Trichloroethylene Removal Research Articles

Theoretical analysis and application of immobilized methanotrophs as typical adsorbent materials for adsorption/degradation of trichloroethylene

ABSTRACT Trichloroethylene (TCE) contamination presents a significant environmental challenge, necessitating efficient treatment solutions. This study aimed to develop an optimized immobilized bioreactor using methanotrophs for TCE degradation. Activated carbon fibres were identified as the optimal immobilization material, with an adsorption rate of 6–23 h – significantly faster than over 50 h for other materials – and the highest methane oxidation capacity of 0.970 mL·g−1·h−1. Adsorption kinetics indicated that activated carbon fibres followed a second-order kinetic model with a constant of 0.598 g·mg−1·h−1, suitable for low-concentration bacterial solutions. Thermodynamic analysis confirmed an exothermic process, favouring lower temperatures (288.15 K). The negative interaction energies, as per DLVO theory, suggested electrostatic attraction as a key mechanism. The bioreactor achieved 99% TCE removal within 1 h at an initial concentration of 10 mg·L−1, with visible microbial immobilization within 5 days. This research provides a novel and effective approach for using immobilized methane-oxidizing bacteria in TCE treatment, offering both theoretical and practical advancements for chlorinated hydrocarbon wastewater management.

Synergistic biodegradation of trichloroethylene-contaminated soil using Typha angustifolia L. and an anaerobic degrading bacterial consortium

Plant-microorganism combined bioremediation is a highly efficient and environmentally sustainable method for the remediation of contaminated soils. Despite its potential, the synergistic effects of wetland plants and anaerobic microbial consortium on the removal of chlorinated hydrocarbons (CAHs) from soil remain inadequately understood. In this study, an anaerobic bacterial consortium, capable of completely dechlorinating trichloroethylene (TCE), was enriched and screened from long-term CAH-contaminated soil. Subsequently, the combined effects of the wetland plant Typha angustifolia L. and the degrading bacterial consortium on the removal of TCE from soil were investigated, along with the underlying microbial mechanisms. The results demonstrated that the bacterial consortium was able to completely convert 0.5 mM TCE to vinyl chloride (VC) within 7 days, and subsequently degrade VC to ethylene within 48 days. The integration of Typha angustifolia L. with the degrading bacterial consortium significantly enhanced both the removal and complete dechlorination of TCE from the soil compared to either treatment alone. Furthermore, this combination substantially increased the diversity and richness of soil bacterial communities, enriched dechlorinating microorganisms, and elevated the relative abundance of dehalogenating enzymes and peroxidases involved in pollutant degradation. In addition, the combination resulted in a more complex soil bacterial community, closer microbial interactions, and a more stable microbial co-occurrence network. This study extends the scope of plant-microorganism combined bioremediation for CAH- contaminated soils.

Effective electrochemical trichloroethylene removal from water enabled by selective molecular catalysis

Effective electrochemical trichloroethylene removal from water enabled by selective molecular catalysis

S-ZVI@biochar constructs a directed electron transfer channel between dechlorinating bacteria, Shewanella oneidensis MR-1 and trichloroethylene

The combination of micron zero-valent iron (mZVI) and microorganisms is an effective method for trichloroethylene (TCE) degradation, but electron transfer efficiency needs improvement. A new chem-bio hybrid process using a composite material (S-ZVI@biochar) was developed, consisting of sulfurized mZVI and biochar as a chemical remover, and Shewanella oneidensis MR-1 and dechlorinating bacteria (DB) as a biological agent for TCE degradation. S-ZVI@biochar showed improved stability, biocompatibility, and TCE removal compared to ZVI and S-ZVI. The hybrid system DB + MR-1 + S-ZVI@biochar exhibited the highest TCE removal efficiency at 96.5% after 30 days, which was 3.7 times higher than that of bare ZVI. The study revealed that the enhanced dechlorination performance was due to improved electron transfer efficiency, adjustment of microbial community structure, and iron recycling. S-ZVI@biochar constructed electron transport channels in the composite system, improving the overall dechlorination capacity. This system shows promise for long-term TCE removal in anaerobic environments.

