Dechlorination Research Articles

Microbial water quality investigation through flow cytometry fingerprinting: from source to tap

Abstract Ensuring the quality of treated drinking water is crucial for preventing potential health impacts, regulatory fines, and reputation damage. Traditional culture-based microbiological methods often fail to capture the heterogeneity of the bacterial communities in drinking water. This study employed daily interstage monitoring and flow cytometry (FCM) analysis over a period of one year to investigate the dynamics of water treatment processes and service reservoirs. The objective of this study was to test the utility of FCM fingerprints for aiding in microbial event detection. We found that the chlorine concentration contact time was pivotal for microbial log reduction across the treatment works. FCM fingerprints exhibited significant deviations during operational events, such as process interruptions, but did not correlate with the presence of bacterial indicator organisms in the distributed and tap water. Furthermore, the diversity of bacterial fingerprints, quantified by the Bray–Curtis dissimilarity index, served as an indicator for identifying potentially poor microbial water quality. In chlorinated waters with low cell counts, the background signal shows potential as a metric to differentiate between different water sources, thereby offering the possibility to characterize breakthrough events in these circumstances that challenge most other microbial analytical methods. Interestingly, groundwater from simpler treatment works showed a higher occurrence of bacterial indicators, whereas surface water works had a lower incidence. These findings underpin the importance of appropriate disinfection even for “low-risk” source waters and the added value that the statistical interpretation of FCM data can offer objective decision making.

Study on unconfined compressive strength and deformation characteristics of chlorine saline soil

The distribution of saline soil is wide and the area is large in China. The saline soil in different regions shows their own characteristics. The saline soil of single salt is configured by adding different contents of NaCl to the loess in Xi'an. The effects of chlorine content and water content on soil strength and volume change in a large water content range was studied, and the change mechanism was analyzed by scanning electron microscopy. The results show that the strength of chloride saline soil increases with the decrease of water content. The moisture content of 12% is the critical point of strength change of chloride saline soil. When the moisture content is greater than 12%, the strength of soil decreases with the increase of salt content. When the water content is less than 12%, the strength of saline soil is 3% NaCl content > 1% NaCl content > 5% NaCl content > 0% NaCl content. The volume change of the sample consists of three parts: elastic deformation during sample pressing, volume shrinkage during water loss and salt expansion. In the absence of NaCl and 1% NaCl content, the sample was in the state of shrinkage during the loading process, in which with the decrease of moisture content shrinkage rate slowed down. The volume change rate of 3% and 5% NaCl showed an inflection point from negative to positive when the water content was 15%. When the water content is less than 12%, the saline soil with 3% NaCl content has the characteristics of high strength and unobvious salt expansion. The method of adding 3% NaCl to loess in Xi 'an area can be used to simulate the cement between soil particles, which provides a reference for artificially preparing structural soil. According to the microstructure analysis, the higher the salt content of saline soil, the smaller the soil pores, and the contact form of soil particles gradually develops from the point contact between soil particles to the salt-wrapped structure.

Mechanochemical nitridation of micron zero-valent iron for enhanced dechlorination of trichloroethylene: Mechanistic insights into nitrogen sources and ball milling conditions

The performance optimization of zero-valent iron (ZVI) based materials for reductive dechlorination remains challenging. After extensive research on sulfidation modification, the doping of heteroatom nitrogen (N) into ZVI for reductive dechlorination of chlorinated hydrocarbons (CHCs) becomes a new promising trend. In this study, surface modification of microscale ZVI (mZVI) was carried out by a facile ball milling method, and Fe–N(C) coated mZVI (abbreviated as N(C)-mZVIbm) synthesized from different N sources of dimethylimidazole, urea and melamine were characterized. The effects of nitrogen-to-iron ratios (N/Fe), ball milling time and speed on the reductive dechlorination of trichloroethylene (TCE) were further investigated. A series of characterization and mechanistic analysis showed that the high reactivity of N(C)-mZVIbm with melamine as nitrogen source (abbreviated as N(C)-mZVIbm(M)) was attributed to the properties and thickness of its particle passivation layer, and faster electron transfer from the reduced iron species to the surface layer. In addition, N(C)-mZVIbm(M) exhibited great performance for dechlorination at a wide pH range of 3 to 11, due to alleviated passivation of the Fe0 core under alkaline conditions by Fe–N(C). This study presents new ideas and evidences for the environmentally friendly synthesis of N-modified ZVI materials and their practical application in groundwater remediation.

