Remediation Of Trichloroethylene Research Articles

Comparison of trichloroethylene dechlorination in seawater by sulfidated nanoscale zero-valent iron particles prepared by two methods

Sulfidated nanoscale zero-valent iron (S-nZVI) particles have demonstrated great potential in the remediation of trichloroethylene (TCE) due to their high reactivity and electron selectivity. However, very few studies have been carried out to investigate their application in salinity water or seawater. In this work, two kinds of S-nZVI particles were prepared through different methods including the chemical reduction method (CH-S-nZVI) and the bioprecipitation method (BP-S-nZVI), and then their performances in TCE remediation in seawater environment were thoroughly compared. The results suggested that the TCE removal by CH-S-nZVI particles in seawater is reduced compared to that in fresh water. However, the difference is negligible for BP-S-nZVI particles. It indicates that the seawater has a relatively strong inhibitory effect on the TCE degradation by CH-S-nZVI, but the inhibition for BP-S-nZVI is very weak. Furthermore, this work verified that sodium chloride and organic matters have obvious inhibitory effects on the TCE dichlorination, while coexisting ions such as NO3-, SO42- and Mg2+ are helpful to the degradation of TCE. The research proved that the performance of BP-S-nZVI particles in seawater is superior to CH-S-nZVI particles, providing a suitable candidate for the treatment of polluted aquifers in coastal and near-shore areas.

Theoretical and Experimental Adsorption of Silica Gel and Activated Carbon onto Chlorinated Organic Compounds in Water: A Case Study on the Remediation Assessment of a Contaminated Groundwater Site

Chlorinated organic compounds (COCs) are a serious threat to human health and the ecological environment due to their toxicity, mutagenicity and carcinogenicity. A number of corresponding treatment techniques have been developed thus far; among these techniques, adsorption is considered an efficient and low-cost method. However, it is very important to find suitable and economical adsorbent types and usage amounts. In this study, the adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) onto two different adsorbents (silica gel and activated carbon) was investigated, and the obtained adsorption constants were then introduced into Langmuir and Freundlich adsorption models. The adsorption isotherm constants of these two models were used to predict the adsorbate removal efficiency and the required adsorbent mass. The results showed that the Langmuir and Freundlich models predicted the removal efficiency and adsorbent quality of the TCE and PCE adsorbed onto silica gel and activated carbon, and the errors were less than 10% compared with the measured values obtained through adsorption experiments. According to the differences in adsorption efficiency and cost between silica gel and activated carbon, it was found that, when the adsorption efficiency of the silica gel for TCE and PCE significantly decreased, adding activated carbon to continue the adsorption effectively reduced the adsorption cost of on-site remediation. This result was demonstrated by taking the Radio Corporation of America (RCA) pollution incident in Taiwan as an example, and it was estimated that 6427 ± 172 tons and 343 ± 21 tons of silica gel and activated carbon, respectively, would be required for the on-site remediation of TCE, and the total cost would be approximately 4,390,000 USD. The remediation of PCE would require 7553 ± 57 tons of silica gel and 350 ± 68 tons of activated carbon, with a total cost of approximately 5,030,000 USD. Therefore, silica gel should be used to reduce the pollutant concentration first, and then activated carbon should be added for continuing adsorption. This method of adding adsorbents is economical and can effectively reduce the adsorption cost.

Trichloroethylene remediation using zero-valent iron with kaolin clay, activated carbon and bacteria

Nanoscale particles of zero-valent iron were used to form a permeable reactive barrier whose performance in dechlorinating a solution of trichloroethylene was compared with that of a barrier formed from limestone. The iron was combined with kaolin by calcination. The test liquid contained sewage sludge, and also added NH4Cl and KH2PO4. The average removal rates of trichloroethylene and phosphorus over 365 days both exceeded 94%. Chemical oxygen demand was reduced by 92% and ammonium nitrogen by 43.6%. All were significantly greater than the removals with the limestone barrier. The ceramsite barrier retained 85% of its effectiveness even after 365 days of use. Dechloromonas sp. was the main dechlorinating bacterium, but its removal ability is limited. The removal of trichloroethylene in such a barrier mainly depends on reduction by the zero-valent iron and biodegradation. The results show that the prepared ceramsite is stable and effective in removing trichloroethylene from water. It is a promising in-situ remediation material for groundwater.

