Trichloroethylene Degradation Research Articles

Even Incorporation of Nitrogen into Fe0 Nanoparticles as Crystalline Fe4N for Efficient and Selective Trichloroethylene Degradation.

Surface modification of microscale Fe powder with nitrogen has emerged recently to improve the reactivity of Fe0 for dechlorination. However, it is unclear how an even incorporation of a crystalline iron nitride phase into Fe0 nanoparticles affects their physicochemical properties and performance, or if Fe0 nanoparticles with a varied nitridation degree will act differently. Here, we synthesized nitridated Fe0 nanoparticles with an even distribution of N via a sol-gel and pyrolysis method. Nitridation expanded the Fe0 lattice and provided the Fe4N species, making the materials more hydrophobic and accelerating the electron transfer, compared to un-nitridated Fe0. These properties well explain their reactivity and selectivity toward trichloroethylene (TCE). The TCE degradation rate by nitridated Fe0 (up to 4.8 × 10-2 L m-2 h-1) was much higher (up to 27-fold) than that by un-nitridated Fe0, depending on the nitridation degree. The materials maintained a high electron efficiency (87-95%) due to the greatly suppressed water reactivity (109-127 times lower than un-nitridated Fe0). Acetylene was accumulated as the major product of TCE dechlorination via β-elimination. These findings suggest that the nitridation of Fe0 nanoparticles can change the materials' physicochemical properties, providing high reactivity and selectivity toward chlorinated contaminants for in situ groundwater remediation.

The role of nitrate in simultaneous removal of nitrate and trichloroethylene by sulfidated zero-valent Iron

Sulfidated zero-valent iron (S-ZVI) is commonly used to degrade trichloroethylene (TCE). The reactivity of S-ZVI is related to not only the properties of S-ZVI but also the geochemical conditions in groundwater, such as coexisted NO3−. Therefore, the effect of NO3− on TCE degradation by S-ZVI and its mechanism were systematically studied. 95.17% of TCE was degraded to acetylene, dichloroethene, ethene, ethane and multi‑carbon products via β-elimination by fresh S-ZVI that contained 85.31% Fe0 and 14.69% FeS in the presence of NO3−, demonstrating that NO3− did not affect the degradation pathway of TCE. While high concentration of NO3− (> 10 mg/L) competed for electrons at the Fe/FeOx interface with degradation products, leading to a continuous rising of acetylene. Moreover, the rapid reduction of NO3− to NH4+ (89.79%) at the Fe0 interface contributed to the release of 5.08 mM Fe2+ from S-ZVI, which promoted the formation of Fe3O4 with excellent electron conduction properties on the surface of S-ZVI. Accordingly, NO3− improved the degradation and electron selectivity of TCE by 51.07% and 2.79 fold, respectively. This study demonstrated that S-ZVI could remediate the contamination of NO3− and TCE simultaneously and the presence of NO3− could effectively enhance the degradation of TCE in groundwater.

Mechanism of trichloroethylene degradation in Fe(II)-activated peroxymonosulfate coupled with citric acid system in the presence of surfactants.

This study demonstrated that peroxymonosulfate (PMS) activated by Fe(II)/citric acid (CA) could effectively degrade trichloroethylene (TCE) in the presence of Tween-80 (TW-80) or sodium dodecyl sulfate (SDS). Significant TCE removal of 91.6% (90.1%) with 1.3g L-1 TW-80 (2.3g L-1 SDS) were achieved at the PMS/Fe(II)/CA/TCE molar ratio of 4/4/4/1 (20/20/20/1). TCE degradation could be greatly elevated by Fe(II) and CA addition, while the existence of surfactants restrained TCE removal and the inhibitory effect increased with the higher surfactant concentration. The tests of the electron paramagnetic resonance (EPR) and reactive radicals scavenging experiments proved that sulfate radical (SO4-•), hydroxyl radical (HO•), and superoxide radical (O2-•) were responsible for TCE degradation and SO4-• acted as the major one. The influences of initial solution pH and inorganic anions k(Cl- and HCO3-) on TCE removal were also investigated. Eventually, TCE removal in actual groundwater tests with surfactants confirmed that the PMS/Fe(II)/CA process has a huge potential of practical application in remediating the groundwater contaminated by TCE after the pretreatment by solubilization using surfactants.

