precursor for halonitromethanes during disinfection, posing a significant threat to water quality. During UV/chlorine disinfection, the presence of Br− promotes the formation of brominated halonitromethanes (Br-HNMs), which exhibit higher toxicity compared to chlorinated halonitromethanes. Nevertheless, limited studies have been conducted on the Br-HNMs formation from algal precursors during UV/chlorine disinfection in the presence of Br−. Therefore, in this study, the formation pattern and toxicity variation of Br-HNMs from the intracellular organic matter (IOM) of anabaena during UV/chlorine disinfection was investigated. The results showed that monobromonitromethane, bromochloronitromethane, and bromodichloronitromethane could be detected during UV/chlorine disinfection. When the Br− concentration raised, the total concentration and toxicity of Br-HNMs exhibited an increase followed by a decline. Additionally, the concentration and toxicity of three Br-HNMs were promoted by increasing UV intensity, free chlorine dosage, and anabaena concentration but inhibited by increasing pH. Based on the experiment results, possible pathways for Br-HNMs formation from anabaena IOM in the presence of Br− were deduced. Moreover, anabaena IOM could also be converted to Br-HNMs during UV/chlorine disinfection of actual water, with a formation pattern similar to that found in distilled water. This research offers valuable insights into Br-HNMs formation from algal-containing waters.

Transformation of dissolved organic matter leached from biodegradable and conventional microplastics under UV/chlorine treatment and the subsequent effect on contaminant removal

The ultraviolet (UV)/chlorine process has been widely applied for water treatment. However, the transformation of microplastic-leached dissolved organic matter (MP-DOM) in advanced treatment of real wastewater remains unclear. Here, we investigated alterations in the photoproperties of MP-DOM leached from biodegradable and conventional microplastics (MPs) and their subsequent effects on the degradation of sulfamethazine (SMT) by the UV/chlorine process. Spectroscopy was used to assess photophysical properties, focusing on changes in light absorption capacity, functional groups, and fluorescence components, while photochemical properties were determined by calculating the apparent quantum yields of reactive intermediates (ΦRIs). For photophysical properties, our findings revealed that the degree of molecular structure modification, functional group changes, and fluorescence characteristics during UV/chlorine treatment are closely linked to the type of MPs. For photochemical properties, the ΦRIs increased with higher chlorine dosages due to the formation of new functionalities. Both singlet oxygen (1O2) and hydroxyl radicals (•OH) formation were strongly correlated with excited triplet state of DOM (3DOM*) in the UV/chlorine treatment. Additionally, we found that the four types of MP-DOM inhibit the degradation of SMT and elucidated the mechanisms behind this inhibition. We also proposed degradation pathways for SMT and assessed the ecotoxicity of the resulting intermediates. This study provides important insights into how the characteristics and transformation of MP-DOM affect contaminant degradation, which is critical for evaluating the practical application of UV-based advanced oxidation processes (UV-AOPs).

Emergency control of dinoflagellate bloom in freshwater with chlorine enhanced by solar radiation: Efficiency and mechanism

Dinoflagellate requires a lower temperature and blooms frequently in the spring and autumn compared to regular cyanobacteria. The outbreak of dinoflagellate bloom will also lead to the death of some aquatic organisms. However, research on freshwater dinoflagellates is still lacking due to the challenges posed by classification and culture in laboratory. The removal effect and mechanism of Peridinium umbonatum (P. umbonatum, a typical dinoflagellate) were investigated using solar/chlorine in this study. The effect of simulated solar alone on the removal of algae was negligible, and chlorine alone had only a slight effect in removing algae. However, solar/chlorine showed a better removal efficiency with shoulder length reduction factor and kmax enhancement factor of 2.80 and 3.8, respectively, indicating a shorter latency period and faster inactivation rate for solar/chlorine compared to solar and chlorine alone. The removal efficiency of algae gradually increased with the chlorine dosage, but it dropped as the cell density grew. When the experimental temperature was raised to 30 °C, algal removal efficiency significantly increased, as the temperature was unsuitable for the survival of P. umbonatum. Attacks on cell membranes by chlorine and hydroxyl radicals (•OH) produced by solar/chlorine led to a decrease in cell membrane integrity, leading to a rise in intracellular reactive oxygen species and an inhibition of photosynthetic and antioxidant systems. Cell regeneration was not observed in either the chlorine or solar/chlorine systems due to severe cell damage or cysts formation. In addition, natural solar radiation was demonstrated to have the same enhancing effect as simulated solar radiation. However, the algal removal efficiency of solar/chlorine in real water was reduced compared to 119 medium, mainly due to background material in the real water substrate that consumed the oxidant or acted as shading agents.