Exposure to chlorinated drinking water alters the murine fecal microbiota

An abundant body of scientific studies and regulatory guidelines substantiates antimicrobial efficacy of freshwater chlorination ensuring drinking water safety in large populations worldwide. In contrast to the purposeful use of chlorination ensuring antimicrobial safety of drinking water, only a limited body of research has addressed the molecular impact of chlorinated drinking water exposure on the gut microbiota. Here, for the first time, we have examined the differential effects of drinking water regimens stratified by chlorination agent [inorganic (HOCl) versus chloramine (TCIC)] on the C57BL/6J murine fecal microbiota. To this end, we exposed C57BL/6J mice to chlorinated drinking water regimens followed by fecal bacterial microbiota analysis at the end of the three-week feeding period employing 16S rRNA sequencing. α-diversity was strongly reduced when comparing chlorinated versus control drinking water groups and community dissimilarities (β-diversity) were significant between groups even when comparing HOCl and TCIC. We detected significant differences in fecal bacterial composition as a function of drinking water chlorination observable at the phylum and genus levels. Differential abundance analysis of select amplicon sequence variants (ASVs) revealed changes as a function of chlorination exposure [up: Lactobacillus ASV1; Akkermansia muciniphila ASV7; Clostridium ss1 ASV10; down: Ileibacterium valens ASV5; Desulfovibrio ASV11; Lachnospiraceae UCG-006 ASV15]. Given the established complexity of murine and human gastrointestinal microbiota and their role in health and disease, the translational relevance of the chlorination-induced changes documented by us for the first time in the fecal murine microbiota remains to be explored.

Impact of gate electrode on free chlorine sensing performance in solution-gated graphene field-effect transistors.

Free chlorine is widely used to disinfect water used for drinking and food processing. This requires highly sensitive, simple, and capable continuous-measurement sensors to enable the concentration of free chlorine in water to be monitored and controlled. Free chlorine sensors based on solution-gated graphene field-effect transistors (GFETs) are a suitable platform for highly sensitive and continuous measurements. However, their sensing mechanisms require further elucidation to improve their performance. In this study, we focused on the gate electrode and investigated its influence on the sensing performance. Using the free chlorine sensor based on the solution-gate GFET, we showed that the Dirac point voltage in the transfer curve changed significantly as the free chlorine concentration changed, and the electric double-layer capacitance of the gate electrode decreased. Furthermore, we demonstrated that a solution-gated GFET using graphene or boron-doped diamond as the gate electrode could be used to detect changes in the free chlorine concentration in the concentration range of tap water. The sensing performance in the low concentration range benefits from the wide potential window of carbon-based electrodes, which do not have electrochemically active sites. Using these carbon-based materials as gate electrodes, GFETs have the potential to be used as durable sensors that are resistant to surface fouling and oxidation.

Effects of humic electron mediators on reductive dechlorination of polychlorinated biphenyl by consortia enriched from terrestrial and marine environments.

Humic electron mediators can facilitate the reductive dehalogenation of organohalogenated compounds by accelerating electron transfer. To investigate the effect of humic electron mediators on the microbial anaerobic reductive dechlorination of Polychlorinated biphenyls (PCBs), three types of humic electron mediators, humin (HM), humic acid (HA), and anthraquinone-2,6-disulfonic acid (AQDS, HA analogs), were added to PCB dechlorination cultures enriched from different sources in terrestrial and marine environments (T and M cultures). The results showed that meta- and para-site dechlorination occurred in the M culture, while only meta-site dechlorination occurred in the T culture. The dechlorination process N and the dechlorination process H or H' are presented in both cultures. HM enhanced PCB dechlorination metabolic activity in both cultures mainly by promoting meta-site dechlorination. HA showed a weak promoting effect on the M culture by promoting para-chlorine removal but inhibited the dechlorination metabolism of the terrestrial-origin culture, inhibiting meta-chlorine removal. AQDS showed inhibitory effects on both cultures by inhibiting the microbial removal of meta-chlorine. High-throughput sequencing and qPCR results suggest that HM is not a carbon source for the potential dechlorinating metabolism of Dehalococcoides but may promote reductive dechlorination by changing the community structure, and AQDS may inhibit anaerobic reductive dechlorination of PCBs by inhibiting the growth of Dehalococcoides. This study provides insights into the mechanism of enhancing PCB microbial dechlorination mediated by humic substances and plays a significant role in extending the application prospects of PCBs bioremediation technology.

