Dechlorination Research Articles

Drinking water chlorination in dairy beef fattening bulls: water quality, potential hazards, apparent total tract digestibility, and growth performance

The first study aimed to evaluate the effect of drinking water disinfection (chlorination: NaClO 15%) and conditioning (acidification: H3PO4 diluted 1:5 in water) on water quality, water and feed consumption, apparent total tract digestibility, and its potential hazardous effects on Holstein bulls fed high-concentrate diets. Twenty-four animals (221 ± 20.9 kg of BW, and 184 ± 9.9 days of age) were individually assigned to one of four treatments according to a 2 × 2 factorial arrangement: conditioning (with or without acidification) and disinfection (with or without chlorination). The entire study lasted 210 days. Physicochemical and microbiological water quality, water and feed consumption, haematological and biochemical blood parameters, and apparent total tract digestibility were measured; data were analysed via a mixed-effects model. Chlorination and acidification increased (P = 0.02) free residual chlorine in water, and chlorination reduced (P = 0.01) total coliform and Clostridium perfringens counts in water. Treatment did not affect water consumption, total DM intake, or blood parameters. At the beginning of the study, NDF digestibility decreased (P = 0.04) with acidification, however, this was restored at the end of the study. The second study evaluated the potential benefit of drinking water chlorination and acidification on the performance of crossbred Holstein bulls fed high-concentrate diets under commercial conditions. Ninety-six animals (322 ± 35.0 kg of BW, and 220 ± 14.2 days of age) were allocated into six pens assigned to one of the two treatments: untreated drinking water or drinking water treated with chlorination and acidification for a total of 112 days. Physicochemical and microbiological water quality, water and concentrate consumption, eating behaviour, growth performance, and carcass quality were analysed via a mixed-effects model. Water conditioning and disinfection increased (P = 0.01) free residual chlorine concentration and reduced (P = 0.04) total coliform count in water. Although water consumption and eating behaviour were similar between treatments, water conditioning and disinfection increased average daily weight gain (P = 0.03), BW before slaughter (P = 0.01), and hot carcass weight (P = 0.01). In conclusion, drinking water chlorination and acidification in fattening dairy beef bulls is recommended as it improves growth performance without any detrimental side effects on health or nutrient digestibility.

Reductive dehalogenation in groundwater by Si-Fe(II) co-precipitates enhanced by internal electric field and low vacancy concentrations

Fe(II) and silicate can form Si-Fe(II) co-precipitates in anoxic groundwater and sediments, but their phase composition and reactivity towards subsurface pollutants are largely unknown. Three types of Si-Fe(II) co-precipitations with the same chemical composition, namely Si-Fe(II)-I, Si-Fe(II)-II, and Si-Fe(II)-III, have been synthesized by different hydroxylation sequences in this work. It was found that Si-Fe(II)-III reduce carbon tetrachloride (CT) much faster (k1=0.04419 min−1) than Si-Fe(II)-I (0 min−1) and Si-Fe(II)-II (7.860 × 10−4 min−1). XRD results show that the main component of Si-Fe(II)-III is ferrous silicate (FeSiO3), which is quite different from that of Si-Fe(II)-I and Si-Fe(II)-II. The unique arrangement of hydroxyl coordination, the less distorted octahedral structure, the polyhedral morphology and the absence of Si-A center vacancies in Si-Fe(II)-III are responsible for its high reductive dehalogenation reactivity. The highest redox activity of Si-Fe(II)-III was shown by electrochemical characterization. The [FeII-O-Si]+ in Si-Fe(II)-III may stabilize the dichlorocarbene anion (˸CCl2−), which favors the transformation of CT to methane (9.2%). The Si-Fe(II) co-precipitates consist of countless internal electric fields, and the transformation of hydroxyl and CT both consumed electrons. The coexistence of hydroxyl and CT increases the electron density in the electron-rich region due to their electronegativity, enhancing their electron-accepting capabilities. This study deepens our understanding of the phase composition and electronic structure of Si-Fe(II) co-precipitates, which fills the gap in the reductive dehalogenation of halides by Si-Fe(II) co-precipitates.

Characterization of Hexachlorocyclohexane Isomer Dehydrochlorination by LinA1 and LinA2 Using Multi-element Compound-Specific Stable Isotope Analysis.