Degrading chlorinated aliphatics by reductive dechlorination of groundwater samples from the Santa Susana Field Laboratory

Microbial reductive dechlorination is one of the chosen methods for remediation of chlorinated compounds in anaerobic environments. In this study we examined the degradation of chlorinated aliphatics in groundwater samples from the Santa Susana Field Laboratory (SSFL) containing a concentration of 0.228 mM trichloroethylene (TCE) and 0.279 mM 1,2 dichloroethylene (DCE). We tested the influence of adding different carbon sources on the dechlorinating activity in batch cultures with and without dechlorinating bacteria. In-situ microcosms were established using SSFL groundwater supplemented with EVO (5%) (vol/vol) SRS emulsion and with or without species of Dehalocococcoides (DCB-1, DCB-2 or DCB-3). Emulsified vegetable oil (EVO) gave the highest dechlorinating activity with DCB-1 added compared to any other substrate addition tested. All three bacterial cultures tested had significant dechlorinating activities while the native populations in the SSFL groundwater samples only showed limited degradation of trichloroethylene into intermediates in the form of DCE, vinyl chloride and ethane. The conversion of chlorinated ethylenes (CEs) was optimal in the bioreactors amended with DCB-1 followed by DCB-2, and DCB-3 all supplemented with EVO. We further analyzed the TCE degradation first order kinetics in batch cultures and found that the culture with DCB-1 supplemented with EVO showed 43.59% and 51.38% increased degradation rate compared to the same condition with cultures of DCB-2 or DCB-3 added. The microcosm studies further showed that with DCB-1 and EVO, reductive dechlorination of TCE in the SSFL converted 90% of the input TCE to ethane with a degradation rate of 0.0039 mM/day.

RuO2 nanoparticles-accommodated graphitic carbon nitride for significant enhancement in photocatalytic oxidation of trichloroethylene

It is greatly desired to construct bifunctional photocatalysts to achieve extremely effective photocatalytic ability. Herein, RuO2 nanoparticles (10 nm), accommodated in porous g-C3N4 to construct mesoporous RuO2/g-C3N4 heterojunctions, were prepared utilizing a modified sol-gel process in the existence of soft surfactant. The synthesized RuO2/g-C3N4 heterostructures were employed as photocatalysts in the mineralization of trichloroethylene (TCE) in an aqueous solution through visible light. The synthesized RuO2/g-C3N4 nanocomposites exhibited superior photocatalytic performance with 100% degradation of TCE within 150 min. The photodegradation rate of TCE of RuO2/g-C3N4 photocatalyst was remarkably promoted, compared with g-C3N4 and RuO2. The rate constant of 3%RuO2/g-C3N4 was determined to be 0.0127 min−1, which was 4.88 and 6.68 times higher than RuO2 (0.0026 min−1) and g-C3N4 (0.0019 min−1). This magnificent photocatalytic ability of RuO2/g-C3N4 nanocomposites can be interpreted to highly crystalline RuO2 NPs with small size, enhanced electron and mass transfer, visible light harvest and heterojunction structure with a synergistic effect. Furthermore, the synthesized photocatalyst could be recycled for five cycles with insignificant remarkable diminish in its photocatalytic ability. Fortunately, the photocatalytic ability of RuO2/g-C3N4 nanocomposites for TCE mineralization exhibited varied advances by utilizing visible light at room temperature without the employ of any oxidant.

Experimental study of viscosity modification coupled with phase transfer catalysis for enhanced remediation of non-aqueous phase trichloroethene polluted heterogeneous aquifer

