Reductive Dechlorination Research Papers - Academia.edu (original) (raw)

2025, Environmental Science & Technology

Green rusts (GRs), mixed iron(II)/iron(III) hydroxide minerals found in many suboxic environments, have been shown to reduce a range of organic and inorganic contaminants, including several chlorinated hydrocarbons. Many studies have demonstrated the catalytic activity of transition metal species in the reduction of chlorinated hydrocarbons, suggesting the potential for enhanced reduction by GR in the presence of an appropriate transition metal catalyst. Reductive dechlorination of carbon tetrachloride (CT) was examined in aqueous suspensions of GR amended with Ag I , Au III , or Cu II . The CT reduction rates were greatly increased for systems amended with Cu II , Au III , and Ag I (listed in order of increasing rates) relative to GR alone. Observed intermediates and products included chloroform, dichloromethane, chloromethane, methane, acetylene, ethene, ethane, carbon monoxide, tetrachloroethene, and various nonchlorinated C 3 and C 4 compounds. Product distributions for the reductive dechlorination of CT were highly dependent on the transition metal used. A reaction pathway scheme is proposed in which CT is reduced primarily to methane and other nonchlorinated end products, largely through a series of one-electron reductions forming radicals and carbenes/carbenoids. Recently, X-ray absorption fine structure analysis of aqueous GR suspensions amended with Ag I , Au III , or Cu II showed that the metals were reduced to their zerovalent forms. A possible mechanism for CT reduction is the formation of a galvanic couple involving the zerovalent metal and GR, with reduction of CT occurring on the surface of the metal and GR serving as the bulk electron source. The enhanced reduction of CT by GR suspensions amended with Ag I , Au III , or Cu II may prove useful in the development of improved materials for remediation of chlorinated organic contaminants.

2025, Environmental science & technology

Matrix diffusion must be considered when assessing natural attenuation and remediation of chlorinated ethenes in fractured porous bedrock aquifers. In this study, intact sandstone rock and groundwater from a trichloroethene (TCE)-contaminated site were used in microcosms (maintained for approximately 600 days) to simulate a single fracture-matrix system with a chamber at the top of the core allowing advection to represent fracture flow. Diffusion-coupled degradation with and without biostimulation were evaluated and compared to crushed-rock, batch microcosms. In the diffusion-transport microcosms, lactate stimulated reductive dechlorination of TCE to cis-1,2-dichloroethene (cDCE) and sulfate reduction. Reduction of TCE to cDCE led to a higher rate of chlorinated ethene removal from the cores, likely due to higher concentration gradients, along with lower sorption and a higher diffusion coefficient for cDCE relative to TCE. Reduction of cDCE to vinyl chloride or ethene did not occur ...

2025

In this study, the mechanism for the removal of the antibiotic ciprofloxacin (CIP) from aquatic solutions by nanoscale zero valent iron modificated by Mg-aminoclay particles was established. Firstly, MgAC coated NZVI were prepared and characterized by analythical methods such as scanning electron microscope(SEM) and X-ray Powder Diffraction (XRD).These analyzes showed that cluster linked and amorphous spheres as nanochain traditionally do, between from – C. Overall, the results of this research proposed that the synthesized MgAC coated NZVI composite is an effective and promising material for removal of antibiotics from the wastewater of industry.

2025, Bioresource Technology

h i g h l i g h t s " Aerobic/anaerobic/aerobic treatment biodegrades complex chlorinated solvent mixture. " First aerobic step: low-and mediumchlorinated solvents degraded by cometabolism. " Anaerobic step: tetrachloroethene degraded to cis-dichloroethene or trichloroethene. " Second aerobic step: cisdichloroethene or trichloroethene degraded by cometabolism. " The anaerobic step is likely fed with dead cells grown during the aerobic step. g r a p h i c a l a b s t r a c t 3-step sequenced treatment: Complete biodegradation of the pollutant mixture Decrease in environmental toxicity, with 3 of the 4 tested growth substrates Soil and groundwater from a site contaminated by tetrachloroethene (PCE), trichloroethene (TCE), vinyl chloride (VC), 1,1,2-trichloroethane (TCA) and chloroform (CF) 1) Aerobic cometabolic biodegradation of TCE, VC, TCA , CF 2) Reductive dechlorination of PCE to cis-dichloroethene (cis-DCE) or TCE 3) Aerobic cometabolic biodegradation of cis-DCE or TCE a r t i c l e i n f o Article history:

2025, Environmental Science & Technology

Reductive dehalogenation of chlorinated compounds is the most important process occurring within the zerovalent iron (Fe 0 ) barrier. The relative reaction rates of individual halocarbons with Fe 0 can vary considerably. This variability has been the stimulus for using various chemical descriptors for a priori predictions of transformation rates via linear free-energy relationships (LFERs). Our objective was to determine the efficacy of four molecular descriptors to describe the transformation rates of three chloromethanes, three chloroethanes, and six chloropropanes by Fe 0 . This was accomplished by generating an internally consistent set of rate constants under controlled environmental conditions (16 °C, anaerobic) and regressing the surfacearea normalized rate constants (k SA ) against (i) energy of the lowest unoccupied molecular orbital (E LUMO ); (ii) vertical attachment energies (VAE); (iii) thermal electron attachment rate constants; and (iv) the molar response from a commercial electron capture detector (ECD). Results showed good correlations between k SA 's and all four descriptors (r 2 : 0.72-1.0), but a separate trend line was required for the chloromethanes and the chloro-ethanes/ propanes. Given the availability and ease with which ECD response can be obtained, this physical measurement may provide a practical means of determining relative rates of reactivity of various halocarbons in permeable reactive iron barriers.