Analysis of Ultrasound Supported Antimicrobial and Antibiofilm Activities of Disinfection By-product Bromochloroacetonitrile

Introduction: Some microorganism threaten human health by forming biofilm in water systems. Because microorganism in the biofilm structure are more resistant to antimicrobials. Methods: Water systems are disinfected with physical methods, such as ultrasonication techniques and chemical disinfectants. Bromochloroacetonitrile is produced as a by-product from algae and fulvic acid sources during water chlorination. This study aimed to investigate the antimicrobial and antibiofilm effects of bromochloroacetonitrile on some bacteria alone and with ultrasound treatment. The study used Escherichia coli ATCC 25922, Klebsiella pneumoniae MCTC 13438, and Staphylococcus aureus ATCC 25923 strains. The antimicrobial and antibiofilm activities of the test substance were analyzed alone with bromochloroacetonitrile and Ultrasound-assisted. Minimum Inhibitory Concentration values of the test substance against Escherichia coli ATCC 25922, Klebsiella pneumoniae MCTC 13438, and Staphylococcus aureus ATCC 25923 strains were 25, 25 and 50 mM, respectively, and Minimum Bactericidal Concentration values were 50, >50, and >50 mM, respectively. Results: The obtained data show that bromochloroacetonitrile is a potential disinfection agent that can be used against biofilm formation in water systems. Besides, it was revealed that when ultrasound treatment was applied with bromochloroacetonitrile, it showed 100% antibiofilm activity on E. coli and K. pneumoniae and 79.45% antibiofilm activity on S. aureus strains. The obtained data show that bromochloroacetonitrile is a potential disinfection agent that can be used against biofilm formation in water systems. This study is preliminary and planned to reveal the cytotoxic effects of bromochloroacetonitrile on healthy human skin and liver cells in the following study. Conclusion: These results will contribute to the literature, as no study reveals the antimicrobial and antibiofilm activities of bromochloroacetonitrile.

MONITORAMENTO DE TRIHALOMETANOS (THMs) E DA QUALIDADE DA ÁGUA PARA ABASTECIMENTO PÚBLICO DA CIDADE DE CAVALCANTE, GOIÁS

MONITORING OF TRIHALOMETHANES (THMs) AND WATER QUALITY FOR PUBLIC SUPPLY IN THE CITY OF CAVALCANTE, GOIÁS. Trihalomethanes (THMs) are organohalogens compounds formed from the reaction between free residual chlorine and natural matter organic (humic substances) present in raw water from surface sources. This study aimed to evaluate the formation of THMs resulting from the application of chlorine for disinfection, in the water treating process for public supply in the city of Cavalcante, GO, located in the region of Chapada dos Veadeiros (Brazil). The results of physical-chemical analyses apparent color, turbidity, pH, free residual chlorine, consumed oxygen, hardness, total alkalinity and THMs demonstrated a positive and strong correlation between the formation of THMs and the hardness of treated water, as well as the chlorine consumed during disinfection process. It was observed an increase in apparent color, turbidity and consumed oxygen in the rainy season. These parameters indicate the presence of organic matter and that present a positive and moderate correlation with the formation of THMs.

Catalytic dehalogenation with activated borane, a porous borane cluster polymer

Catalytic reductive dehalogenation of aliphatic C–X bonds (X = F, Cl) was achieved using triethylsilane and a halogen- and metal-free solid porous polymer based on borane clusters as a catalyst.

Water and war: The effect of functioning chlorinated water stations in reducing waterborne diseases during conflict in northwest Syria, 2017-2021.

