Chlorine Disinfection Research Articles

Toxicity assessment of wastewater using a battery of bioassays in two textile wastewater treatment plants from a large industrial park in Guangxi, Southwest China.

Textile effluents are important sources of pollutants in aquatic environments. The textile industry in China has been relocating from developed to less developed regions, yet the potential environmental impact of textile effluents remains unclear. Here, we investigated the acute toxicity of wastewater collected from different processing units of two textile wastewater treatment plants (WWTPs) in a large industrial park in Guangxi province (Southwest China), using whole effluent toxicity testing. Moreover, we explored the relationships between the toxicity of wastewater and its characteristics, including physicochemical parameters, heavy metals, fluorescence intensity, and non-persistent and persistent organic pollutants. Untreated textile effluents were highly toxic to all test organisms, with toxic units reaching 42.9 for lux-modified bacteria, 14.0 for green algae, 10.1 for duckweed, and 17.3 for zebrafish embryos. Their toxicity was reduced significantly but not removed completely, following treatment processes that included coagulation, anaerobic-aerobic process, Fenton oxidation process, chlorine disinfection and wetland treatment systems. In the wetland effluent, both toxicity and physicochemical parameters met the textile effluent discharge standards in China and other countries. The toxicity of wastewater was associated with various characteristics, such as chemical oxygen demand (COD), fluorescence intensity related to fulvic acid-like materials, 4-nonylphenol, bisphenol A, bis(2-ethylhexyl) phthalate, perfluorobutane sulfonic acid, and acenaphthene. These results suggest the effectiveness of the investigated WWTPs in treating textile effluents concerning both physicochemical parameters and acute toxicity. The present study highlights the importance of integrating ecotoxicological data alongside chemical data to enhance the risk assessment and evaluation of the environmental safety of effluent discharges.

Phenols Coupled During Oxidation Upstream of Water Treatment Would Generate Higher Toxic Coupling Phenolic Disinfection By-products During Chlorination Disinfection

Phenolic compounds usually produce coupling phenols during the upstream oxidation treatment of water, but the disinfection by-products (DBPs) of coupling phenols in the subsequent disinfection process have been overlooked. Herein, we demonstrated the generation and higher toxicity of these DBPs. In Songhua River water, 0.355ng/L 4-(4-bromophenoxy)phenol and 122.67ng/L phenol were detected. Pre-oxidation with K2FeO4 and KMnO4 resulted in the formation of 0.68ng/L and 0.506ng/L 4-(4-iodophenoxy)phenol in subsequent disinfection, respectively, which were 2-3 times that without pre-oxidation. Coupling of phenolic compounds during pre-oxidation and then halogenated during chlorination was shown to be the main pathway for the generation of coupling phenolic DBPs. The maximum rate constants for the reactions of hypochlorous acid with phenol and its coupling products (4-phenoxyphenol, 2,2’-biphenol, and [1,1’-biphenyl]-2,4’-diol) were 115.61M-1s-1, 65.85M-1s-1, 143.13M-1s-1, and 212.52M-1s-1, respectively, with 2,2’-biphenol and [1,1’-biphenyl]-2,4’-diol breaking through lower energy barriers and releasing more energy than phenol. This indicated coupling phenols have a higher potential to form DBPs. Additionally, coupling phenolic DBPs (4-(4-chlorophenoxy)phenol, 4-(4-bromophenoxy)phenol, and 4-(4-iodophenoxy)phenol) was 1-3 orders of magnitude more toxic than their precursors (4-phenoxyphenol, 2,2’-biphenol, [1,1’-biphenyl]-2,4’-diol, and phenol) and uncoupled DBPs (4-iodophenol). Therefore, the formation and hazards of coupling phenolic DBPs require more attention.

Revealing Molecular Connections between Dissolved Organic Matter in Surface Water Sources and Their Cytotoxicity Influenced by Chlorination Disinfection.

