Trichloroethylene Degradation Research Articles

Application of Combined In Situ Chemical Reduction and Enhanced Bioremediation to Accelerate TCE Treatment in Groundwater

Groundwater at trichloroethylene (TCE)-contaminated sites lacks electron donors, which prolongs TCE’s natural attenuation process and delays treatment. Although adding electron donors, such as emulsified oil, accelerates TCE degradation, it also causes the accumulation of hazardous metabolites such as dichloroethylene (DCE) and vinyl chloride (VC). This study combined in situ chemical reduction using organo-iron compounds with enhanced in situ bioremediation using emulsified oil to accelerate TCE removal and minimize the accumulation of DCE and VC in groundwater. A self-made soybean oil emulsion (SOE) was used as the electron donor and was added to liquid ferrous lactate (FL), the chemical reductant. The combined in situ chemical reduction and enhanced in situ bioremediation achieved favorable results in a laboratory microcosm test and in an in situ biological field pilot test. Both tests revealed that SOE+FL accelerated TCE degradation and minimized the accumulation of DCE and VC to a greater extent than SOE alone after 160 days of observation. When FL was added in the microcosm test, the pH value decreased from 6.0 to 5.5; however, during the in situ biological pilot test, the on-site groundwater pH value did not exhibit obvious changes. Given the geology of the in situ pilot test site, the SOE+FL solution that was injected underground continued to be released for at least 90 days, suggesting that the solution’s radius of influence was at least 5 m.

Comparative study of trichloroethylene removal by different carbons and FeNi-carbon composites

Nanoscale zero-valent iron (NZVI) has been proven effective at degrading environmental ‎contaminants of concern, yet field performance as an in situ remedy is lacking due to short ‎reactive lifetimes and poor transport through porous media. The main ‎objective of this study was to investigate and compare the performance of different carbon ‎powders with different properties (surface ‎area, pore-volume, conductivity, functional groups) on trichloroethylene (TCE) removal and transport ‎properties. Carbon ‎powders were used as the support for bimetallic FeNi nanoparticles, the composites were stabilized by poly(vinyl pyrrolidone), and the performance of ‎the modified novel FeNi-carbon composites was compared. It was confirmed that several properties of the carbon were found to not affect TCE degradation by the FeNi-C composites while ‎surface area, pore size, and functional groups are responsible for TCE adsorption by carbon ‎powders. Carbon particle size was found to inversely affect the transport of the composite ‎through porous media, with smaller carbon supports such as carbon black correlating to a wider ‎radius of influence, as compared to larger biochar carbon particulates. Significantly, FeNi-C ‎shows improved TCE degradation over Fe or FeNi nanoparticles alone, indicating the utility of ‎using carbon supports to promote dehalogenation reactions and increase NZVI longevity‎.

Enhanced dechlorination of trichloroethene by sulfidated microscale zero-valent iron under low-frequency AC electromagnetic field

In this study an electromagnetic heating strategy is proposed for remediation of trichloroethene (TCE) by ball milled, sulfidated microscale zero valent iron (S-mZVIbm) particles. S-mZVIbm is ferromagnetic, which generates heat under the application of a low-frequency alternating current electromagnetic field (AC EMF). We found that the temperature reached up to ~120 ℃ during 30-min electromagnetic induction heating of 10 g/L S-mZVIbm (with S/Fe molar ratio of 0.1), compared with ~55 ℃ and ~80 ℃ for ZVI and ball milled mZVIbm, respectively. The application of AC EMF accelerated the TCE degradation rate (kTCE = 5.5 × 10-1 h-1) by up to 4-fold without compromising or even enhancing electron efficiency of S-mZVIbm compared to no-heating. Furthermore, this process halved the generation of chlorinated intermediate, cis-DCE. In contrast, water-bath heating only increased the dechlorination rate 2-fold with unchanged cis-DCE generation and lowered electron efficiency. This is attributed to both rising temperature by induction heating and accelerated ZVI corrosion and surface Fe0 exposure caused by AC EMF. In real groundwater, the AC EMF maintained the same promoting effects for TCE dechlorination by S-mZVIbm. This study shows that combination of filed-scale available AC EMF with S-mZVIbm provides a promising approach for remediation of chlorinated hydrocarbons in contaminated groundwater.