Since 2011, Syria has been engulfed in a complex conflict marked by both targeted and indiscriminate attacks on civilians and civilian infrastructure. Water infrastructure has been continuously targeted, exacerbating problems with contamination of and access to clean adequate drinking water, and increasing the risk of waterborne diseases. We aimed to determine whether having access to more functional and chlorinated water stations is associated with a reduced risk of waterborne disease in northwest Syria. We examined the effect of functioning chlorinated water stations on the incidence of waterborne disease in 10 districts of Northwest Syria between January 1, 2017, and June 30, 2021, using weekly reported disease surveillance data and data from a water, sanitation, and hygiene (WASH) system evaluation program of the Assistance Coordination Unit (ACU). We ran eight negative binomial models to examine the association between functioning chlorinated water stations and the incidence of four of the five waterborne diseases: acute bloody diarrhea (ABD), acute other diarrhea (AOD), acute jaundice syndrome (AJS), and severe typhoid fever (STF). Dose-response models were used to investigate how the incidence of disease can theoretically be reduced as functioning and chlorinated water stations strategically increase. Compared to areas with lower quintiles of functioning and chlorinated water stations, the rates of the four waterborne diseases were lower in areas with higher quintiles of functioning and chlorinated water stations. Exposure to functioning water stations had a stronger association with lower rates of waterborne diseases than exposure to chlorinated water stations. Dose-response models demonstrate a potential for curbing the incidence of acute diarrhea and acute jaundice syndrome. The results of this study provide an understanding of the effects of water station functionality and chlorination in conflict settings. These findings support greater prioritization of WASH activities in countries experiencing violence against civilian infrastructure.

ANALYSIS OF APPLYING SURFACE WATER TREATMENT TECHNOLOGY WHEN USING CHLORINE DIOXIDE AT WATER SUPPLY PLANTS

The results of the conducted research made it possible to establish that in EU countries chlorine dioxide (CD) is more often used for secondary or final disinfection of drinking water. By-products of this process are chlorites and chlorates, which are subject to control in the drinking water of all EU countries. Aldehydes and carboxylic acids can also be formed in drinking water, which leads to a decrease in the microbiological stability of tap water. Ozonation and filtration using a carbon filter are used in the final stage of drinking water purification, which contributes to a significant reduction in the dose of CD and water contamination with toxic chlorites. In the case of pre-oxidation of water with sodium hypochlorite, the largest amount of chlorites and chlorates is formed, while in the case of using potassium permanganate for the same purpose, the need for CD and the amount of chlorites and chlorates in drinking water reduced. Chlorination of natural water that has undergone CD pre-oxidation leads to complete oxidation of the chlorites that have formed, increases the effectiveness of disinfection, and provides a bacteriostatic effect in the distribution network. During 2021-2022, when using CD for the treatment of drinking water at the Dniprovska WTP in Kyiv it was established that the process of treating natural water with CD is accompanied by the formation of its by-products, mainly toxic chlorites, the levels of which depend on the applied doses of CD and are the lowest in winter, while the largest ones are observed in summer and do not always reach regulatory values (0,2 mg/l) and range up to 0,7 mg/l, which corresponds to the WHO recommended standard for this substance in drinking water. Italian scientists focus their attention on the fact that during the first years of using CD at each water supply station, optimal conditions must be ensured for the safe and effective use of this reagent. Therefore, CD is becoming widespread in the EU countries and Ukraine for the treatment of tap drinking water; it is an alternative method of water effective disinfection at water supply stations with traditional surface water purification technology. Using such a method for treating surface water requires a preliminary pilot experiment and should be carried out along with an analysis of the feasibility of using the methods for preliminary and/or final purification of drinking water from organic substances and additional disinfection. Today, based on experimental and natural studies, it is relevant to expand knowledge about the properties of CD in the case of its use in drinking water supply for the treatment of surface water with a high content of organic substances.