Dissolved organic matter (DOM) is the primary precursor of disinfection products (DBPs) during chlorination. However, the compositional characteristics of DOM transformation during the chlorination process in different source waters and its relationship to cytotoxicity remain understudied. Here, we used high-resolution mass spectrometry to evaluate chlorination-induced molecular-level changes in DOM derived from different surface water sources. We correlated DOM components with the cytotoxicity profiles of selected DBPs using new alternative methods with predictive toxicological assessments. Our findings indicate a selective chlorination of DOM in natural waters and a tendency for lignin and protein conversion during the manual chlorination process. The reactivity of bioactive compounds decreased in the order of lignin > protein > tannin or ConAC. The cytotoxicity of DOM from source waters is mainly attributed to lignin- and protein-like compounds within the CHO and CHNO groups. Additionally, mitochondrial damage is a highly sensitive indicator of DOM-induced cytotoxicity. The toxicity profiles of DBPs revealed 37 common toxicity-driving components characterized by low mass, medium H/C ratio, low O/C ratio, reduction state, and hydrophobicity. Our findings highlight the need to exploit the health effects of DOM and provide substantial experimental evidence for the necessity to remove potential toxicants.

Investigation of Transformation Pathways of Polyfluoroalkyl Substances during Chlorine Disinfection.

Recent regulations on perfluorinated compounds in drinking water underscore the need for a deeper understanding of the formation of perfluorinated compounds from polyfluoroalkyl substances during chlorine disinfection. Among the compounds investigated in this study, N-(3-(dimethylaminopropan-1-yl)perfluoro-1-hexanesulfonamide (N-AP-FHxSA) underwent rapid transformation during chlorination. Within an hour, it produced quantitative yields of various poly- and per-fluorinated products, including perfluorohexanoic acid (PFHxA). Sixteen reactions involving chlorine with N-AP-FHxSA and its quaternary ammonium analog were investigated; seven were confirmed, while the remainder were either disproved or found to be insignificant. The quaternary ammonium moiety did not determine a polyfluoroalkyl substance's reactivity toward chlorine. For example, while 6:2 fluorotelomer sulfonamide betaine transformed rapidly to PFHxA, other quaternary-ammonium-containing polyfluoroalkyl substances, such as 5:1:2 and 5:3 fluorotelomer betaines, showed significant resistance to chlorination. Further investigation identified potential sites for electrophilic attacks near the amine region by examining the highest occupied molecular orbitals of the polyfluoroalkyl substances. Visualization techniques helped pinpoint electron-deficient and electron-rich sites as potential targets for nucleophilic and electrophilic attacks, respectively. Increasing the solution pH from 6 to 10 did not diminish the apparent degradation of the studied polyfluoroalkyl substances, likely due to the greater reactivity of the deprotonated forms compared to the conjugate acids. Finally, we also examined the hydrolysis of polyfluoroalkyl substances at pH 6 to 11 in the absence of chlorine.

High-performance thin-layer chromatography-umu combined with nontarget analysis-a sensitive genotoxicity screening tool applicable for potable water analysis.

Monitoring of genotoxic chemicals released into the water cycle or formed through transformation processes is critical to prevent harm to human health. The development of the high-performance thin-layer chromatography (HPTLC)-umu bioassay combines sample separation and detection of genotoxic substances in the low ng/L concentration range. In this study, raw, process, and drinking water samples from 11 different waterworks in Germany were analyzed using the HPTLC-umu. A genotoxic response was detected in three out of 42 samples (one raw water sample and two drinking water samples). Genotoxicity testing using the micronucleus and p53-CALUX (chemical activated luciferase gene expression) assays revealed genotoxic effects for the raw water sample and one of the drinking water samples. Fortunately, only minor genotoxic effects could be detected in the two drinking water samples, with estimated 4-nitroquinoline-N-oxide equivalency concentrations of 0.12 ng/L and 0.17 ng/L, respectively. After extraction of the genotoxic zones from HPTLC plates, identification attempts were conducted with nontarget analysis (NTA). A prioritization approach based on chlorine and bromine isotope pattern revealed several halogenated features for both drinking water samples. These tentatively identified substances were previously reported in the literature as possible carcinogens. Although the detected features could not be conclusively identified, the presence of halogenated features in the genotoxic effective zone of the HPTLC-umu assay strongly suggests that the chlorine disinfection process in both waterworks was responsible for the formation of the genotoxic substances in the drinking water samples. These findings emphasize that the HPTLC-umu in combination with additional genotoxicity assays and NTA can be used to evaluate even relatively clean samples, such as drinking water.