Preparation of zero-valent iron@Fe3O4 and its removal performance study for trichloroethylene

Trichloroethylene (TCE) is a common organic pollutant with low solubility in water, leading to its accumulation within the soil layer and posing risks to groundwater system. In this study, the zero valent iron@Fe3O4 (nZVI@Fe3O4) with diameters in the range of 500 nm to 1500 nm and thickness between 2 and 3 nm were successfully synthesized by ascorbic acid mediated reduction of FeCl2 in an N2-filled glove box, and proposed to boost the degradation of TCE. Research findings indicate that a starting TCE concentration of 20 mg/L can achieve a removal rate exceeding 80 % after 60 min, with an impressive adsorption capacity of 32.09 mg/g. The acidic environment plays a crucial role in enhancing the elimination of TCE by nZVI. Additionally, it was observed that a high NaCl concentration negatively impacts the effectiveness of nZVI in TCE removal, with the most significant inhibition observed at a NaCl concentration of 1000 mg/L. The adsorption of TCE by nZVI was consistent with the Langmuir model for monolayer adsorption, and the removal process was consistent with the quasi-secondary kinetic model. Importantly, the nanomaterials prepared in this experiment using disproportionation reaction have good economic and environmental benefits.

Ultra-efficient peroxymonosulfate utilization and trichloroethylene degradation in heterogeneous catalytic system guided by sheet-like Cu2MnO4 nanoparticles: The role of Cu(III)–O species and free radicals

Synthesizing cubic spinel Cu2MnO4 with nanosheet structure (SCMO) aimed to construct a “non-radical-mediated radical-oxidative reaction”, for increasing PMS utilization efficiency, and solving the defects of SO4•− and •OH through indirect PMS activation by electron transfer process. Compared with box-like Cu2MnO4 (11.1%, 0.0035 min−1) and ordinary Cu2MnO4 nanoparticles (21.3%, 0.0070 min−1), SCMO/PMS showed excellent trichloroethylene removal (98.8%, 0.1577 min−1). The pivotal role of Cu(III) was determined based on EPR analysis, quenching experiments, chemical probe experiments, hydrogen temperature-programmed reduction and Raman spectroscopy analysis, in-situ FTIR and Raman analyses. In brief, the interaction between PMS and SCMO could produce surface-bonded reactive complexes and the subsequent breaking of O–O bond in the sub-stable structure allowed the conversion of Cu(II) to Cu(III), which in turn facilitates the generation of •OH and SO4•−. The density functional theory (DFT) calculations provided supporting evidence for the electron donor role of SCMO and the increase of the electron acceptance capacity of PMS. SCMO/PMS system showed good resistance and degradation efficiency to complex composition and combined pollutants in actually contaminated groundwater, respectively. However, the coexistence of high concentrations of arsenic could significantly affect SCMO performance due to their adsorption on –OH groups, which still need in-depth study.

Single-Atom Iron Can Steer Atomic Hydrogen toward Selective Reductive Dechlorination: Implications for Remediation of Chlorinated Solvents-Impacted Groundwater.

Atomic hydrogen (H*) is a powerful and versatile reductant and has tremendous potential in the degradation of oxidized pollutants (e.g., chlorinated solvents). However, its application for groundwater remediation is hindered by the scavenging side reaction of H2 evolution. Herein, we report that a composite material (Fe0@Fe-N4-C), consisting of zerovalent iron (Fe0) nanoparticles and nitrogen-coordinated single-atom Fe (Fe-N4), can effectively steer H* toward reductive dechlorination of trichloroethylene (TCE), a common groundwater contaminant and primary risk driver at many hazardous waste sites. The Fe-N4 structure strengthens the bond between surface Fe atoms and H*, inhibiting H2 evolution. Nonetheless, H* is available for dechlorination, as the adsorption of TCE weakens this bond. Interestingly, H* also enhances electron delocalization and transfer between adsorbed TCE and surface Fe atoms, increasing the reactivity of adsorbed TCE with H*. Consequently, Fe0@Fe-N4-C exhibits high electron selectivity (up to 86%) toward dechlorination, as well as a high TCE degradation kinetic constant. This material is resilient against water matrix interferences, achieving long-lasting performance for effective TCE removal. These findings shed light on the utilization of H* for the in situ remediation of groundwater contaminated with chlorinated solvents, by rational design of earth-abundant metal-based single-atom catalysts.

