Search

A fungal biotrickling filter (BTF) was employed to treat trichloroethylene (TCE) gas under different magnetic field intensities (MFIs). When the TCE inlet concentrations were approximately 370, 500–900, and 1000 mg/m 3 , the removal performances followed the order: MFI 20.0 mT > MFI 60.0 mT > MFI 80.0 mT > MFI 0 mT. In particular, at a TCE inlet concentration of 1000 mg/m 3 , MFI 20.0 mT was significantly better than MFI 0 mT performance. The corresponding removal efficiencies and maximum elimination capacities were 52.9%, 4854.1 mg/m 3  h and 39.4%, 3594.8 mg/m 3  h, respectively. BTF was shut down completely for 7 days and rapidly recovered in 6–10 days. High-throughput sequencing indicated that MF significantly affected the fungal community and significantly improved the relative abundance of the phylum Ascomycota , achieving the highest abundance of Ascomycota at MFI 20.0 . These results indicated that a lower MFI can efficiently improve TCE removal performance in a fungal BTF. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) is a promising support for electrochemical and environmental applications. However, the role of rGO in dechlorination of chlorinated hydrocarbon by zerovalent iron-based nanoparticles remains unclear. Herein, the rGO-supported bimetallic Fe/Ni nanocomposites were fabricated by chemical reduction method and the microstructures as well as the electrochemical properties of rGO/Fe/Ni, were investigated to elucidate the dechlorination behaviors of trichloroethylene (TCE) under various environmental conditions. Results show that the 10–60 nm Fe/Ni nanoparticles with average particle size of 32 nm are homogeneously dispersed onto the rGO surface. The rGO/Fe/Ni exhibits excellent dechlorination efficiency and rate of TCE is 2.4 times higher than that of free Fe/Ni nanoparticles. Cyclic voltammetric curves and electrochemical impedance spectra indicate that the superior dechlorination activity is attributed to the strong interaction between Fe/Ni and rGO, low internal resistance and rapid diffusion rate of electrons and ions. In addition, the capacitive behavior of rGO can store and transfer 2.7–3.4 electrons produced from Fe 0 to the adsorbed TCE more readily, and then converts TCE to non-toxic ethane via hydrodechlorination in the presence of Ni nanoparticles. The rGO/Fe/Ni can be recycled for at least 8 times to effective dechlorinate TCE. Moreover, the reaction rate of TCE dechlorination can be enhanced 1.26–1.49 times when 5–10 mg L −1 humic acid are added. Results obtained in this study have clearly unveiled the role of rGO in hydrodechlorination of TCE and can provide a new insight into the development of rGO−supported bimetallic Fe/Ni nanoparticles for the enhanced removal of chlorinated pollutants in water and wastewater treatment. [ABSTRACT FROM AUTHOR]

Active species including hydroxyl (HO ) and sulfate radicals (SO 4 − ) play important roles in contaminant degradation during the persulfate based in-situ chemical oxidation (ISCO) process. The generation and contribution of active species are critical and can potentially be evaluated using compound specific isotope analysis (CSIA). However, the evaluation of stable isotope fractionation (or isotope enrichment factor ε values) for contaminants degraded by individual active species of concern is required but lacking. This study firstly determined the carbon isotope fractionation of trichloroethene (TCE) degradation by SO 4 · − with chemical probe methods to obtain ε values from −6.4 ± 0.7 to −6.9 ± 0.5‰. The ε values were significantly different from those reported for TCE degradation by HO , which could be used to identify the competing TCE degradation by HO and SO 4 − . Relying on the observed ε values and the extended Rayleigh-type equation, the contributions of SO 4 − and HO to TCE degradation were evaluated in persulfate activated by Fe 0 or Fe(II). This study provides an illuminating idea to determine stable isotope fractionation for contaminant degradation by individual active species, which is crucial for the application of CSIA in relevant environments. [ABSTRACT FROM AUTHOR]