Occurrence and risk of microplastics and hexabromocyclododecane in urban drinking water systems: From source water to tap water.

The widespread presence of microplastics (MPs) in drinking water systems and their risk of releasing additives have caused widespread concern. However, current research on the migration and risks of MPs and additives in the complete drinking water supply chain remains inadequate. In this study, micro-Raman spectrometer was used to track the entire transport process of MPs from the water source to the tap water, with concentrations ranging from 805 to 4960 items/L, and polyethylene and Polyethylene terephthalate were dominant. The removal efficiency of MPs at the drinking water treatment plant was 85.0±5.2%. However, chlorination increased the proportion of polystyrene by 40.1±5.3%. Chlorination increases the surface roughness and carbonyl index of polystyrene standards, and promotes the release of hexabromocyclododecane (HBCD) (482.0ng/g-2208.7ng/g). The non-carcinogenic risk index of HBCD ingestion through drinking water remains well below 1 for residents. Complete water treatment processes significantly reduce the risks posed by MPs, achieving reductions of 54.3% in the pollution load index and 82.1% in the potential ecological risk index. The estimated daily intake of MPs ingested by residents through tap water ranges from 33.4 to 45.6 items/kg/d. This study investigated the occurrence of MPs in the complete drinking water supply chain and the risk of chlorine disinfection for HBCD release, which could help develop more effective MPs control measures and risk management strategies.

Degradation of levofloxacin by dielectric barrier discharge plasma/chlorine process: Roles of reactive species and control of chlorination disinfection byproducts.

In this study, a novel process of dielectric barrier discharge (DBD)/chlorine for levofloxacin (LEV) degradation was investigated. The combined system boosted the degradation efficiency of LEV from 77.8% to 97.5%, improved the reaction rate constant by 2.3 times, and reduced energy consumption by 64.5%. DBD/chlorine process was highly efficient for LEV degradation across a pH range of 3.3-10.8, with removal rates varying from 90.3% to 97.5%. The electron paramagnetic resonance and scavenging experiments demonstrated the generation of reactive oxygen species (ROS, including HO•, 1O2, and O2•-) and reactive chlorine species (RCS) in the DBD/chlorine system, with 1O2 in the nonradical pathway being crucial for LEV removal. Crucially, effective activation of chlorine not only encouraged the production of reactive species but also prevented the formation of disinfection by-products (DBPs), successfully controlling the ecotoxicity of the reaction system. DBD could activate chlorine to form chlorate and HO•, which in turn triggered the production of RCS. The comparison of the LEV degradation pathway was proposed with or without chlorine in the DBD process. Finally, the effects of different water quality and water bodies demonstrated the application prospects of the DBD/chlorine process. This work provided an efficient technique for the elimination of antibiotics by non-thermal plasma/chlorine.

Evaluation of MC-LR Removal by Sodium Hypochlorite Disinfection as Best Available Technology (BAT) for Algal Toxin Removal

Harmful cyanobacteria produce various toxic substances, among which microcystin is the most commonly detected toxin in water resources, with microcystin-LR(MC-LR) known to be the most toxic. For the removal of microcystin, sodium hypochlorite(NaOCl) disinfection is recognized as an effective best available technology(BAT) in water treatment facilities for MC-LR removal, within limits that minimize the formation of disinfection by-products. However, chlorine disinfection of microcystin is affected by various factors, including temperature and pH, with environmental factors such as the presence of organic matter in raw water potentially influencing the efficiency of microcystin removal. In this study, raw water was collected from the Nakdong River, and Intracellular Organic Matter(IOM) was extracted from algal cells. NaOCl was then added to both the IOM raw water and DI water to assess the chlorine disinfection rate of MC-LR removal and to analyze the pseudo-first-order reaction kinetics, evaluating the impact of organic matter in raw water on MC-LR chlorination. The results showed that the MC-LR removal rate in IOM by chlorine disinfection was a maximum of 17%, while the MC-LR removal in deionized water reached up to 99%. The pseudo-first-order reaction rate constants were 3.99×10<sup>-5</sup>s<sup>-1</sup> and 9.11×10<sup>-4</sup>s<sup>-1</sup> for IOM and deionized water, respectively, indicating that MC-LR removal in IOM was slower and had a lower removal rate compared to that in deionized water. This study demonstrates that chlorine disinfection is suitable as the BAT for algal toxin removal and highlights the need to reduce the amount of organic matter through pre-treatment before chlorine disinfection.