Innovative strategy for the effective utilization of coal waste slag in the Fenton-like process for the degradation of trichloroethylene

In response to environmental concerns at the global level, there is considerable momentum in the exploration of materials derived from waste that are both sustainable and eco-friendly. In this study, CS-Fe (carbon, silica, and iron) composite was synthesized from coal gasification slag (CGS) and innovatively applied as a catalyst to activate PS (persulfate) for the degradation of trichloroethylene (TCE) in water. Scanning electron microscope (SEM), fourier transmission infrared spectroscopy (FTIR), energy dispersive x-ray spectroscopy (EDS), brunauer, emmet, and teller (BET) technique, and x-ray diffractometer (XRD) spectra were employed to investigate the surface morphology and physicochemical composition of the CS-Fe composite. CS-Fe catalyst showed a dual nature by adsorption and degradation of TCE simultaneously, displaying 86.1% TCE removal in 3 h. The synthesized CS-Fe had better adsorption (62.1%) than base material CGS (36.4%) due to a larger BET surface area (770.8 m2 g−1), while 24.0% TCE degradation was recorded upon the activation of PS by CS-Fe. FTIR spectra confirmed the adsorption and degradation of TCE by investigating the used and fresh samples of CS-Fe catalyst. Scavengers and Electron paramagnetic resonance (EPR) analysis confirmed the availability of surface radicals and free radicals facilitated the degradation process. The acidic nature of the solution favored the degradation while the presence of bicarbonate ion (HCO3−) hindered this process. In conclusion, these results for real groundwater, surfactant-added solution, and degradation of other TCE-like pollutants propose that the CS-Fe composite offers an economically viable and favorable catalyst in the remediation of organic contaminants within aqueous solutions. Further investigation into the catalytic potential of coal gasification slag-based carbon materials and their application in Fenton reactions is warranted to effectively address a range of environmental challenges.

Green and one-step synthesis of nitrogen-doped carbon supported Fe3N as highly stable magnetic absorbent for trichloroethene removal

N-doped carbon supported Fe3N (Fe3N/NBC) was obtained via direct carbonization of potassium ferrate (PF), urea and biowaste in nitrogen. The use of PF simultaneous realized nitridation of iron without using ammonia atmosphere, formation of Fe3N and activation of the NBC. Fe3N/NBC used as magnetic absorbent showed good ability to absorb trichloroethene (TCE) at pH = 3–11 or under co-presence of various inorganic anions (Cl − , SO42 − , NO3 − and PO43 − ) and could be easily separated from liquid and regenerated with steady performance. This study may provide new insights into cost-effective and green production of Fe3N-based composites.

Influence of microbial inoculation site on trichloroethylene degradation in electrokinetic-enhanced bioremediation of low-permeability soils

The integration of electrokinetic and bioremediation (EK-BIO) represents an innovative approach for addressing trichloroethylene (TCE) contamination in low-permeability soil. However, there remains a knowledge gap in the impact of the inoculation approach on TCE dechlorination and the microbial response with the presence of co-existing substances. In this study, four 1-dimensional columns were constructed with different inoculation treatments. Monitoring the operation conditions revealed that a stabilization period (∼40 days) was required to reduce voltage fluctuation. The group with inoculation into the soil middle (Group B) exhibited the highest TCE dechlorination efficiency, achieving a TCE removal rate of 84%, which was 1.1–3.2 fold higher compared to the others. Among degraded products in Group B, 39% was ethylene. The physicochemical properties of the post-soil at different regions illustrated that dechlorination coincided with the Fe(III) and SO42− reduction, meaning that the EK-BIO system promoted the formation of a reducing environment. Microbial community analysis demonstrated that Dehalococcoides was only detected in the treatment of injection at soil middle or near the cathode, with abundance enriched by 2.1%–7.2%. The principal components analysis indicated that the inoculation approach significantly affected the evolution of functional bacteria. Quantitative polymerase chain reaction (qPCR) analysis demonstrated that Group B exhibited at least 2.8 and 4.2-fold higher copies of functional genes (tceA, vcrA) than those of other groups. In conclusion, this study contributes to the development of effective strategies for enhancing TCE biodechlorination in the EK-BIO system, which is particularly beneficial for the remediation of low-permeability soils.