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.

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.

Poplar wood and tea biochars for trichloroethylene remediation in pure water and contaminated groundwater

Four biochars from pyrolysis of poplar wood (biochar P) and tea (biochar T) at 450 and 750 °C have been tested in a first time as adsorbents for trichloroethylene (TCE) removal in groundwater. The physico-chemical properties of biochars were systematically investigated with organic elemental analyser, scanning electron microscopy, N2 adsorption measurement, IR spectroscopy and X-ray photoelectron microscopy. Three kinetic models were used to follow the TCE removal by biochars. The best kinetic performances were obtained with biochars P with the smallest particle size diameter (50 – 100 µm) due to their porosity and the mass transfer limitation for the TCE remediation. Remediation of a real sample of groundwater polluted by chlorinated organic compounds showed that biochar P produced at 750 °C is more efficient to remove vinyl chloride (65% adsorbed) than commercial activated carbon powder (40%). The TCE sorption capacity is similar in pure water and in polluted groundwater. The results also highlighted better retention capacity for the most substituted molecules (tri and tetrachloroethylene) for biochar P750.

Advancement in Fenton-like reactions using PVA coated calcium peroxide/FeS system: Pivotal role of sulfide ion in regenerating the Fe(II) ions and improving trichloroethylene degradation

This study demonstrated the prolonged benefits of polyvinyl-coated calcium peroxide (PVA@CP) in Fe(II)/nFeS mediated Fenton-like reaction. PVA@CP was prepared by a coating of PVA on calcium peroxide (CP) and synthesized nano-sized iron sulfide (nFeS) was characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) with energy dispersive spectroscopy (EDS) elemental mapping, X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), inductively coupled plasma optical emission spectroscopy (ICP-OES) and Fourier transmission infrared (FTIR) techniques. Trichloroethylene (TCE) degradation in various oxic environments (H2O2, CP, or PVA@CP) was investigated using Fe(II)/nFeS, and the slowest rate constant of 0.031 M−1 min−1 with 91 % TCE removal highlighted the long-lasting effects of PVA@CP. The effect of initial solution pH revealed that the acidic condition was most favorable. PVA@CP system accumulated the least amount (6.34 mg/L) of Fe(III) than H2O2 and CP systems. Electron paramagnetic resonance (EPR) and scavenging tests highlighted that free hydroxyl radicals (HOfree) contributed dominantly in H2O2 system while both free and surface-bound species participated well in CP and PVA@CP systems. Moreover, the insight mechanism of regenerated Fe(II) on the nFeS surface was explored by XPS. Both oxidation and reduction of sulfur were discussed and declared that S(-II) was responsible for regenerating Fe(II). The recycling sample checked the reusability of nFeS, and 98.8 % TCE removal in actual groundwater emphasized that PVA@CP/Fe(II)/nFeS is a viable technique. In conclusion, the PVA@CP/Fe(II)/nFeS system is highly recommended for long-lasting remediation of TCE contaminated groundwater.

Trichloroethylene degradation by PVA-coated calcium peroxide nanoparticles in Fe(II)-based catalytic systems: enhanced performance by citric acid and nanoscale iron sulfide.