Bisulfite reduction of soil iron for the reductive degradation of trichloroethylene

This study explored the potential reactivities of various reductants in inducing subsurface TCE degradation in natural soils. It was found that bisulfite (HSO3−) exhibited the ability to induce reduction in soil iron minerals, and increase the degradation of TCE in the soil slurry system; however, no TCE degradation occurred in the aqueous system. The role of TCE degradation by soil constituents, such as major soil mineral elements, Fe and humic acid (HA) on HSO3−, was examined in aqueous phase. It was seen that by themselves, the presence of Fe3+, HA, Fe2O3, FeOOH, and Fe3O4 did not result in substantial TCE removals. However, the presence of HSO3− can significantly induce iron reduction, producing a reducing condition that can result in complete TCE degradation. Furthermore, the reductive pathway was identified as the dominant degradation route via electron scavenging with periodate ion. To demonstrate the applicability of HSO3− reduction enhancement, a HSO3−/TCE mixed solution was flushed through a soil column, with gradually increased HSO3− concentrations, at a fixed flow rate, and also with varied flushing rates at a fixed HSO3− concentration. Based on our study, a 10 mM HSO3− solution may be effective for some environmental sites; however, each site requires specific evaluation based on contaminant concentrations and subsurface conditions.

Vitamin B12 and Magnesium: a Healthy Combo for the Degradation of Trichloroethylene

Vitamin B12 and Magnesium: a Healthy Combo for the Degradation of Trichloroethylene

Insights into carbon isotope fractionation on trichloroethene degradation in base activated persulfate process: The role of multiple reactive oxygen species

Understanding the role of reactive oxygen species (ROS) is essential to elucidate the mechanism of contaminants degradation in in-situ chemical oxidation (ISCO). In this study, compound specific isotope analysis (CSIA) and radicals quenching methods were integrated to investigate the roles of hydroxyl radical (HO), sulfate radical (SO4−), and superoxide radical (O2−) on trichloroethene (TCE) degradation during persulfate (PS) activated with base. The carbon isotope fractionation of TCE was found to be dependent of the base:PS ratios, yielding carbon enrichment factors (ε values) from −9.8 ± 0.5‰ to −16.7 ± 1.0‰ at base:PS molar ratios between 0.5:1 and 10:1, which was attributed to multi-pathways degradation of TCE by multiple ROS. The expected ε value (−31.6 ± 1.6‰) for TCE degradation via O2− attacking pathway, was more negative than those values via SO4− or HO pathways. The relative contributions of HO, SO4− and O2− for TCE degradation during base activated PS were estimated with observed ε values. HO and O2− were the predominant ROS for TCE degradation (with the relative contribution of 55–69% and 22–45%, respectively) in base activated PS. This work highlights the prospect of CSIA application for identifying degradation pathways of contaminants with ROS in environment.

Bioprecipitation facilitates the green synthesis of sulfidated nanoscale zero-valent iron particles for highly selective dechlorination of trichloroethene

Compared with nanoscale zero-valent iron particles (nZVI), sulfidated zero-valent iron nanoparticles (S-nZVI) exhibit higher reactivity and selectivity towards the remediation of halogenated organic pollutants such as trichloroethene (TCE). However, traditional methods of preparing S-nZVI are not safe and environmentally friendly to some degree. In this study, we developed a biological precipitation method to prepare S-nZVI, in which sulfate-reducing bacteria (SRB) played an important role for the in situ formation of ferrous disulfide on the surface of nZVI. The results show that the obtained sulfidated nZVI particles (BP-S-nZVI) exhibit excellent performance in TCE degradation, and the first-order rate coefficient (Kobs) and the efficiency of electron utilization were up to (1.66 ± 0.1)× 10-1 h-1 and 85%, respectively. Moreover, zero-valent iron utilization efficiency of BP-S-nZVI reached 95%. Meanwhile, the particles were well characterized and the mechanism for enhanced reactivity was explored. The prominent advantage of this novel method is that the harmful chemical sulfidating agents such as dithionite (S2O42−) and sodium sulfide (Na2S) are not required, making the preparation process more environmental-friendly, green and sustainable.