Microplastic inhibits the sorption of trichloroethylene on modified biochar.

Biochar (BC) was used to remove trichloroethylene (TCE) from soil and water phases, and BC modification changed the sorption behavior of pollutants. Microplastics are emerging pollutants in the soil and water phases. Whether microplastics can affect the sorption of TCE by modified BC is not clear. Thus, batch sorption kinetics and isotherm experiments were conducted to elucidate the sorption of TCE on BC, and BC combined with polyethylene (PE) or polystyrene (PS). The results showed that HCl and NaOH modification increased TCE sorption on BC, while HNO3 modification inhibited TCE sorption on BC. When PE/PS and BC coexisted, the TCE sorption capacity decreased significantly on BC-CK + PE, BC-HCl + PE, BC-HNO3 + PE, BC-NaOH + PE, and BC-NaOH + PS, which was likely due to the preferential sorption of PE/PS on BC samples. We concluded that microplastics can change TCE sorption behavior and inhibit TCE sorption on BC samples. Thus, the interaction of BC and microplastics should be considered when BC is used for TCE removal in soil and water remediation.

Bioremediation of trichloroethylene-contaminated groundwater using green carbon-releasing substrate with pH control capability

In this research, a sustainable substrate, termed green and long-lasting substrate (GLS), featuring a blend of emulsified substrate (ES) and modified rice husk ash (m-RHA) was devised. The primary objective was to facilitate the bioremediation of groundwater contaminated with trichloroethylene (TCE) using innovative GLS for slow carbon release and pH control. The GLS was concocted by homogenizing a mixture of soybean oil, surfactants (Simple Green™ and soya lecithin), and m-RHA, ensuring a gradual release of carbon sources. The hydrothermal synthesis was applied for the production of m-RHA production. The analyses demonstrate that m-RHA were uniform sphere-shape granules with diameters in micro-scale ranges. Results from the microcosm study show that approximately 83% of TCE could be removed (initial TCE concentration = 7.6 mg/L) with GLS supplement after 60 days of operation. Compared to other substrates without RHA addition, higher TCE removal efficiency was obtained, and higher Dehalococcoides sp. (DHC) population and hydA gene (hydrogen-producing gene) copy number were also detected in microcosms with GLS addition. Higher hydrogen concentrations enhanced the DHC growth, which corresponded to the increased DHC populations. The addition of the GLS could provide alkalinity at the initial stage to neutralize the acidified groundwater caused by the produced organic acids after substrate biodegradation, which was advantageous to DHC growth and TCE dechlorination. The addition of m-RHA reached an increased TCE removal efficiency, which was due to the fact that the m-RHA had the zeolite-like structure with a higher surface area and lower granular diameter, and thus, it resulted in a more effective initial adsorption effect. Therefore, a significant amount of TCE could be adsorbed onto the surface of m-RHA, which caused a rapid TCE removal through adsorption. The carbon substrates released from m-RHA could then enhance the subsequent dechlorination. The developed GLS is an environmentally-friendly and green substrate.