2025, Environmental Science and Pollution Research

The dechlorination of chlorinated organic pollutants by zero valent iron (ZVI) is an important water treatment process with a complex dependence on many variables. This complexity means that there are reported inconsistencies in terms of dechlorination with ZVI and the effect of ZVI acid treatment, which are significant and are as yet unexplained. This study aims to decipher some of this complexity by combining Raman spectroscopy with gas chromatography-mass spectrometry (GC-MS) to investigate the influence of the mineralogy of the iron oxide phases on the surface of ZVI on the reductive dechlorination of pentachlorophenol (PCP). Two electrolytic iron samples (ZVI-T and ZVI-H) were found to have quite different PCP dechlorination reactivity in batch reactors under anoxic conditions. Raman analysis of the Bas-received^ZVI-T indicated the iron was mainly covered with the ferrous oxide (FeO) wustite, which is non-conducting and led to a low rate of PCP dechlorination. In contrast, the dominant oxide on the Bas-received^ZVI-H was magnetite which is conducting and, compared to ZVI-T, the ZVI-H rate of PCP dechlorination was four times faster. Treating the ZVI-H sample with 1 N H 2 SO 4 made small change to the composition of the oxide layers and also minute change to the rate of PCP dechlorination. However, treating the ZVI-T sample with H 2 SO 4 led to the loss of wustite so that magnetite became the dominant oxide and the rate of PCP dechlorination increased to that of the ZVI-H material. In conclusion, this study clearly shows that iron oxide mineralogy can be a contributing factor to apparent inconsistencies in the literature related to ZVI performance towards dechlorination and the effect of acid treatment on ZVI reactivity.

2025, Environmental Science & Technology

2025, Journal of Contaminant Hydrology

The occurrence of chlorinated ethene transformation in a streambed was investigated using concentration and carbon isotope data from water samples taken at different locations and depths within a 15 × 25 m study area across which a tetrachloroethene (PCE) plume discharges. Furthermore, it was evaluated how the degree of transformation is related to groundwater discharge rates, redox conditions, solid organic matter content (SOM) and microbial factors. Groundwater discharge rates were quantified based on streambed temperatures, and redox conditions using concentrations of dissolved redox-sensitive species. The degree of chlorinated ethene transformation was highly variable in space from no transformation to transformation beyond ethene. Complete reductive dechlorination to ethane and ethene occurred at locations with at least sulfate-reducing conditions and with a residence time in the samples streambed zone (80 cm depth) of at least 10 days. Among these locations, Dehalococcoides was detected using a PCR method where SOM contents were N 2% w/w and where transformation proceeded beyond ethene. However, it was not detected at locations with low SOM, which may cause an insufficient H 2 supply to sustain a detectably dense Dehalococcoides population. Additionally, it is possible that other organisms are responsible for the biodegradation. A microcosm study with streambed sediments demonstrated the potential of VC oxidation throughout the site even at locations without a pre-exposure to VC, consistent with the detection of the epoxyalkane:coenzyme M transferase (EaCoMT) gene involved in the degradation of chlorinated ethenes via epoxidation. In contrast, no aerobic transformation of cDCE in microcosms over a period of 1.5 years was observed. In summary, the study demonstrated that carbon isotope analysis is a sensitive tool to identify the degree of chlorinated ethene transformation even in hydrologically and geochemically complex streambed systems. In addition, it was observed that the degree of transformation is related to redox conditions, which in turn depend on groundwater discharge rates.

2025, Environmental Science & Technology

Carbon isotope fractionation during dechlorination of chlorinated ethenes was investigated using a methanogenic microbial enrichment culture. Subcultures were amended with trichloroethene (TCE), cis-1,2-dichloroethene (cis-DCE), and vinyl chloride (VC), respectively. Carbon isotope ratios and concentrations of reactants and of all dechlorination products were monitored during two experiments. All dechlorination steps were accompanied by significant isotope fractionation. The isotope ratios of the reactants were described with a Rayleigh type model, and the following enrichment factors ( P/R ) were obtained: -6.6 and -2.5‰ for dechlorination of TCE, -14.1 and -16.1‰ for dechlorination of cis-DCE, and -26.6 and -21.5‰ for dechlorination of VC. Isotope and mass balances suggested that ethene (ETH) was degraded. In additional experiments with ETH as reactant, ETH became enriched in 13 C as its concentration decreased indicating the cultures were capable of degrading ETH. The average value for the enrichment factor obtained for the degradation of ETH was -3.0‰. The large carbon isotope fractionation observed in this study confirms that carbon isotope ratios are a sensitive tool for monitoring dechlorination of chlorinated ethenes to nontoxic end products.

2025, Water Science and Technology

In situ anaerobic reductive dechlorination, using slow-release electron donors, is emerging as an effective and sustainable (low-cost and low-maintenance) technology to remediate aquifers contaminated by chloroethenes. In the present study, we investigated the use of poly-b-hydroxybutyrate (PHB), a fully biodegradable polymer, as a slow-release source of hydrogen and acetate for the reductive dechlorination of trichloroethene (TCE). Results of this study indicated that TCE dechlorination in PHB-amended microcosms was 2.3-times higher than in non-amended controls. This higher activity was explained by a higher H 2 level in PHB-amended microcosms. As usual, acetate was the major sink (,90%) of reducing equivalents available from PHB degradation, whereas no acetotrophic dechlorination was observed.