Dehydrochlorination is one of the main (thus far discovered) processes for aerobic microbial transformation of hexachlorocyclohexane (HCH) which is mainly catalyzed by LinA enzymes. In order to gain a better understanding of the reaction mechanisms, multi-element compound-specific stable isotope analysis was applied for evaluating α- and γ-HCH transformations catalyzed by LinA1 and LinA2 enzymes. The isotopic fractionation (εE) values for particular elements of (+)α-HCH (εC = -10.8 ± 1.0‰, εCl = -4.2 ± 0.5‰, εH = -154 ± 16‰) were distinct from the values for (-)α-HCH (εC = -4.1 ± 0.7‰, εCl = -1.6 ± 0.2‰, εH = -68 ± 10‰), whereas the dual-isotope fractionation patterns were almost identical for both enantiomers (ΛC-Cl = 2.4 ± 0.4 and 2.5 ± 0.2, ΛH-C = 12.9 ± 2.4 and 14.9 ± 1.1). The εE of γ-HCH transformation by LinA1 and LinA2 were -7.8 ± 1.0‰ and -7.5 ± 0.8‰ (εC), -2.7 ± 0.3‰ and -2.5 ± 0.4‰ (εCl), -170 ± 25‰ and -150 ± 13‰ (εH), respectively. Similar ΛC-Cl values (2.7 ± 0.2 and 2.9 ± 0.2) were observed as well as similar ΛH-C values (20.1 ± 2.0 and 18.4 ± 1.9), indicating a similar reaction mechanism by both enzymes during γ-HCH transformation. This is the first data set on 3D isotope fractionation of α- and γ-HCH enzymatic dehydrochlorination, which gave a more precise characterization of the bond cleavages, highlighting the potential of multi-element compound-specific stable isotope analysis to characterize different transformation processes (e.g., dehydrochlorination and reductive dehalogenation).

Revisiting UV/sulfite exposed to air: A redox process for reductive dechlorination and oxidative mineralization

2,4-Dichlorophenol (2,4-DCP) widely exists in many industrial wastewaters and is considered a priority pollutant due to its high toxicity. In this work, we proposed a UV/sulfite process without aeration for high-efficiency dechlorination and enhanced mineralization. The UV/sulfite system significantly improved the removal of 2,4-DCP (93.33 % in 60 min) and dechlorination rate (85.13 % in 60 min) compared with UV alone and sulfite alone, and the synergistic factor was 6.59. The UV/sulfite system without aeration improved the mineralization rate (49.80 %) compared with the nitrogen aeration system. UV/sulfite was a reduction-oxidation coupled process and was more suitable for neutral and alkaline conditions. Reducing species (hydrated electrons and H•) made 2,4-DCP dechlorinate to form dechlorination products such as p-chlorophenol (4-CP), o-chlorophenol (2-CP), and phenol, which were further mineralized by oxidized species (SO4•-). UV/sulfite remained highly efficient in the presence of coexisting ions and under different water quality conditions. This process was also suitable for removing a wide range of chlorinated organic compounds. The UV/sulfite process without aeration can achieve high dechlorination and enhanced mineralization with simple operation and low cost (1.78 $·m−3 order−1), which has a broad and cost-effective application prospect in removing refractory halogenated organic pollutants.

Reductive Dehalogenation of Herbicides Catalyzed by Pd0NPs in a H2-Based Membrane Catalyst-Film Reactor.

More food production required to feed humans will require intensive use of herbicides to protect against weeds. The widespread application and persistence of herbicides pose environmental risks for nontarget species. Elemental-palladium nanoparticles (Pd0NPs) are known to catalyze reductive dehalogenation of halogenated organic pollutants. In this study, the reductive conversion of 2,4-dichlorophenoxyacetic acid (2,4-D) was evaluated in a H2-based membrane catalyst-film reactor (H2-MCfR), in which Pd0NPs were in situ-synthesized as the catalyst film and used to activate H2 on the surface of H2-delivery membranes. Batch kinetic experiments showed that 99% of 2,4-D was removed and converted to phenoxyacetic acid (POA) within 90 min with a Pd0 surface loading of 20 mg Pd/m2, achieving a catalyst specific activity of 6.6 ± 0.5 L/g-Pd-min. Continuous operation of the H2-MCfR loaded with 20 mg Pd/m2 sustained >99% removal of 50 μM 2,4-D for 20 days. A higher Pd0 surface loading, 1030 mg Pd/m2, also enabled hydrosaturation and hydrolysis of POA to cyclohexanone and glycolic acid. Density functional theory identified the reaction mechanisms and pathways, which involved reductive hydrodechlorination, hydrosaturation, and hydrolysis. Molecular electrostatic potential calculations and Fukui indices suggested that reductive dehalogenation could increase the bioavailability of herbicides. Furthermore, three other halogenated herbicides─atrazine, dicamba, and bromoxynil─were reductively dehalogenated in the H2-MCfR. This study documents a promising method for the removal and detoxification of halogenated herbicides in aqueous environments.

