Trichloroethylene Concentrations Research Articles

Ecological Risk Assessment of Three Pesticide Additives in Soil and Application to the Remediation of Contaminated Soil.

Pesticide additives (PAs) are auxiliary ingredients added to the pesticide manufacturing and use processes, constituting 1% to 99% of the pesticide and often composed of benzene and chlorinated hydrocarbons. We selected three typical PAs, toluene, chloroform, and trichloroethylene, to evaluate their retention function toxicity and ecological risk in soil. Soil immobilization techniques and aquatic model organisms were used to demonstrate the effectiveness of the immobilized soil method to determine the ecological risk of chemicals. The 48-h median lethal concentrations of toluene, chloroform, and trichloroethylene alone in spiked soil on Daphnia magna were 10.5, 2.3, and 1.1 mg/L (medium, high, and high toxicity, respectively). The toxicity of the three-PA mixtures showed an antagonistic effect. The risk levels of toluene, chloroform, and trichloroethylene in the soil were evaluated as moderate to high, low to high, and high risk, respectively. The toxicity of two pesticide-contaminated sites in the Yangtze River Delta before and after remediation was successfully evaluated by immobilized soil technology. The toxicity of two soil sampling points was reduced from medium toxic to low toxic and no toxic, respectively, after remediation. The results of our study give a rationale for and prove the validity of the aquatic model organisms and soil immobilization techniques in assessing the soil retention functions toxicity of PAs. Environ Toxicol Chem 2024;00:1-13. © 2024 SETAC.

Impact of Hurricanes, Tropical Storms, and Coastal Extratropical Storms on Indoor Air VOC Concentrations

AbstractUnderstanding vapor intrusion (VI) temporal variability is key for the design of sampling strategies intended to assess reasonable maximum exposure of indoor air concentrations of volatile organic compounds (VOCs) as well as risk evaluation and mitigation planning. VI temporal variability has previously been shown to be dependent on the complex interactions of multiple independent variables—meteorological, hydrogeological, and human behavioral. Several meteorological variables, including barometric pressure, wind speed, and rainfall, are linked during tropical and extratropical storm events. High‐frequency meteorological and indoor VOC data from a series of seven tropical storms and four extratropical storms were collected at a single industrial building with multiple heating, ventilation, and air conditioning (HVAC) zones. The storms and sampling zones showed a variety of effects on trichloroethylene (TCE) concentrations in indoor air. In one zone (supply room), increases in TCE concentrations often, but not always, closely coincided with decreasing barometric pressure, sustained wind speeds over 32 km/h (20 mph), and differential pressures indicating subslab to indoor flow. A second zone, in a restroom, did not show a consistent pattern of temporal correlation between meteorological factors and indoor air concentrations. While peak indoor air concentrations may be associated with the passage of cyclonic storms at some sampling locations, this does not appear to be generalizable to all sampling locations. The observed increase in indoor air concentration potentially attributable to these storms is typically less than an order of magnitude and the duration ranges from a day to a week.

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.

Real-time monitoring and predictive analysis of VOC flux variations in soil vapor: Integrating PID sensing with machine learning for enhanced vapor intrusion forecasts

In the rapidly evolving domain of vapor intrusion (VI) assessments, traditional methodologies encompass detailed groundwater and soil vapor sampling coupled with comprehensive laboratory measurements. These models, blending empirical data, theoretical equations, and site-specific parameters, evaluate VI risks by considering a spectrum of influential factors, from volatile organic compounds (VOC) concentrations in groundwater to nuanced soil attributes. However, the challenge of variability, influenced by dynamic ambient conditions and intricate soil properties, remains. Our study presents an advanced on-site gas sensing station geared towards real-time VOC flux monitoring, enriched with an array of ambient sensors, and spearheaded by the reliable PID sensor for VOC detection. Integrating this dynamic system with machine learning, we developed predictive models, notably the random forest regression, which boasts an R-squared value exceeding 79 % and mean relative error near 0.25, affirming its capability to predict trichloroethylene (TCE) concentrations in soil vapor accurately. By synergizing real-time monitoring and predictive insights, our methodology refines VI risk assessments, equipping communities with proactive, informed decision-making tools and bolstering environmental safety. Implementing these predictive models can simplify monitoring for residents, reducing dependence on specialized systems. Once proven effective, there's potential to repurpose monitoring stations to other VI-prone regions, expanding their reach and benefit. The developed model can leverage weather forecasting data to predict and provide alerts for future VOC events.

