Degradation Of Chloroform Research Articles

The investigation of highly efficient chlorinated hydrocarbons removal based on metal nanoparticles carbonaceous synthetic particles: The degradation behavior and selective transformation mechanism

Overconsumption in industrial manufacturing has led to critical emissions of chloroalkanes, posing a significant environmental threat. In this study, the innovative biochar (BC) particles containing nanocrystalline: NZVI, Fe/Pd, Fe/Ni were prepared by impregnation-liquid phase reduction using the pyrolysis of coconut husk as precursors to explore the degradation capabilities of chloroform (CF) via orthogonal experiment. The results indicated that when the pH value was 3, the temperature was 20 ℃, and the reaction time was 60 min, the CF removal efficiency of Fe/Ni-BC reached 80.38 ± 2.08 %, outperforming all other tested synthetic particles. Advanced characterization techniques showed that the abundant dispersed metallic nanoparticle sites would refresh the surface crystal morphology, improve the adsorption enrichment ability of biochar, enhance electron transfer capacity of synthetic particles, and further participate in reductive dechlorination by inducing an electrophilic attack of active hydrogen. Theoretical calculations verified that hydrogen activation and CF facile adsorption would be easily achieved after the introduction of metal nanoparticles, profiting from the multiple synergistic effects between special π-delocalized bond of biochar in carbon layer and multiple nanoparticles docking sites, and thus enhancing the specific CF catalytic selectivity of Fe/Ni as the active center. Collectively, the CF degradation on Fe/Ni-BC was a complex chemisorption process along with reductive hydrogenation decomposition, which achieved the parent CF reduction and promoted the conversion of the low-chlorinated benign products. These findings offer new insights into the developed multifunctional BC and their comprehensive assessment of CF sewage remediation.

A simple spectrophotometric method for chloroform quantification and its application in chloroform degradation from laboratory wastewater using polyphenolic co-activators

A simple spectrophotometric method for measuring high concentration of chloroform in water was developed based on the Reimer-Tiemann reaction. The reaction between chloroform and resorcinol under alkaline conditions has the limit of detection (LOD) and limit of quantification (LOQ) values at 1.28 mg/mL and 3.88 mg/mL, respectively. The experimental and response surface methodology (RSM) proposed the optimal conditions for the removal of chloroform (RoC) using tannic acid as a polyphenolic co-activator and spectrophotometric method for chloroform detection. The acceptable dechlorination process was suggested as persulfate (0.1–0.11 M), NaOH (0.6–0.8 M), and tannic acid (1.8 g/L) to obtain the yield of RoC from 76.14 to 77.90%. In situ experiments were then designed for RoC from the laboratory’s aqueous and organic solvent waste. After being treated with the system mentioned above, the yields of RoC were around 70%. In addition, a critical aspect of the innovation process was replacing pure tannic acid with other natural agents, which are more economically efficient and eco-safety. The EtOH extract from Elaeocarpus hygrophilus leaves (EEL) was suggested as a natural source of polyphenols, which could co-activate persulfate, with the yield of RoC rising to 63.29%. The findings of this study provide a novel strategy for chloroform degradation from laboratory wastewater using polyphenols.

Controlling chloroform content to a safe level in a pharmaceutical oral solution of chloral hydrate