2025, Toxics

Trichloroethylene (TCE) and more in general chlorinated aliphatic hydrocarbons (CAHs) can be removed from a contaminated matrix thanks to microorganisms able to perform the reductive dechlorination reaction (RD). Due to the lack of electron donors in the contaminated matrix, CAHs' reductive dechlorination can be stimulated by fermentable organic substrates, which slowly release molecular hydrogen through their fermentation. In this paper, three different electron donors constituted by lactate, hydrogen, and a biocathode of a bioelectrochemical cell have been studied in TCE dechlorination batch experiments. The batch reactors evaluated in terms of reductive dechlorination rate and utilization efficiency of the electron donor reported that the bio-electrochemical system (BES) showed a lower RD rate with respect of lactate reactor (51 ± 9 µeq/d compared to 98 ± 4 µeq/d), while the direct utilization of molecular hydrogen gave a significantly lower RD rate (19 ± 8 µeq/d), due to hydrogen low solubility in liquid media. The study also gives a comparative evaluation of the different electron donors showing the capability of the bioelectrochemical system to reach comparable efficiencies with a fermentable substrate without the use of other chemicals, 10.7 ± 3.3% for BES with respect of 3.5 ± 0.2% for the lactate-fed batch reactor. This study shows the BES capability of being an alternative at classic remediation approaches.

2025, Chemosphere

Problems of co-occurrence of organic and heavy metals pollutants in water. Impacts of heavy metals on 1,2-dichloroethane (1,2-DCA) degradation. Bioremediation of 1,2-DCA degradation in water co-contaminated with heavy metals. Microbial population and diversity profiling in the co-contaminated water. Identification of important bacterial phylotypes involved in the bioremediation process.

2025, Groundwater Monitoring & Remediation

Trichloroethene (TCE) was detected in cores of trees growing above TCE‐contaminated ground at three sites: the Carswell Golf Course in Texas, Air Force Plant PJKS in Colorado, and Naval Weapons Station Charleston in South Carolina. This was true even when the depth to water was 7.9 m or when the contaminated aquifer was confined beneath ∼3 m of clay. Additional ground water contaminants detected in the tree cores were cis–1,2‐dichloroethene at two sites and tetrachloroethene at one site. Thus, tree coring can be a rapid and effective means of locating shallow subsurface chlorinated ethenes and possibly identifying zones of active TCE dechlorination. Tree cores collected over time were useful in identifying the onset of ground water contamination. Several factors affecting chlorinated ethene concentrations in tree cores were identified in this investigation. The factors include ground water chlorinated ethene concentrations and depth to ground water contamination. In addition, differ...

2025

This research was to study the effect of blast furnace dust (BFD) as a new reactive material
for the degradation of chlorinated organic (COCs) and endocrine disrupting compounds
(EDCs). When 100 g/L of BFD was used, the effective degradation of tetrachloroethylene
(PCE) was obtained. The cis-DCE (0.93 mM) was dechlorinated to below detection limit
within 120 hr of reaction. Among various COCs and EDCs, they were degraded at least 90%
except for sodium perchlorate. The metabolites of `4-tert-octylphenol (4-t-OP) were identified
as 2,4,4-trimethyl-2-pentanol, hydroquinone and 2-tert-octylhydroquinone, respectively. The
effective degradation of PCE and 4-t-OP was occurred at range of pH 4 to 7. A total of 100%
of cis-DCE and 86% of 4-t-OP were degraded in fed-batch experiments after 264 hr. A
solution of highly enriched bacteria completely insolubilized 2.14 mM of Zn eluted from BFD
within 168 hr of culture. These researches will provide more information related to the
application for other contaminated water and wastewater treatments.

2025, Nanotechnology and the Environment

Reactions and Catalysis (nanosized metals, Vitamin B12, Enzymes) Tunable Separations (with Polypeptides)

2025, Environmental Progress & Sustainable Energy

Iron nanoaggregates have been prepared using the sodium borohydride reduction method and postcoated with Pd using aqueous phase electro‐deposition. The Fe/Pd nanoaggregates were used to examine dechlorination of trichloroethylene (TCE) with regard to matrix effects using materials representative of a potential zero‐valent metal remediation site surrounding the Paducah gaseous diffusion plant in Paducah, KY. A surface‐area‐normalized first‐order rate constant of 1.4 × 10−1 L m−2 h−1 was obtained for the case of ideal dechlorination of 19.6 mg L−1 TCE at room temperature and pH 6.2 using 0.5 g L−1 Fe/Pd (0.42 wt % Pd) loading. This value decreases by an order of magnitude to 1.9 × 10−2 L m−2 h−1 when the reaction is carried out in a realistic background matrix when the pH is high (8.8). For all variables tested, Pd content has the most impact on reaction rates. Circulating batch‐column experiments are used to study dechlorination under flow conditions and demonstrate the ability of no...

2025, Remediation Journal

An in situ bioremediation (ISB) pilot study, using whey powder as an electron donor, is being performed at Site 19, Edwards Air Force Base, California, to treat groundwater contaminated with trichloroethene (TCE) via anaerobic reductive dechlorination. Challenging site features include a fractured granitic aquifer, complex geochemistry, and limited biological capacity for reductive dechlorination. ISB was conducted in two phases with Phase I including one-and-a-half years of biostimulation only using whey powder and Phase II including biostimulation with buffered whey powder and bioaugmentation. Results of Phase I demonstrated effective distribution of whey during injections resulting in depletion of high concentrations of sulfate and methanogenesis, but acid production due to whey fermentation and limited buffering capacity of the aquifer resulted in undesirable impacts to pH. In addition, cis-1,2-dichloroethene (cis-1,2-DCE) stall was observed, which correlated to the unsuccessful growth of native Dehalococcoides populations. Therefore, Phase II included the successful buffering of whey powder using bicarbonate, which mitigated negative pH effects. In addition, bioaugmentation resulted in successful transport of Dehalococcoides populations to greater than 50 feet away from the injection point four months after inoculation. A concomitant depletion of accumulated cis-1,2-DCE was observed at all wells affected by bioaugmented Dehalococcoides. O

