Dechlorination Research Articles

Evaluation of the biological treatment of a real contaminated groundwater through reductive dechlorination biostimulation

Chlorinated aliphatic hydrocarbons (CAHs) are common groundwater contaminants due to improper utilization in past industrial activity. Anaerobic reductive dechlorination, where bacteria use CAHs as electron acceptors, is crucial for bioremediation. Environmental conditions, such as nutrient availability and electron donors (i.e., molecular hydrogen), can influence the effectiveness of bioremediation processes. Also, bioremediation strategies like bioaugmentation (i.e., the supply of the enriched dechlorinating consortium) and bio-stimulation (i.e., the supply of electron donor) can improve CAHs removal performances. Here, a microcosm study is presented to assess the effectiveness of bioaugmentation with an enriched dechlorinating consortium for groundwater remediation. Target contaminants used were tetrachloroethane (TeCA), trichloroethylene (TCE) and sulphate ion. Various conditions, including biostimulation and bioaugmentation approaches were tested to evaluate the feasibility of biological treatment. Operating conditions, i.e., mineral medium and lactate, facilitated the dechlorination of TCE into ETH, leading to an increase in the dechlorinating population (Dehalococcoides mccartyi) to 67% of the total bacteria, with reductive dechlorination (RD) rates up to 7 µeq/Ld. Conversely, the RD performance of microcosms with real contaminated groundwater was negatively affected by the combined presence of TeCA and sulphate, indicated by a low abundance of D. mccartyi (<3%) and low RD rates (up to 0.39 µeq/Ld), suggesting that the native microbial population lacked the capacity for effective dechlorination. Moreover, the principal component analysis plot highlighted distinct groupings based on microbial community across different microcosm conditions, indeed, microbial community structures dominated by D. McCarty were associated with higher reductive dechlorination rates while non-augmented and non-stimulated microcosms reflected distinct microbial communities dominated by non-dechlorinating taxa. Additionally, RD decreased (48, 23, 22, and 14 µeq/Ld) with increasing sulphate concentrations (0, 150, 225, and 450 mgSO4 -2/L), further demonstrating the inhibitory effect of sulphate in the treated contaminated groundwater. Overall, this study highlights the complex interplay between environmental conditions, treatment strategies, and microbial communities in driving dechlorination processes. Specifically, the effectiveness of reductive dechlorination is heavily influenced by the availability of electron donors and the composition of the medium or groundwater, which can drive significant shifts in microbial community dynamics, either supporting or hindering the reductive dechlorination process.

Electrosynthesis of Fluoroalkenes from Alpha-CF3 and Alpha-CF2H Benzyl Halides.

We have developed an efficient synthesis of fluoroalkenes via tandem electrochemical dehalogenation-elimination protocol. The key step is the generation of carbon anion by electrochemical reductive dehalogenation of alkyl halides. Various gem-difluoroalkenes and monofluoroalkenes were prepared in moderate to good yields from α-difluoromethylated/α-trifluoromethylated benzyl halides.

Scalable Electrochemical Dehalogenative Carboxylation without a Sacrificial Metal Anode

A scalable electrochemical procedure for the synthesis of carboxylic acids from organic halides has been developed using a spinning cylinder electrode electrochemical reactor. The electrochemical process is based on the reductive dehalogenation of the starting material followed by trapping of the resulting carbanion with CO2. The protocol is compatible both with organic chlorides and bromides and uses inexpensive graphite and stainless steel as electrode materials. As sacrificial metal anodes are avoided, the method can be readily scaled up in flow mode. The procedure is compatible with a wide range of substrates (24 examples), including aryl and alkyl halides as well as heterocyclic compounds. Multigram scale preparations in flow mode have been demonstrated by processing 600 mL of reaction mixture in an electrolyte recirculation setup.