Abstract Chloral hydrate is a halogenated hydrocarbon with sedative and hypnotic properties and has been used for its medicinal properties for many years. Its solubility and permeability determine it as a Biopharmaceutical Classification System class 1 compound, and as such is ideal to be pharmaceutically presented as an aqueous oral liquid presentation. Its primary route of degradation is by hydrolysis to form formic acid and chloroform and hence licensed pharmaceutical presentations require validated methods to analyse these degradants. The content of the toxic chloroform degradation product was determined via a head-space gas chromatograph with a flame ionisation detector, and its content was controlled to a safe pharmaceutically acceptable level. This can be achieved by solution pH optimisation in the oral solution, incorporating a buffering system to control the rate of this degradation mechanism. Where other behavioural and pharmacological therapies have failed for the treatment of short-term severe insomnia, a chloral hydrate 500 mg/5 ml oral solution presentation with an optimised safety profile has been developed as a medication for prescription. Extensive analytical and formulation development work has arrived at a room temperature stable oral solution, with a multiyear expiry date. Key findings: The use of Chloral hydrate in medicinal practice is often associated with high levels of the carcinogen chloroform as a degradation product. The research described herein has shown that the rate of formation of chloroform can be reduced by controlling the impact that the pH has on the stability of the oral solution. The Ph Eur monograph for Chloral hydrate oral solution (unlicensed medicines) does not include a criterion for chloroform quantification, hence Specials manufacturers of this oral solution are potentially risking the safety of patients without appropriate control of chloroform. This research has used validated analytical techniques to support the detection of chloroform, and other possible impurities, thus ensuring a safe product can be provided to the patient.

Toluene-driven anaerobic biodegradation of chloroform in a continuous-flow bioelectrochemical reactor

Subsurface co-contamination by multiple pollutants can be challenging for the design of bioremediation strategies since it may require promoting different and often antagonistic degradation pathways. Here, we investigated the simultaneous degradation of toluene and chloroform (CF) in a continuous-flow anaerobic bioelectrochemical reactor. As a result, 47 μmol L−1 d−1 of toluene and 60 μmol L−1 d−1 of CF were concurrently removed, when the anode was polarized at +0.4 V vs. Standard Hydrogen Electrode (SHE). Analysis of the microbial community structure and key functional genes allowed to identify the involved degradation pathways. Interestingly, when acetate was supplied along with toluene, to simulate the impact of a readily biodegradable substrate on process performance, toluene degradation was adversely affected, likely due to competitive inhibition effects. Overall, this study proved the efficacy of the developed bioelectrochemical system in simultaneously treating multiple groundwater contaminants, paving the way for the application in real-world scenarios.

Degradation of Chloroform by Zerovalent Iron: Effects of Mechanochemical Sulfidation and Nitridation on the Kinetics and Mechanism.

Chloroform (CF) is a widely used chemical reagent and disinfectant and a probable human carcinogen. The extensive literature on halocarbon reduction with zerovalent iron (ZVI) shows that transformation of CF is slow, even with nano, bimetallic, sulfidated, and other modified forms of ZVI. In this study, an alternative method of ZVI modification─involving simultaneous sulfidation and nitridation through mechanochemical ball milling─was developed and shown to give improved degradation of CF (i.e., higher degradation rate and inhibited H2 evolution reaction). The composite material (denoted as S-N(C)-ZVI) gave synergistic effects of nitridation and sulfidation on CF degradation. A complete chemical reaction network (CRN) analysis of CF degradation suggests that O-nucleophile-mediated transformation pathways may be the main route for the formation of the terminal nonchlorinated products (formate, CO, and glycolic polymers) that have been used to explain the undetected products needed for mass balance. Material characterizations of the ZVI recovered after batch experiments showed that sulfidation and nitridation promoted the formation of Fe3O4 on the S-N(C)-ZVI particles, and the effect of aging on CF degradation rates was minor for S-N(C)-ZVI. The synergistic benefits of sulfidation and nitridation on CF degradation were also observed in experiments performed with groundwater.

Photocatalytic degradation of chloroform using rGO-CuS nanocomposite under UV/VIS irradiation from gaseous phase.

Environmental pollutants such as organic solvents pose potential hazards to the environment. One of the most commonly used solvents, chloroform, is known to cause heart attacks, respiratory problems, and central nervous system disorders. At the pilot scale, the efficacy of the photocatalytic process for removing chloroform from gas streams using the rGO-CuS nanocomposite was investigated. The results indicated that chloroform degradation at 1.5 L min*1 (74.6%) was more than twice as fast as at 2.0 L min-1 (30%). With increasing relative humidity, the chloroform removal efficiency increased up to 30% and then declined. Therefore, 30% humidity was found to be the optimal humidity for the photocatalyst. As the rGO-CuS ratio increased, the photocatalytic degradation efficiency decreased, and the chloroform oxidation rate increased at higher temperatures. The process efficiency increases with increasing pollutant concentrations until the vacant sites are saturated. After the saturation of these active sites, process efficiency does not change.