The degradation of dense non-aqueous phase liquid trichloroethene in low permeability zone is a challenging issue due to limited mass transfer between water-soluble oxidants (i.e., MnO4-) and residual phase trichloroethene and the bypassing of amendments in low permeability zone. This work accomplished trichloroethene oxidation enhancement through coupling viscosity modification by using xanthan with phase transfer of MnO4- by using phase transfer catalyst (PTC). Experiments were conducted by sand columns and 2D-tanks, and results revealed that after ~11.7 g of trichloroethene was injected in each tank, the mass of trichloroethene degradation was 1.3, 5.9, 6.9 and 8.5 g in MnO4-, MnO4- + xanthan, MnO4- + PTC and MnO4- + PTC + xanthan reaction systems, respectively. Combining PTC and xanthan with MnO4- increased the rate of continuous formation of Cl-, reflected in the acceleration of heterogeneous reactions and MnO4- transport enhancement in low permeability zone by PTC and xanthan. Moreover, PTC promoted dissolved Mn (Ⅱ) and Mn (Ⅲ) formation in the process of MnO4- reduction, and thus effectively inhibited MnO2 generation. In conclusion, the results revealed that PTC and xanthan could perform their respective contributions to mass transfer and amendment transport for jointly enhanced the remediation of trichloroethene polluted heterogeneous aquifer.

Comparative studies on trichloroethylene degradation by Fe foam catalyzing three hydrogen peroxide-based oxidants

In this paper, the effect of Fe foam (FF) (without any modification) catalyzing hydrogen peroxide (H2O2), sodium percarbonate (SPC), and calcium peroxide (CP) on trichloroethylene (TCE) removal in an aqueous solution was studied for the first time. FF has good recycling and stability in oxidant/FF system for TCE removal, which was innovative and friendly to the environment with no iron leaching. Combining the SEM and EDS changes before and after FF application and the measurement results of the divalent iron, it was found that the surface of FF was destroyed and the oxygen content increased after the reaction. In addition, no dissolved iron was detected by spectrophotometry during the experiment, which revealed that the reaction basically proceeded on the catalyst surface rather than in solution. The activation effect of FF in multiple H2O2-based oxidant systems was investigated on the basis of adjusting the pH to 2.5. Hydroxyl radical (HO•) produced in H2O2/FF, SPC/FF, and CP/FF systems was identified by the free radical scavenging tests, EPR spectra, H2O2 release, and HO• generation. FF owned a good recycling performance, and the removed TCE was almost completely mineralized. In the presence of surfactants, the inhibitory effect could be eliminated by increasing the dosage of the oxidant and FF. The above researches verified the effectiveness of FF activation for H2O2-based oxidants on TCE removal, which provided a basis for the application of oxidant/FF system in groundwater remediation of actual contaminated sites.

S-scheme mesoporous Li2MnO3/g-C3N4 heterojunctions as efficient photocatalysts for the mineralization of trichloroethylene in aqueous media

Novel mesoporous Li2MnO3/g-C3N4 heterostructures were prepared for the first time by utilizing the sol–gel route in the presence of a nonionic surfactant. TEM and XRD measurements showed that Li2MnO3 (5–10 nm) with monoclinic structures was uniformly distributed onto porous g-C3N4 for the construction of Li2MnO3/g-C3N4 heterojunctions. The obtained photocatalysts were assessed for mineralization and removal of trichloroethylene (TCE) in aqueous media under visible light exposure. Complete degradation of TCE over a 3 %Li2MnO3/g-C3N4 heterostructure within 120 min was achieved. The degradation rate over Li2MnO3/g-C3N4 heterostructures was significantly enhanced, and the 3% Li2MnO3/g-C3N4 heterostructure exhibited a large degradation rate of 7.04 µmolL−1 min−1, which was enhanced by 5 and 3.8 fold compared to those of pristine g-C3N4 (1.39 µmolL−1 min−1) and Li2MnO3 (1.85 µmolL−1 min−1), respectively. The photocatalytic efficiency of the Li2MnO3/g-C3N4 heterojunction was outstandingly promoted because integrating Li2MnO3 with g-C3N4 could create close interfaces with well-matched band potentials for easy mobility and low recombination of photoinduced carriers. The coexistence of Li2MnO3/g-C3N4 interfaces led to a synergic effect, which is considered the key factor in photoinduced electron-hole separation. The synthesis procedure that was employed here is a promising process for the preparation of effective g-C3N4-based photocatalyst systems for photocatalysis applications.