Evaluation of drinking water quality and associated health risks in Adama City, Ethiopia

Drinking water deterioration causes to risk of public health which is essential to supply safe water to the public. This study assessed groundwater quality and health risks in Adama City by analyzing groundwater and chlorine samples. Ion photometry techniques detected anions and cations, ensuring accuracy with quality control protocols. Water Quality Index (WQI) and chlorine decay modeling via WaterGEMs assessed water quality. Hazard index (HI) calculations evaluated exposure risks; Pearson correlation analyzed physicochemical relationships. Findings highlighted water quality and hazards. Aquachem software analyzed Adama's groundwater, revealing high total alkalinity and potassium exceeding WHO limits. Other parameters (nitrate, nitrite, chloride, fluoride, and sulfate) met WHO standards. Sodium, calcium, magnesium, iron, manganese, and boron also complied. Multivariate analysis showed significant parameter associations. Water types included Ca–Na–HCO3 (27.27 %), Na–Ca–HCO3 (36.36 %), Na–Ca–Mg–HCO3, Na–HCO3 (9.09 % each), and Na–Mg–HCO3 (18.18 %). Drinking Water Quality Index rated boreholes as "Good." Health risk assessments found no significant fluoride, iron, or manganese risks across ages. Chlorine residual analysis indicated 74 % had levels below WHO recommendations, prompting chlorine dosing adjustments. Findings inform groundwater management in Adama City.

Impact of chlorine disinfection on intracellular and extracellular antimicrobial resistance genes in wastewater treatment and water reclamation

Wastewater treatment plants and water reclamation facilities are reservoirs of antimicrobial resistance genes (ARGs). These ARGs are not limited solely to intracellular DNA (inARGs) but include extracellular DNA (exARGs) present in wastewater. The release of exARGs from cells can be exacerbated by treatment processes, including chlorine disinfection, which disrupts bacterial cells. Given the potential for exARGs to drive horizontal gene transfer and contribute to the proliferation of antimicrobial resistance, it is imperative to recognize these fractions as emerging environmental pollutants. In this study, we conducted a comprehensive year-long assessment of both inARGs and exARGs, further differentiating between dissolved exARGs (Dis_exARGs) and exARGs adsorbed onto particulate matter (Ads_exARGs), within a full-scale wastewater treatment and water reclamation facility. The results revealed that Ads_exARGs comprised up to 30 % of the total ARGs in raw sewage with high biomass content. Generally, treatments at low and high doses of chlorine increased the abundance of Dis_exARGs and Ads_exARGs. The fate of ARG levels that varied depending on the type of ARGs suggested variations in the susceptibility of the host bacteria to chlorination. Moreover, co-occurrence of several potential opportunistic pathogenic bacteria and ARGs were observed. Therefore, we propose higher doses of chlorination as a prerequisite for the effective removal of inARGs and exARGs.

Widespread Antioxidants during Storm Events Could Serve as Precursors of Regulated, Priority, and New Disinfection Byproducts.

Widely used antioxidants can enter the environment via urban stormwater systems and form disinfection byproducts (DBPs) during chlorination in downstream drinking water processes. Herein, we comprehensively investigated the occurrence of 39 antioxidants from stormwater runoff to surface water. After a storm event, the concentrations of the antioxidants in surface water increased by 1.4-fold from 102-110 ng/L to 128-139 ng/L. Widespread antioxidants during the stormwater event could transform into toxic DBPs during disinfection. Moreover, the yields of trihalomethanes, haloacetaldehydes, haloacetonitriles (HANs), and halonitromethanes during the chlorination of widely used antioxidants considerably increased with an increasing chlorine dose and contact time. Specifically, the yields of dichloroacetonitrile during the chlorination of diphenylamine (DPA) and N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) were higher than those of most reported amino acid precursors, indicating that DPA and 6PPD might be important precursors of HANs. Exploring the intermediates using GC × GC-time-of-flight high-resolution mass spectrometry helped reveal potential pathways from DPA to HANs, whose formation could be attributed to the intermediate carbazole and indole moieties detected in this study. This study provides insights into the transport and transformation of commonly used antioxidants in a water environment and during water treatment processes, highlighting the potential risks of anthropogenic pollutants from a DBP perspective.