Chlorine disinfectant significantly changed microfauna habitat, community structure, and colonization mode in wastewater treatment plants.

This study revealed that chlorine disinfectant significantly changed microfauna habitat, community structure, and colonization mode in wastewater treatment plants during the coronavirus disease 2019 pandemic. Chlorine disinfectant could destroy the structure and stability of sludge flocs, reduce the abundance of beneficial microfauna in activated sludge, and even affect the colonization of sedentary ciliates on sludge. In addition, chlorine disinfectants might induce environmental and ecological risks related to microfauna, such as elevated suspended solids and release of bacteria and microfauna in the effluents.

Residual level of chlorine disinfectant, the formation of disinfection by-products, and its impact on soil enzyme activity.

Disinfectants can kill pathogenic microorganisms, effectively block the spread of infectious diseases, and are widely used during epidemics. However, a little has been studied about the environmental hazards caused by the heavy use of disinfectants. In this paper, the residual situation of chlorine ions in the soil, possible disinfection by-products (DBPs), and effects on soil enzyme activities after using 84 disinfectants (main component: sodium hypochlorite) and hypochlorite disinfectant (main component: hypochlorous acid) were investigated. It was found that the residual rates were generally higher than 92% for the 84 disinfectant treatment and between 80% ~ 90% for the hypochlorite disinfectant treatments. The overall change in chlorine ion concentration in the soil-leaching solution of the hypochlorite disinfectant treatments was relatively small and stable compared to the 84 disinfectant treatments. Several types of trihalomethanes (THMs) were detected after 24h of disinfection. The generation concentration of THMs was higher for the 84 disinfectant than for the hypochlorite disinfectant. The generation of trichloromethane was the highest, ranging from 1000 to 3000μg/L. Soil enzyme activities changed much when the soil was treated with the disinfectant for 28days. The above results indicated that hypochlorite disinfectant was safer and more stable than 84 disinfectants, and trichloromethane should be strictly controlled as a key indicator among the disinfection by-products. In addition, the long-term application of disinfectants affects soil enzyme activities obviously.

The formation and removal of disinfection byproducts in bioretention cells for treating stormwater runoff with chlorine disinfectant

The formation and removal of disinfection byproducts in bioretention cells for treating stormwater runoff with chlorine disinfectant

Effect of surfactants on inactivation of Bacillus subtilis spores by chlorine.

Bacterial spores pose significant risks to human health, yet the inactivation of spores is challenging due to their unique structures and chemical compositions. This study investigated the synergistic effect between surfactants and chlorine on the inactivation kinetics of Bacillus subtilis spores. Two surfactants, cocamidopropyl betaine (CAPB) and cetyltrimethylammonium chloride (CTMA) were selected to investigate chlorine disinfection in absence and presence of surfactants. The concurrent presence of both chlorine and surfactant resulted in a moderate reduction in the lag-phases for spore inactivation and negligible increase in the second-order inactivation rate constants. In contrast, when the spores were pre-exposed to surfactants, the lag-phases decreased by about 50 % for both CAPB and CTMA, and the second-order inactivation rate constants during post-chlorination remained constant for CAPB but increased by a factor of 2.3 for CTMA, compared to the control group with phosphate buffer. This synergistic effect became more pronounced with longer surfactant pre-exposure times, reaching its maximum at 3-6 h. The observed synergistic effect suggests that surfactants can potentially enhance the permeability of the coat which is the outmost layer of B. subtilis spores and a primary barrier for chemical disinfectants. Tracing a group of B. subtilis spores sequentially treated with surfactant and chlorine by atomic force microscopy, a significant decrease in compressive stiffness of the spores was observed due to exposure to surfactants, indicating alterations in the coat by surfactants. The trend in reducing compressive stiffness aligned well with the decrease of lag-phases in inactivation kinetics. Furthermore, CTMA was found to inactivate B. subtilis spores through mechanisms different from chlorine. Chlorine primarily inactivated B. subtilis spores before damaging the inner membrane of the spores which plays a crucial role in protecting the genetic material stored in the core of the spores. In comparison, CTMA damaged 22 % of the inner membrane for an inactivation efficiency of 99 %. A synergistic effect in damaging the inner membrane was observed when applying CTMA and chlorine simultaneously instead of sequentially.