Influence of preparation method on copper ferrite characteristics for the efficient degradation of trichloroethylene in persulfate activated system

In this study, the morphology, surface features, textural properties, size of particles and the catalytic efficiencies of synthesized CuFe2O4 by three different methods including sol–gel (SG), coprecipitation (CP), and solvothermal (ST) were evaluated. Various analytical techniques including SEM, TEM, XRD, N2 adsorption–desorption, EDS elemental mapping, FTIR, and XPS were employed for characteristics exploration. The characterization results showed that the synthesis method could influence the characteristics of spinal ferrite and ST-CuFe2O4 catalyst exhibited larger specific surface area (65.2 m2/g) and micro-pore volume (0.4512 cm3/g) than the catalyst prepared by CP (30.6 m2/g and 0.1298 cm3/g) and SG (18.2 m2/g and 0.0521 cm3/g) methods, respectively. Further, the XRD and FTIR results validated the formation of a highly crystalline ferrite structure synthesized by the ST method. Consequently, the catalytic results revealed that ST-CuFe2O4 catalyst exhibited excellent TCE removal (94.6%) in the persulfate (6 mM) (PS) process along with significant reusability. Moreover, scavenging test and EPR analysis validated the dominant role of SO4•− radicals for TCE removal in the PS/ST-CuFe2O4 system. Lastly, the TCE removal performance of ST-CuFe2O4 catalyst in real water matrix elucidated that PS/ST-CuFe2O4 system has promising potential and can practically be applied for remediation of TCE contaminated groundwater in ISCO practice. The ferrite synthesized by the ST method exhibited excellent catalytic performance among the three methods underlining the importance of preparation means in determining the catalytic potential of ferrite.

Enhanced trichloroethylene biodegradation: Roles of biochar-microbial collaboration beyond adsorption

Trichloroethylene (TCE) is a pollutant widely found in groundwater, especially in the heavily contaminated industrial sites. Biological dechlorination method is environmentally friendly and low-cost. However, microorganisms grow slowly and their activity is susceptible to environmental fluctuations. This study used biochar as an additive to promote anaerobic biodegradation of TCE with mixed culture. Results showed that biochar with dose of 0.1–0.4% (w/v) brought a rapid initial decrease of TCE concentration by 39.4–88.8% in 24 h via adsorption mechanism. Biochar produced at 500 °C pyrolysis temperature (BC500) achieved the highest TCE adsorption in comparison to BC300 and BC700. Subsequently, a significantly shortened microbial stagnation phase (from 85 h to 37 h) was observed in the system with the presence of biochar. During the exponential growth phase, BC700 outperformed BC300 and BC500 in terms of TCE degradation efficiency. Electrochemical analysis demonstrated that BC700 possessed the greatest electron transfer capability. Finally, biochar shortened the time for achieving 100% removal of TCE by 54.5–69.7% (from approximate 330 h to 100–150 h). Even at high concentration of TCE (20–30 mg·L−1) that could lead to serious microbial growth inhibition, the TCE degradation efficiency could be recovered in the presence of BC500. The high-throughput sequencing data revealed that biochar promoted the relative abundance of co-metabolizing dechlorinating microorganisms (Pseudomonas, Burkholderia) in the aqueous solution, and simultaneously led to the selective colonization of reductive dechlorinating microorganisms (Enterobacteriaceae, Clostridium) attached on biochar surface. On the other hand, biochar addition decreased the relative abundance of hydrogen-competing microorganisms, thereby forming an efficient co-metabolism-reductive dechlorination system. These findings allow a better understanding of the promotion mechanism of biochar for microbial dechlorination technology supporting the biochar-assisted bioremediation in practice.

Water quality assessment of East Kolkata Wetland with a special focus on bioremediation by nitrifying bacteria.