Zerovalent iron (ZVI) based technology has been applied to remediate contaminated groundwater and has been paid great attention as an economic alternative. But it is still remains highly challenging to remove chlorinated pollutants such as trichloroethylene (TCE) with ZVI. Low molecular weight carboxylic ligands (formic acid (FA), oxalic acid (OA), and citric acid (CA)) were chosen to study the influence on the performance of ZVI in groundwater, including the morphology of Fe surface and the Fe dissolution. The removal rate of TCE with ZVI in the presence of 30 mM carboxylic groups followed an order of FA > OA > pure water ≅ CA. FA provides protons to promote the surface corrosion and generated more magnetite on the ZVI surface, which was further responsible for a high adsorption of TCE. With the strong complexing ability of OA and CA, passive layers could form dissoluble complexes via a ligand-promoted dissolution process. However, high concentration of OA resulted in Fe oxalate reprecipitated back onto the ZVI surface then inhibited the reactivity of ZVI. The Fe-ligand complexes also have ability to transform TCE depending on their redox properties. It is expected that effectiveness of carboxylic ligands on the ZVI: those low molecular weight carboxylic ligands in groundwater and soil may enhance the reaction efficiency of ZVI by altering the surface characteristics of ZVI. Therefore, the carboxylic ligands could increase the reactivity and the longevity of ZVI. [ABSTRACT FROM AUTHOR]

The article discusses the detection and mitigation of vapor intrusion from beneath buildings. Topics include the role of soil contamination with chlorinated solvents such as trichloroethylene (TCE) and tetrachloroethylene (perchloroethylene or perc) in vapor intrusion, the use of air purifiers and vapor intrusion mitigation systems, and the roles of sewers and groundwater in vapor intrusion.

The degradation of trichloroethylene (TCE) by ferrate generated from electrochemical synthesis has been studied. The degradation efficiency of TCE in aqueous solution was observed at various pH (3, 7, 11), ferrate dosages (5, 8, 11, 13, 15 and 17 mg/L), and temperature (10, 25, 35 and 50°C). The experimental results showed that TCE removal efficiency increased with an increase in ferrate dosages. For the effect of pH, the highest value ofkapp, 893.54 M−1s−1, was observed at pH 7. The TCE degradation pathways have been proposed based on the intermediate products such as ethyl chloride, dichloroethylene, chloroform, 1,1-dichloropropene, trichloroacetic acid and trichloroethane, and Cl−was identified as an end product. [ABSTRACT FROM PUBLISHER]

The objective of this field-scale study was to evaluate the effectiveness of controlling trichloroethylene (TCE) plume migration using the polycolloid substrate (PS) biobarrier. The developed PS (containing soybean oil, lactate and surfactants) could release substrate to enhance the TCE dechlorination. In this study, a biobarrier comprising PS injection wells was installed. Injection wells were installed at 5-m intervals, and approximately 15 L of PS was injected into each well. Results show that TCE concentrations in the injection wells dropped from an average of 87 μg/L to below 1 μg/L after 35 days of PS injection. The total organic carbon concentrations in the injection wells increased from an average of 2.1-543 mg/L after 30 days of PS injection. The dissolved oxygen (DO) concentrations and oxidation-reduction potential (ORP) values dropped from an average of 1.6 mg/L to below 0.1 mg/L and from 124 mv to -14 mv after 20 days of injection, respectively. The DO and ORP remained in anaerobic conditions during the remaining 100 days of the operational period. TCE degradation by-products were observed in groundwater samples during the operational period. This reveals that the addition of PS could effectively enhance the reductive dechlorinating of TCE. [ABSTRACT FROM AUTHOR]