Metagenomic sequencing reveals mechanisms of adaptation and biodegradation of dechlorinating bacteria to trichloroethylene

Bioremediation is a sustainable, cost-effective, and eco-friendly way to remediate pollutants. However, the effectiveness of bioremediation is constrained by the underground environmental conditions, resulting in poor natural attenuation of organic pollution and degradation by functional microorganisms. In this study, a dechlorinating bacteria (DB) was enriched from contaminated soil and used to degrade trichloroethylene (TCE) in wastewater. The adaptation and degradation mechanisms of DB to TCE were investigated by degradation product analysis and metagenomic sequencing. The degradation of TCE by DB is pH and additional carbon source dependent. The highest TCE removal amount (1.86 × 10−7 mmol/CFU) was achieved at pH=8, 1% DB inoculum volume, and 400 mg/L sodium acetate concentration. Moreover, DB has a high acid resistance and a removal capacity of 1.18×10−7 mmol/CFU for TCE at pH =2. None of the co-occurring pollutants Cr (VI) and toluene had a significant effect on the ability of DB to degrade TCE in wastewater (maintained at 1.13–1.22×10−7 mmol/CFU). DB dechlorinated TCE mainly through the action of extracellular enzymes (contributed 91% of the total removal ability). DB playing a major role in degradation is Paraclostridium. Significant differences in alpha diversity indices were revealed in the reaction systems after 15 days of exposure to TCE (p < 0.01). The degradation of TCE by DB is mainly accomplished through the defense system, energy synthesis, electron supply and biodegradation. Metagenomic sequencing demonstrated that DB achieved adaptation and degradation of TCE through gene-regulated biological processes such as xenobiotic biodegradation and metabolism, carbohydrate metabolism, biosynthesis of other secondary metabolites, amino acid metabolism, membrane transport, and signal transduction. This study reveals for the first time the biodegradation efficiency and biotransformation process of DB under TCE stress.

Surfactant enhanced persulfate system for the synergistic oxidation and reduction of mixed chlorinated hydrocarbons

Surfactant-enhanced in-situ chemical oxidation (S-ISCO) is widely applied in soil and groundwater remediation. However, the role of surfactants in the reactive species (RSs) transformation remains inadequately explored. This work introduced nonionic surfactant Tween-80 (TW-80) into a nano zero-valent iron (nZVI) activated persulfate (PS) system. The findings indicate that PS/nZVI/TW-80 system can realize the concurrent removal of trichloroethylene (TCE), tetrachloroethene (PCE), and carbon tetrachloride (CT), whereas CT cannot be eliminated without TW-80 presence. Further analysis unveiled that hydroxyl (HO•) and sulfate radicals (SO4－•) were the primary species for TCE and PCE degradation, while CT was reductively eliminated by surfactant radicals generated from TW-80. Moreover, the surfactant radicals were found to accelerate Fe(III)/Fe(II) cycle, reduce the production of iron sludge, and increase PS decomposition. The possible degradation routes of mixed chlorinated hydrocarbons (CHCs) and the decomposition pathways of TW-80 were proposed through the density function theory (DFT) calculation and intermediates analysis. Additionally, the effects of other nonionic surfactants on the simultaneous removal of TCE, PCE, and CT, and the practical applications using the actual contaminated groundwater were also evaluated. This study provides theoretical support for the simultaneous removal of CHCs, particularly those containing perchlorinated contaminants, using the S-ISCO techniques.

Synthesis of CaCO3 supported nano zero-valent iron-nickel nanocomposite (nZVI-Ni@CaCO3) and its application for trichloroethylene removal in persulfate activated system

Nano zero-valent (nZVI) based composite have been widely utilized in environmental remediation. However, the rapid agglomeration and quick deactivation of nZVI limited its application on large scale. In this work, CaCO3 supported nZVI-Ni catalyst, namely nZVI-Ni@CaCO3 was prepared and used for the efficient removal of trichloroethylene (TCE) in PS oxidation process. The successful disbursement of nZVI-Ni on CaCO3 support material not only increased the surface area of nZVI-Ni@CaCO3 (69.45 m2/g) with respect to CaCO3 (5.92 m2/g) and bare nZVI (13.29 m2/g) but also improved the catalytic activity. XRD, XPS and FTIR analysis confirmed the successful formation of nZVI-Ni@CaCO3 nanoparticles. The nZVI-Ni@CaCO3 nanoparticles combined with PS had achieved complete removal of TCE (99.8%) with dosage of 36 mg/L and 1.34 mM respectively. These results showed that the use of CaCO3 as support material for nZVI-Ni could have significant influence on contaminant removal process. Scavenging and EPR tests validated the existence of SO4•–, OH• and O2•– radicals in PS/nZVI-Ni@CaCO3 system and highlighted the dominant role of SO4•– radicals in TCE removal process. HCO3ˉ ions and humic acid have shown adverse effect on TCE removal due to radical scavenging and buffering effect. Owing to improved catalytic activity and easy preparation, the nZVI-Ni@CaCO3 nanoparticles could be served as an alternative strategy for environmental remediation.