In this study, the enhanced trichloroethylene (TCE) degradation performance was investigated by polyvinyl alcohol coated calcium peroxide nanoparticles (PVA@nCP) as an oxidant in Fe(II)-based catalytic systems. The nanoscale iron sulfide (nFeS), having an average particle size of 115.4 nm, was synthesized in the laboratory and characterized by SEM, TEM, HR-TEM along with EDS elemental mapping, XRD, FTIR, ICP-OES, and XPS techniques. In only ferrous iron catalyzed system (PVA@nCP/Fe(II)), TCE degradation was recorded at 58.9% in 6 h. In comparison, this value was increased to 97.5% or 99.7% with the addition of citric acid (CA) or nFeS in PVA@nCP/Fe(II) system, respectively. A comparative study was performed with optimum usages of chemical reagents in both PVA@nCP/Fe(II)/CA and PVA@nCP/Fe(II)/nFeS systems. Further, the probe compounds tests and electron paramagnetic resonance (EPR) analysis confirmed the generation of reactive oxygen species. The scavenging experiments elucidated the dominant role of HO• to TCE degradation, particularly in PVA@nCP/Fe(II)/nFeS system. Both CA and nFeS strengthened PVA@nCP/Fe(II) system, but displayed completely different mechanisms in the enhancement of active radicals generation; hence, their different contribution to TCE degradation. The acidic environment was favorable for TCE degradation, and a high concentration of HCO3- inhibited TCE removal in both systems. Conclusively, compared to PVA@nCP/Fe(II)/nFeS system, PVA@nCP/Fe(II)/CA system resulted in encouraging TCE degradation outcomes in actual groundwater, showing great potential for prolonged benefits in the remediation of TCE polluted groundwater. Graphical abstract.

Trichloroethylene degradation performance in aqueous solution by Fe(II) activated sodium percarbonate in the presence of surfactant sodium dodecyl sulfate.

The performance of trichloroethylene (TCE) degradation by sodium percarbonate (SPC) activated with Fe(II) in the presence of 3.0g/L sodium dodecyl sulfate (SDS) as well as the role of SDS in the SPC/Fe(II) system was investigated since SDS is a common surfactant used in groundwater remediation for improving TCE dissolution to the aqueous phase. The results showed that though the introduction of SDS could inhibit the TCE degradation, the inhibiting effect was less with the increasing SDS dose. In the presence of SDS, TCE could be completely removed with the SPC/Fe(II)/TCE molar ratio of 40/80/1. Experiments with free radical probe compounds and radical scavengers elucidated that TCE was mainly oxidized by both HO· and . A weakly acidic environment was more favorable to TCE degradation. Nevertheless, at a high concentration had a strongly inhibitive effect on the TCE degradation but the influence of Cl- was negligible. Finally, the excellent TCE degradation achieved in actual groundwater demonstrated that Fe(II) activated SPC technique was applicable in the remediation of TCE contaminated groundwater in the presence of SDS. PRACTITIONER POINTS: The effects of SDS were evaluated SPC/Fe(II)/SDS system applied to remediate TCE The mechanism of HO· and generation had been investigated Cl- and affected TCE degradation at different levels The performance of TCE removal in actual groundwater had been studied.

Using adaptive management to guide multiple partners in TCE remediation using a permeable reactive barrier

The US Department of Agriculture-Agricultural Research Service (USDA-ARS) worked together with the University of Maryland, College Park and BMT Designers and Planners (Consultant) to design a biowall to remediate the groundwater of a Superfund site located in Beltsville, MD. The US Environmental Protection Agency (US EPA) oversaw the remediation plan as per the regulations of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) program. A hybrid adaptive management strategy was employed to to guarantee the use of a science-based approach to the remediation efforts, to ensure that new information could be incorporated into the remediation plan, and to avoid the shortcomings of other remediation efforts elsewhere. Laboratory experiments and a historic-data assessment were conducted in conjunction with the monitoring plan to provide the Consultant and USDA with comprehensive feedback, to strengthen and to modify the monitoring and biowall construction plans as the requirements of the site changed. This feedback mechanism was repeated multiple times to make certain that the highest quality and most effective methods were used. The scope of the project also grew to include investigations of the soil microbial community for future structural biostimulation and bioaugmentation activities. While the biowall has reduced the concentration of trichloroethylene (TCE) to levels at or below its Maximum Contaminant Level, work is on-going to improve the functionality of the biowall and to address emerging challenges.