2025, Remediation Journal

2025

At the confined nanospace and/or nanoscale interface, the catalytic nature of active sites on the molecule level still remains elusive. Herein, with the catalytic hydride reduction of 4-nitrophenol (4-NP) over gold nanoparticles (NPs) catalysts as a prototype reaction, the influence of delicate change of microenvironment of catalytic active site on the reaction kinetics of 4-NP to 4-aminophenol (4-AP) with the introduction of varied alkali-metal ion (AM + ) salt, have been deeply investigated. We demonstrate that structural water (SW) adsorbed on Au NPs in the form of {OH -•H2O@Au NPs} is the real catalytic active sites (not alone Au NPs), and in the presence of lithium chloride (LiCl), it shows the best catalytic performance. In addition, the isotope labeling and kinetic isotope effect (KIE) experiments evidences that, the reduction of 4-NP does not follow the classical Langmuir-Hinshelwood (L-H) bimolecular mechanism, but an interfacial SW dominated electron and proton transfer mechanism. The proposed mechanism answers why the dissociation of O-H bond of water is the rate-determining step (RDS) of 4-NP reduction, and, counter-intuitively, the solvent water is the hydrogen source of final product 4-AP, instead of sodium borohydride (NaBH4) reducer. Importantly, the co-existence of Li + and Cl -ions synergistically stabilizes the transition state of reaction and accelerates the interfacial electron and proton transfer, consequently enhancing the reaction kinetics. The model of structural water as a bridge to transfer electron and proton at nanoscale interface is the reminiscent of working mechanism of photosystem two (PSII) for water splitting on Mn4CaO5 cluster.

2025, Water Research

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2025, Water Research

2025, Journal of Chemistry

Chlorinated alkanes were heavily used in a wide range of industrial applications including as degreasers, paint strippers, chemical intermediates, and soil fumigants. These compounds are an environmental concern due to the adverse health effects associated with them and have been detected in environmental matrices including soils and groundwater. Chlorinated alkanes are recalcitrant, and current remediation methods that employ zero-valent iron (ZVI) are unable to directly dehalogenate these compounds, limiting the available approaches forin situremediation of these widely utilized chemicals. This study employed a novel approach for the remediation of 1,2,3-trichloropropane (TCP), 1,2-dichloropropane (1,2-DCP), 1,3-dichloropropane (1,3-DCP), 1-chloropropane (1-CP), and 1,2-dichloroethane (1,2-DCA) in the presence of ZVI and vitamin B12, a naturally occurring electron mediator. Batch reactions were performed in order to determine a kinetic model for the associated degradation mechanis...

2025, Environmental Science and Pollution Research

Where surface-functionalized engineered nanoparticles (NP) occur in drinking water catchments, understanding their transport within and between environmental compartments such as surface water and groundwater is crucial for risk assessment of drinking water resources. The transport of NP is mainly controlled by (i) their surface properties, (ii) water chemistry, and (iii) surface properties of the stationary phase. Therefore, functionalization of NP surfaces by organic coatings may change their fate in the environment. In laboratory columns, we compared the mobility of CeO 2 NP coated by the synthetic polymer polyacrylic acid (PAA) with CeO 2 NP coated by natural organic matter (NOM) and humic acid (HA), respectively. The effect of ionic strength on transport in sand columns was investigated using deionized (DI) water and natural surface water with 2.2 mM Ca 2+ (soft) and 4.5 mM Ca 2+ (hard), respectively. Furthermore, the relevance of these findings was validated in a near-natural bank filtration experiment using HA-CeO 2 NP. PAA-CeO 2 NP were mobile under all tested water conditions, showing a breakthrough of 60% irrespective of the Ca 2+ concentration. In contrast, NOM-CeO 2 NP showed a lower mobility with a breakthrough of 27% in DI and < 10% in soft surface water. In hard surface water, NOM-CeO 2 NP were completely retained in the first 2 cm of the column. The transport of HA-CeO 2 NP in laboratory columns in soft surface water was lower compared to NOM-CeO 2 NP with a strong accumulation of CeO 2 NP in the first few centimeters of the column. Natural coatings were generally less stabilizing and more susceptible to increasing Ca 2+ concentrations than the synthetic coating. The outdoor column experiment confirmed the low mobility of HA-CeO 2 NP under more complex environmental conditions. From our experiments, we conclude that the synthetic polymer is more efficient in facilitating NP transport than natural coatings and hence, CeO 2 NP mobility may vary significantly depending on the surface coating.