Nano-zerovalent iron (nZVI) formed under sulfidic conditions results in a biphasic material (Fe/FeS) that reduces trichloroethene (TCE) more rapidly than nZVI associated only with iron oxides (Fe/FeO). Exposing Fe/FeS to dissolved metals (Pd2+, Cu2+, Ni2+, Co2+, and Mn2+) results in their sequestration by coprecipitation as dopants into FeS and FeO and/or by electroless precipitation as zerovalent metals that are hydrogenation catalysts. Using TCE reduction rates to probe the effect of metal amendments on the reactivity of Fe/FeS, it was found that Mn2+ and Cu2+ decreased TCE reduction rates, while Pd2+, Co2+, and Ni2+ increased them. Electrochemical characterization of metal-amended Fe/FeS showed that aging caused passivation by growth of FeO and FeS phases and poisoning of catalytic metal deposits by sulfide. Correlation of rate constants for TCE reduction (kabs) with electrochemical parameters (corrosion potentials and currents, Tafel slopes, and polarization resistance) and descriptors of hydrogen activation by metals (exchange current density for hydrogen reduction and enthalpy of solution into metals) showed the controlling process changed with aging. For fresh Fe/FeS, kobs was best described by the exchange current density for activation of hydrogen, whereas kobs for aged Fe/FeS correlated with electrochemical descriptors of electron transfer. [ABSTRACT FROM AUTHOR]

We constructed a multispecies biofilm model for simultaneous reduction of trichloroethene (TCE) and nitrate (NO3 -) in the biofilm of a H2-based membrane biofilm reactor (MBfR). The one-dimensional model includes dual-substrate Monod kinetics for a steady-state biofilm with multiple solid and dissolved components. The model has five solid components: autotrophic denitrifying bacteria (ADB), heterotrophic denitrifying bacteria (HDB), Dehalococcoides (DHC), inert biomass (IB), and extracellular polymeric substances (EPS). The model has eight dissolved components: NO3 -, TCE, dichloroethene (DCE), vinyl chloride (VC), ethene, hydrogen (H2), substrate-utilization-associated products (UAP), and biomass-associated products (BAP). We used this model to simulate a benchscale experiment in a H2-based MBfR. The model simulated the trends well: almost complete removal of nitrate, incomplete reduction of TCE, and almost no accumulation of DCE and VC. To gain insight into reductive dehalogenation in a H2-based MBfR, we also simulated the concentrations of nitrate, TCE, DCE, VC, and ethene in the reactor effluent while varying the influent nitrate concentration. Simultaneous low concentrations of nitrate and the three chlorinated ethenes can occur as long as the influent ratio of NO3 - to TCE is not too large, so that DHC are a significant fraction of the biofilm. [ABSTRACT FROM AUTHOR]

Microbial dechlorination of trichloroethene (TCE) is inhibited at elevated TCE concentrations. A batch experiment and modeling analysis were performed to examine whether this self-inhibition is related to an enhanced cell decay or a reduced dechlorination activity at increasing TCE concentrations. The batch experiment combined four different initial TCE concentrations (1.4-3.0 mM) and three different inoculation densities (4.0 × 105 to 4.0 × 107 Geobacter cells·mL-1). Chlorinated ethene concentrations and Geobacter 16S rRNA gene copy numbers were measured. The time required for complete conversion of TCE to cis-DCE increased with increasing initial TCE concentration and decreasing inoculation density. Both an enhanced decay and a reduced activity model fitted the experimental results well, although the reduced activity model better described the lag phase and microbial decay in some treatments. In addition, the reduced activity model succeeded in predicting the reactivation of the dechlorination reaction in treatments in which the inhibiting TCE concentration was lowered after 80 days. In contrast, the enhanced decay model predicted a Geobacter cell density that was too low to allow recovery for these treatments. Conclusively, our results suggest that TCE self-inhibition is related to a reduced dechlorination activity rather than to an enhanced cell decay at elevated TCE concentrations. [ABSTRACT FROM AUTHOR]