A Study in the Contamination of Desalinated Water with Microorganisms, and Analysis of Chemical and Physical in Western Libya

Monitoring the changes that occur to water during distribution is vital to ensure water safety. The biological stability of reverse osmosis (RO) produced drinking water, characterized by low cell concentration and low assailable organic carbon, in combination with chlorine disinfection was investigated. Water quality at several locations throughout the existing distribution network was monitored to investigate whether microbial water quality changes can be identified. Libya is located in an arid and semi-arid region of Africa with no permanent rivers or true freshwater lakes and average annual rainfall of less than 100 mm. Limited access to surface water resources has led to a heavy reliance on groundwater. Extensive use of conventional water resources such as groundwater, poor awareness of how to optimally use and save water, and seawater intrusion into coastal aquifers have all contributed to a severe water crisis in Libya. The water crisis issues in Libya are exacerbated by the population distribution relative to available water resources. 75% of Libya’s population is concentrated in only 1.5% of the total land area in the western coastal centers of Jufra and Misrata, and the eastern coastal area of ​​Jebel Akhdar. The results from this study highlight the importance of implementing multiple barriers to ensure water safety. Changes in water quality detected even when high-quality disinfected reverse osmosis (RO) -produced water is distributed highlight microbiological challenges that chlorinated systems endure, especially at high water temperatures. The aim of this paper is to shed light on the conventional and non-conventional water resources in Libya. In this context, the research aims to provide an overview of seawater desalination technology in Libya and why desalination should be embraced as a strategic and ultimate solution to the water shortage problem. In addition to the bacterial contamination of desalinated water in western Libya. This study was investigated the quality of drinking water supplied in Some Commercial Water Purification Systems at Sabratha area. Water samples were collected from five stations at Sabratha region. The physicochemical parameters were mainly, pH, Alkalinity, Chloride, Nitrate, Sulfate, Magnesium, Calcium, Sodium, Potassium and TDS. The result shows that all these parameters were fall below WHO guidelines, except pH. The bacteriological result revealed that one of the studied stations was contaminated by E. coli bacteria.

Regulated 1-2 Carbon Disinfection Byproducts do not Correlate with Cytotoxicity with Increasing Disinfectant Contact Time During Chlorination, Chlorination Followed by Chloramination or Granular Activated Carbon Followed by Chlorination.

Regulations typically use four trihalomethanes (THM4) and five haloacetic acids (HAA5) as metrics of consumer exposure to disinfection byproducts (DBPs) and their chronic health risks. Their use as exposure metrics assumes that their concentrations correlate with DBP-associated toxicity. For a chlorine-disinfected surface water, this study demonstrates that increasing chlorine contact time from 1 to 7 days was associated with a 62-76% increase in THM4 and HAA5 but a 40-47% decrease in total cytotoxicity. Thus, the use of THM4 and HAA5 may divert regulatory attention away from the low water age sections of distribution systems near treatment facilities that may feature the highest cytotoxicity but lowest THM4/HAA5 concentrations. Among common options to reduce THM4/HAA5, this study also shows that chlorine disinfection followed by chloramines for maintaining a distribution system residual did not substantially reduce cytotoxicity. Granular activated carbon followed by chlorine reduced cytotoxicity by 28-80%, even at the lowest water ages where cytotoxicity was maximized. These findings highlight the need to identify DBPs that better correlate with toxicity than THM4/HAA5 to serve as metrics of exposure. These metrics could help identify distribution system locations exhibiting higher consumer risk and develop modifications to disinfection systems that effectively reduce consumer risk.

Research progress on environmental stability of SARS-CoV-2 and influenza viruses.