2025, SDRP Journal of Earth Sciences & Environmental Studies

Microorganisms including bacteria, archeae, fungi etc., on
the earth. Unculturable bacteria are of prime focus in
scientific community because of their vital role in pro
duction of many important enzymes and degradation
capabilities. Mostly, researcher all over the world are
using NGS technologies to decode their genome which
is costly when multiple isolates to be tested at initial
level. In order to answer this question, we have tried
gold standard Sanger sequencing technique to se
quence metagenomic DNA extracted from soil. We
used 16s rDNA approach and found microbes in the
samples which are involved in processes such as Nitro
gen fixation, oil-bioremediation, reduction of sulphate
unculturable bacteria

2025, Biotechnology and Bioengineering

A model was developed to describe toxicity from high concentrations of chlorinated aliphatic hydrocarbons (CAHs) on reductively dechlorinating cultures under batch-growth conditions. A reductively dechlorinating anaerobic Evanite subculture (EV-cDCE) was fed trichloroethene (TCE) and excess electron donor to accumulate cis-1,2-dichloroethene (cDCE) in batch-fed reactors. A second Point Mugu (PM) culture was also studied in the cDCE accumulating batch-fed experiment, as well as in a time-and concentration-dependent cDCE exposure experiment. Both cultures accumulated cDCE to concentrations ranging from 9,000 to 12,000 mM before cDCE production from TCE ceased. Exposure to approximately 3,000 and 6,000 mM cDCE concentrations for 5 days during continuous TCE dechlorination exhibited greater loss in activity proportional to both time and concentration of exposure than simple endogenous decay. Various inhibition models were analyzed for the two cultures, including the previously proposed Haldane inhibition model and a maximum threshold inhibition model, but neither adequately fit all experimental observations. A concentration-dependent toxicity model is proposed, which simulated all the experimental observations well. The toxicity model incorporates CAH toxicity terms that directly increase the cell decay coefficient in proportion with CAH concentrations. We also consider previously proposed models relating toxicity to partitioning in the cell wall (K M/B ), proportional to octanolwater partitioning (K OW ) coefficients. A reanalysis of previously reported modeling of batch tests using the Haldane model of Yu and Semprini, could be fit equally well using the toxicity model presented here, combined with toxicity proportioned to cell wall partitioning. A companion paper extends the experimental analysis and our modeling approach to a completely mixed reactor and a fixed film reactor.

2025, Biotechnology and Bioengineering

A model that was used to describe toxicity from high concentrations of chlorinated aliphatic hydrocarbons (CAHs) on reductively dechlorinating cultures in batch reactors (Sabalowsky and Semprini (in press)) was extended here to simulate observations in continuous flow suspended and attached growth reactors. The reductively dechlorinating anaerobic Evanite subculture (EV-cDCE) was fed trichloroethene (TCE) and excess electron donor to accumulate cis-1,2-dichloroethene (cDCE) in a continuous flow stirred tank reactor (CFSTR); and an attached growth recirculating packed column (RPC). A concentrationdependent toxicity model used to simulate the results of batch reactors in part I (Sabalowsky and Semprini (in press) Biotechnol Bioeng) also simulated well the observations for the CFSTR and RPC growth modes. The toxicity model incorporates cDCE and TCE toxicity coefficients that directly increase the cell decay coefficient in proportion with cDCE and TCE concentrations. Simulated estimates of the cDCE and TCE toxicity coefficients indicate reductively dechlorinating cells are most sensitive to high concentrations of cDCE and TCE in batch-fed growth, followed by CFSTR, with attached growth being least sensitive. The greater toxicity of TCE than cDCE, and ratio of the modeled toxicity coefficients, agrees with previously proposed models relating toxicity to partitioning in the cell wall (K M/B ), proportional to octanol-water partitioning (K OW ) coefficients.

2025

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2025, European Journal of Soil Biology

Bioaugmentation of microbial cultures is a potential method to enhance the performance of in situ bioremediation. In this study we evaluated the bioaugmentation of aerobic microorganisms that grow on butane that can transform chlorinated... more

2025, Journal of Hazardous Materials

Tetrabutoxysilane (TBOS), which yields 1-butanol upon abiotic hydrolysis, was evaluated as a slow-release substrate for the reductive dechlorination of tetrachloroethylene (PCE) as a dense non-aqueous-phase liquid (DNAPL). Dechlorination was achieved using an anaerobic binary mixed (BM) culture, which consisted of the Pt. Mugu (PM) and the Evanite (EV) mixed cultures. In batch reactor experiments, TBOS was mixed with PCE DNAPL to achieve different PCE mol fractions (PCE mol/(PCE mol + TBOS mol)), and different PCE aqueous concentrations based on Raoult's Law. The reductive dechlorination activity was determined based on the amount of chloride ions released and the mass balances of the transformation products formed. The mass balances of the total chlorinated aliphatic hydrocarbons (CAHs) between water, NAPL and gas phases were performed using independently measured NAPL/water partition coefficients. The amounts of chloride released (directly measured in aqueous samples) agreed with the total chloride produced based on the mass balances. The abiotic rates of TBOS hydrolysis were first-order with respect to TBOS NAPL concentration. A higher electron transfer efficiency to dechlorination was correlated with lower rates of TBOS hydrolysis. The total amounts of PCE DNAPL and TBOS were important factors for the reductive dechlorination of PCE. The dechlorination activity was suppressed at high NAPL concentrations. Direct contact of the PCE/TBOS NAPL mixture may have caused toxicity to the dechlorinating bacteria. Decreases in pH likely lowered the microbial activity for reductive dechlorination due to the accumulation of acetate and/or butyrate. These studies showed the potential of TBOS as a slow-release substrate for enhancing bioremediation of DNAPL contaminated sites.