Evaluation of alternate hosts for recombinant expression of a reductive dehalogenase

Organohalides are recalcitrant, toxic environmental pollutants. Reductive dehalogenase enzymes (RDases) found in organohalide respiring bacteria (OHRB) utilise organohalides as electron acceptors for cellular energy and growth, producing lesser-halogenated compounds. Consequently, microbial reductive dehalogenation via organohalide respiration represents a promising solution for clean-up of organohalide pollutants. Dehalobacter sp. UNSWDHB is an OHRB capable of respiring highly toxic chloroform (CF) and converting it to dichloromethane (DCM). TmrA has been identified as an RDase responsible for this conversion and different strategies for generation of functional recombinant TmrA is the focus of this article. In this study, TmrA was recovered from inclusion bodies expressed in E. coli and refolded in the presence of FeCl3, Na2S and cobalamin to yield functional enzyme. TmrA has been previously expressed in a soluble and functional form in the corrinoid-producing Bacillus megaterium. Using a fractional experimental design for cultivation and induction combined with purification under anaerobic conditions resulted in substantially higher activity of recombinant and native TmrA than previously reported. TmrA was then expressed in a soluble and active form in Shimwellia blattae. Co-expression with two different putative chaperone proteins from the original host did not increase the level of soluble expression in S. blattae, however activity assays showed that removing the TAT signal from TmrA increases the dechlorination activity compared to when the TAT signal is present. Finally, TmrA was successfully expressed in a soluble and active form in the H2-oxidizing C. necator H16, a novel host for the expression of RDases.

Biodegradation of chloroethene compounds under microoxic conditions.

The biodegradation of chloroethene compounds under oxic and anoxic conditions is well established. However, the biological reactions that take place under microoxic conditions are unknown. Here, we report the biostimulated (BIOST: addition of lactate) and natural attenuated (NAT) degradation of chloroethene compounds under microoxic conditions by bacterial communities from chloroethene compounds-contaminated groundwater. The degradation of tetrachloroethene was significantly higher in NAT (15.14% on average) than in BIOST (10.13% on average) conditions at the end of the experiment (90 days). Sporomusa, Paracoccus, Sedimentibacter, Pseudomonas, and Desulfosporosinus were overrepresented in NAT and BIOST compared to the source groundwater. The NAT metagenome contains phenol hydrolase P1 oxygenase (dmpL), catechol-1,2-dioxygenase (catA), catechol-2,3-dioxygenases (dmpB, todE, and xylE) genes, which could be involved in the cometabolic degradation of chloroethene compounds; and chlorate reductase (clrA), that could be associated with partial reductive dechlorination of chloroethene compounds. Our data provide a better understanding of the bacterial communities, genes, and pathways potentially implicated in the reductive and cometabolic degradation of chloroethene compounds under microoxic conditions.

Integrated Advanced Molecular Tools Predict In Situ cVOC Degradation Rates: Field Demonstration.

Chlorinated volatile organic compound (cVOC) degradation rate constants are crucial information for site management. Conventional approaches generate rate estimates from the monitoring and modeling of cVOC concentrations. This requires time series data collected along the flow path of the plume. The estimates of rate constants are often plagued by confounding issues, making predictions cumbersome and unreliable. Laboratory data suggest that targeted quantitative analysis of Dehalococcoides mccartyi (Dhc) biomarker genes (qPCR) and proteins (qProt) can be directly correlated with reductive dechlorination activity. To assess the potential of qPCR and qProt measurements to predict rates, we collected data from cVOC-contaminated aquifers. At the benchmark study site, the rate constant for degradation of cis-dichloroethene (cDCE) extracted from monitoring data was 11.0 ± 3.4 yr-1, and the rate constant predicted from the abundance of TceA peptides was 6.9 yr-1. The rate constant for degradation of vinyl chloride (VC) from monitoring data was 8.4 ± 5.7 yr-1, and the rate constant predicted from the abundance of TceA peptides was 5.2 yr-1. At the other study sites, the rate constants for cDCE degradation predicted from qPCR and qProt measurements agreed within a factor of 4. Under the right circumstances, qPCR and qProt measurements can be useful to rapidly predict rates of cDCE and VC biodegradation, providing a major advance in effective site management.