East Kolkata Wetlands (EKW) is designated as International Ramsar site and are the hotspot for large-scale wastewater aquaculture practices. However, the continued surveillance of physicochemical properties of water and application of an eco-friendly approach are essential to ensure safe aquaculture practices. In the present study, we assessed the seasonal variation in physicochemical parameters of water across EKW and investigated the role of nitrifying bacteria as probiotics. We statistically analyzed various physicochemical properties of water samples from EKW. Results of the statistical analysis indicated a significant variation in all the physicochemical parameters across the selected water bodies of EKW (p < 0.01). We isolated and enumerated Nitrosomonas sp. and Nitrobacter sp. and assessed their ability to degrade trichloroethylene (TCE). The role of Nitrosomonas sp. and Nitrobacter sp. were further investigated and established through a small-scale experiment. Two microbial isolates, NSW3 and NBW2, displayed superior TCE degradation ability at pH 5, and the application of these strains as probiotics were found to improve the quality of water and survival rate of fishes in the treated experimental tanks. Our findings suggest that the application of the above mixed bacterial cultures in aquaculture could be an effective and environment-friendly approach for safe and productive aquaculture operations.

Mechanism of contaminants degradation in aqueous solution by persulfate in different Fe(II)-based synergistic activation environments: Taking chlorinated organic compounds and benzene series as the targets

In this study, trichloroethene (TCE) removal was remarkably enhanced with the addition of Fe(II)/CA (citric acid), Fe(II)/nZVI (nano zero-valent iron) and Fe(II)/S-nZVI (sulfidated nano zero-valent iron), respectively, as synergistic activated catalysts in persulfate environment. Among them, the better performance of TCE removal followed the order of PS/Fe(II)/S-nZVI > PS/Fe(II)/nZVI > PS/Fe(II)/CA ≫ PS/Fe(II), and the majority of TCE was declorinated to Cl−. The scavenger and EPR tests indicated that HO and SO4− were responsible for TCE degradation. Further study was conducted through the calculation of reaction rate constants, demonstrating HO produced from SO4− was of greater significance than SO4− itself. With the presence of CA, the concentration of Fe(II) was maintained at a desired level to proceed the catalytic activity. Meanwhile, S-nZVI and nZVI had ability to convert Fe(III) to Fe(II), and sulfur species, especially S(-II) in S-nZVI acted as an reductant to a certain extent. Sufficient Fe(II) in solution activated PS to produce adequate HO for TCE degradation. Furthermore, the broad-spectrum reactivity in different systems were investigated, and the results indicated that most of the chloroalkenes and benzene series frequently detected in contaminated sites could also be removed at the desired chemicals ratio. In conclusion, this research revealed the superiority of synergistic activated catalysts and provided theoretical bases for the remediation of TCE and other pollutants in actual contaminated groundwater.

Degradation of trichloroethene by citric acid chelated Fe(II) catalyzing sodium percarbonate in the environment of sodium dodecyl sulfate aqueous solution

In this study, the common chlorinated solvent trichloroethene (TCE) was selected as the target contaminant. The aqueous solution after solubilization treatment (containing TCE and sodium dodecyl sulfate (SDS)) was used as the research object to carry out the remediation technology research of citric acid (CA) enhanced Fe(II) activation in sodium percarbonate (SPC) system. In 0.15 mM TCE and 1 critical micelle concentration (CMC) SDS solution, CA chelating Fe(II) activated SPC could effectively promote 93.2% degradation of TCE when the dosages of SPC, Fe(II) and CA were 3.0, 6.0 and 3.0 mM, respectively. SDS had a significant inhibitory effect on the degradation of TCE, and the surface tension changed after the reaction. The addition of CA greatly increased the generation of hydroxyl radicals (HO) in the system, while the removal of TCE was mainly attributed to HO, and the removed TCE was almost completely dechlorinated. The pH range from 3 to 7 could keep the TCE degradation above 80.0%. In the actual groundwater remediation, this technique could also efficiently degrade TCE (including SDS), showing a great application potential and development prospective in practice.