Arsenic Release and Attenuation Processes in a Groundwater Aquifer During Anaerobic Remediation of TCE with Biostimulation

AbstractArsenic in groundwater in excess of the drinking water limit is usually from natural sources. The release of As, however, can be amplified by anthropogenic inputs of carbon, including those associated with the remediation of chlorinated solvents such as trichloroethylene (TCE). Large laboratory columns (15.2 cm diameter, 183 cm long) packed with aquifer solids from a TCE contaminated site near Hill Air Force Base (Utah) were fed with groundwater containing TCE and were biostimulated, bioaugmented, and monitored for TCE dechlorination over 7.5 years. This is a basin‐fill aquifer with As bearing geologic features. The objective of this study was to evaluate the biogeochemical changes that affect As solubilization that occurred after 7.5 years of feeding the columns with either whey or two formulations of Newman Zone® emulsified oil, and a no carbon addition control. The columns were analyzed in 10.16 cm sections for pore water and sediment quality parameters, parameters descriptive of redox conditions, and As geochemistry. The whey treatment resulted in 52.9% (±1.36%) (average ± standard deviation) of the total As in the solids leaching from the columns. The oil treatments promoted loss of 20.9% (±6.40%) of the total As. Arsenic solubility was associated with strongly reducing conditions developed with whey addition, leading to dissolution of crystalline Fe oxides and release of As. Arsenic was attenuated within the oil treated columns with As associated with carbonates in the lower layers. A consequence of adding whey, resulting in the desired full dechlorination of TCE in this aquifer, is the mobilization of As in groundwater.

Application of molecular biological tools for monitoring efficiency of trichloroethylene remediation

Trichloroethylene (TCE) is one of the most ubiquitous halogenated organic compounds of concerns of carcinogens in groundwater in Taiwan. Bioremediation has been recognized as a cost-effective approach in reducing TCE concentration. Five pilot-scale wells were constructed to monitor TCE concentrations in contaminated groundwater. With injection of EOS®, TCE was effectively degraded to 42%–93% by the end of 175 days. The biostimulation with EOS® was useful in establishing a micro-site anaerobic but with limited contribution. Dilution of the aquifer movement also caused the TCE reduction among injection and monitoring wells. The degradability was affected by the location and the proximity from the injection well. TCE concentrations found to be negatively correlated with the associated Dehalococcoides spp. and functional genes levels. Dhc concentration of 108 copies L−1 caused the initial 40% of TCE degradation. The well with the optimal degradation owned tceA of 109 cells L−1. T-RFLP results indicate the wells with the superior TCE degradability also performed the highest Shannon index number (means the highest diversity), which occurred on the same day that Dhc levels started to enlarge. Desulfovibrio desulfuricans and Desulfuromonas chloroethenica were predominant species identified in the T-RFLP fingerprint profile. In brief, a variety of different factors including well locations, geochemical indicators, and microbial contribution were useful to explain the site-specific optimal TCE remediation approach. The consistence among TCE degradation, Dhc growing pattern, functional gene levels, and the dynamics of the microbial community structure present the novelty of this study.