We reviewed research on SARS-CoV-2 and influenza virus detection on surfaces, their persistence under various conditions, and response to disinfectants. Viral contamination in community and healthcare settings was analyzed, emphasizing survival on surfaces influenced by temperature, pH, and material. Findings showed higher concentrations enhance survivability at room temperature, whereas stability increases at 4°C. Both viruses decline in low pH and high heat, with influenza affected by salinity. On various material surfaces, SARS-CoV-2 and influenza viruses demonstrate considerable variations in survival durations, and SARS-CoV-2 is more stable than influenza virus. On the skin, both virus types can persist for ≥2 h. Next, we delineated the virucidal efficacy of disinfectants against SARS-CoV-2 and influenza viruses. In daily life, exposure to ethanol (70%), isopropanol (70%), bleach (10%), or hydrogen peroxide (1-3%) for 15-30 min can effectively inactive various SARS-CoV-2 variants. Povidone-iodine (1 mg/mL, 1 min) or cetylpyridinium chloride (0.1 mg/mL, 2 min) may be used to inactive different SARS-CoV-2 variants in the mouth. Chlorine disinfectants (500 mg/L) or ultraviolet light (222 nm) can effectively inhibit different SARS-CoV-2 variants in public spaces. In conclusion, our study provides a scientific basis and practical guidance for reduction of viral persistence (retention of infectivity) on surfaces and environmental cleanliness.

Cancer incidence associations with drinking water arsenic levels and disinfection methods in Maine, USA.

Maine is a largely rural state where nearly half of the population uses drinking water from private wells. Arsenic (As) is present in some Maine groundwater, has been linked to cancer, and a lack of testing and treatment may expose people with private wells to elevated As levels. Disinfection byproducts (DBPs) include known and suspected carcinogens that form when chlorine or chloramines are added to water. People served by public water systems may be exposed to elevated levels of regulated DBPs such as trihalomethanes and haloacetic acids associated with chlorine and/or unregulated nitrogenous DBPs, or N-DBPs, such as nitrite and N-nitrosodimethylamine associated with chloramines. Contrary to initial expectations, there were no significant associations between median town As in well water and bladder, lung, kidney, or skin cancer incidence. Furthermore, bladder, melanoma, and other skin cancer incidence rates were negatively correlated with the percent of the town population using private wells. Analysis of cancer incidence associated with chlorine and chloramine disinfection showed elevated melanoma, and other skin cancer with chloramine use and elevated bladder and non-melanoma skin cancer with chlorine use compared to the no disinfectant case. We recommend more research on the links between disinfectant use and cancer.

Co-selective effect of dissolved organic matter and chlorine on the bacterial community and their antibiotic resistance in biofilm of drinking water distribution pipes

The proliferation of pathogenic bacteria and antibiotic resistance genes (ARGs) in the biofilm of drinking water distribution pipes poses a serious threat to human health. This work adopted 15 polyethylene (PE) pipes to study the co-selective effect of dissolved organic matter (DOM) and chlorine on the bacterial community and their antibiotic resistance in biofilm. The results indicated that ozone and granular activated carbon (O3-GAC) filtration effectively removed lignins and proteins from DOM, and chlorine disinfection eliminated carbohydrate and unsaturated hydrocarbons, which both contributed to the inhibition of bacterial growth and biofilm formation. After O3-GAC and disinfection treatment, Porphyrobacter, unclassified_d_bacteria, and Sphingopyxis dominated in the biofilm bacterial community. Correspondingly, the bacterial metabolism pathways, including the phosphotransferase system, phenylalanine, tyrosine and tryptophan biosynthesis, ABC transporters, and starch and sucrose metabolism, were downregulated significantly (p < 0.05), compared to the sand filtration treatment. Under such a situation, extracellular polymeric substances (EPS) secretion was inhibited in biofilm after O3-GAC and disinfection treatment, postponing the interaction between EPS protein and pipe surface, preventing bacteria, especially pathogens, from adhering to the pipe surface to form biofilm, and restraining the spread of ARGs. This study revealed the effects of various water filtration and disinfection processes on bacterial growth, metabolism, and biofilm formation on a molecular level, and validated that the O3-GAC filtration followed by chlorine disinfection is an effective and promising pathway to control the microbial risk of drinking water.