Efficient catalytic degradation of trichloroethylene in persulfate system by Ca-Fe2O3 and Cu-Fe2O3 nanoparticles: Mechanistic insights

M-metal (Ca and Cu) doped Ca-Fe2O3 and Cu-Fe2O3 catalysts were synthesized using solvothermal method. The Ca-Fe2O3 and Cu-Fe2O3 catalysts were characterized by XRD, Raman spectroscopy, SEM, TEM and XPS spectroscopy. The catalytic performance of 6%Ca-Fe2O3 and 5%Cu-Fe2O3 catalysts for trichloroethylene (TCE) removal were improved by M-metal doping leading to TCE removal at 99.8% in 1 h, which were three folds greater than by simple a-Fe2O3 in the presence of persulfate (PS). Ca and Cu doping formed defective structure and created more oxygen vacancies thereby generating abundant active species during PS activation process. Further, the influence of catalysts’ dosage, oxidant dosage, solution pH, inorganic anions, and dissolved oxygen were evaluated. Complete removal of TCE was also obtained at weak alkaline pH condition. The greater specific surface area and the improved electrical conductivity was attributed to the huge generation of O2•– and 1O2 species which played major part in TCE removal. Scavenging tests and ESR spectroscopy confirmed the dominant role of O2•– and 1O2 in TCE degradation. The stability and viability of 6%Ca-Fe2O3 and 5%Cu-Fe2O3 catalysts were evaluated by repetition tests and in the presence of surfactants, TCE removal in real water matrix, and in the degradation of multi-pollutants.

Green synthesis of porous Cu2ZnSnS4/g-C3N4 heterostructured for promoted photocatalytic degradation of trichloroethylene

Accelerating the photo-induced carrier separation in semiconducting materials under visible-light exposure is a great challenge in effective organic pollutant degradation. Herein, a mesoporous Cu2ZnSnS4/g-C3N4 heterojunction was synthesized through a facile sol-gel approach with hard and soft templates leading to a high-surface-area material. TEM analysis showed spherical Cu2ZnSnS4 nanocrystals (5 nm in diameter) with a high and uniform distribution on the g-C3N4 nanosheets. The Cu2ZnSnS4/g-C3N4 photocatalyst (3%) showed photocatalytic trichloroethylene (TCE) degradation to Cl− and CO2 of approximately 100% in an aqueous medium. The optimal rate for this photocatalyst was approximately 7.754 μmol L−1·min−1, which was 4 and ∼5.75 folds higher than that of bare Cu2ZnSnS4 and g-C3N4, respectively. Moreover, the apparent rate constant of 3% Cu2ZnSnS4/g-C3N4 was 7.6 and 4.1 times higher than that of bare g-C3N4 and Cu2ZnSnS4, respectively. Recycling experiments confirmed that the Cu2ZnSnS4/g-C3N4 photocatalyst exhibited remarkably stable photocatalytic activity and could be recycled five times. This work provides a novel insight into the design and preparation of visible-light-based photocatalysts with high and stable photocatalytic efficiency.

Fe3+-NTA-Catalyzed Homogenous Fenton-Like Degradation of Trichloroethylene in Groundwater at Natural pH (∼8.0): Efficacy, By-Products, and H2O2 Utilization

The ferric-nitrilotriacetate (Fe3+-NTA)-catalyzed homogenous Fenton-like reaction (i.e., Fe3+-NTA/H2O2) has received increasing interest for environmental applications, but its potential in degrading trichloroethylene (TCE) in groundwater still is not well known. The results of this study showed that Fe3+-NTA/H2O2 was more effective than other Fe3+-chelate/H2O2 processes (e.g., including ethylenediaminetetraacetate, ethylenediamine-N,N′-disuccinate, citrate, malonate, and tartrate) in degrading TCE in groundwater at natural pH (∼8.0). The effects of important parameters including the ratio of NTA∶Fe3+, and the dosages of Fe3+-NTA and H2O2 were investigated. Greater than 98% degradation efficiency of TCE in actual groundwater was obtained after 60 min of reaction time under the given conditions of NTA∶Fe3+=1.5∶1, 0.1 mM Fe3+-NTA, 5 mM H2O2, and pH 8.0. Hydroxyl radical (HO•) was responsible for the degradation of TCE, and the by-products were identified as formic acid and chloride ion (Cl−). Greater than 90% degradation efficiency of TCE in a sand column was achieved under dynamic conditions [0.5 mM Fe3+-NTA (1∶1.5), 4 mM H2O2, and hydraulic retention time of 4 h], resulting in stoichiometric ratios of ΔCl−∶ΔTCE and ΔTCE∶ΔH2O2 of ∼3∶1 and 4%, respectively. Compared with iron mineral (e.g., magnetite)-catalyzed Fenton-like processes, Fe3+-NTA/H2O2 led to much smaller consumption of H2O2 (at least 1 order of magnitude smaller). In addition, the buffering capacity of bicarbonate anions (HCO3−) in groundwater had a positive effect on the degradation of TCE by Fe3+-NTA/H2O2.