Molybdenum disulfide modified microscale zero-valent iron (MoS-mZVI) for enhanced trichloroethylene dechlorination

The potential of microscale zero-valent iron (ZVI) for dechlorinating chlorinated hydrocarbons holds promise in pollution remediation. However, Fe0 passivation presents a challenge, leading to slow dechlorination and the buildup of hazardous incomplete dechlorinated intermediates. To address these concerns, we introduce molybdenum disulfide (MoS2)-modified microscale ZVI (MoS-mZVI). Our study demonstrates the significant enhancement of trichloroethylene (TCE) dechlorination by MoS-mZVI compared to standard mZVI. Remarkably, the optimal Fe/MoS2 molar ratio of 20 in MoS-mZVI achieves a remarkable 26.8-fold acceleration in TCE removal compared to mZVI. Acetylene emerges as the primary intermediate in TCE dechlorination by MoS-mZVI, peaking at 38%, accompanied by major end products including ethene (45%) and ethane (31%). Importantly, the MoS-mZVI-20 system avoids toxic byproducts, diverging from the dichloroethylene accumulation observed in the mZVI system. Notably, electron utilization efficiency shows significant improvement, with MoS-mZVI reaching 65.6% compared to mZVI's 7.2%. Furthermore, MoS2′s selective OH- adsorption triggers pH reduction, mitigating mZVI passivation and optimizing its reactivity. This innovative approach highlights the effectiveness of MoS2-modified microscale ZVI as an environmentally friendly solution for enhancing TCE dechlorination processes.

Comparative investigation of organic contaminant removal in the synthesized greigite (Fe3S4)- and other iron sulfide-enhanced PDS/Fe(II) systems: Efficiencies, kinetics, and mechanism insights

In this research, greigite (Fe3S4) was innovatively applied for the enhancement of PDS/Fe(II) system. From XRD and SEM analyses, Fe3S4 was successfully synthesized and appeared uniform sphere-like particles with a petal-like structure. Trichloroethylene (TCE), as the target, was significantly degraded from 28.5 % to 92.8 % in PDS/Fe(II)/Fe3S4 system. The enhanced mechanisms, differences, and superiority of Fe3S4 against the other three iron sulfides were elucidated as follows: (1) on account of the abundant reduction sites on its surface, Fe3S4 could not only directly release Fe(II) and accelerate Fe(II) regeneration by sulfur substances, but also participate in the process of O2−• generation, and (2) the reaction mainly took place on Fe3S4 surface, in which the surface-bound reactive species (RSs) were of great importance for TCE degradation. Through EPR, quantification, and scavenging tests of RSs, HO•, SO4−•, and O2−• were all the dominant RSs responsible for TCE removal. Besides, these enhanced systems had high tolerance on complex water conditions and could remediate various contaminants in actual groundwater. Three TCE degradation pathways were deduced in four iron sulfide-enhanced systems and the toxicities of intermediates were evaluated, recommending that Fe3S4-enhanced system was of the least toxicity and most favorable for application in practice.