Photoinduced Promiscuity of Cyclohexanone Monooxygenase for the Enantioselective Synthesis of α-Fluoroketones.

The development of mild, efficient, and enantioselective methods for preparing chiral fluorinated compounds has been a long-standing challenge. Herein, we report a promiscuous cyclohexanone monooxygenase (CHMO) for the photoinduced synthesis of chiral α-fluoroketones via enantioselective reductive dehalogenation of α,α-halofluoroketones. Wild-type CHMO from Acinetobacter sp. possesses this promiscuous ability innately; however, the yield and stereoselectivity are low. A structure-guided rational design of CHMO improved the yield and stereoselectivity remarkably. Mechanistic studies and molecular simulations demonstrated that this photoinduced CHMO catalyzes the reductive dehalogenation via a novel electron transfer (ET)/proton transfer (PT) mechanism, distinct from that of previously reported reductases with similar promiscuity. This methodology was expanded to various substrates, and desirable chiral α-fluoroketones were obtained in high yields (up to 99 %) and e.r. values (up to 99:1).

Photoinduced Promiscuity of Cyclohexanone Monooxygenase for the Enantioselective Synthesis of α‐Fluoroketones

AbstractThe development of mild, efficient, and enantioselective methods for preparing chiral fluorinated compounds has been a long‐standing challenge. Herein, we report a promiscuous cyclohexanone monooxygenase (CHMO) for the photoinduced synthesis of chiral α‐fluoroketones via enantioselective reductive dehalogenation of α,α‐halofluoroketones. Wild‐type CHMO from Acinetobacter sp. possesses this promiscuous ability innately; however, the yield and stereoselectivity are low. A structure‐guided rational design of CHMO improved the yield and stereoselectivity remarkably. Mechanistic studies and molecular simulations demonstrated that this photoinduced CHMO catalyzes the reductive dehalogenation via a novel electron transfer (ET)/proton transfer (PT) mechanism, distinct from that of previously reported reductases with similar promiscuity. This methodology was expanded to various substrates, and desirable chiral α‐fluoroketones were obtained in high yields (up to 99 %) and e.r. values (up to 99:1).

Microbiome reengineering by four environmental factors for the rapid biodegradation of trichloroethylene

Trichloroethylene (TCE) was once a widely applied industrial solvent, but is now an infamous contaminant in groundwater. Although anaerobic reductive dechlorination is considered a greener remediation approach, the accumulation of toxic intermediates, such as vinyl chloride (VC), and a longer remediation period are highly concerning. Biostimulation and bioaugmentation have been developed to solve these problems. The former method may not be effective, and the latter may introduce foreign genes. Here, we propose a new approach by applying environmental stresses to reshape the indigenous microbiome. In this study, by using the Taguchi method, the effects of heating, pH, salinity, and desiccation were systematically examined. The optimum conditions were defined as 50 °C, pH 9, 3.50% salinity (w/v), and 21% volumetric water content (θW). The top performing group, G7, can complete the conversion of 11.81 mg/L TCE into ethene in 3.0 days with a 1.23% abundance of Dehalococcoides mccartyi 195 (Dhc 195). Redundancy analysis confirmed that temperature and salinity were the predominant factors in reorganizing the microbiomes. The microbiome structure and its effectiveness can last for at least 90 d. The repetitive selection conditions and sustainable degradation capability strongly supported that microbiome reengineering is feasible for the rapid bioremediation of TCE-contaminated environmental matrices.