Polydimethylsiloxane dialysis passive sampler monitoring of chlorinated solvent contaminated sites – A field study

The complexity of the subsurface contaminated by chlorinated solvents such as trichloroethylene (TCE) makes it challenging to gain a complete understanding of contamination distribution and establish a conceptual site model (CSM). High-resolution vertical contaminant concentration profiling across both the unsaturated zone and the saturated aquifer is desirable for mapping the distribution of contamination. A Fick's law-based polydimethylsiloxane (PDMS) dialysis passive sampler was developed and evaluated on a field scale for its potential application. This study tests the passive sampler at two TCE contaminated sites, and the sampling results were compared with the results from different sampling methods based on the relative percent difference. The PDMS dialysis passive sampler obtained more representative soil gas concentrations in the unsaturated zone than a portable monitoring and sampling device, which caused soil gas flow disturbance by soil gas pumping during sample collection. In the saturated aquifer sampling, the results obtained by the PDMS dialysis passive sampler correlated well with those obtained by a commercial polyethylene passive diffusion bag, and exhibited higher sensitivity under low TCE concentration conditions. Furthermore, the PDMS dialysis passive samplers were densely deployed inside each monitoring well at multiple depths, at two sites, to achieve high-resolution monitoring across the unsaturated zone and saturated aquifer. Based on the PDMS dialysis sampler data, a more comprehensive three-dimensional CSM was systematically established.

Oxalate-modified microscale zero-valent iron for trichloroethylene elimination by adsorption enhancement and accelerating electron transfer

Trichloroethylene (TCE) with trace concentrations is often detected in soils and groundwater, posing potential damages to public health. The elimination of TCE can be achieved through reductive dechlorination using zero-valent iron (ZVI). However, ZVI usually suffers from the presence of passive iron (hydro)oxides layer and low electron transfer rate, thus leading to the unsatisfactory reactivity. Herein, we fabricated oxalated ZVI (Ox-ZVIbm) by mechanical ball-milling of micro-scale ZVI and H2C2O4·2H2O to modify the ZVI surface composition. To be specific, the modification of the iron oxide shell by oxalic acid facilitated the generation of unsaturated coordination Fe(II), enhancing TCE adsorption. Furthermore, the formed FeC2O4 on the iron oxide shell improved electron transfer efficiency, contributing to the enhanced TCE reductive dechlorination. Impressively, the rate of TCE degradation by Ox-ZVIbm was 10-fold higher than that of ZVIbm without oxalate modification. Moreover, Ox-ZVIbm samples were filled in a laboratory Permeable Reactive Barriers (PRB) column to treat actual underground wastewater containing TCE pollutants. The effluent concentration of TCE maintained steadily below 0.21 mg/L for over 10 days, complying with the National Groundwater Class IV standard (GBT 14848–2017). This marks a significant step toward practical groundwater treatment.

Enhanced visible-light activation of peroxymonosulfate by novel Bi2O2SO4/Bi,N,S-TiO2 heterojunction toward efficient trichloroethylene degradation: Insight into function of Bi2O2SO4

The photocatalytic performance of Bi2O2SO4 (BOS) has not been widely noticed. In this work, a novel heterojunction of Bi2O2SO4/Bi, N, S-TiO2 (BOS/BNST) was synthesized. The heterojunction exhibited high efficiency for trichloroethylene (TCE) degradation. Degradation rate of TCE could be over 99 % in 1 h, when concentration of TCE was 7 mg/L, and reaction rate constant could be 0.06573 min−1. The main reasons for the enhancement are depicted as follows: (1) TiO2 was doped with Bi, N and S, which enhanced the visible light response; (2) The combination of BOS and BNST improves the separation efficiency of photo-induced carriers; (3) Loading of BOS prompts PMS adsorption; (4) The Bi4+ and Bi3+ cycling in BOS/BNST facilitated PMS activation. This paper introduces a novel photocatalyst which exhibited excellent photoactivity, and provides a new perspective for the research of PMS activation under visible light.