Interaction between nitrate and trichloroethene bioreduction in mixed anaerobic cultures

Bioremediation of trichloroethene (TCE)-contaminated sites often leads to groundwater acidification, while nitrate-polluted sites tend to generate alkalization. TCE and nitrate often coexist at contaminated sites; however, the pH variation caused by nitrate self-alkalization and TCE self-acidification and how these processes affect nitrate reduction and reductive dichlorination, have not been studied. This study investigated the interaction between nitrate and TCE, two common groundwater co-contaminants, during bioreduction in serum bottles containing synthetic mineral salt media and microbial consortia. Our results showed that TCE concentrations up to 0.3 mM stimulated nitrate reduction, while the effect of nitrate on TCE reductive dechlorination was more complex. Nitrate primarily inhibited the reduction of TCE to dichloroethene (DCE) but enhanced the reduction of vinyl chloride (VC) to ethene. Mechanistic analysis suggested that this inhibition was due to the thermodynamic favorability of nitrate reduction over TCE reduction, while the promotion of VC reduction was linked to pH stabilization via self-alkalization. As the initial nitrate concentration increased from 0 to 3 mM, the relative abundance of putatively denitrifying genera, such as Petrimonas and Trichlorobacter, increased. However, the abundance of fermentative Clostridium sharply declined from 31.11 to 1.51%, indicating strong nitrate inhibition. Additionally, the relative abundance of Dehalococcoides, a genus capable of reducing TCE to ethene, slightly increased from 23.91 to 24.26% at nitrate concentrations up to 0.3 mM but decreased to 18.65% as the nitrate concentration increased to 3 mM, suggesting that Dehalococcoides exhibits a degree of tolerance to high nitrate concentrations under specific conditions. Overall, our findings highlight the potential for simultaneous reduction of TCE and nitrate, even at elevated concentrations, facilitated by self-regulating pH control in anaerobic mixed dechlorinating consortia. This study provides novel insights into bioremediation strategies for addressing co-contaminated sites.

Monitoring the impact of chlorinated drinking water on the developing gut microbiota of adolescent mice using genetic profiling

ABSTRACT Water chlorination as a method to deter the growth of disease-causing microbes has been standard practice in the United States for over a century. Toxicological studies that originally designated chlorinated water as safe for the human host failed to consider its impact on the developing gut microbiota. Here, this oversight was addressed through comparative assessment of the gut microbiota from post-weaned mice (B6) provided either chlorine-free water or water containing 1–5 mg/L chlorine. Mice provided chlorinated water had a statistically significant decrease in levels of Clostridiaceae 1 and Peptostreptococcaceae, which corresponded to a decrease in virulence factors associated with porphyrin metabolism, which was considered related to a decrease in genes involved in adenosylcobalamin biosynthesis. Taken together, the results demonstrated that the gut microbiota of post-weaned mice were resilient to low levels of chlorine and chlorinated water did not elicit changes to diversity or cause any major community restructuring to occur.

Palladium Nanosheet Enables Synergistic Electrocatalytic Dehalogenation via Direct and Indirect Electron Transfer Mechanisms.

Electrocatalytic dehalogenation is a promising method for the remediation of chlorinated organic pollutants. The dehalogenation performance is controlled by catalytic activity, and the underlying electrocatalytic dehalogenation mechanisms need to be carefully investigated for guiding the design of catalyst. Here we report the preparation of a new Pd-based catalyst with a nanosheet structure (Pd NS) by a simple wet-chemical reduction method. This Pd NS catalyst showed a superior electrocatalytic activity toward the reductive dehalogenation of a chlorinated organic pollutant (e.g., 4-chlorophenol) with the dehalogenation rate of 0.324 h-1. Importantly, the obtained Pd NS catalyst had a good durability that could operate well over 30 h under high concentration of 4-chlorophenol with removal efficiency beyond 82%. Experimental results confirmed the simultaneous occurrence of direct electrocatalytic dehalogenation and H*-mediated indirect electron transfer mechanisms in the dehalogenation process, and their quantitative contributions to the dehalogenation performance were established based on the cyclic voltammetry and quenching experiments. This study provides a promising dehalogenation catalyst and sheds light on the mechanism of electrocatalytic dehalogenation as well as the development of a dual-functional electrocatalyst.

Nitrogen doping turns carbonaceous materials into fast-reacting catalysts for reductive dechlorination.