2025, Water Research

Microcosm studies were conducted to demonstrate the effectiveness of tetrabutoxysilane (TBOS) as a slow-release anaerobic substrate to promote reductive dehalogenation of trichloroethylene (TCE). The abiotic hydrolysis of TBOS and tetrakis(2-ethylbutoxy)silane (TKEBS), and the biotic transformations of the hydrolysis products from both were also investigated. Comparison of TCE reductive dehalogenation was performed with microbial communities stimulated from three different sites: Site 300 Lawrence Livermore National Laboratory (LLNL), CA, Point Mugu Naval Weapons Facility, CA, and the Evanite site in Corvallis, OR. Poisoned microcosms showed that 1 mol of TBOS slowly and abiotically hydrolyzes to 4 mol of 1-butanol, while the live microcosms showed the 1-butanol ferments to butyrate and/or acetate, producing H 2 . The hydrolysis of TBOS and TKEBS was abiotic and not enhanced by biotic processes under the anaerobic conditions of these tests. Hydrogen consumption was correlated with reductive dehalogenation, indicating it served as an electron donor for reductive dehalogenation. TBOS was found to be a slow-release anaerobic substrate to support long-term dechlorination of TCE to ethylene in Point Mugu microcosms, and in the LLNL microcosm bioaugmented with the Evanite culture. Electron mass balances showed most of the electron flow went into the creation of organic acids, especially acetate, and the production of methane. Electron efficiencies for reductive dechlorination were as high as 14% based on the electrons used for dechlorination to the total electrons associated with the mass of TBOS and TKEBS hydrolyzed. Rates of TBOS hydrolysis increased with greater TBOS concentrations as a light nonaqueous-phase liquids (LNAPL). These results indicate that TBOS has promise as an effective anaerobic substrate for remediating a wide range of CAH concentrations at different CAH contaminated sites.

2025, Water Research

AbstractÐPolyhalogenated compounds are known to resist aerobic degradation but are subject to anaerobic reductive dehalogenation. The anaerobic biotransformation often result in the accumulation of toxic and carcinogenic compounds. An example is the production of trichloroethylene (TCE), cis-1,2dichloroethylene (cDCE), trans-1,2-dichloroethylene (tDCE), 1,1-dichloroethylene (1,1-DCE) and vinyl chloride (VC), from anaerobic dechlorination of tetrachloroethylene (PCE). However, the anaerobic dehalogenation products are known to be susceptible to aerobic methanotrophic oxidative mineralization. Therefore, the treatment of polyhalogenated compounds and ®eld remediation of sites contaminated by these compounds involve anaerobic biotransformation followed by aerobic mineralization. As opposed to two stage treatment and remediation which involve anaerobic environment followed by an aerobic environment in two separate systems or environments, recent focus on the detoxi®cation of polyhalogenated compounds involve the development of engineering systems which can accomplish anaerobic biotransformation and aerobic oxidative mineralization in a single reaction environment. Periodic aerated anaerobic batch systems, including systems for ex-situ and in-situ biodetoxi®cation of polyhalogenated compounds are being developed at San Jose State University under the direction of Dr Udeme J. Ndon. These systems and results of preliminary studies are presented in this report. Results of the preliminary experiments showed minimum accumulation of PCE biotransformation products in comparison to strict anaerobic conditions. Results also show that PCE degradation may have occurred during the transition between anaerobiosis and aerobiosis.

2025, Tạp chí Y học Việt Nam

Mục tiêu: Đánh giá đáp ứng điều trị và một số tác dụng không mong muốn của phác đồ Gemcitabine-Cisplatin trong điều trị hóa chất dẫn đầu ở nhóm bệnh nhân nghiên cứu. Đối tượng và phương pháp nghiên cứu: Nghiên cứu mô tả cắt ngang. Có 78 bệnh nhân ung thư vòm mũi họng giai đoạn III-IVa điều trị hóa chất dẫn đầu phác đồ Gemcitabine-Cisplatin tại Bệnh viện Ung bướu Hà Nội và Bệnh viện K từ tháng 02/2020 đến 03/2022. Bệnh nhân được đánh giá đáp ứng theo tiêu chuẩn đánh giá đáp ứng cho khối u đặc (RECIST), độc tính theo tiêu chuẩn CTACE 5.0. Kết quả: : Tỷ lệ đáp ứng của phác đồ là 78,3%; trong đó: 18% bệnh nhân đáp ứng hoàn toàn, 60,3% đáp ứng một phần. Độc tính: tỷ lệ thiếu máu: 60,2%, tỷ lệ hạ hạch cầu trung tính: 34,6%, hạ tiểu cầu: 30,8%, nôn, buồn nôn: 82,0% chủ yếu ở độ I-II. Kết luận: Phác đồ Gemcitabine-Cisplatin cho bệnh nhân ung thư vòm mũi họng có tỷ lệ đáp ứng cao, độc tính chủ yếu trên huyết học và bệnh nhân dung nạp thuốc tốt

2025, Transport and Communications Science Journal

Tích chập suy rộng mới với hàm trọng đối với hai phép biến đổi tích phân Fourier cosine và Fourier sine được chúng tôi xây dựng và nghiên cứu trong bài báo này. Chúng tôi chứng minh sự tồn tại của tích chập suy rộng mới này trong không gian L(R¬+). Đẳng thức nhân tử hóa cốt yếu với sự có mặt của hai phép biến đổi tích phân khác biệt là Fourier cosine, Fourier sine và hàm trọng cùng một số tính chất khác như tính không giao hoán, tính không kết hợp khác với các tích chập của một phép biến đổi tích phân được phát biểu và chứng minh. Cuối cùng là áp dụng tích chập suy rộng mới được xây dựng để giải hệ phương trình tích phân kiểu Toeplitz-Hankel và nhận được nghiệm dưới dạng đóng. Trong ba thập niên trở lại đây, tích chập suy rộng được các nhà toán học quốc tế và trong nước quan tâm nghiên cứu. Đồng thời các nhà toán học cũng ứng dụng chúng trong việc giải các bài toán về phương trình tích phân, phương trình vi tích phân,… Vì vậy, việc nghiên cứu tích chập suy rộng là vấn đề thời sự. Do...