Isotopic evidence (δ13C, δ37Cl, δ2H) for distinct transformation mechanisms of chloroform: Catalyzed H2-water system vs. zero-valent iron (ZVI)

Catalytic hydrodechlorination is an efficient technology for degrading organochlorinated compounds, such as chloroform (CF), into harmless products. Compound-specific stable isotope analysis (CSIA) of multiple elements is widely used for the investigation of degradation mechanisms. Yet, its application in the study of catalytic hydrodechlorination is still limited. We have applied CSIA to derive chlorine, carbon, and hydrogen isotope enrichment factors (ε) during the degradation of CF over Pd/Al2O3 and over Rh/Al2O3. In addition, the enrichment factors for the same isotopes were derived for the reaction of CF with zero-valent iron (ZVI) for comparison. For the reactions of CF over Pd/Al2O3 and Rh/Al2O3, εC values (−21.9 ± 0.25 ‰ and −23.4 ± 2.3 ‰) and εCl values (−12.1 ± 1.7 ‰ and −10.3 ± 0.6 ‰) were determined, respectively. The corresponding εC and εCl values, for the dechlorination of CF with ZVI were −22.2 ± 2.8 ‰ and −4.7 ± 0.45 ‰, respectively. The apparent kinetic isotope effects (AKIE) of Cl suggest that the transformation mechanism in the catalyzed hydrogen-water system is a non-concerted reaction, unlike the known reductive dechlorination of CF with ZVI. Moreover, dual-isotope slopes (ΛC/Cl) for both catalyzed reactions (ΛPd = 1.8 ± 0.13 and ΛRh = 2.1 ± 0.14) are markedly different than for the ZVI (ΛZVI = 5.8 ± 0.41), reflecting that the reactions proceed in different mechanisms. For hydrogen isotopes, while there was no clear trend for the catalyzed reactions, an inverse secondary hydrogen isotope effect was observed for the reaction of CF with ZVI.

Process optimization of dielectric barrier discharge reactor for chloroform degradation using central composite design

The increased detection of chloroform in wastewater and surface water bodies has become an environmental concern. However, conventional treatment methods such as biodegradation, incineration, and photocatalysis are challenging to scale up, inducing high operation costs and generating toxic byproducts. Hence, this study employs the Response surface methodology (RSM) to optimize chloroform degradation using a spray dielectric barrier discharge (DBD) reactor for the first time. The independent and interactive influence of the DBD parameters (power: 100–200 W, treatment time: 5–20 minutes, recirculating flow rate: 50–200 mL/M) and responses (chloroform degradation ratio (R), total organic carbon removal ratio (TOC)) were optimized using the Rotatable central composite design (RCCD), and a second-order polynomial equation was proposed to predict process efficiency. Results showed significantly predicted values (p < 0.05) and coefficient of determination of 0.96, and 0.93 for TOC and R, respectively, with treatment time and power having significant independent and interactive effects on the responses (TOC: p < 0.0001, R: p < 0.0001) concerning the variance analysis. Accordingly, the model yielded optimum recirculating flow rate, discharge power, and treatment time of 50 mL/min, 200 W, and 20 mins, respectively, which amounted to complete dechlorination of 300 mg/L chloroform, a 43% TOC removal ratio and an energy yield of 4.6 g/kW·h. In addition, the TOC removal ratio was enhanced with the increase in pH and conductivity of the solution.