Oxidative removal of dissolved manganese(II) by peroxymonosulfate: Non-radical mechanism and influencing factors

In this study, the oxidative removal of Mn(II) by peroxymonosulfate (PMS) was investigated. PMS was found to be a more efficient oxidant than chlorine for Mn(II) oxidation. Weak autocatalysis kinetics were observed in PMS/Mn(II) system suggesting that the Mn(II) oxidation consisted of both homogeneous (direct oxidation) and heterogeneous (amorphous MnO2 catalytic oxidation) processes. Homogeneous oxidation of Mn(II) by PMS showed strong pH dependency with apparent second-order rate constants of 3.1–249.9 M−1s−1 at pH 7.0–9.0. Stoichiometry of PMS to Mn(II) was about 1:1 suggesting a two-electron transfer pathway (O transfer), which was further confirmed by the XPS analysis results. However, the change in the coordination structure of Mn(II) was found to greatly affect the oxidation rate and mechanism of Mn(II). Complexion with inorganic or organic ligands could inhibit the oxidation rate of Mn(II) and alter the oxidation mechanism from two-electron to one-electron pathway. Furthermore, coexisting metal ions such as Ca(II), Zn(II), and Fe(II)/Fe(III) ions could greatly accelerate the oxidation of Mn(II) by PMS and chlorine by promoting the heterogeneous oxidation process. Oxidative removal of Mn(II) by PMS was more efficient than chlorine in real waters (56 %–100 % versus 12 %–17 %). The combination of PMS oxidation with coagulation could further increase the removal efficiency from 56 % to 92 %. These findings highlight that PMS oxidation is an attractive alternative technology for Mn(II) removal and may also provide a fundamental understanding of the Mn materials-based advanced oxidation processes.

Flow-based green ceramics microdevice with smartphone image colorimetric detection for free chlorine determination in drinking water

The residual free chlorine concentration is an important parameter to evaluate the potability of water and the efficiency of disinfection in the water treatment system. As a restricted range of residual free chlorine concentration at all points of the distribution network is needed to ensure efficiency and to avoid deleterious effects, fast and in situ quantification of this specie is important. This work deals with the development and validation of two procedures based on DPD (N,N-diethyl-p-phenylenediamine) and OT (ortho-tolidine, 3,3-dimethylbenzidine) for the determination of residual free chlorine in water by exploiting a flow-based microdevice built with Low Temperature Co-Fired Ceramic (LTCC) technology. The analytical signal was monitored by a smartphone camera through RGB values obtained by a free application (Color Grab®). Under optimized conditions, linear ranges within 0.6–2.5 mg/L and 0.1–2.3 mg/L were obtained for DPD and OT methods, with limits of detection and quantification of 0.023 and 0.077 mg/L (DPD) and 0.026 and 0.089 mg/L (OT). Precision expressed as RSD (2.0 mg/L free chlorine, n = 10), was 1.3 % and 0.7 %, respectively. Both procedures were successfully applied to the analysis of samples from a water treatment plant. The flow-based microdevice coupled to digital-image colorimetry is an innovative, sustainable, and cost-effective analytical tool for in-field chemical analysis.

The importance of proper pH adjustment and control to achieve complete in situ enhanced reductive dechlorination.

In situ bioremediation of chlorinated compounds such as perchloroethylene (PCE) and trichloroethylene (TCE) through enhanced reductive dechlorination (ERD) requires appropriate growth conditions for organohalide-respiring bacteria (OHRB). One of the most important factors controlling OHRB metabolism is groundwater pH. Dehalococcoides spp. (DHC) growth may be inhibited when pH is lower than 6.0, which can lead to the accumulation of toxic daughter compounds including cis-dichloroethylene (cDCE) and vinyl chloride (VC). Aquifer pH may decline as HCl is released during reductive dechlorination and from substrate fermentation to fatty acids and carbonic acid. In this article, we demonstrate that using proper pH adjustment and control in situ is an appropriate strategy to achieve complete ERD (i.e., complete conversion of PCE and TCE to nontoxic ethylene) in remediation sites with inherently low pH values and/or low buffering capacity. To analyze the effectiveness of this approach, field monitoring results are presented for a challenging site containing high concentrations of PCE and TCE (>10 000 µg/L and >1000 µg/L, respectively) and low aquifer pH (~4.9). Addition of a bioaugmentation culture, emulsified vegetable oil (EVO), and a colloidal buffer (CoBupHTM ) to increase pH, stimulated rapid conversion of PCE and TCE to cDCE and VC. However, further conversion of cDCE and VC was very limited. To stimulate complete conversion to ethylene, additional CoBupHTM and nutrients were injected, resulting in a rapid increase in metabolic rates, and maintained the aquifer pH at ~6.5 for more than five years, thus demonstrating that complete ERD can be achieved in sites with similar characteristics. Proper pH adjustment and control is needed to limit the accumulation of toxic intermediates, maintaining in situ bioremediation as an efficient, affordable, and environmentally friendly option to treat chlorinated compounds. Integr Environ Assess Manag 2023;19:943-948. © 2022 SETAC.