Establishment of Relationship Between Coagulant and Chlorine Dose Using Artificial Neural Network

Establishment of Relationship Between Coagulant and Chlorine Dose Using Artificial Neural Network

Influence of Lateral Length and Residual Chlorine Concentration on Soil Nitrogen and Soil Enzyme Activities under Drip Irrigation with Secondary Sewage Effluent

Chlorination has been demonstrated to be an effective method for the prevention and reduction in emitter biological blockage in drip irrigation systems. The injected chlorine dose is generally determined by chlorine concentration at the terminal of the laterals which may lead to a high concentration of residual chlorine at the front of the system and bring detrimental impact to the soil environment and growth of crops, especially in large irrigation units with long laterals. A two-season experiment was undertaken to determine the effects of chlorine disinfection and lateral length on soil NO3-N, enzyme activities, and maize yield under wastewater drip irrigation. The experiments were constructed with lateral lengths ranging from 20 to 80 m and injection chlorine concentrations at the end of laterals ranging from 2 to 6 mg L−1. Lateral length had a major impact on enzyme activities in the partial growth stage, although the effects of lateral length and chlorine concentration on soil nitrogen content and maize yield were negligible. Enzyme activity and soil nitrogen concentration decreased throughout the lateral length as a result of chlorination. A higher detrimental impact on soil characteristics and maize yield is probably going to result from a high concentration of chlorine and a long lateral length mode. The maize yield peaked at L80 with a concentration of 2 mg L−1 chlorine, while it peaked at L40 with 6 mg L−1 chlorine concentration. A chlorination scheme with long lateral length and low chlorine concentration is recommended in consideration of maize yield and minimizing potential negative effects on the soil environment.

Formation of halonitromethanes from different nitrophenol compounds during UV/post-chlorination: Impact factors, DFT calculation, reaction mechanisms, and toxicity

As ubiquitous chemical substances in water bodies, nitrophenol compounds (NCs) can form chlorinated halonitromethanes (Cl-HNMs) in the chlorination process. This work chose six typical NCs to explore Cl-HNMs produced during the UV/post-chlorination process, and Cl-HNMs yields from these NCs followed the increasing order of 4-, 2-, 2-amino-3-, 2-methyl-3-, 3-, and 2-chloro-3-nitrophenol. The Cl-HNMs yields increased continually or increased firstly and declined with post-chlorination time. Increasing chlorine dosage favored Cl-HNMs formation, while excessive chlorine dosage decreased Cl-HNMs produced from 2- and 4-nitrophenol. Besides, appropriate UV radiation, acidic pH, and higher precursor concentrations facilitated Cl-HNMs formation. Then, the reaction mechanisms of Cl-HNMs generated from these different NCs were explored according to density functional theory calculation and identified transformation products (TPs), and the main reactions included chlorine substitution, benzoquinone compound formation, ring opening, and bond cleavage. Moreover, the Cl-HNMs generated from 2-chloro-3-nitrophenol were of the highest toxicity, and the six NCs and their TPs also presented ecotoxicity. Finally, two kinds of real waters were used to explore Cl-HNMs formation and toxicity, and they were significantly distinguishable compared to the phenomena observed in simulated waters. This work will give new insights into Cl-HNMs formation from different NCs in water disinfection processes and help better apply the UV/post-chlorination process to water treatments.

Optimizing the number, locations, and chlorine dosages of booster chlorination stations in water distribution networks

ABSTRACT Safe and reliable drinking water is essential for sustaining life. Chlorination is widely used for disinfection in water distribution networks (WDNs). A higher dose of chlorine is required in an overhead service reservoir to maintain minimum residual chlorine at the farthest end in WDNs. However, delivering high dosages of chlorine from storage tanks can pose public health issues, especially for the residents living near overhead service reservoirs due to the formation of trihalomethanes, haloacetic acids, and chlorophenols. In addition, a higher dosage will lead to increased chlorine consumption and will accelerate pipe corrosion. Booster chlorination (BC) stations with smaller dosages are a solution to this problem. However, identifying the optimal number, locations, and dosage of each BC station in a cost-effective manner is challenging. This study proposes a methodology for determining the optimal number, locations, and chlorine dosages of BC stations in WDNs using a mixed integer linear programming problem. The methodology is illustrated through a simplified WDN in Holeta town, Ethiopia. The results indicate that if one adds two BC stations beyond the three dosage stations at the source, it will lead to a 49% reduction in chlorine use and a 27% decrease in the life cycle cost.