Bioelectrochemically-assisted degradation of chloroform by a co-culture of Dehalobacter and Dehalobacterium

Using bioelectrochemical systems (BESs) to provide electrochemically generated hydrogen is a promising technology to provide electron donors for reductive dechlorination by organohalide-respiring bacteria. In this study, we inoculated two syntrophic dechlorinating cultures containing Dehalobacter and Dehalobacterium to sequentially transform chloroform (CF) to acetate in a BES using a graphite fiber brush as the electrode. In this co-culture, Dehalobacter transformed CF to stoichiometric amounts of dichloromethane (DCM) via organohalide respiration, whereas the Dehalobacterium-containing culture converted DCM to acetate via fermentation. BES were initially inoculated with Dehalobacter, and sequential cathodic potentials of −0.6, −0.7, and −0.8 V were poised after consuming three CF doses (500 μM) per each potential during a time-span of 83 days. At the end of this period, the accumulated DCM was degraded in the following seven days after the inoculation of Dehalobacterium. At this point, four consecutive amendments of CF at increasing concentrations of 200, 400, 600, and 800 μM were sequentially transformed by the combined degradation activity of Dehalobacter and Dehalobacterium. The Dehalobacter 16S rRNA gene copies increased four orders of magnitude during the whole period. The coulombic efficiencies associated with the degradation of CF reached values > 60% at a cathodic potential of −0.8 V when the degradation rate of CF achieved the highest values. This study shows the advantages of combining syntrophic bacteria to fully detoxify chlorinated compounds in BESs and further expands the use of this technology for treating water bodies impacted with pollutants.

Transformation mechanism of carbon tetrachloride and the associated micro-ecology in landfill cover, a typical functional layer zone

Landfill is one of the important sources of carbon tetrachloride (CT) pollution, and it is important to understand the degradation mechanism of CT in landfill cover for better control. In this study, a simulated landfill cover system was set up, and the biotransformation mechanism of CT and the associated micro-ecology were investigated. The results showed that three stable functional zones along the depth, i.e., aerobic zone (0-15 cm), anoxic zone (15-45 cm) and anaerobic zone (> 45 cm), were generated because of long-term biological oxidation in landfill cover. There were significant differences in redox condition and microbial community structure in each zone, which provided microbial resources and favorable conditions for CT degradation. The results of biodegradation indicated that dechlorination of CT produced chloroform (CF), dichloromethane (DCM) and Cl- in anaerobic and anoxic zones. The highest concentration of dechlorination products occurred at 30 cm, which were degraded rapidly in aerobic zone. In addition, CT degradation rate was 13.2-103.6 μg/(m2·d), which decreased with the increase of landfill gas flux. The analysis of diversity sequencing revealed that Mesorhizobium, Thiobacillus and Intrasporangium were potential CT-degraders in aerobic, anaerobic and anoxic zone, respectively. Moreover, six species of dechlorination bacteria and eighteen species of methanotrophs were also responsible for anaerobic transformation of CT and aerobic degradation of CF and DCM, respectively. Interestingly, anaerobic dechlorination and aerobic transformation occurred simultaneously in the anoxic zone in landfill cover. Furthermore, analysis of degradation mechanism suggested that generation of stable anaerobic-anoxic-aerobic zone by regulation was very important for the harmless removal of full halogenated hydrocarbon in vadose zone, and the increase of anoxic zone scale enhanced their removal. These results provide theoretical guidance for the removal of chlorinated pollutants in landfills.

Methanogenesis suppression and increased power generation in microbial fuel cell during treatment of chloroform containing wastewater

Chloroform is a commonly found solvent in industrial wastewater and is very toxic if present in high concentration. Chloroform degradation in anaerobic processes has been reported earlier and it has also been used as a methanogenesis suppressor in rumen and rice fields. Methanogenesis is undesirable in a microbial fuel cell (MFC) operation, as it results in substrate competition between methanogens and exoelectrogens, thereby reducing the electricity output. Hence, an attempt has been made in this research work to study the effect of chloroform on the performance of MFCs and its effectiveness as methanogenesis suppressor. MFCs with different chloroform dosages in batch as well as continuous mode (0 mM, 8 mM, 16 mM and 22 mM; 0 mM and 22 mM) were operated. High open circuit voltages in batch MFC22 (781 mV) and 53 % higher peak power densities in dosed continuous MFC confirmed its efficiency as a methanogenesis suppressor. Further experimentations showed 74 % lower internal resistance in dosed MFCs. Higher coulombic efficiencies of 31.2 % (MFC22) and 18 % (MFCC22) were noted in dosed reactors than the control reactors (MFC0 – 23.8 % and MFCC0 - 8%). At the end of batches, chloroform concentration was found to be negligible, confirming its degradation in MFC.