Synergistic effect and removal mechanism of trichloroethylene (TCE) by nano scale zero-valent iron (nZVI) supported on biological calcium carbonate (CaCO3)

Microbial induced calcium carbonate precipitation (MICP) is a green and environmentally friendly technology. Herein, porous biological CaCO3 was prepared by MICP technology and then used as the carrier material for nZVI to prepare CaCO3@nZVI composite. Afterwards, the various properties of the CaCO3@nZVI composite were methodically characterized. Subsequently, the adsorption kinetic equation and adsorption isotherm model of TCE were carefully investigated, and the CaCO3@nZVI composite dosage, initial pH, temperature, aging time and the number of cycles on the TCE removal efficiency were examined. Finally, the degradation mechanism of TCE by CaCO3@nZVI composite was revealed. The results showed that nZVI particles were successfully supported on the biological CaCO3 surface, and the specific surface area of the CaCO3@nZVI composite was 52.641 m2/g, which was much higher than that of bare nZVI (8.757 m2/g). The adsorption kinetics of CaCO3@nZVI composite for TCE removal was conformed to the pseudo-second-order kinetic equation, and Freundlich model was more appropriate as the adsorption isotherm model. The optimal conditions for the TCE removal were obtained to be 0.24 g/L CaCO3@nZVI composite dosage, 25 ℃, and initial pH of 7.0, respectively. Furthermore, the CaCO3@nZVI composite exhibited good stability and reusability. The main degradation products of TCE by CaCO3@nZVI composite were acetylene, ethylene, and ethane, and the synergistic effects of adsorption and degradation were the main mechanisms of TCE removal. Generally, this paper provides experimental support for the selection of nZVI carrier materials, which is useful for promoting the development and advancement of green repair materials.

Development of Slow-Releasing Tablets Combined with Persulfate and Ferrous Iron for In Situ Chemical Oxidation in Trichloroethylene-Contaminated Aquifers

Slow-releasing tablets combined with persulfate acting as an oxidant and ferrous iron acting as an activator were manufactured for in situ chemical oxidation. The trichloroethylene (TCE) removal efficiency according to the molar ratio of the oxidizer and activator in the 0, 0.5, 1, 1.5, 2, and 2.5 molar ratio (persulfate: ferrous iron) reactors were 15%, 89%, 90%, 82%, 71%, and 55%, respectively. In a batch reactor injected with an oxidation-activation combined tablet (OACT) and a liquid oxidizing/activator, the TCE removal efficiencies were 100% and 70%, respectively, showing that the tablet form had a high efficiency in contaminant removal. The evaluation of the dissolution characteristics and TCE removal efficiency of OACT 0.5 (tablet with a 1:0.5 molar ratio of persulfate to activator) and OACT 1.0 (tablet with a 1:1 molar ratio of persulfate to activator) under continuous flow conditions showed that the TCE removal efficiency of the OACT 1.0 column was approximately 1.4 times higher than that of OACT 0.5. The longevities of persulfate and ferrous iron of the OACT 1.0 tablet were 43.2 days and 41.7 days, respectively. Thus, OACT 1.0, which was manufactured effectively, was suitable for in situ slow-release chemical oxidation systems.

Tannic acid promotes the activation of persulfate with Fe(ii) for highly efficient trichloroethylene removal.

Trichloroethylene (TCE) is an Environmental Protection Agency (EPA) priority pollutant that is difficult to be removed by some remediation methods. For instance, TCE removal using persulfate (PS) activated by ferrous iron (Fe(ii)) has been tested but is limited by the unstable Fe(ii) concentration and the initial pH of contaminated water samples. Here we reported a new TCE removal system, in which tannic acid (TA) promoted the activation of PS with Fe(ii) (TA-Fe(ii)-PS system). The effect of initial pH, temperature, and concentrations of PS, Fe(ii), TA, inorganic anions and humic acid on TCE removal was investigated. We found that the TA-Fe(ii)-PS system with 80 mg L-1 of TA, 1.5 mM of Fe(ii) and 15 mM of PS yielded about 96.2-99.1% TCE removal in the pH range of 1.5-11.0. Radical quenching experiments were performed to identify active species. Results showed that SO4˙- and ˙OH were primarily responsible for TCE removal in the TA-Fe(ii)-PS system. In the presence of TA, the Fe-TA chelation and the reduction of TA could regulate Fe(ii) concentration and activate persulfate for continuously releasing reactive species under alkaline conditions. Based on the excellent removal performance for TCE, the TA-Fe(ii)-PS system becomes a promising candidate for controlling TCE in groundwater.