Sulfidated Microscale Zero-Valent Iron/Reduction Graphene Oxide Composite (S-Mzvi/Rgo) for Enhanced Degradation of Trichloroethylene: The Role of Hydrogen Spillover

Sulfidated Microscale Zero-Valent Iron/Reduction Graphene Oxide Composite (S-Mzvi/Rgo) for Enhanced Degradation of Trichloroethylene: The Role of Hydrogen Spillover

Synergistic Strengthening of Spc/Fe(Ii) System by Ca Coupled with Mzvi for Trichloroethylene Degradation in Sds-Containing Aqueous Solution

Synergistic Strengthening of Spc/Fe(Ii) System by Ca Coupled with Mzvi for Trichloroethylene Degradation in Sds-Containing Aqueous Solution

Comparative Study on Trichloroethylene Degradation Enhanced by Three Organic Acid Chelating Agents in Sodium Percarbonate/Fe(Ii) System in the Presence of Surfactant

Comparative Study on Trichloroethylene Degradation Enhanced by Three Organic Acid Chelating Agents in Sodium Percarbonate/Fe(Ii) System in the Presence of Surfactant

Grainy Nano Zero-Valent Iron with Kaolin Clay and Activated Carbon for Trichloroethylene Degradation: Preparation, Performance, and Mechanism

Grainy Nano Zero-Valent Iron with Kaolin Clay and Activated Carbon for Trichloroethylene Degradation: Preparation, Performance, and Mechanism

Synergistic Strengthening of Spc/Fe(Ii) System by Ca Coupled with Mzvi for Trichloroethylene Degradation in Sds-Containing Aqueous Solution

Synergistic Strengthening of Spc/Fe(Ii) System by Ca Coupled with Mzvi for Trichloroethylene Degradation in Sds-Containing Aqueous Solution

Plasma degradation of trichloroethylene: process optimization and reaction mechanism analysis

In this study, a multi-pin-to-plate negative corona discharge reactor was employed to degrade the hazardous compound trichloroethylene (TCE). The response surface methodology was applied to examine the influence of various process factors (relative humidity (RH), gas flow rate, and discharge power) on the TCE decomposition process, with regard to the TCE removal efficiency, CO2 and CO selectivities. The variance analysis was used to estimate the significance of the single process factors and their interactions. It has been proved that the discharge power had the most influential impact on the TCE removal efficiency, CO2 and CO selectivities and subsequently the gas flow rate, and finally RH. Under the optimal conditions with 20.83% RH, 2 W discharge power and 0.5 l min–1 gas flow rate, the optimal TCE removal efficiency (86.05%), CO2 selectivity (8.62%), and CO selectivity (15.14%) were achieved. In addition, a possible TCE decomposition pathway was proposed based on the investigation of byproducts identified in the exhaust gas of the non-thermal plasma reactor. This work paves the way for control of chlorinated volatile organic compounds.

Oxidative degradation of commingled trichloroethylene and 1,4-dioxane by hydroxyl radicals produced upon oxygenation of a reduced clay mineral