Tannic acid enhances the removal of chloroform from water using NaOH-activated persulfate

Pollution of waters by chlorinated organic pollutants is difficult to clean using actual remediation methods because these pollutants are highly stable. For instance, chloroform (CHCl3) is poorly reactive with common oxidants such as iron-activated persulfate, ozone and Fenton’s reagents. Therefore, there is a need to develop new oxidants. Here, we designed a new dechlorination system, in which tannic acid and NaOH work synergistically to activate persulfate. We tested the effect of temperature and concentrations of persulfate, NaOH and tannic acid, on chloroform removal from water. Free radical-quenching experiments were performed to identify active species. Results show that chloroform removal increased from 42.5 to 97.6 wt.% after the addition of 300 mg/L tannic acid in 0.4 M NaOH. Superoxide radicals (O 2 ·− ) was primarily responsible for the degradation of chloroform in the persulfate/NaOH/tannic acid system, in which tannic acid reacts with persulfate to produce hydroperoxide. Hydroperoxide then reduces persulfate to generate sulfate radicals (SO4·−), and produces O 2 ·− . NaOH-activated persulfate produces hydroxyl radicals (HO·), which can oxidize chloroform. This dechlorination system showed excellent degradation efficiency for recalcitrant halogenated compounds, making it a very promising candidate for practical applications.

Effect of visible light on the removal of trichloromethane by graphene oxide

In this experimental study, the degradation of disinfection by-products using graphene oxide was studied. Degradation of chloroform, which is the most common type of trihalomethanes in water, was investigated. Graphene oxide (GO) was synthesized by the Modified Hummers' Method. TEM images showed that the synthesized graphene oxide was exfoliated layer by layer and was very stable according to the zeta potential result. In the degradation studies; the effect of time, chloroform concentration and graphene oxide concentration were investigated both under visible light and under darkness. According to the experimental results, studies containing 100 μg/L trichloromethane and 250 mg/L GO were stabilized after 30 min and the removal of 70.6% for darkness increased to 98% under visible light. When the graphene oxide concentration is increased, it is seen that the positive effect of visible light increases from 22% to 30%. According to the isotherm and kinetic model research, it was found that the studies conducted in both conditions were appropriate to Freundlich isotherm and Pseudo second-order kinetic model. The maximum adsorption capacities based on Pseudo second-order kinetic modeling was obtained as 350 and 450 μg/g for darkness and visible light, respectively.

Effect of various electrolytes and other wastewater constituents on the degradation of volatile organic compounds in aqueous solution by pulsed power plasma technology

SO4˙− radicals were produced in sulfate containing solution by plasma discharge in air, which enhanced the degradation of chlorobenzene, chloroform, toluene and MIBK.

Rapid decomposition of chloroform by a liquid phase plasma reaction with titanium dioxide and hydrogen peroxide

• Chloroform in aqueous solution was successfully degraded by liquid phase plasma reaction. • The operation parameters of power supply played an important role in the chloroform degradation reaction. • Degradation rate of chloroform is proportional to an increase in operation parameter. • Addition of titanium dioxide or hydrogen peroxide to liquid phase plasma reaction improved the degradation of chloroform. • When titanium dioxide and hydrogen peroxide used simultaneously, the synergetic effect was observed. The degradation of chloroform in a liquid phase plasma (LPP) reactor was examined according to the operating parameters and other influencing factors. The operating parameters included the applied voltage, frequency, and pulse width. The effects of titanium dioxide, hydrogen peroxide, and their combination on the degradation of chloroform were evaluated in terms of the influencing factors. Increasing the operating parameters up to the maximum allowed in the LPP process made chloroform decompose much faster than that of the minimum. On the other hand, increasing either the titanium dioxide or hydrogen peroxide concentrations in the reactant solution did not always destroy the chloroform efficiently compared to degradation without their loading. Although the impact of titanium dioxide was slightly higher than that of hydrogen peroxide, the synergistic effect between them enhanced the breakdown of chloroform further. Overall, both the operating parameters and influencing factors should be determined carefully to maximize the decomposition efficiency in the given treatment system, particularly for processes involving the LPP reaction.