Degradation of trichloroethylene in aqueous solution by nanoscale calcium peroxide in the Fe(II)-based catalytic environments

In this study, nCaO2 was synthesized successfully and applied in the Fe(II)-based catalytic environments in investigating trichloroethylene (TCE) removal performance. nCaO2 with the particle sizes in the range of 50–200 nm was prepared, and it performed better for TCE removal when compared to the conventional CaO2. Further experimental results showed that 70.4% of TCE could be removed in 180 min at the nCaO2/Fe(II)/TCE molar ratio of 1/2/1, while this data was elevated to 86.1% in the presence of citric acid (CA) at the nCaO2/Fe(II)/CA/TCE molar ratio of 1/2/2/1 in the same test period. Probe compound tests, specifically designed for free radicals confirmation, demonstrated the presence of HO and O2−. Moreover, scavenging tests indicated that HO was the major radical responsible for TCE degradation but O2− promoted the removal of TCE in both nCaO2/Fe(II) and nCaO2/Fe(II)-CA system. In addition, the effects of initial solution pH and anions (Cl−, HCO3−) were also evaluated. The performance of TCE degradation in actual groundwater demonstrated that both nCaO2/Fe(II) and nCaO2/Fe(II)-CA systems can be applicable for TCE removal in ISCO practice and the nCaO2/Fe(II)-CA system is much promising technique. These fundamental data strongly confirmed the feasibility and potential of nCaO2 based technique in the remediation of TCE contaminated groundwater.

Trichloroethylene solubilization using a series of commercial biodegradable ethoxylated fatty alcohol surfactants

AbstractBACKGROUNDAlthough certain pollutants are prohibited or heavily regulated, particularly in Europe and the USA, contaminated sites still represent a serious threat to the environment and health. The physical and chemical properties of ‘dense non‐aqueous phase liquid’ (DNAPL) pollutants such as trichloroethylene (TCE), including their low solubility, high specific density and tendency to remain adsorbed to organic materials, make their removal from polluted sites extremely difficult.RESULTSThis study tested the ability of a series of commercial fatty alcohol ethoxylated surfactants of CiEj type (i = number of carbons in the alkyl chain; j = number of ethylene oxide (EO) units), known to be biodegradable and low‐cost, to improve the solubility of TCE in water; this would make its removal from contaminated sites more effective. The solubility of TCE in Synperonic™ 91/5 (C10E5), 91/6 (C10E6), 91/8 (C10E8), 91/10 (C10E10) and 13/8 (C13E8) aqueous solutions was evaluated and the solubilization performances were reported as molar and weight solubilization ratios (MSR and WSR). Solubility was measured above the critical micelle concentration (CMC) up to 0.7 mol L−1 at 5, 20 and 30 °C to assess the feasibility of the approach for TCE removal from sites located in different climatic areas. Increasing EO units contributed to improved TCE solubility (at constant alkyl chain length).CONCLUSIONThe best surfactant was Synperonic™ 91/10 with an MSR of 3.54 at 19 °C. The results show that an optimal combination of EO units and alkyl chain length, and not only the hydrophilic–lipophilic balance (HLB) value, is key for the design of effective TCE remediation systems from groundwater. © 2019 Society of Chemical Industry

Actively facilitated permeable reactive barrier for remediation of TCE from a low permeability aquifer: Field application

Proven in situ treatment and remediation approaches are limited for low-permeability aquifers materials, particularly because of limitations to the delivery of reactive chemicals or access to contaminated plumes. In this paper, we describe the development of a cutting-edge solution for the remediation of contaminated groundwater in a low-permeability and low water-bearing aquifer contaminated with the chlorinated hydrocarbon trichloroethylene (TCE). The remediation technique introduced coupling of large-diameter permeable reactive barrier wells (PRB wells) with: (1) extraction wells through in a highly impacted plume; and (2) re-injection wells at the fringe of the plume. A pump-and-treat system (PTS) was employed at the site in a separate plume to reduce the mass of TCE near the second source zone. This research focuses only on the large diameter PRB well system. Conceptual site model development, design considerations, implementation and performance evaluation demonstrated how each of these elements were applied in the field. Approaches for coupling technologies to increase technical and economic feasibility are presented. Extraction and reinjection wells of treated groundwater at the fringe of the plume promoted a positive hydraulic gradient, facilitated groundwater transport through the reactive media, and contained the plume. Detailed geospatial and statistical analysis with over 10 years’ monitoring data showed that dissolved TCE plume delineation shrank, and still concentration continues to decline, and were projected to meet the demands of remediation compliance regulations in the next few years. The results of this study indicate that significant remediation was achieved despite the challenging hydraulic conditions of the aquifer. The developed the remediation technology and conclusions indicate the system’s usefulness at other sites.