Nitrogen (N) doping of biomass prior pyrolysis has been identified as an effective approach for enhancing biochar catalytic reactivity. However, high-temperature pyrolysis of N-rich biomass may produce N-devoid biochars with high reactivity, calling for attention to the true causes of the reactivity increases and the role of nitrogen. In this study, N-doped wheat straw biochar (N-BC) materials were produced using urea as N dopant and different pyrolysis conditions, and their catalytic reactivity assessed for the reduction of trichloroethylene (TCE) by green rust (GR), a layered Fe(II)Fe(III) hydroxide. Overall, the extent and rate of TCE reduction increased from ∼8 to ∼90 % and 0.064 to 0.299 h-1, respectively, with increasing urea dosage from 0 to 25 wt%. A similar increase in catalytic activity was also seen with an increase in pyrolysis temperature during N-doping, from 600 to 800 or 1000 oC, while increasing pyrolysis duration had a lower impact. Principal component analysis and Pearson correlation analysis demonstrated some correlation between TCE catalytic reactivity and structural properties of N-BC materials. However, little correlation was seen between catalytic reactivity, and N content and N surface functional groups of N-BC materials; even though N surface functional groups are often described as the key redox active sites in these dechlorination reactions, and also the reason why N-doping is applied. For comparison, N-doping and TCE catalytic reactivity with GR was also performed with a highly conductive graphene (GP) substrate. N-doping of GP led to a similar increase in the rate and extent of TCE as was observed for N-BC, demonstrating the importance of N-doping to create catalytically active sites in these carbonaceous materials. Surprisingly, highly reactive N-GP materials produced at 800 and 1000 °C exhibited no N surface functional groups but instead, N-doping created structural defect sites. Overall, this study demonstrates that N-doping of the bio-substrate may increase catalysis of reductive dechlorination by a factor of ∼5 times but this is not due to the formation of catalytically active N-functional groups, rather we attribute it to changes of the carbonaceous material structure. With this understanding we can then embark on the production of catalytic active biochar materials also from other substrates than wheat straw, forming the basis for optimizing other reductive contaminant degradation systems.

Electrochemical reduction for chlorinated hydrocarbons contaminated groundwater remediation: Mechanisms, challenges, and perspectives.

Electrochemical reduction technology is a promising method for addressing the persistent contamination of groundwater by chlorinated hydrocarbons. Current research shows that electrochemical reductive dechlorination primarily relies on direct electron transfer (DET) and active hydrogen (H⁎) mediated indirect electron transfer processes, thereby achieving efficient dechlorination and detoxification. This paper explores the influence of the molecular charge structure of chlorinated hydrocarbons, including chlorolefin, chloroalkanes, chlorinated aromatic hydrocarbons, and chloro-carboxylic acid, on reductive dechlorination from the perspective of molecular electrostatic potential and local electron affinity. It reveals the affinity characteristics of chlorinated hydrocarbon pollutants, the active dechlorination sites, and the roles of substituent groups. It also comprehensively discusses the current progress on electrochemical reductive dechlorination using metal, carbon-based, and 3D electrode catalysts, with an emphasis on the design and optimization of electrode materials and the impact of catalyst microstructure regulation on dechlorination performance. It delves into the current application status of coupling electrochemical reduction technology with biodegradation and electrochemical circulating well technology for the remediation of groundwater contaminated by chlorinated hydrocarbons. The paper discusses practical application challenges such as electron transfer, electrode corrosion, water chemistry environment, and aquifer heterogeneity. Finally, considerations are presented from the perspectives of environmental impact and sustainable application, along with a summary and analysis of potential future research directions and technological prospects.

Degradation kinetics, pathways, transformation products, and toxicity assessment of fluorochloridone in agricultural soils.

Flurochloridone (FLC) is a pyrrolidone herbicide used to control broad-leaved weeds in various crop fields. However, there is still a lack of comprehensive research on the environmental fate of the Qinghai-Tibet Plateau (QTP) and the toxicity of its potential transformation products (TPs). In this study, laboratory experiments were conducted to investigate the degradation kinetics, pathways, and toxicity of FLC's TPs. Nine TPs were identified in soil using Ultra-Performance Liquid Chromatography Quadrupole-Orbitrap Mass Spectrometry (UPLC-Q-Exactive Orbitrap MS) and Compound Discoverer software, employing suspect and nontarget screening strategies. The initial report of two TPs, TP204, and TP191 was confirmed through the acquisition or synthesis of their standards. High Performance Liquid Chromatography coupled with Tandem Mass Spectrometry (HPLC-MS/MS) was subsequently used for further quantification of these TPs in all samples under examination. The primary transformation reactions of FLC in the environment include oxidative dechlorination, reductive dechlorination, reductive defluorination, acetylation, and hydrolysis. Predictive assessments via ECOSAR, alongside empirical laboratory experiments, revealed that most novel TPs exhibit significantly lower acute toxicity towards Danio rerio, Daphnia magna Straus, and Algae compared to FLC. However, TP204 demonstrated neutral chronic toxicity towards Daphnia magna Straus and Green algae, potentially posing a latent threat to aquatic ecosystems. These results are crucial for elucidating the environmental fate of FLC, assessing environmental risks, and guiding scientific and reasonable use. This research holds significant importance for the ecological environment protection in the Tibetan Plateau region.