Enhanced trichloroethylene degradation in the presence of surfactant: Pivotal role of Fe(II)/nZVI catalytic synergy in persulfate system

Trichloroethylene (TCE) removal performance in non-ionic surfactant Tween-80 (TW-80) and anionic surfactant sodium dodecyl sulfate (SDS) involved solution by Fe(II) activated persulfate (PS) was investigated through the strengthening of nanoscale zero valent iron (nZVI). 99.5% removal of TCE could be obtained at the PS/Fe(II)/nZVI/TCE molar ratio of 8/4/4/1 with 1.0 critical micelle concentration (CMC) of TW-80 presence (13 mg L−1), while this value was slightly decreased to 88.3% at the molar ratio of 40/20/20/1 with 1.0 CMC of SDS presence (2.3 g L−1) in 180 min. The addition of nZVI significantly promoted TCE degradation, while TW-80 or SDS definitely inhibited TCE removal. Further, TCE removal declined with TW-80 or SDS concentration increasing from 0 to 10 CMC, and continuously decreased at 20 CMC of TW-80 but elevated TCE removal at 20 CMC of SDS. Tests of radical scavengers revealed that HO and SO4− contributed a major part while O2− had less contribution to TCE degradation in PS/Fe(II)/nZVI system. The dichlorination of TCE in PS/Fe(II)/nZVI system was 94.5% with TW-80 and 97.2% with SDS. In addition, TCE (with TW-80) removal was decreased with the initial pH increase from 3.0 to 11.0, while TCE (with SDS) degradation was always beyond 83% in the initial pH change from 3.0 to 11.0. Moreover, the effects of inorganic anions (Cl−, HCO3−) in the solution were evaluated. Experimental results using the actual groundwater revealed the excellent availability of PS/Fe(II)/nZVI system in remediating TCE contaminated field involved with TW-80 or SDS surfactants. In summary, these findings provide a new direction in remediating groundwater from contaminated sites polluted by chlorinated organic solvents after pretreatment by surfactant solubilization.

Ligand-Enhanced Electron Utilization for Trichloroethylene Degradation by ·OH during Sediment Oxygenation.

The potential of oxygenating Fe(II)-bearing sediments for hydroxyl radical (·OH) production and contaminant degradation has been proposed recently. Here, we further show that specific ligands can largely enhance contaminant degradation during sediment oxygenation due to increased utilization efficiency of sediment electrons. With the addition of 0-2 mM sodium ethylene diamine tetraacetate (EDTA) or sodium tripolyphosphate (TPP) in sediment suspension (50 g/L, pH 7.0), trichloroethylene (TCE, 15 μM) degradation increased from 13% without ligand to a maximum of 80% with 2 mM TPP and was much higher with TPP than EDTA because EDTA competes for ·OH. Electron utilization efficiency for ·OH production increased with increased ligand concentration and was enhanced by up to 6-7 times with 2 mM EDTA or TPP. Electron transfer from sediment to dissolved Fe(III)-ligand is mainly accountable for the enhanced electron utilization efficiency by the ligands with low adsorption affinity (i.e., EDTA), and additional variation of sediment surface Fe(II) coordination is mainly responsible for the enhancement by the ligands with high adsorption affinity (i.e., TPP). Output of this study provides guidance and optional strategies for enhancing contaminant degradation during sediment oxygenation.

Unveiling the catalytic ability of carbonaceous materials in Fenton-like reaction by controlled-release CaO2 nanoparticles for trichloroethylene degradation

Carbonaceous materials (CMs) have been applied extensively for enhancing the catalytic performance of environmental catalysts, however, the self-catalytic mechanism of CMs for groundwater remediation is rarely investigated. Herein, we unveiled the catalytic ability of various CMs via Fe(III) reduction through polyvinyl alcohol-coated calcium peroxide nanoparticles (PVA@nCP) for trichloroethylene (TCE) removal. Among selected CMs (graphite (G), biochar (BC) and activated carbon (AC)), BC and AC showed enhancement of TCE removal of 89% and 98% via both adsorption and catalytic degradation. BET and SEM analyses showed a higher adsorption capacity of AC (27.8%) than others. The generation of solution-Fe(II) and surface-Fe(II) revealed the reduction of Fe(III) on CMs-surface. The role of O-containing groups was investigated by the FTIR technique and XPS quantified the 52% and 57% surface-Fe(II) in BC and AC systems, respectively. EPR and quenching tests confirmed that both solution and surface-bound species (HO•, O2−• and 1O2) contributed to TCE degradation. Acidic pH condition encouraged TCE removal and the presence of HCO3− negatively affected TCE removal than other inorganic ions. Both schemes (PVA@nCP/Fe(III)/BC and PVA@nCP/Fe(III)/AC) exhibited promising results in the actual groundwater, surfactant-amended solution, and removal of other chlorinated-pollutants, opening a new direction towards green environmental remediation for prolonged benefits.