Improper disposal of chlorinated solvents such as trichloroethylene (TCE) and its stabilizer 1,4-dioxane has resulted in extensive contamination in soils and groundwater. Oxidative degradation of these contaminants by strong oxidants has been proposed recently as a remediation strategy, but specific mechanisms and degradation efficiencies are still poorly understood, especially in commingled systems. In this study, a reduced iron-bearing clay (RIC), nontronite (rNAu-2), was oxygenated to produce hydroxyl radicals (•OH) for degradation of TCE and 1,4-dioxane under circumneutral and dark conditions. Results showed that TCE and 1,4-dioxane could be effectively degraded during oxygenation of rNAu-2 in both single and commingled systems. Compared with the single compound system, the degradation rates and efficiencies of TCE and 1,4-dioxane decreased in the commingled system. The negative effect was more significant for TCE than 1,4-dioxane. The commingled TCE and 1,4-dioxane impacted the degradation pattern of each other, due to their difference in •OH scavenging efficiency, surface affinity to rNAu-2 and solubility. Moreover, solution pH, buffer type, rNAu-2 dosage, and dissolved organic matter all affected •OH production and contaminant degradation efficiency. Our findings provide new insights for investigating the natural attenuation of commingled chlorinated solvents and 1,4-dioxane by RIC in redox-fluctuating environments and offer guidance for developing possible in-situ remediation strategies.

Promoting streamer propagation, active species generation and trichloroethylene degradation using a three-electrode nanosecond pulsed sliding DBD nanosecond plasma

This work is devoted to exploring the streamer dynamic of a nanosecond pulsed sliding dielectric barrier discharge (SLDBD) based on a three-electrode geometry, and evaluating its effectiveness for the degradation of a representative chlorinated volatile organic compound (VOC)-trichloroethylene (TCE) at ambient temperature. The surface streamer of nanosecond pulsed SLDBD presents two distinct phases: primary streamer with higher velocity and secondary streamer with lower velocity. The luminous intensity, propagation distance, and propagation velocity of the primary streamer are greatly promoted by increasing the negative DC voltage (U-DC) applied at the third electrode, whereas only a little difference can be observed in the luminous intensity and propagation velocity for the secondary streamer with different U-DC. The surface potential difference between the pulsed excited high-voltage and the negatively biased third electrodes (Upulse-DC) is the major cause for streamers propagation because of the increased electric field at the streamer head. The production of excited species such as N2(C3Πu), N2+(B2Σu+), and OH(A2Σ) are promoted with increasing U-DC. The formation of N2(C3∏u→B3∏g,337 nm ) accompanies the streamer propagation process by electrons impact process. The TCE degradation experiment exhibits that the degradation efficiency and energy yield are significantly improved when Upulse-DC exceeds 20 kV where an SLDBD plasma is ignited, which can be attributed to the promoted surface streamers propagation as well as greater number of chemical active species.

Enhanced trichloroethene degradation performance in innovative nanoscale CaO2 coupled with bisulfite system and mechanism investigation

• HSO 3 – significantly enhanced HO• generation and TCE degradation. • HO• was the dominant ROSs in nCaO 2 /Fe(III)/HSO 3 – system. • The double effect of CaO 2 as both oxidant and O 2 source was clarified. • The enhancement mechanism caused by HSO 3 – was revealed. The effect of bisulfite (HSO 3 – ) in nCaO 2 /Fe(III)/HSO 3 – system on improving HO• generation and trichloroethene (TCE) removal was innovatively reported. The enhancement mechanism of HSO 3 – for TCE removal in nCaO 2 /Fe(III)/HSO 3 – system was caused not only by the complexing and reducing effects on promoting the conversion of Fe(III) to Fe(II), but also due to the reaction with O 2 in water to produce SO 4 – • for accelerating TCE degradation. A double effect of nCaO 2 as an oxidant source to generate HO• and as a O 2 source to promote SO 4 – • generation was revealed. A pseudo-second-order kinetic model of TCE removal was determined and 94.6% TCE degradation was achieved within 60 min at the nCaO 2 /Fe(III)/HSO 3 – /TCE molar ratio of 6/12/9/1, in which 82.8% TCE was dechlorinated. The scavenger test and EPR detection found that various kinds of reactive oxygen species (ROSs) including HO•, SO 4 – •, O 2 – • and 1 O 2 were generated, all contributed to TCE removal and HO• was the dominant one in nCaO 2 /Fe(III)/HSO 3 – system. The effects of surfactant presence and the complex matrix in the actual groundwater were evaluated. The experiments of high efficiency for chlorinated olefins and benzene series removals but low applicability for chlorinated alkanes provided an alternative technique to remedy groundwater based on the various kinds of contaminants performance.