Formation of corrosion-based ZVMg nanoparticles for reductive degradation of high-level trichloroethylene in aqueous solution

This study discovered that nanosized zero valent magnesium (nZVMg) could be formed during the electrochemical corrosion of microsized ZVMg (mZVMg) in aqueous solution. It is observed that the nZVMg particle sizes were less than 50 nm with the specific surface area of 54.63 m2/g after it was corroded for 96 h (ZVMg96) at the expense of losing about 60 wt% Mg0. However, the XPS characterization indicated the thickness of Mg(OH)2 layer over ZVMg96 being less than 5 nm, accompanied by the faster electron transfer rate but slower corrosion rate than mZVMg. Most importantly, the removal efficiency of 82 % under high-level trichloroethylene (TCE) at 100 mg/L was achieved by ZVMg96 within one hour relative to 48 % by mZVMg. The rate constant normalized by surface area was 3.11 × 10−2 L/m2/h by ZVMg96 due to the high surface energy of nanoparticles. The degradation products were dependent on the initial TCE concentrations, with environmentally friendly and biodegradable degradation products being generated via hydrodechlorination, hydrogenation and polymerization pathways according to the density functional theory calculations. ZVMg corroded for 14 days illustrated a long-term chemical stability and excellent degradation performance, demonstrating significant application potential in remediating the TCE plumes in groundwater.

Facile fabrication of three-dimensional MnO2 for trichloroethylene degradation by plasma catalysis

Non-thermal plasma (NTP) coupled with catalyst is a cutting-edge technique for the abatement of chlorinated volatile organic compounds (Cl-VOCs), which are typically chemically stable, highly toxic and non-biodegradable. In this study, different morphologies of 3D MnO2 catalysts were fabricated facilely through a hydrothermal method and coupled with NTP for trichloroethylene (TCE) degradation. Among the various catalysts tested, MnO2 IV exhibited the highest TCE degradation performance, with removal efficiency, mineralization and energy yield ranging from 44.3% to 94.8%, 28.9% to 90.1% and 5.76 to 2.31 g/kWh, respectively, at voltage levels between 7 and 11 kV. The relationship between the physicochemical properties of the catalysts and their degradation performance was established through various characterization methods. The exceptional catalytic efficiency of MnO2 IV can be ascribed to its hierarchical flower-like structure, the greatest specific surface area (120 m2/g), the weakest Mn-O bonds, increased lattice defects and oxygen vacancies, and lower H2 reduction temperature. These characteristics facilitate enhanced transfer, adsorption, and utilization of reactive oxygen species in NTP on the surface of MnO2 IV, promoting the deep oxidation of TCE. The optimization of operational parameters was achieved using response surface methodology, with results indicating that the applied voltage exerted the greatest influence on both the mineralization rate and energy yield. The optimal operating conditions were determined, with initial TCE concentration, applied voltage, and gas flow rate values identified as 393 ppm, 7.3 kV, and 0.83 L/min, respectively. Lastly, the TCE degradation mechanism in the NTP-MnO2 catalyst system was hypothesized based on the identification of various plasma reactive species and organic intermediates. This study provides new insights for the improvement of the VOCs oxidation performance in plasma catalytic system.

Degradation of trichloroethylene in aqueous solution by FeS2 catalyst under innovative oxic environments

Rapid growth and industrialization have become a major threat to water contamination with carcinogenic chlorinated hydrocarbons such as trichloroethylene (TCE). Therefore, this study aims to assess the TCE degradation performance through advanced oxidation process (AOP) using catalyst FeS2 in combination with oxidants persulfate (PS), peroxymonosulfate (PMS), and hydrogen peroxide (H2O2) in PS/FeS2, PMS/FeS2, and H2O2/FeS2 systems, respectively. TCE concentration was analyzed using gas chromatography (GC). The results found the trend for TCE degradation by the systems was PMS/FeS2>PS/FeS2>H2O2/FeS2 (99.84, 99.63, and 98.47%, respectively). Degradation of TCE was analyzed at different pH ranges (3–11) and maximum degradation at a wide pH range was observed for PMS/FeS2. The analysis using electron paramagnetic resonance (EPR) and scavenging tests explored responsible reactive oxygen species (ROS) for TCE degradation and found that HO• and SO4−• played the most effective role. The results of catalyst stability showed PMS/FeS2 system the most promising with the stability of 99, 96 and 50% for the first, second and third runs, respectively. The system was also found efficient in the presence of surfactants (TW-80, TX-100, and Brij-35) in ultra-pure water (89.41, 34.11, 96.61%, respectively), and actual groundwater (94.37, 33.72, and 73.48%, respectively), but at higher reagents dosages (5X for ultra-pure water and 10X actual ground water). Furthermore, it is demonstrated that the oxic systems have degradation capability for other TCE-like pollutants. In conclusion, due to its high stability, reactivity, and cost-effectiveness, PMS/FeS2 system could be a better choice for the treatment of TCE contaminated water and can be beneficial for field application.