Use of dual element isotope analysis and microcosm studies to determine the origin and potential anaerobic biodegradation of dichloromethane in two multi-contaminated aquifers

Many aquifers around the world are impacted by toxic chlorinated methanes derived from industrial processes due to accidental spills. Frequently, these contaminants co-occur with chlorinated ethenes and/or chlorinated benzenes in groundwater, forming complex mixtures that become very difficult to remediate. In this study, a multi-method approach was used to provide lines of evidence of natural attenuation processes and potential setbacks in the implementation of bioremediation strategies in multi-contaminated aquifers. First, this study determined i) the carbon and chlorine isotopic compositions (δ13C, δ37Cl) of several commercial pure phase chlorinated compounds, and ii) the chlorine isotopic fractionation (εCl = −5.2 ± 0.6‰) and the dual CCl isotope correlation (ΛC/Cl = 5.9 ± 0.3) during dichloromethane (DCM) degradation by a Dehalobacterium-containing culture. Such data provide valuable information for practitioners to support the interpretation of stable isotope analyses derived from polluted sites. Second, the bioremediation potential of two industrial sites contaminated with a mixture of organic pollutants (mainly DCM, chloroform (CF), trichloroethene (TCE), and mono-chlorobenzene (MCB)) was evaluated. Hydrochemistry, dual (CCl) isotope analyses, laboratory microcosms, and microbiological data were used to investigate the origin, fate and biodegradation potential of chlorinated methanes. At Site 1, δ13C and δ37Cl compositions from field samples were consistent with laboratory microcosms, which showed complete degradation of CF, DCM and TCE, while MCB remained. Identification of Dehalobacter sp. in CF-enriched microcosms further supported the biodegradation capability of the aquifer to remediate chlorinated methanes. At Site 2, hydrochemistry and δ13C and δ37Cl compositions from field samples suggested little DCM, CF and TCE transformation; however, laboratory microcosms evidenced that their degradation was severely inhibited, probably by co-contamination. A dual CCl isotopic assessment using results from this study and reference values from the literature allowed to determine the extent of degradation and elucidated the origin of chlorinated methanes.

Applicability of pulsed corona discharge treatment for the degradation of chloroform

Degradation of chloroform was investigated using plasma corona discharge by a needle-plate reactor. Chloroform concentration of 200 mg/L was completely degraded in 10 min of treatment. Almost complete dechlorination happened in 10 min and 91% total organic carbon (TOC) removal occurred in 12 min of treatment. Several important parameters such as input voltage, initial concentration, pH, conductivity, alkalinity, presence of OH radical and aqueous electron scavengers were evaluated to understand their effect on rate of chloroform degradation. The degradation rate of chloroform increased with increase in pH, conductivity and alkalinity of the solution. The maximum concentrations of OH radical, H2O2 and superoxide produced after 10 min of corona discharge were estimated to be 0.260 mM, 0.353 mM and 0.046 mM respectively. Various intermediates such as dichloromethane, dichloroethane, trichloroethane, trichloroethylene (TCE), tetrachloroethylene (PCE), trichloronitromethane and acetaldehyde were identified using GC-MS purge and trap technique. Based on the identified intermediates, reductive and oxidative degradation pathway of chloroform is proposed.