Hydroxyl-aluminum pillared bentonite enhanced Mn(II) removal by chlorine oxidation

Al-PILC was used to catalyze the chlorine oxidation of Mn(II) in aqueous solution. The effects of various catalysts, catalyst dosage, chlorine dosage, pH value, temperature and organic content on the oxidation process were investigated. Results show that 1.5 mg/L chlorine can quickly oxidize Mn(II) from 0.5 mg/L to less than 0.04 mg/L with 10 mg/L Al-PILC. Using catalysts with higher porosity and higher SA, increase in chlorine concentration, increase in catalyst dosage, higher pH, and higher temperature can significantly enhance the rate of Mn(II) catalytic oxidation. The Mn(II) oxidation process includes the homogeneous oxidation, catalytic oxidation on the surface of the catalysts and self-catalytic oxidation produced by the newly produced MnOx. Al-PILC surface provides active sites for chlorine oxidation Mn(II) in the water, and also provides binding sites for the newly produced MnOx, which has higher catalytic activity and thus has an self-catalytic oxidation effect. The higher the porosity and SA of Al-PILC, the more catalytic oxidation active sites and loading sites, and the better the catalytic oxidation effect. The study promotes the understanding of chlorine catalyzed oxidation Mn(II) in aqueous solution, but also provide important guide to study newly efficient catalysts to oxidize Mn(II) with chlorine in aqueous solution.

Formation and health risk assessment of trihalomethanes in coastal wells impacted by seawater intrusion

The formation of trihalomethanes (THMs) in coastal wells impacted by seawater intrusion (SWI) is relatively understudied. Coastal wells, unlike typical groundwater sources, frequently exhibit elevated levels of chloride and bromide ions, potentially influencing the formation and speciation of THMs. The current study investigated the THM formation in coastal well water from a location affected by SWI. Samples were chlorinated with 2.5 mg L−1 and 5 mg L−1 chlorine doses to replicate field conditions. The THM concentration in the samples exceeded the maximum permissible limit for drinking water. The well with the highest chloride-to-bromide (Cl/Br) ratio (Cl/Br = 645) exhibited the highest total THM concentration (503.2 μg L−1). Samples with high bromide concentration had more brominated THMs over the 5-day reaction period. The bromine substitution factors for wells after 24 h with a chlorine dose of 2.5 mg L−1 were 1.89, 2.21, and 2.78, corresponding to bromide concentrations of 0.098, 0.109, and 1.275 mM, respectively. The average cancer risk associated with the well water was estimated to be 20.9 × 10−06 through dermal contact and 6.84 × 10−04 through inhalation. The study area had an estimated average cancer risk of 705 cases per million population. The study area's common diseases and cancer incidence data for the past four decades indicated a decreasing trend for waterborne diseases and a steep increase in cancers. While several factors may contribute to increasing cancer cases, our study highlights chlorinated coastal well water as an additional potential cancer risk agent.

A novel route for urea abatement in UPW production: Pre-chlorination/VUV/UV under acidic circumstances and its enhancement mechanisms

Urea abatement has been a prominent challenge for UPW production. This research proposed a productive strategy combining pre-chlorination and VUV/UV processes under acidic conditions to settle this problem. This study first revealed the reaction kinetics between urea and free chlorine in a large pH range from 2.5 to 9.6, where the reaction constant rate varied from 0.06 to 0.46 M−1·s−1. Substitution reaction mediated by Cl2 was the dominant process at low pH (pH<3). The differences of dominant pathways resulted in the differences in reaction products: The detected concentration of dichloramine at pH 2.5 was twice that at pH 4.5 and 6.5. Further, this study found that pre-chlorination/VUV/UV process could achieve the thorough removal of 2-mg/L urea with chlorination of less than 5 min and VUV/UV irradiation of less than 200 mJ/cm2. Chloride ions, low pH, and higher chlorine dosage were found to be the positive factors to improve urea removal efficiency in pre-chlorination/VUV/UV process. The reaction rate constants between chlorourea with·OH and·Cl were calculated to be 3.62 × 107 and 2.26 × 109 L·mol−1·s−1, respectively.·Cl,·OH and photolysis contributed 60.5 %, 22.9 % and 16.6 % in chlorourea degradation, respectively. Pre-chlorination/VUV/UV achieved a DOC removal efficiency of 78.5 %. And nitrogen in urea was converted into inorganic nitrogenous compounds. Finally, compared with direct VUV/UV/chlorine and VUV/UV/persulfate processes, this process saved more than 70 % of energy in VUV/UV unit.