Degradation of trichloroethylene vapors by micrometric zero-valent Fe[sbnd]Cu and Fe[sbnd]Ni bimetals under partially saturated conditions

The degradation of trichloroethylene (TCE) vapors by zero-valent Iron-Copper (Fe–Cu) and Iron-Nickel (Fe–Ni) bimetals with 1%, 5% and 20% weight content (%wt) of Cu or Ni was tested in anaerobic batch vapor systems carried out at ambient room temperature (20 ± 2 °C) under partially saturated conditions. The concentrations of TCE and byproducts were determined at discrete reaction time intervals (4 h-7 days) by analyzing the headspace vapors. In all the experiments, up to 99.9% degradation of TCE in the gas phase was achieved after 2–4 days with zero-order TCE degradation kinetic constants in the range of 134–332 g mair−3d−1. Fe–Ni showed a higher reactivity towards TCE vapors compared to Fe–Cu, with up to 99.9% TCE dechlorination after 2 days of reaction, i.e., significantly higher than zero-valent iron alone that in previous studies was found to achieve comparable TCE degradation after minimum 2 weeks of reaction. The only detectable byproducts of the reactions were C3–C6 hydrocarbons. Neither vinyl chloride or dichloroethylene peaks were detected in the tested conditions above their method quantification limits that were in the order of 0.01 g mair−3. In view of using the tested bimetals in horizontal permeable reactive barriers (HPRBs) placed in the unsaturated zone to treat chlorinated solvent vapors emitted from contaminated groundwater, the experimental results obtained were integrated into a simple analytical model to simulate the reactive transport of vapors through the barrier. It was found that an HPRB of 20 cm could be potentially effective to ensure TCE vapors reduction.

Thermal Conduction Heating for a 125 ft Deep TCE Source—Multiple Lines of Evidence for Verification of Remedial Goals

AbstractThis paper describes thermal conduction heating of a trichloroethylene (TCE) source zone within vadose zone soils consisting of glacial till at depths of 50 to 125 ft below an active manufacturing facility. The performance objectives and metrics used to determine remediation success are presented. Access limitations inside the facility prevented traditional spatial soil confirmation sampling, which made performance assessment a unique challenge. Instead, the project team developed an approach utilizing multiple lines of evidence to document remedy completeness. These lines of evidence included achievement of target temperatures within the treatment volume, demonstration of asymptotic vapor concentrations extracted from the treatment volume, achieving modeled energy input goals, and verifying TCE concentrations in post‐treatment soil samples collected at the few accessible locations within the operational facility. The treatment volume was divided into three discrete treatment areas or heating groups, each constructed and heated independently in order to meet an aggressive project schedule. Additionally, each line of evidence was required to be met in each group. After approximately 283 days of heating, temperatures exceeded 90 °C at 95% of the temperature monitoring points, TCE levels had diminished to asymptotic levels in the recovered vapors, and mass removal rates from the treatment volume declined to minimal levels. Confirmatory soil sample results indicated that average TCE concentrations achieved were more than an order of magnitude below the remedial goal of 1 mg/kg.

Contaminant sorption on soil and indoor materials and its possible impact on transients in vapor intrusion – An example based upon trichloroethylene (TCE)

Although building materials are well recognized as potential sources and sinks of indoor volatile organic compounds (VOCs), knowledge about how they affect indoor air concentrations and measurements in vapor intrusion scenarios is limited. This study investigates the potential influence of sorption processes on indoor air contamination in vapor intrusion, relying upon laboratory measurements at relevant concentration levels, and applying these in a numerical transient vapor intrusion model. It was found that the sink effect of adsorption on building materials can lower indoor air concentrations or delay their achieving a steady state, thus cautioning that these processes can affect observed indoor air concentration variability. Building materials can also serve as secondary sources of pollutants in vapor intrusion mitigation scenarios, which might affect the evaluation of the efficiency of mitigation efforts. For example, it was predicted that in a cinderblock structure it could take up to 305 h to reduce indoor trichloroethylene (TCE) concentrations by 50 % due to the re-emission of TCE from the cinderblock, whereas it would take only 1.4 h without the re-emission process.