Continuous trichloroethylene biodegradation by Pseudomonas putida F1 in a biofilm reactor and determination of an optimal feeding path via a response surface model

AbstractReactor design and feeding strategies are the key to successful trichloroethylene (TCE) treatment via cometabolism. An easy to maintain and operate laboratory scale packed‐bed biofilm reactor, featuring recycled gas and liquid effluent streams, was developed for continuous aerobic aqueous‐phase TCE biodegradation using Pseudomonas putida F1 as the biocatalyst and toluene as the primary substrate. The impacts of the influent toluene and TCE concentrations, flow rates, and recycle rates on TCE biodegradation were studied. Multivariate factors, including influent toluene and TCE concentrations, their interactions, and flow rates were further analyzed via a response surface model (RSM). Results showed that such bioreactor design eliminated oxygen limitation and removed or substantially reduced toluene competitive inhibition on TCE degradation. A TCE removal efficiency of &gt;90% was achieved at an influent TCE concentration of ≤0.3 mg/L under an ˜8‐min mean hydraulic retention time. Toluene and TCE concentrations, in both linear and quadratic forms, were the most significant factors for TCE degradation, indicating both cell regenerating and inhibiting effects from toluene and a toxic effect from TCE. This RSM analysis has successfully identified an optimal influent toluene concentration path for each influent TCE concentration and provided insight for an extended TCE degradation at higher TCE concentrations.

Highly efficient degradation of trichloroethylene in groundwater based on persulfate activation by polyvinylpyrrolidone functionalized Fe/Cu bimetallic nanoparticles

Polyvinylpyrrolidone coated nano zero valent iron-copper (PVP-nZVI-Cu) bimetallic nanoparticles were successfully synthesized for dechlorination of trichloroethylene (TCE) into non-toxic byproducts in the presence of persulfate oxidant. The average size of PVP-nZVI-Cu nanoparticles (3–25 nm) was smaller than PVP-nZVI (25–60 nm) and nZVI (50–90 nm) particles due to PVP role in the prevention of iron aggregation and agglomerations. The synthesized PVP-nZVI-Cu nanoparticles were used as an efficient persulfate (PS) activator to generate reactive oxygen species (ROSs) for the degradation of TCE. The complete removal of TCE (99.6%) was achieved in the presence of 0.4 g/L of PVP-nZVI-Cu nanoparticles and 6 mM of persulfate oxidant at acidic pH (3.2) with 82.3% of TCE dechlorination and 84.4% of total organic carbon (TOC) removal within 1 h. Further, the catalytic activity of PVP-nZVI-Cu particles for TCE removal in the presence of four surfactants (TW-80, BRIJ-35, TX-100, and SDS) was also investigated, showing 99%, 83%, 65% and 70% removal of TCE, respectively. The intermediate products of TCE elucidated by GC-MS investigation, i.e., dichloroacetic acid, vinyle chloride, oxalic acid and glyoxylic acid, further transformed into chloride ions, carbon dioxide and water as environmentally friendly end products. The scavenging results revealed that both OH• and SO4•— radicals primarily contributed to TCE removal that was further confirmed with EPR analysis. Finally, the test of TCE removal in real groundwater validated that PS/PVP-nZVI-Cu system has significant potential and can be applied for remediation of TCE contaminated groundwater in in-situ practice.