Simultaneous dehalogenation and oxidation of dichloroacetamide by Cu-modified CoFe-LDH in three-dimensional continuous flow aerated electrocatalytic reactor

Searching for catalysts and degradation systems for synchronous dehalogenation and oxidation of haloacetamides (HAcAms) is pressing. In this study, a novel three-dimensional continuous flow aerated electrocatalytic reactor (3D CFAER) system, which employed Cu-modified CoFe layered double hydroxides (CoFe-LDH) composite/activated carbon as a catalytic particle electrode for the degradation of dichloroacetamide (DCAcAm) was constructed. Under the experiment’s optimal operating parameters, the maximum degradation rate of DCAcAm reached 91.7 %. The superior performance for the degradation of DCAcAm was due to the enhanced electron transfer induced by the modification of Cu in CoFe-LDH. Moreover, Density Functional Theory (DFT) calculations indicated that Cu doping improved the ability of LDH to dissociate water, thereby enhancing its electrocatalytic performance. Scavenger experiments and Electron Paramagnetic Resonance (EPR) results revealed that •OH, O2•– and electrochemical direct dehalogenation were responsible for DCAcAm removal. Additionally, the electrocatalytic stability of the electrode was tested upon repeated use with DCAcAm degradation remaining as high as 81.7 % after five consecutive experiments. More importantly, in 3D CFAER, electrocatalytic treatment lasting 90 min reduced the TOC and COD of the actual chlorine disinfection wastewater by 64.1 % and 74.9 %, respectively. This study provides new theoretical basis and technical support for control of HAcAms.

Degradation of extracellular antibiotic resistance genes using peracetic acid (PAA) and performic acid (PFA)

Antibiotic resistant bacteria (ARB) associated infections are identified as a major threat to human health in the 21st century. Wastewater contains antibiotic resistance determinants and they are discharged to aquatic environments with treated or untreated effluents. These antibiotic resistance determinants can be taken up by environmental bacteria via horizontal gene transfer (HGT) and they can become antibiotic resistant. Among antibiotic resistance determinants, extracellular DNA containing antibiotic resistance genes can be up taken by environmental bacteria via natural transformation. Therefore, we evaluated the suitability of low-cost disinfectants peracetic acid (PAA) and performic acid (PFA) on inactivating total and functional extracellular ARGs in ultrapure water and secondary wastewater effluent matrices using pUC19 as a model ARG. Performance of PAA and PFA in inactivating extracellular ARGs was compared with the performance of free chlorine disinfection. RT-qPCR results showed that inactivation of ampR gene in pUC19 plasmid suspended in ultrapure water and wastewater secondary effluent by free chlorine was higher compared to PAA and PFA. However, the reduction of functional pUC19 by PAA and PFA were comparable to free chlorine. Transformation frequency of pUC19 treated by PAA and PFA achieved the maximum possible reduction within a shorter time compared to free chlorine treatment, highlighting the possibility of having disinfection chambers with smaller footprints in wastewater treatment plants. These results suggest the suitability of PAA and PFA for inactivation of ARGs in aquatic samples as alternative disinfectants to free chlorine.

Impacts of iodoacetic acid on reproduction: current evidence, underlying mechanisms, and future research directions.

In light of the undeniable and alarming fact that human fertility is declining, the harmful factors affecting reproductive health are garnering more and more attention. Iodoacetic acid (IAA), an emerging unregulated drinking water disinfection byproduct, derives from chlorine disinfection and is frequently detected in the environment and biological samples. Humans are ubiquitously exposed to IAA daily mainly through drinking water, consuming food and beverages made from disinfected water, contacting swimming pools and bath water, etc. Mounting evidence has indicated that IAA could act as a reproductive toxicant and bring about multifarious adverse reproductive damage. For instance, it can interfere with gonadal development, weaken ovarian function, impair sperm motility, trigger DNA damage to germ cells, perturb steroidogenesis, etc. The underlying mechanisms predominantly include cytotoxic and genotoxic effects on germ cells, disturbance of the hypothalamic-pituitary-gonadal axis, oxidative stress, inhibition of steroidogenic proteins or enzymes, and dysbiosis of gut microbiota. Nevertheless, there are still some knowledge gaps and limitations in studying the potential impact of IAA on reproduction, which urgently need to be addressed in the future. We suppose that necessary population epidemiological studies, more sensitive detection methods for internal exposure, and mechanism-based in-depth exploration will contribute to a more comprehensive understanding of characteristics and biological effects of IAA, thus providing an important scientific basis for revising sanitary standards for drinking water quality.