Edema disease in two gold-spotted pond frogs (Pelophylax chosenicus) raised in captivity: two case reports

Two gold-spotted pond frogs (Pelophylax chosenicus) experienced anorexia, buoyancy without diving, and systemic swelling for 1 month and died several days later. On necropsy, the liver had protruding dark gray nodules scattered on its surface, and the kidneys were fat-like beige. Bacteriology showed the presence of Citrobacter braakii, Delftia acidovorans, Elizabethkingia spp., and Chryseobacterium indologenes. On microscopy, the liver showed melanomacrophagic aggregates, inflammatory cell infiltration, and fibrosis. In the case of these frogs, the edema disease is suspected to have been caused by long-term exposure to chlorine and chloramines in tap water rather than infection.

Amplicon sequences of sourdough starter cultures treated with varying levels of water chlorination.

Here, we present amplicon sequences from sourdough starter cultures that have been treated with a chlorine concentration gradient mirroring public water distribution systems. Data derived present insights into the effect of important environmental factors that may influence the formation of microbial communities in food biomes.

Modeling Water Age and Chlorine Reduction Effects on Water Quality in the Distribution Network of the Lower Usuma Dam Using EPANET

Modeling Water Age and Chlorine Reduction Effects on Water Quality in the Distribution Network of the Lower Usuma Dam Using EPANET

Dehalogenimonas Strain W from Estuarine Sediments Dechlorinates 1,2-Dichloroethane under Elevated Salinity.

Organohalide-respiring bacteria (OHRB) have been found in various environments and play an indispensable role in the biogeochemical cycling and detoxification of halogenated organic compounds (HOCs). Currently, few ORHB have been reported to perform reductive dechlorination under high salinity conditions, indicating a knowledge gap on the diversity of OHRB and the survival strategy of OHRB in saline environments (e.g., estuarine, marine). This study reports the characterization of an enrichment culture dominated by a new Dehalogenimonas population strain W derived from estuarine sediments, which demonstrates the capability to dechlorinate 1,2-dichloroethane (1,2-DCA) to ethene under elevated salinity (≥5.1% NaCl, w/v). Metagenomic and proteomic analyses revealed that the distinctive high-salinity dechlorination of strain W is primarily attributed to a putative reductive dehalogenase (RDase) DdeA, which shares >91.4% amino acid identity with the dihaloeliminating RDase DcpA from other Dehalogenimonas strains. Additionally, ectoine biosynthesis enzymes (EctABC) contribute to the strain's salt tolerance. These findings underscore the potential of OHRB, particularly Dehalogenimonas, to detoxify HOCs in high-salinity environments, such as estuarine and marine ecosystems, by employing compatible solutes as an adaptive mechanism.

Assessing the factors affecting the use of chlorine dispensers for household water treatment in rural Kenya, Malawi, and Uganda

ABSTRACT Although chlorination is widely accepted as a safe and cost-effective water treatment method, its adoption by the rural populations remains low. This leaves about 26% of the world's population – including 70% in Sub-Saharan Africa – with a lack of access to safely managed drinking water and exposure to hazards of drinking unsafe water. This work used data collected in a repeated cross-sectional study conducted between 2021 and 2022 in Kenya, Uganda, and Malawi to assess factors that influence a community's adoption of chlorine to treat water. The results indicate that households that observed good water storage and handling practices, had knowledge on the benefits of chlorine, understood the correct procedure of using chlorine dispensers, received promotional messages, and used functional chlorine dispensers were more likely to have chlorine residual in their drinking water. Conversely, households where children collected the drinking water were less likely to have chlorine residual in their drinking water. Community promoters who themselves used chlorinated water were associated with a higher chlorine adoption by the communities they serve. The study recommends continuous community education on chlorine water treatment; training on water collection, storage, and handling practices; extending water treatment education to children; and ensuring robust chlorine supply chains.