2025, Environmental Science & Technology

Stable carbon isotope fractionation is a valuable tool for monitoring natural attenuation and to establish the fate of groundwater contaminants. In this study, we measured carbon isotope fractionation during aerobic and anaerobic degradation of two chlorinated benzenes: monochlorobenzene (MCB) and 1,2,4-trichlorobenzene (1,2,4-TCB). MCB isotope fractionation was measured in anaerobic methanogenic microcosms, while 1,2,4-TCB isotope experiments were carried out in both aerobic and anaerobic microcosms. Large isotope fractionation was observed in both the anaerobic microcosm experiments. Enrichment factors (ε) for anaerobic reductive dechlorination of MCB and 1,2,4-TCB were À5.0% ( 0.2% and À3.0% ( 0.4%, respectively. In contrast, no significant isotope fractionation was found during aerobic microbial degradation of 1,2,4-TCB. The cleavage of a CÀCl σ bond occurs during anaerobic reductive dechlorination of MCB and 1,2,4-TCB, while no σ bond cleavage is involved during aerobic degradation via dioxygenase. The difference in isotope fractionation for aerobic versus anaerobic biodegradation of MCB and 1,2,4-TCB can be explained by the difference in the initial step of aerobic versus anaerobic biodegradation pathways.

2025, Environmental Science & Technology

Stable carbon isotope analysis of chlorinated ethenes and ethene was performed at a site contaminated with trichloroethene (TCE), a dense non-aqueous phase liquid (DNAPL). The site is located in fractured bedrock and had variable groundwater hydraulic gradients during the study due to a local excavation project. Previous attempts to biostimulate a pilot treatment area at the site resulted in the production of cis-1,2-dichloroethene (cis-DCE), the first product of reductive dechlorination of TCE. Cis-DCE concentrations accumulated however, and there was no appreciable production of the breakdown products from further reductive dechlorination, vinyl chloride (VC) and ethene (ETH). Consequently, the pilot treatment area was bioaugmented with a culture of KB-1, a natural microbial consortium known to completely reduce TCE to nontoxic ETH. Due to ongoing dissolution of TCE from DNAPL in the fractured bedrock, and to variable hydraulic gradients, concentration profiles of dissolved TCE and its degradation products cis-DCE, VC, and ETH could not convincingly confirm biodegradation of the chlorinated ethenes. Isotopic analysis of cis-DCE and VC, however, demonstrated that biodegradation was occurring in the pilot treatment area. The isotope values of cis-DCE and VC became significantly more enriched in 13 C over the last two sampling dates (in one well from -17.6‰ to -12.8‰ and from -22.5‰ to -18.2‰ for cis-DCE and VC, respectively). Quantification of the extent of biodegradation in the pilot treatment area using the Rayleigh model indicated that, depending on the well, between 21.3% and 40.7% of the decrease in cis-DCE and between 15.2% and 36.7% of the decrease in VC concentrations can be attributed to the effects of biodegradation during this time period. Within each well, the isotope profile of TCE remained relatively constant due to the continuous input of undegraded TCE due to DNAPL dissolution.

2025, Applied and Environmental Microbiology

We isolated a strain of Rhodopseudomonas palustris (RCB100) by selective enrichment in light on 3-chlorobenzoate to investigate the steps that it uses to accomplish anaerobic dechlorination. Analyses of metabolite pools as well as enzyme assays suggest that R. palustris grows on 3-chlorobenzoate by (i) converting it to 3-chlorobenzoyl coenzyme A (3-chlorobenzoyl–CoA), (ii) reductively dehalogenating 3-chlorobenzoyl–CoA to benzoyl-CoA, and (iii) degrading benzoyl-CoA to acetyl-CoA and carbon dioxide. R. palustris uses 3-chlorobenzoate only as a carbon source and thus incorporates the acetyl-CoA that is produced into cell material. The reductive dechlorination route used by R. palustris for 3-chlorobenzoate degradation differs from those previously described in that a CoA thioester, rather than an unmodified aromatic acid, is the substrate for complete dehalogenation.

2025, Environmental Pollution

A novel non-dsrAB (without dissimilatory sulfite reductase genes) sulfate-reducing bacterium (SRB) Clostridium sp. BXM was isolated from a paddy soil. Incubation experiments were then performed to investigate the formation of reduced sulfur compounds (RSC) by Clostridium sp. BXM, and RSC-induced dechlorination of p,p 0 -DDT in culture medium and soil solution. The RSCs produced were 5.8 mM and 4.5 mM in 28 mM sulfate amended medium and soil solution respectively after 28-day cultivation. The p,p 0 -DDT dechlorination ratios were 74% and 45.8% for 5.8 mM and 4.5 mM RSCs respectively at 6 h. The metabolites of p,p 0 -DDT found in the two reaction systems were identified as p,p 0 -DDD and p,p 0 -DDE. The dechlorination pathways of p,p 0 -DDT to p,p 0 -DDD and p,p 0 -DDE were proposed, based on mass balance and dechlorination time-courses. The results indicated that RSC-induced natural dechlorination may play an important role in the fate of organochlorines.

2025, International Journal of Advance Research, Ideas and Innovations in Technology

With the era of industrialization and excessive dependence on chemicals, there is increased indiscriminate disposal of especially chlorinated solvents causing a variety of environmental problems. Chlorinated solvents including trichloroethylene (TCE) and perchloroethylene are significant groundwater contaminants causing severe health effects. Various technical strategies have been developed and applied, often with limited success. Time frames for remediation tend to be long, usually measured in decades. In this review we focus on remediation of chlorinated solvents in groundwater by the addition of exogenous microorganisms, specifically members of the genus Dehalococcoides (DHC) referred to as bioaugmentation. Many potential technologies for remediation of chlorinated solvents, its past, present and future as well as how bioaugmentation is superior to these techniques are discussed.