Enhanced solubility of trichloroethylene (TCE) by a poly-oxyethylene alcohol as green surfactant

Abstract In this paper we tested a commercially available synthetic fatty alcohol ethoxylated surfactant (synperonic 91/5, SYN), known to be a low-impact and biodegradable green surfactant, to improve the aqueous solubility of trichloroethylene (TCE). The alcohol is a non-ionic surfactant that easily forms O/W emulsions and it can emulsify several oils, waxes and solvents and it is also used as a wetting agent in a wide variety of applications, its biocompatibility and biodegradability have been tested in several conditions both in pharmaceutical and environmental fields. We measured the critical micelle concentration of the surfactant by means of the pyrene method; the dissolution of TCE into water solutions at increasing [SYN] was investigated by means of UV–VIS technique and the solubilization performances were evaluated in terms of WSR (Weight Solubilization Ratio) and MSR (Molar Solubilization Ratio). Finally, the dependence of TCE solubility upon temperature variation was also assessed. In the microemulsion regime the solubility of TCE was found to increase up to fifteen times with respect to pure water at 20° C, corresponding to a MSR of about 0.21. The MSR was found to increase at lower temperatures up to 0.24 at 4° C. Synperonic can thus be applied for TCE remediation from soils and groundwaters by taking advantage of techniques such as pump and treat and enhanced surfactant flushing.

Degradation of TCE, PCE, and 1,2–DCE DNAPLs in contaminated groundwater using polyethylenimine-modified zero-valent iron nanoparticles

Remediation of dense non-aqueous phase liquid (DNAPL), which consists primarily of chlorinated solvents, is considered a top priority in the field of groundwater decontamination. Downward migration of DNAPL can lead to formation of impermeable strata due to low solubility and high density. Remediation is therefore one of the most complex technical challenges faced by environmental engineers. In the present work, remediation of trichloroethylene (TCE), perchloroethene (PCE), and 1,2-dichloroethene (1,2-DCE) DNAPL-contaminated groundwater was studied by a reductive reaction with polyethylenimine (PEI) surface-modified zero-valent iron nanoparticles (PEI–nZVI). Compared with fresh nZVI, PEI–nZVI exhibited smaller spherical particles of 20–80 nm and a greater surface area of 53.4 m2/g. Furthermore, slow desorption of the PEI indicated its potential application as a protective shell layer for efficient delivery of active nZVI to the water/DNAPL interface. Laboratory batch remediation results indicate that both nZVI and PEI–nZVI can remove 99% of TCE, PCE, and 1,2-DCE. The rate of reaction for fresh nZVI was higher in the early stage. Comparatively, PEI–nZVI had a higher removal rate and efficiency after 2 h. The kinetic studies also revealed that the removal rate for 1,2-DCE was greater than that for TCE and PCE. Additionally, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy studies indicated that the nZVI and PEI–nZVI have two central Fe atoms coordinated by primarily FeO and FeFe with bond distances of 1.87 Å and 3.05 Å, respectively. Furthermore, after the reductive reaction, nZVI and PEI–nZVI were oxidized to Fe3O4, and bond distance values for the reacted samples were 1.94 Å and 1.96 Å, respectively.

Wheat straw biochar-supported nanoscale zerovalent iron for removal of trichloroethylene from groundwater.