Catalytic Promiscuity of Fatty Acid Photodecarboxylase Enables Stereoselective Synthesis of Chiral α-Tetralones.

In the field of biocatalysis, discovering novel reactivity from known enzymes has been a longstanding challenge. Fatty acid photo-decarboxylase from Chlorella variabilis (CvFAP) has drawn considerable attention as a promising photoenzyme with potential green chemistry applications; however, its non-natural reactivity has rarely been exploited to date. Herein we report a non-natural reductive dehalogenation (deacetoxylation) reactivity of CvFAP inspired by its natural oxidative decarboxylation process, enabling the stereoselective synthesis of a series of chiral α-substituted tetralones with high yields (up to 99 %) and e.r. values (up to 99 : 1). Mechanistic studies demonstrated that the native photoenzyme catalyzed the reductive dehalogenation via a novel mechanism involving oxidized state (FADox)/semiquinone state (FADsq) redox pair and an electron transfer (ET)/proton transfer (PT) process of radical termination, distinct from the previous reports. To our knowledge, this study represents a new example of CvFAP promiscuity, and thus expands the reactivity repertoire of CvFAP and highlights the versatility of CvFAP in asymmetric synthesis.

INTENSITY OF CHEMICAL NEUTRALISATION OF CHLORINE DURING PRECIPITATION BY A FINELY DISPERSED LIQUID STREAM

One of the main tasks of the unified state system of civil protection is to forecast and assess the socio-economic consequences of emergencies, determine the need for forces, means, material and financial resources based on the forecast; carry out rescue and other urgent work to eliminate the consequences of emergencies, and organise life support for the affected population. The paper modifies the model of chlorine sorption by a fine liquid flow. The developed mathematical model allows to take into account the following basic parameters of sorption, environmental parameters, parameters of the liquid flow supplied for deposition and physical and chemical properties of the liquid in this flow. The developed model allows minimising the number of input parameters and the forecasting time, which is critical for emergency response. The results of numerical modelling have shown that the deposition of chlorine, which is a low-valent gas in water, is determined by the Henry's constant, and not by the intensity of the liquid flow, as previously thought. The poor solubility of chlorine in water does not provide significant efficiency (6% compared to ammonia) of its deposition by dispersed streams even at maximum intensity, which confirms the need for rescue units to use water-soluble additives that are chemically active to react with chlorine. It is also worth noting the logarithmic nature of the dependence of gas deposition intensity on the intensity of the dispersed flow. This can be explained by the fact that the intensity of sorption decreases due to a decrease in gas concentration, which in turn decreases due to the absorption process. Therefore, it is possible to determine the critical intensity of the liquid dispersion flow at which the sorption intensity almost stabilises. This confirms the urgent need for rescue units to use chemical neutralisers in the elimination of accidents involving chlorine emissions into the atmosphere.

WQI Improvement Based on XG-BOOST Algorithm and Exploration of Optimal Indicator Set

This paper takes a portion of the Manas River Basin in Xinjiang Province, China, as an example and proposes an improved traditional comprehensive water quality index (WQI) method using Extreme Gradient Boosting (XG-BOOST) to analyze the groundwater quality levels in the region. Additionally, XG-BOOST is used to screen the existing dataset of ten water quality indicators, including fluoride (F), chlorine (Cl), nitrate (NO), sulfate (SO), silver (Ag), aluminum (Al), iron (Fe), lead (Pb), selenium (Se), and zinc (Zn), from 246 monitoring points, in order to find the dataset that optimizes model training performance. The results show that, in the selected study area, water quality categorized as “GOOD” and “POOR” accounts for the majority, with “GOOD” covering 48.7% of the area and “POOR” covering 31.6%. Regions with water quality classified as “UNFIT” are mainly distributed in the central–eastern parts of the study area, located in parts of the Changji Hui Autonomous Prefecture. Comparatively, water quality in the western part of the study area is better than that in the eastern part, while areas with “EXCELLENT” water quality are primarily distributed in the southern parts of the study area. The optimal water quality indicator dataset consists of five indicators: Cl, NO, Pb, Se, and Zn, achieving an accuracy of 98%, RMSE = 0.1414, and R2 = 0.9081.