Synergistic Bacterial Inactivation by Silver Ions and Free Chlorine in Natural Waters

Synergistic Bacterial Inactivation by Silver Ions and Free Chlorine in Natural Waters

Shift to remote learning degrades water quality in buildings

AbstractCommercial and institutional buildings now experience weeks and even months with below‐normal occupancy due to remote work/learning, which results in reduced water use and has the potential to adversely impact water quality. This study monitored the variations in water quality in multiple university buildings during several months of below‐normal occupancy followed by several months of normal occupancy. The levels of free chlorine, copper, and cellular ATP in water varied within buildings and between buildings. Using Wi‐Fi activity as a surrogate for building occupancy, the free chlorine concentration in water increased as Wi‐Fi counts increased. The copper concentration in building water was higher when the occupancy was below‐normal compared with normal occupancy, and the copper concentration decreased as Wi‐Fi counts increased. Throughout the study, flushing a fixture at the time of use decreased the concentrations of copper and cellular ATP and increased the concentration of free chlorine.

Remediation of chlorinated aliphatic hydrocarbons (CAHs) contaminated site coupling groundwater recirculation well (IEG-GCW®) with a peripheral injection of soluble nutrient supplement (IEG-C-MIX) via multilevel-injection wells (IEG-MIW)

An innovative Groundwater Circulation Well (GCW) process was configured, installed, and tested for optimizing the distribution of a soluble nutrient supplement in a heterogeneous aquifer for reductive dehalogenation. This generated an in-situ bioreactor for the enhanced treatment of chlorinated aliphatic hydrocarbons (CAHs). At a site in Barcelona, Spain, trichloroethylene (TCE) concentration was found in the source area to a maximum value of up to 170 mg/L, while the degradation products like 1,2-dichloroethylene (1,2-DCE) and vinyl chloride (VC) were detected in significantly lower concentrations or were even absent. The novel system combined a vertical recirculation well (IEG-GCW®) and four multilevel injection wells (IEG-MIWs) to introduce the carbon solution into the aquifer. A 12 m deep IEG-GCW® equipped with 2 screened sections were located in the center of the 4 IEG-MIWs. The GCW induced flow moves the groundwater in an ellipsoidal recirculation cell to spread the supplements from the central GCW and from the peripheral MIWs in the aquifer body. Two multilevel sampling wells (IEG-MLSWs®) in the radius of influence (ROI) monitor the remediation process to capture hydrochemical variations along the vertical aquifer sections. A multi-source model harmonizes geological and hydrochemical information during different remediation stages, guiding the adaptation of the remediation strategy to physicochemical conditions and unmasking the decontamination mechanics induced by the remedial actions. Hydrochemical monitoring of MLWS and the stable carbon isotopic signature of cis-1,2-DCE and VC show the mobilization of secondary contamination sources triggered by recirculation during remediation, the stimulation of microbiological activity following nutrient supplement via GCW and MIWs, and the strong decrease of CAHs concentrations at different aquifer levels. Evidence from the first application at the field scale reveals a significant increase in the chloroethane biodegradation rate and short-term effectiveness of the innovative remediation strategy. GCW-MIWs synergy represents a promising strategy to degrade CAHs in a shorter period through the combination of a controllable hydraulic system, effective nutrient distribution, and the monitoring of the remediation process.