2025, International Journal of Advance Research, Ideas and Innovations in Technology

2025, Environmental Science & Technology

This research investigated the long-term performance of zero-valent iron aggregates for reductive dechlorination of trichloroethylene (TCE) and perchloroethylene (PCE). The effects of elapsed time, mass transfer limitations, and influent halocarbon concentration on reductive dechlorination rates were investigated using groundwater obtained from a field site contaminated with chlorinated organic compounds. Over the first 300 days of operation, reaction rates for TCE and PCE gradually increased due to increasing porosity of the iron aggregates. Although there was microbial growth in the column, biological activity did not measurably contribute to reductive dechlorination. Dechlorination rates were pseudo-first-order in reactant concentration for submillimolar halocarbon concentrations. TCE concentrations near aqueous saturation resulted in passivation of the iron surfaces and deviation from firstorder reaction kinetics. However, this passivation was slowly reversible upon lowering the influent TCE concentration. Tafel polarization diagrams for an electrode constructed from the iron aggregates indicated that corrosion of the aggregates was anodically controlled. At all halocarbon concentrations, aggregate oxidation by water accounted for more than 80% of the corrosion. Throughout the course of the 3-yr column investigation, reaction rates for TCE were 2-3 times faster than those for PCE. However, current measurements with the aggregate electrode indicated that direct PCE reduction was faster than that for TCE. This disparity between amperometrically measured reaction rates and those measured in the column reactor indicated that halocarbon reduction may occur via direct electron transfer or may occur indirectly through reaction with atomic hydrogen adsorbed to the iron. Comparison of aggregate corrosion rates with those of fresh iron suggested that anodic control of corrosion leads to predominance of the indirect reduction mechanism. The faster reaction rate for TCE under anodically controlled conditions can therefore be attributed to its faster rate of indirect reduction as compared to PCE.

2025

ABSTRACTChloroform (CF) and dichloromethane (DCM) contaminate groundwater sites around the world, which can be remediated through bioaugmentation. Although several strains ofDehalobacter restrictuscan reduce CF to DCM, and multiple Peptococcaceae can ferment DCM, these processes cannot happen simultaneously due to CF sensitivity in the known DCM-degraders or electron donor competition. Here we present a mixed microbial culture that can simultaneously metabolize CF and DCM to carbon dioxide and create an additional enrichment culture fed only DCM. Through species-specific qPCR, we find that aDehalobacterstrain grows both while CF alone and DCM alone are converted, indicating its involvement in both metabolic steps. Additionally, the culture was maintained for over 1400 days without addition of exogenous electron donor, and through electron balance calculations we show that DCM mineralization produces sufficient reducing equivalents (likely hydrogen) for CF respiration. Together, thes...

2024, Journal of Hazardous Materials

Research was conducted to examine the effects of various fractions of cosolvent solutions on dechlorination of toxaphene by zero-valent iron (Fe 0 ). Experimental results showed that toxaphene degradation in solution was found to be the result of dechlorination at the Fe 0 surface. The rate of toxaphene dechlorination was also found to reduce with the increase of cosolvent in solution, as the cosolvent presence caused a reduction in toxaphene adsorption to Fe 0 surfaces. Toxaphene sorption to Fe 0 was found to correspond to a Freundlich nonlinear sorption equation and indicated that the linearity of this isotherm in the presence of cosolvent was related to the saturation of solution, which was the ratio of aqueous concentration to the solubility (C a /S c ). When C a /S c > 0.2, the sorption isotherm was almost linear and the concept of cosolvency power can be applied mathematically to describe this process. A mathematical model detailing the sorption and dechlorination of toxaphene by Fe 0 was developed, and showed that experimental data agreed with the theoretically derived data. Overall, results indicated that dechlorination of complex chlorinated substances, such as toxaphene, by Fe 0 can be greatly dependent upon adsorption to the iron surface.

2024, Biodegradation

The enrichment culture SL2 dechlorinating tetrachloroethene (PCE) to ethene with strong trichloroethene (TCE) accumulation prior to cis-1,2dichloroethene (cis-DCE) formation was analyzed for the presence of organohalide respiring bacteria and reductive dehalogenase genes (rdhA). Sulfurospirillum-affiliated bacteria were identified to be involved in PCE dechlorination to cis-DCE whereas ''Dehalococcoides''-affiliated bacteria mainly dechlorinated cis-DCE to ethene. Two rdhA genes highly similar to tetrachloroethene reductive dehalogenase genes (pceA) of S. multivorans and S. halorespirans were present as well as an rdhA gene very similar to the trichloroethene reductive dehalogenase gene (tceA) of ''Dehalococcoides ethenogenes'' strain 195. A single strand conformation polymorphism (SSCP) method was developed allowing the simultaneous detection of the three rdhA genes and the estimation of their abundance. SSCP analysis of different SL2 cultures showed that one pceA gene was expressed during PCE dechlorination whereas the second was expressed during TCE dechlorination. The tceA gene was involved in cis-DCE dechlorination to ethene. Analysis of the internal transcribed spacer region between the 16S and 23S rRNA genes revealed two distinct sequences originating from Sulfurospirillum suggesting that two Sulfurospirillum populations were present in SL2. Whether each Sulfurospirillum population was catalyzing a different dechlorination step could however not be elucidated.

2024, Environmental Science & Technology

2024

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2024, European geosciences union general assembly

2024, University Consortium for Field-Focused Groundwater Contamination Research, 2009 Annual Meeting, May 19-20, Guelph, Ontario