Microbiome Reengineering by Heat Selection for Rapid Biodegradation of Trichloroethylene with Minimal Vinyl Chloride Formation

Trichloroethylene (TCE) was a widely used industrial solvent but is now regarded as a notorious groundwater contaminant. Both physicochemical and biological methods have been applied to remediate groundwater contaminated by TCE. For medium to low level of TCE contamination, bioremediation could be more cost-effective. However, bioremediation approaches suffer from slow degradation rates and accumulation of vinyl chloride (VC). In addition, bioaugmentation is often highly encouraged but may introduce foreign genes and increase the pace of microbial evolution. In this study, a microbiome reengineering strategy by heat selection is applied to solve these problems. Out of eight heat-treated mixed cultures, two showed a much-improved TCE degradation rate, more than 70 times higher than the untreated. The biodegradation half-life (t1/2) of TCE was 0.0627 d or shorter. No VC was detected by a gas chromatography equipped with flame ionization detector (GC-FID) and only a minimal amount by a GC-mass spectrometer (GC-MS). Ethene achieved a fairly good mass balance. Polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) and next-generation sequencing (NGS) results showed that the heating process did not kill most bacteria, but Dehalococcoides were either not present or very scarce. Acetoanaerobium and Methanosarcina could be the most important species in this reductive dechlorination process. Kinetic study results showed that the maximum specific TCE degradation rate was approximately 1,271 nmole/min/mg cell protein, which are two orders of magnitude higher than that of the mixed cultures reported in literature. These results suggest that apart from biostimulation and bioaugmentation, microbiome reengineering could be a promising approach for rapid bioremediation of TCE-contaminated aquifers.

Transition metal doping effect and high catalytic activity of CeO2–TiO2 for chlorinated VOCs degradation

A series of transition metals (Fe, Co, Ni, Cu, Cr and Mn)-doped CeO2–TiO2 catalysts were prepared by the sol–gel method and applied for the catalytic removal of 1,2-dichloroethane (DCE) as a model for chlorinated VOCs (CVOCs). The various characterization methods including X-ray diffraction (XRD), N2 adsorption–desorption, UV-Raman, NH3 temperature-programmed desorption (NH3-TPD) and H2 temperature-programmed reduction (H2-TPR) were utilized to investigate the physicochemical properties of the catalysts. The results show that doping Fe, Co, Ni or Mn can obviously promote the activity of CeO2–TiO2 mixed oxides for DCE degradation, which is related to their improved texture properties, acid sites (especially for strong acidity) and low-temperature reducibility. Particularly, CeTi–Fe doped with moderate Fe exhibits excellent activity for 1,2-dichloroethane (DCE) degradation, giving a T90% value as low as 250 °C. More importantly, only trace chlorinated byproducts were produced during the low-temperature degradation of various CVOCs (dichloromethane (DCM), trichloroethylene (TCE) and chlorobenzene (CB)) over CeTi–Fe1/9 catalyst with high durability.

Remediation of trichloroethylene by microscale zero-valent iron aged under various groundwater conditions: Removal mechanism and physicochemical transformation

Microscale zero-valent iron (mZVI) has been widely used for the in-situ groundwater remediation of various pollutants. However, the aging behavior of injected mZVI particles limits the widespread application in groundwater remediation projects. To assess the long-term reactivity of mZVI particles, the mechanism of trichloroethylene (TCE) degradation by various aged mZVI particles (A-mZVI) was determined by quantitatively evaluating the contributions of chemical reduction and adsorption. Further, this study investigated the physicochemical transformation of mZVI particles aged under various hydraulic conditions (static and dynamic), redox conditions (anoxic and aerobic) and aging durations (152 d and 455 d). The results show that the removal of TCE by different A-mZVI particles increased the sorption capacity in the initial period (0–6 h). However, in the long term, a significant inhibition of TCE removal was observed because of the decreased TCE reduction capacity caused by the hindrance of electron transfer, which was generated by corrosion precipitates. Furthermore, the characterization results demonstrated that despite the significant differences in the apparent morphology of the A-mZVI particles in various groundwater conditions, the final crystal corrosion products were mainly Fe3O4. Thus, the aging and inactivation of mZVI particles on TCE removal were promoted under the aerobic conditions. In addition, the structure of mZVI particles collapsed from the micro- to nanoscale under anaerobic dynamic over 455 d. No substantial impact on the final TCE removal was observed for the A-mZVI particles prepared under various hydraulic conditions and aging times. These findings provide insights regarding the impact mechanisms of corrosion precipitates on the removal of target contaminant and provide implications for long-term mZVI application under various target aquifer conditions.