General analytical solutions of multispecies advective-dispersive solute transport equations coupled with a complex reaction network

Stepwise reductive dechlorination of tetrachloroethene (PCE) to trichloroethene (TCE), three dichloroethylene (DCE) isomers (1,1-DCE, cis −1,2- DCE, and trans −1,2- DCE), vinyl chloride (VC), and ethane (ETH) may proceed under anaerobic conditions. However, most multispecies transport models for describing the plume migration of a chemical mixture comprising the original chlorinated solvent and its dechlorinated byproducts in the literature are often simplified to a sequential first-order reaction network which cannot account for the divergent reactions from TCE to the three DCE isomers and convergent reactions from the three DCE isomers to VC. In this study, general analytical solutions to multispecies transport equations with a complex reaction network were derived for a combination of semi-infinite and finite systems. The developed analytical solutions were robustly verified against a semi-analytical solution that can consider the same complex reaction network. The verification results indicated that the derived analytical solutions were accurate and robust. The general solutions derived in the present study were also used to investigate the effects of the outlet boundary conditions on solute transport involving a complex reaction network. The results showed that the analytical solution derived for infinite outlet BCs predicted lower concentrations of contaminants near the outlet boundary than those for finite outlet BCs. Moreover, a straight decay chain model may over- or under- estimate the DCE and VC concentrations compared to the multiple branching isomer reaction model. The developed analytical solutions with a complex reaction network provide more realistic and efficient tools for assessing the movement of chlorinated solvents and their degradation-related byproducts in soil–water systems.

A starch-based controlled-release targeted nutrient agent to stimulate the activity of volatile chlorinated hydrocarbon-degrading indigenous microflora present in groundwater

Volatile chlorinated hydrocarbons (VCHs) contaminated groundwater has a low indigenous microorganism population, and lack of nutrient substrates involved in degradation reactions, resulting in a weak natural remediation ability of groundwater ecosystems. In this study, based on the principle of degradation of VCHs by indigenous microorganisms in groundwater, and combined with biostimulation and controlled-release technology, we developed a starch-based encapsulated targeted bionutrient (YH-1) with easy uptake, good stability, controllable slow-release migration, and long timeliness for the remediation of groundwater contaminated by VCHs by indigenous microorganisms. The results showed that YH-1 is easily absorbed by microorganisms and can rapidly initiate itself to stimulate the microbial degradation of VCHs, and the degradation rate of various VCH components within 7 days was 82.38–92.38 %. The release rate of nutrient components in YH-1 increases with increasing VCH concentrations in groundwater; this could effectively prolong the action time of nutrient components, while also improving the degradation efficiency of pollutants with a sustained effect of more than 15 days. Simultaneously, owing to the fluidity, water solubility, and biodegradability of YH-1 in lithologic media, YH-1 injection did not cause blockage of the lithologic media in the aquifer. Through YH-1 stimulation, indigenous microorganisms grew rapidly in the underground environment, the diversity of microbial communities and the total number of species increased, and the correlation between genera strengthened. Simultaneously, YH-1 improved the ability of microbial community to convert inorganic electron donors/acceptors, thereby strengthening the co-metabolic mechanism between microorganisms. Additionally, there was a significant increase in the percentage of many microorganisms (e.g., Sphingomonas, Janthinobacterium, Duganella, etc.) that mediated the reductive dechlorination process and were redox inorganic electron donors/acceptors. This was conducive to the reductive dechlorination process of VCHs and achieved the efficient degradation of VCHs.

Thermally Enhanced Biodegradation of TCE in Groundwater

In situ remediation is usually restricted by temperature, lack of substrate for reductive dechlorination (anaerobic respiration), the presence of dehalogenating microorganisms, and specific bedrock conditions. In this work, trichloroethene (TCE) degradation was studied by a number of methods, from physical–chemical analyses to molecular biological tools. The abundance changes in dechlorinating bacteria were monitored using real-time PCR. The functional genes vcrA and bvcA as well as the 16S rRNA specific for representatives of genera Dehalococcoides, Dehalobacter, and Desulfitobacterium were monitored. Furthermore, the sulfate-reducing bacteria and denitrifying bacteria were observed by amplifying the functional genes apsA and nirK. The elevated temperature and the substrate (whey) addition significantly affected TCE dechlorination. The chlorine index decreased after nine weeks from 2.5 to 0.1 at 22 °C, to 1.1 at 17 °C and 1.7 at 12 °C and complete dechlorination was achieved at 22 °C with whey addition. The achieved results of this work show the feasibility and effectiveness of biological dechlorination of TCE enhanced with elevated temperature and whey addition.