Generating colloidal Fe/C composites via hydrothermal carbonization – A critical study

The increasing need for water remediation due to water scarcity and the accumulation of persistent pollutants in water cycles requires innovative materials and their more sustainable synthesis processes. The aim of this work was therefore to develop an approach for the bottom-up synthesis of colloidal Fe/C composites. It was tested whether the composites fulfill the main criteria for use as injectable adsorbents and reducing agents for the removal of chlorinated pollutants in in-situ groundwater remediation. After screening different Fe and C precursors, the bottom-up synthesis of a particulate and reactive Fe/C composite was developed via hydrothermal carbonization (HTC) of mixtures of ferrous and sodium gluconate in a one-pot HTC and subsequent carbothermal reduction at 800 °C. The produced particles show good dispersibility with particle diameters in the range of d10 ≥ 2 µm, d50 ≈ 11 µm and d90 ≤ 40 µm in aqueous suspensions. By varying the molar ratio of Fe to gluconate in the HTC process, the final content of zero-valent iron equivalents (ZVI) in the composite could be adjusted between (24 ± 12) and (49 ± 15) wt.-%. The chemical reactivity of the composite was tested by reductive dechlorination of chloroform (CF) as a test reaction. The characterization of the composites before and after reductive dechlorination with X-ray diffraction (XRD) shows that not only pristine Fe0 but also Fe3C is active in the reductive dechlorination reaction. Palladization of the composite material shifts the product selectivity from dichloromethane as the main product to the non-chlorinated products methane (up to 77 mol-%) and ethane (up to 9 mol-%) without any external H2 feed. The dispersiblity and intrinsic reactivity of the synthesized composites meet the requirements for application in water remediation where contaminants need to be retained and degraded, e.g. for groundwater remediation or protection by the in-situ generation of permeable barriers using modern injection technologies.

Formation of halogenated forms of bisphenol A (BPA) in water: Resolving isomers with ion mobility – mass spectrometry and the role of halogenation position in cellular toxicity

Halogenated BPA (XBPA) forms resulting from water chlorination can lead to increased toxicity and different biological effects. While previous studies have reported the occurrence of different XBPAs, analytical limitation have hindered the analysis and differentiation of the many potential isomeric forms. Using online solid-phase extraction - liquid chromatography - ion-mobility - high-resolution mass spectrometry (OSPE-LC-IM-HRMS), we demonstrated a rapid analysis method for the analysis of XBPA forms after water chlorination, with a total analysis time of less than 10 min including extraction and concentration and low detection limits (∼5–80 ng/L range). A multi in-vitro bioassay testing approach for the identified products revealed that cytotoxicity and bioenergetics impacts were largely associated with the presence of halogen atoms at positions 2 or 2’ and the overall number of halogens incorporated into the BPA molecule. Different XBPA also showed distinct impacts on oxidative stress, peroxisome proliferator-activated receptor gamma - PPARγ, and inflammatory response. While increased DNA damage was observed for chlorinated water samples (4.14 ± 1.21-fold change), the additive effect of the selected 20 XBPA studied could not explain the increased DNA damage observed, indicating that additional species or synergistic effects might be at play.

Approaching easy water disinfection for all: Can in situ electrochlorination outperform conventional chlorination under realistic conditions?

Electrochlorination has gained research interest for its potential application as decentralized water treatment. A number of studies have displayed promising efficiency for water disinfection. However, a comprehensive comparison of in situ electrodisinfection to existing disinfection techniques, particularly under realistic water composition and flow rates, still needs additional research efforts. The aim of this study is to evaluate in situ electrochlorination while comparing the treatment with conventional chemical chlorination for point-of-entry decentralized disinfection at the household level. An electrochemical flow cell reactor was operated in a single pass mode considering water flow and water consumption for a household of four family members. Disinfection efficiency assessment of both electrochemical and chemical chlorination was conducted using bacterial and viral surrogates, E. coli and MS2 bacteriophage. Furthermore, a techno-economic analysis was conducted, using the levelized cost of water, to compare two electrochemical chlorination scenarios (i.e., electrical grid energy use, and solar panel powered system) and benchmarked against the baseline treatment of chemical chlorination. The findings revealed increased inactivation efficiency of in situ electrochlorination over conventional chlorination (p-value < 0.05). The synergetic impact of radicals and chlorine, and/or contribution of high chlorine concentration at acidic pH near anode surface were identified as key factors that could enhance disinfection performance of in situ electrochlorination. The techno-economic analysis demonstrated that electrochemical treatment, when operated using renewable energy sources, is not only a more environmentally sustainable approach, but also emerges as a more economically feasible solution for decentralized water treatment application. The results highlight that in situ electrochlorination is a more advanced alternative to decentralized water chlorination. However, further fundamental research on products and by-products formation under various water matrices is required.