Transition-Metal Free Amination and Hydrodefluorination of Aryl Fluorides Promoted by Solvated Electrons.

Cross-coupling reactions for constructing C-N bonds represent a pivotal advancement in chemical science. Traditional methodologies, including nucleophilic aromatic substitution (SNAr) and transition metal-catalyzed cross-couplings, have limitations concerning aryl scope, reliance on toxic and costly transition-metal catalysts, and issues related to atom economy and waste generation from ligands and additives. In this work, we introduce a novel method for aminating neutral, electron-rich, and electron-deficient aryl halides, eliminating the need for transition metals. Our approach involves the activation of aryl halides using solvated electrons generated from granulated lithium and sonication. This serves as a sustainable source of reducing power, facilitating the efficient formation of C-N bonds under near ambient conditions. Competitive selectivity studies between halide and ester functionalities were explored. Reaction scope and conducted mechanistic studies which supported the proposed radical-nucleophilic substitution (SRN1) mechanism for the reaction. Notably, the developed reaction has a highly competitive reductive dehalogenation pathway during the C-N coupling reaction, and this mechanistic divergency was thoroughly explored. This work not only broadens the scope of C-N coupling reactions which typically employs aryl bromides and iodides and rarely aryl fluorides which is also equally abundant, but also introduces a new way to do C-N coupling reactions using solvated electrons.

Ultrafast Synthesis of IrB1.15 Nanocrystals for Efficient Chlorine and Hydrogen Evolution Reactions in Saline Water.

The production of storable hydrogen fuel through water electrolysis powered by renewable energy sources such as solar, marine, geothermal, and wind energy presents a promising pathway toward achieving energy sustainability. Nevertheless, state-of-the-art electrolysis requires support from ancillary processes which often incur financial and energy costs. Developing electrolysers capable of directly operating with water that contains impurities can circumvent these processes. Herein, we demonstrate the efficient and durable electrolysis of saline water to produce chlorine gas (Cl2) and hydrogen using structurally ordered IrB1.15, synthesized through ultrafast joule heating. IrB1.15 exhibits remarkable performance, achieving overpotentials of 75 mV for the chlorine evolution reaction (CER) and 12 mV for hydrogen evolution reactions (HER) at current densities of 10 mA cm-2. Moreover, IrB1.15 displays a durability of over 90 h towards both CER and HER. Density functional theory reveals that IrB1.15 has adsorption energies significantly closer to 0 eV for Cl and H, compared to IrO2 and Pt/C. Furthermore, in situ Raman investigations reveal that Ir in IrB1.15 serves as the active center for CER, while the introduction of B atoms to Ir lattices mitigates the formation of absorbed hydrogen species on the Ir surface, thereby enhancing the performance of IrB1.15 in HER.

Ultrafast Synthesis of IrB1.15 Nanocrystals for Efficient Chlorine and Hydrogen Evolution Reactions in Saline Water

The production of storable hydrogen fuel through water electrolysis powered by renewable energy sources such as solar, marine, geothermal, and wind energy presents a promising pathway toward achieving energy sustainability. Nevertheless, state‐of‐the‐art electrolysis requires support from ancillary processes which often incur financial and energy costs. Developing electrolysers capable of directly operating with water that contains impurities can circumvent these processes. Herein, we demonstrate the efficient and durable electrolysis of saline water to produce chlorine gas (Cl2) and hydrogen using structurally ordered IrB1.15, synthesized through ultrafast joule heating. IrB1.15 exhibits remarkable performance, achieving overpotentials of 75 mV for the chlorine evolution reaction (CER) and 12 mV for hydrogen evolution reactions (HER) at current densities of 10 mA cm−2. Moreover, IrB1.15 displays a durability of over 90 h towards both CER and HER. Density functional theory reveals that IrB1.15 has adsorption energies significantly closer to 0 eV for Cl and H, compared to IrO2 and Pt/C. Furthermore, in‐situ Raman investigations reveal that Ir in IrB1.15 serves as the active center for CER, while the introduction of B atoms to Ir lattices mitigates the formation of absorbed hydrogen species on the Ir surface, thereby enhancing the performance of IrB1.15 in HER.