The diverse roles of bromide in the degradation of tinidazole during UV-LED/chlorine process at different wavelengths: Kinetics, radical contribution, and degradation pathway

Bromide (Br–) is widely present in aquatic environment and plays important roles in pollutant degradation during advanced oxidation processes. This work systematically investigated the effect of Br– on the degradation of tinidazole (TNZ) during ultraviolet light-emitting diode (UV-LED)/chlorine process at different wavelengths (265 and 365 nm). The observed pseudo-first-order constant (k') for the TNZ degradation during UV-LED (365 nm)/chlorine process in the presence of 0.4 mM Br– (0.1125 min−1) was 1.56 times that during UV-LED (365 nm)/chlorine process in the absence of Br–. However, the k' value during UV-LED (265 nm)/chlorine process was reduced by 49.=7 % in the presence of 0.4 mM Br–. At 0–0.4 mM Br−, elevated levels of hydroxyl radicals (HO·) and active bromine species promoted TNZ degradation during UV-LED (365 nm)/chlorine/Br– process, whereas reduced HO· concentration was the main reason for the inhibition of TNZ degradation during UV-LED (265 nm)/chlorine/Br– process. With increasing solution pH from 5.8 to 7.8, the k' value of both processes decreased in the presence of Br–. Meanwhile, the k' value increased with increasing chlorine dosage and decreased with increasing initial TNZ concentration during both processes in the presence of Br–. The presence of Cl− and HCO3– presented negligible effects on the degradation of TNZ. According to the density functional theory calculation and detected intermediates, the degradation pathway of TNZ during both processes in the presence of Br– was proposed. The toxicity evaluation demonstrated that some of the degradation products of TNZ presented lower predicted toxicity values than TNZ. Overall, this work provides a thorough insight into the role of Br– in TNZ degradation during UV-LED/chlorine process at different wavelengths.

Effects of Fe(III) on the formation and toxicity alteration of halonitromethanes, dichloroacetonitrile, and dichloroacetamide from polyethyleneimine during UV/chlorine disinfection

Trace iron ions (Fe(III)) are commonly found in water and wastewater, where free chlorine is very likely to coexist with Fe(III) affecting the disinfectant's stability and N-DBPs’ fate during UV/chlorine disinfection, and yet current understanding of these mechanisms is limited. This study investigates the effects of Fe(III) on the formation and toxicity alteration of halonitromethanes (HNMs), dichloroacetonitrile (DCAN), and dichloroacetamide (DCAcAm) from polyethyleneimine (PEI) during UV/chlorine disinfection. Results reveal that the maxima concentrations of HNMs, DCAN, and DCAcAm during UV/chlorine disinfection with additional Fe(III) were 1.39, 1.38, and 1.29 times higher than those without additional Fe(III), instead of being similar to those of Fe(III) inhibited the formation of HNMs, DCAN and DCAcAm during chlorination disinfection. Meanwhile, higher Fe(III) concentration, acidic pH, and higher chlorine dose were more favorable for forming HNMs, DCAN, and DCAcAm during UV/chlorine disinfection, which were highly dependent on the involvement of HO· and Cl·. Fe(III) in the aquatic environment partially hydrolyzed to the photoactive Fe(III)‑hydroxyl complexes Fe(OH)2+ and [Fe(H2O)6]3+, which undergone UV photoactivation and coupling reactions with HOCl to achieve effective Fe(III)/Fe(II) interconversion, a process that facilitated the sustainable production of HO·. Extensive product analysis and comparison verified that the HO· production enhanced by the Fe(III)/Fe(II) internal cycle played a primary role in increasing HNMs, DCAN, and DCAcAm productions during UV/chlorine disinfection. Note that the incorporation of Fe(III) increased the cytotoxicity and genotoxicity of HNMs, DCAN, and DCAcAm formed during UV/chlorine disinfection, and yet Fe(III) did not have a significant effect on the acute toxicity of water samples before, during, and after UV/chlorine disinfection. The new findings broaden the knowledge of Fe(III) affecting HNMs, DCAN, and DCAcAm formation and toxicity alteration during UV/chlorine disinfection.

Dissolved oxygen facilitates efficiency of chlorine disinfection for antibiotic resistance

Controlling the dissemination of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) is a global concern. While commonly used chlorine disinfectants can damage or even kill ARB, dissolved oxygen (DO) may affect the formation of reactive chlorine species. This leads to the hypothesis that DO may play roles in mediating the effectiveness of chlorine disinfection for antibiotic resistance. To this end, this study investigated the impacts of DO on the efficiency of chlorine disinfection for antibiotic resistance. The results revealed that DO could increase the inactivation efficiency of ARB under chloramine and free chlorine exposure at practically relevant concentrations. Reactive species induced by DO, including H2O2, O2−, and OH, inactivated ARB strains by triggering oxidative stress response and cell membrane damage. In addition, the removal efficiency of extracellular ARGs (i.e. tetA and blaTEM) was enhanced with increasing dosage of free chlorine or chloramine under aerobic conditions. DO facilitated the fragmentation of plasmids, contributing to the degradation of extracellular ARGs under exposure to chlorine disinfectants. The findings suggested that DO facilitates disinfection efficiency for antibiotic resistance in water treatment systems.