Enhanced degradation of florfenicol by microscale SiC/Fe: Dechlorination via hydrogenolysis

Herein, the degradation of florfenicol (FLO) over zero-valent iron (ZVI) enhanced by SiC was systematically investigated. It was found that 5 g/L of ZVI/SiC (1:3) at pH 3.0 could completely degrade 20 mg/L of FLO within 1 h, with a Kobs value of 0.0873 min−1, 12.5 times greater than that of pure ZVI (0.0069 min−1). Vibrating sample magnetometer (VSM) characterizations revealed that the use of SiC supporter reduces the magnetic intensity of ZVI, which mitigates iron particle agglomeration, increases Brunauer-Emmett-Teller (BET) surface area, and enhances FLO degradation efficiency. Furthermore, ZVI/SiC exhibits a much lower hydrogen evolution potential (HEP) and significantly higher corrosion currents compared to pure ZVI. FLO was proposed to undergo degradation via reductive dechlorination, involving a hydrogenolysis mechanism that entails the cleavage of the σ bond. This study provides new insights into the reduction hydrogenation mechanism of ZVI.

Oxalate-modified microscale zero-valent iron for trichloroethylene elimination by adsorption enhancement and accelerating electron transfer

Trichloroethylene (TCE) with trace concentrations is often detected in soils and groundwater, posing potential damages to public health. The elimination of TCE can be achieved through reductive dechlorination using zero-valent iron (ZVI). However, ZVI usually suffers from the presence of passive iron (hydro)oxides layer and low electron transfer rate, thus leading to the unsatisfactory reactivity. Herein, we fabricated oxalated ZVI (Ox-ZVIbm) by mechanical ball-milling of micro-scale ZVI and H2C2O4·2H2O to modify the ZVI surface composition. To be specific, the modification of the iron oxide shell by oxalic acid facilitated the generation of unsaturated coordination Fe(II), enhancing TCE adsorption. Furthermore, the formed FeC2O4 on the iron oxide shell improved electron transfer efficiency, contributing to the enhanced TCE reductive dechlorination. Impressively, the rate of TCE degradation by Ox-ZVIbm was 10-fold higher than that of ZVIbm without oxalate modification. Moreover, Ox-ZVIbm samples were filled in a laboratory Permeable Reactive Barriers (PRB) column to treat actual underground wastewater containing TCE pollutants. The effluent concentration of TCE maintained steadily below 0.21 mg/L for over 10 days, complying with the National Groundwater Class IV standard (GBT 14848–2017). This marks a significant step toward practical groundwater treatment.

Trihalomethanes in developed and developing countries.

The reactions between natural organic matter, anthropogenic contaminants, ions, and disinfectants lead to the formation of disinfection by-products (DBPs) such as trihalomethanes (THMs) in drinking water. The formation of THMs is strongly related to the chlorination of water. The study's central objective was to compare the concentration of THMs in twenty developed and developing countries and their disinfection techniques. The THM concentration in 11 developed and 9 developing countries ranged from 0.5 µg/L (Germany) to 215 µg/L (Russia) and 3 µg/L (China) to 439.2 µg/L (Bangladesh), respectively. The developed country has partially succeeded in reducing THM concentration in drinking water, whereas significant steps are needed in developing countries to reduce the existing high THM concentration. The concentration of THMs in water varies among these countries because of the different water sources, water quality, environmental conditions, and efficiency of water treatment technologies. A meaningful relationship has been observed between the properties of water and the THM formation. The use of chemical disinfectants will result in new forms of DBPs that are undesirable due to their carcinogenic and mutagenic effects on human health. The DBP guidelines by various national and international agencies have helped to control and manage the THM concentration in drinking water. However, these regulatory standards are not continuously monitored. Therefore, the formation of these compounds should be prevented either by removing THMs forming precursors or by using an integrated approach for controlling THM formation by implementing advanced water treatment technology. Extensive research is desirable in domains like THM minimization strategies which are easy to deploy, scalable, and cost-effective.