Changes in microbial community associated with dechlorination of leftover chloroform in two-stage anaerobic Co-fermentation (H2+CH4) of lipid-extracted microalgae waste with food waste leachate

In our previous research, two-stage anaerobic co-fermentation (TSAC) treating lipid-extracted microalgae waste (LEMW) mixed with food waste leachate (FWL) was successfully designed to recover the additional energy (H2 and CH4) while mitigating the inhibition of leftover chloroform (CF). This study aimed to elucidate the change in the microbial community and their association with the CF degradation in the TSAC. 90% of CF was dechlorinated in the acidogenic reactor of TSAC when LEMW was fed with FWL at a ratio of 40:60. The results of microbial analysis clearly showed that Dehalobacter (5.3%) played the role in dehalorespiration while Clostridium (8.9%) and Enterobacter (3.6%) promoted cometabolic dechlorination. In contrast, the microbial consortia were completely inhibited by CF when LEMW was fed without FWL. In the methanogenic reactor of TSAC, increased Methanosarcina (57.8%), Methanobacterium (10.4%), and Methanosaeta (8.6%) were observed. Those were involved in successful conversion of acetate and H2 into CH4.

The reactivity of Fe/Ni colloid stabilized by carboxymethylcellulose (CMC-Fe/Ni) toward chloroform.

The use of stabilizers can prevent the reactivity loss of nanoparticles due to aggregation. In this study, carboxymethylcellulose (CMC) was selected as the stabilizer to synthesize a highly stable CMC-stabilized Fe/Ni colloid (CMC-Fe/Ni) via pre-aggregation stabilization. The reactivity of CMC-Fe/Ni was evaluated via the reaction of chloroform (CF) degradation. The effect of background solution which composition was affected by the preparation of Fe/Ni (Fe/Ni precursors, NaBH4 dosage) and the addition of solute (common ions, sulfur compounds) on the reactivity of CMC-Fe/Ni was also investigated. Additionally, the dried CMC-Fe/Ni was used for characterization in terms of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The experimental results indicated that CMC stabilization greatly improved the reactivity of Fe/Ni bimetal and CF (10mg/L) could be completely degraded by CMC-Fe/Ni (0.1g/L) within 45min. The use of different Fe/Ni precursors resulting in the variations of background solution seemed to have no obvious influence on the reactivity of CMC-Fe/Ni, whereas the dosage of NaBH4 in background solution showed a negative correlation with the reactivity of CMC-Fe/Ni. Besides, the individual addition of external solutes into background solution all had an adverse effect on the reactivity of CMC-Fe/Ni, of which the poisoning effect of sulfides (Na2S, Na2S2O4) was significant than common ions and sulfite.

Dual element (C[sbnd]Cl) isotope approach to distinguish abiotic reactions of chlorinated methanes by Fe(0) and by Fe(II) on iron minerals at neutral and alkaline pH

A dual element CCl isotopic study was performed for assessing chlorinated methanes (CMs) abiotic transformation reactions mediated by iron minerals and Fe(0) to further distinguish them in natural attenuation monitoring or when applying remediation strategies in polluted sites. Isotope fractionation was investigated during carbon tetrachloride (CT) and chloroform (CF) degradation in anoxic batch experiments with Fe(0), with FeCl2(aq), and with Fe-bearing minerals (magnetite, Mag and pyrite, Py) amended with FeCl2(aq), at two different pH values (7 and 12) representative of field and remediation conditions. At pH 7, only CT batches with Fe(0) and Py underwent degradation and CF accumulation evidenced hydrogenolysis. With Py, thiolytic reduction was revealed by CS2 yield and is a likely reason for different Λ value (Δδ13C/Δδ37Cl) comparing with Fe(0) experiments at pH 7 (2.9 ± 0.5 and 6.1 ± 0.5, respectively). At pH 12, all CT experiments showed degradation to CF, again with significant differences in Λ values between Fe(0) (5.8 ± 0.4) and Fe-bearing minerals (Mag, 2 ± 1, and Py, 3.7 ± 0.9), probably evidencing other parallel pathways (hydrolytic and thiolytic reduction). Variation of pH did not significantly affect the Λ values of CT degradation by Fe(0) nor Py.CF degradation by Fe(0) at pH 12 showed a Λ (8 ± 1) similar to that reported at pH 7 (8 ± 2), suggesting CF hydrogenolysis as the main reaction and that CF alkaline hydrolysis (13.0 ± 0.8) was negligible.Our data establish a base for discerning the predominant or combined pathways of CMs natural attenuation or for assessing the effectiveness of remediation strategies using recycled minerals or Fe(0).