This study synthesized the wheat straw biochar-supported nanoscale zerovalent iron (BC-nZVI) via in-situ reduction with NaBH4 and biochar pyrolyzed at 600°C. Wheat straw biochar, as a carrier, significantly enhanced the removal of trichloroethylene (TCE) by nZVI. The pseudo-first-order rate constant of TCE removal by BC-nZVI (1.079 h−1) within 260 min was 1.4 times higher and 539.5 times higher than that of biochar and nZVI, respectively. TCE was 79% dechlorinated by BC-nZVI within 15 h, but only 11% dechlorinated by unsupported nZVI, and no TCE dechlorination occurred with unmodified biochar. Weakly acidic solution (pH 5.7–6.8) significantly enhanced the dechlorination of TCE. Chloride enhanced the removal of TCE, while SO42−, HCO3− and NO3− all inhibited it. Humic acid (HA) inhibited BC-nZVI reactivity, but the inhibition decreased slightly as the concentration of HA increased from 40 mg∙L-1 to 80 mg∙L-1, which was due to the electron shutting by HA aggregates. Results suggest that BC-nZVI was promising for remediation of TCE contaminated groundwater.

Idaho National Laboratory Test Area North: Application of Endpoints to Guide Adaptive Remediation at a Complex Site

Complex sites in the subsurface are defined as those with difficult access, deep, and/or thick zones of contamination, large areal extent, heterogeneities that limit the effectiveness of remediation, or where long-term remedies are needed to address contamination (e.g., because of long-term sources or large extent). The Test Area North at the Idaho National Laboratory, developed for nuclear fuel operations and heavy metal manufacturing, is a complex site that demonstrates the endpoints strategy for adaptive remediation. Liquid wastes and sludge from experimental facilities were disposed in an injection well, which contaminated the subsurface aquifer located deep within fractured basalt. The mixed wastes included organic, inorganic, and low-level radioactive constituents, with the focus of this study on the remediation of trichloroethylene within a systems-based, regulatory framework. The framework facilitates site, regulator, and stakeholder interactions during the remedial planning and implementation process by using a conceptual model description as a technical foundation for decisions identifying endpoints. Endpoints are defined as interim remediation targets or decision points on the path to an ultimate end, and maintaining protectiveness during the remediation process. Results demonstrate that the three-component remedy used at Test Area North as an example of the structured framework is largely functioning as intended and is projected to meet remedial action objectives by 2095. The remedy approach is being adjusted as new data become available. The framework provides a structured process for evaluating and adjusting the remediation approach, allowing site owners, regulators, and stakeholders to manage contamination at complex sites where adaptive remedies are needed. ©2016 Wiley Periodicals, Inc.

Remediation of trichloroethylene by xanthan gum-coated microscale zero valent iron (XG-mZVI) in groundwater: Effects of geochemical constituents

Xanthan gum-coated microscale zero valent iron (XG-mZVI) is potentially an inexpensive and effective material to promote the degradation of environmental contaminants. The effects of geochemical constituents (humic acid (HA), Ca2+/Mg2+-HCO3-,Na+-Cl-) on trichloroethylene (TCE) removal using XG-mZVI were investigated using batch experiments to evaluate the potential performance of XG-mZVI in field treatments. TCE was removed from groundwater by adsorption and chemical reduction. In the co-presence of geochemical constituents, TCE adsorption was not significantly impacted, while its reduction rate was increased by the presence of HA (5–20mgL−1), inhibited with increasing Ca(HCO3)2 and Mg(HCO3)2 concentrations (0.4–2mM) and unaffected by NaCl in the range of 10–100mM. The promotional effect of HA on TCE reduction was primarily due to the Fe-humate complexes in solution that delayed the formation of passivated precipitates. However, the presence of Ca(HCO3)2 and Mg(HCO3)2 exerted an opposite effect on TCE reduction by facilitating the formation of passivated precipitates, such as green iron rust. These findings provide insight into the impact mechanism of XG-mZVI reactivity by organic and inorganic geochemical constituents with particular implications for the XG-mZVI degradation of TCE in real groundwater.