Generation of adsorbed atomic hydrogen by Pd(II) doped Fe(OH)2 enables ultra-fast reductive dechlorination of trichloroethylene

Trichloroethylene (TCE) is a notorious persistent pollutant in groundwater, while most reductive dechlorination processes result in the formation of toxic less-chlorinated by-products. In this work, adsorbed atomic hydrogen (H*) was produced by Pd(II) doped Fe(OH)2, which was used for ultra-fast reductive dechlorination of TCE without the formation of less-chlorinated by-products. When the Fe(OH)2 dosage is 0.5 mM and the Pd(II) dosage is 20 μM, TCE (42 μM) is completely removed in 60 min with the pseudo first-order reaction rate constant of 7.74 h−1. Radical quenching experiment and electrochemical analysis both confirmed that adsorbed H* rather than absorbed H* contribute to the reduction of TCE. Density function theory calculation demonstrated that small Pd clusters were more beneficial to TCE dechlorination than large Pd clusters. The pseudo first-order rate constant for TCE reduction in real groundwater was as high as 0.018 min–1, demonstrating the potential application of Pd/Fe(OH)2 in groundwater remediation.

Metabolome patterns identify active dechlorination in bioaugmentation consortium SDC-9™.

Ultra-high performance liquid chromatography-high-resolution mass spectrometry (UPHLC-HRMS) is used to discover and monitor single or sets of biomarkers informing about metabolic processes of interest. The technique can detect 1000's of molecules (i.e., metabolites) in a single instrument run and provide a measurement of the global metabolome, which could be a fingerprint of activity. Despite the power of this approach, technical challenges have hindered the effective use of metabolomics to interrogate microbial communities implicated in the removal of priority contaminants. Herein, our efforts to circumvent these challenges and apply this emerging systems biology technique to microbiomes relevant for contaminant biodegradation will be discussed. Chlorinated ethenes impact many contaminated sites, and detoxification can be achieved by organohalide-respiring bacteria, a process currently assessed by quantitative gene-centric tools (e.g., quantitative PCR). This laboratory study monitored the metabolome of the SDC-9™ bioaugmentation consortium during cis-1,2-dichloroethene (cDCE) conversion to vinyl chloride (VC) and nontoxic ethene. Untargeted metabolomics using an UHPLC-Orbitrap mass spectrometer and performed on SDC-9™ cultures at different stages of the reductive dechlorination process detected ~10,000 spectral features per sample arising from water-soluble molecules with both known and unknown structures. Multivariate statistical techniques including partial least squares-discriminate analysis (PLSDA) identified patterns of measurable spectral features (peak patterns) that correlated with dechlorination (in)activity, and ANOVA analyses identified 18 potential biomarkers for this process. Statistical clustering of samples with these 18 features identified dechlorination activity more reliably than clustering of samples based only on chlorinated ethene concentration and Dhc 16S rRNA gene abundance data, highlighting the potential value of metabolomic workflows as an innovative site assessment and bioremediation monitoring tool.

Underlying Mechanisms for Low-Molecular-Weight Dissolved Organic Matter to Promote Translocation and Transformation of Chlorinated Polyfluoroalkyl Ether Sulfonate in Wheat.

Dissolved organic matter (DOM) such as fulvic acid (FA) and humic acid (HA) in soil considerably affects the fate of per- and polyfluoroalkyl substances (PFASs). However, the effect of DOM on their behavior in plants remains unclear. Herein, hydroponic experiments indicate that FA and HA reduce the accumulation of an emerging PFAS of high concern, 6:2 chlorinated polyfluoroalkyl ether sulfonate (6:2 Cl-PFESA), in wheat roots by reducing its bioavailability in the solution. Nevertheless, FA with low molecular weight (MW) promotes its absorption and translocation from the roots to the shoots by stimulating the activity and the related genes of the plasma membrane H+-ATPase, whereas high-MW HA shows the opposite effect. Moreover, in vivo and in vitro experiments indicate that 6:2 Cl-PFESA undergoes reductive dechlorination, which is regulated mainly using nitrate reductase and glutathione transferase. HA and FA, particularly the latter, promote the dechlorination of 6:2 Cl-PFESA in wheat by enhancing electron transfer efficiency and superoxide production. Transcriptomic analysis indicates that FA also stimulates catalytic activity, cation binding, and oxidoreductase activity, facilitating 6:2 Cl-PFESA transformation in wheat.