Abstract: Column experiments and numerical simulations were conducted to evaluate the effects of Cr(VI) and dissolved CaCO3 on the iron reactivity towards trichloroethene (TCE) and Cr(VI) reduction. Column experiments included measurements of iron corrosion potential and characterization of surface film composition using Raman spectroscopy. Three columns received different combinations of TCE (5mgL−1), Cr(VI) (10mgL−1) and dissolved CaCO3 (300mgL−1), after short periods of conditioning with Millipore water followed by 10mgL−1 TCE in Millipore water, for a total of 8months. The results showed that co-existence with TCE did not affect Cr(VI) reduction kinetics, however, the presence of Cr(VI) reduced TCE degradation rates significantly. The formation of Fe(III)/Cr(III) products caused progressive passivation of the iron and was consistent with the increase in corrosion potential. The presence of dissolved CaCO3 resulted in a stable corrosion potential and faster degradation rates of TCE and Cr(VI). Over time, however, the accumulation of secondary carbonate minerals on the iron surface decreased the iron reactivity. Numerical simulation using a reactive transport model reproduced the observations from the column experiments reasonably well. The simulation can be valuable in the design of PRBs or in the development of effective maintenance procedures for PRBs treating groundwater co-contaminated with Cr(VI) and TCE in the presence of dissolved CaCO3. [Copyright &y& Elsevier]

Abstract: In this research, we conducted trichloroethylene (TCE) reduction in a column filled with iron and iron-reducing bacteria (IRB) and developed a mathematical model to investigate the critical reactions between active species in iron/IRB/contaminant systems. The formation of ferrous iron (Fe(II)) in this system with IRB and zero-valent iron (ZVI, Fe(0)) coated with a ferric iron (Fe(III)) crust significantly affected TCE reduction and IRB respiration in various ways. This study presents a new framework for transformation property and reducing ability of both dissolved (Fe(II)dissolved) and solid form ferrous iron (Fe(II)solid). Results showed that TCE reduction was strongly depressed by Fe(II)solid rather than by other inhibitors (e.g., Fe(III) and lactate), suggesting that Fe(II)solid might reduce IRB activation due to attachment to IRB cells. Newly exposed Fe(0) from the released Fe(II)dissolved was a strong contributor to TCE reduction compared to Fe(II)solid. In addition, our research confirmed that less Fe(II)solid production strongly supported long-term TCE reduction because it may create an easier TCE approach to Fe(0) or increase IRB growth. Our findings will aid the understanding of the contributions of iron media (e.g., Fe(II)solid, Fe(II)dissolved, Fe(III), and Fe(0)) to IRB for decontamination in natural groundwater systems. [Copyright &y& Elsevier]

Trichloroethylene (TCE) contaminated soil has received extensive attention in the environmental issues. Nanoscale zero-valent iron (NZVI) is considered as an excellent reduction catalyst due to fast degradation of chlorinated solvents. Therefore, this paper aims to evaluate TCE removal from soil by surfactant modified nanoscale zero-valent iron (SNZVI). In this respect, fixed 500 g soil having a diameter range 0.5-1mm was polluted with 10mL TCE and put inside glass column of 2.5 cm diameter × 300 cm length. The NZVI solution was prepared from reduction of FeCL3 by NaBH4 and coating with 2.5 g nonionic surfactant (Tween 85) to produce iron nanoparticle concentration of 0.1 g/L. The prepared iron nanoparticle was poured into contaminated soil and left to stir at a constant rate for 24 days. The reductive dechlorination of TCE was measured as a function of increasing chloride ion. It was found that the TCE dechlorination in the presence of iron surfaces displayed pseudo first-order kinetics. The TCE degradation rate constant (Kobs) is 4 × 10-4h-1. Also, about 30% of TCE was removed within initial 6 days. The obtained specific rate constant (KSA) was 6.081 × 10-4L · h-1 · m-2 and is lower than other studies carried into aqueous phase by about 23 orders of magnitude. Finally, the SNZVI was found to be effective and fully removed to TCE within 456 hours. [ABSTRACT FROM AUTHOR]

Finished Water is a photo feature that profiles working operators and utilities in the news, particularly new and renovated facilities. [ABSTRACT FROM AUTHOR]