Emissions of Trichloroethylene from Bedroom Furniture Set as a Source of Indoor Air Contamination

AbstractShallow trichloroethene (TCE) groundwater and soil contamination associated with a Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) Superfund Site in Michigan resulted in a vapor intrusion (VI) investigation of overlying condominium units. Units with data suggesting a complete VI pathway received subslab depressurization systems (SSDs). Performance monitoring following the installation of an SSD at one unit indicated that the indoor air TCE concentrations remained elevated, despite pressure field extension tests that showed the system should effectively reduce VI from soil gas. Therefore, a cost‐efficient and incremental investigation was launched to identify other potential source(s) of TCE using a field‐portable gas chromatograph/mass spectrometer (GS/MS). The combination of room‐by‐room air sampling, potential VI entry point sampling, and emission tests of potential sources were used, which resulted in successfully identifying a bedroom furniture set as an indoor source of TCE for the unit. Although many common household products are recognized as indoor sources of TCE, emissions from finished furniture products have not been widely discussed in the VI literature. The findings of this study indicate that off gassing from furniture can lead to TCE concentrations in indoor air that exceed regulatory guidelines.

The importance of proper pH adjustment and control to achieve complete in situ enhanced reductive dechlorination.

In situ bioremediation of chlorinated compounds such as perchloroethylene (PCE) and trichloroethylene (TCE) through enhanced reductive dechlorination (ERD) requires appropriate growth conditions for organohalide-respiring bacteria (OHRB). One of the most important factors controlling OHRB metabolism is groundwater pH. Dehalococcoides spp. (DHC) growth may be inhibited when pH is lower than 6.0, which can lead to the accumulation of toxic daughter compounds including cis-dichloroethylene (cDCE) and vinyl chloride (VC). Aquifer pH may decline as HCl is released during reductive dechlorination and from substrate fermentation to fatty acids and carbonic acid. In this article, we demonstrate that using proper pH adjustment and control in situ is an appropriate strategy to achieve complete ERD (i.e., complete conversion of PCE and TCE to nontoxic ethylene) in remediation sites with inherently low pH values and/or low buffering capacity. To analyze the effectiveness of this approach, field monitoring results are presented for a challenging site containing high concentrations of PCE and TCE (>10 000 µg/L and >1000 µg/L, respectively) and low aquifer pH (~4.9). Addition of a bioaugmentation culture, emulsified vegetable oil (EVO), and a colloidal buffer (CoBupHTM ) to increase pH, stimulated rapid conversion of PCE and TCE to cDCE and VC. However, further conversion of cDCE and VC was very limited. To stimulate complete conversion to ethylene, additional CoBupHTM and nutrients were injected, resulting in a rapid increase in metabolic rates, and maintained the aquifer pH at ~6.5 for more than five years, thus demonstrating that complete ERD can be achieved in sites with similar characteristics. Proper pH adjustment and control is needed to limit the accumulation of toxic intermediates, maintaining in situ bioremediation as an efficient, affordable, and environmentally friendly option to treat chlorinated compounds. Integr Environ Assess Manag 2023;19:943-948. © 2022 SETAC.

Emission behavior and impact assessment of gaseous volatile compounds in two typical rural domestic waste landfills

Landfill sites are sources of gaseous volatile compounds. The dumping area (LDA) and leachate storage pool (LSP) of two typical rural domestic waste landfill sites in north China (NLF) and southwest China (SLF) were investigated. We found that 45, 46, 61 and 68 volatile organic compounds (VOC) were present in the air of NLF-LDA, NLF-LSP, SLF-LDA, and SLF-LSP, respectively. And there were 27, 29, 35 and 37 kinds of odorous compounds being detected. Oxygenated compounds (>48.88%), chlorinated compounds (>6.85%), and aromatics (>5.46%), such as organic acid, 1-chlorobutane, and benzene, were the most abundant compounds in both landfills. The SLF-LDA had the highest olfactory effect, with a corresponding total odor activity value of 29,635.39. The ozone-formation potential analysis showed that VOCs emitted from SLF landfills had significantly higher potential for ozone formation than those from NLF landfills, with ozone generation potentials of 166.02, 225.86, 2511.82, and 1615.99 mg/m3 for the NLF-LDA, NLF-LSP, SLF-LDA, and SLF-LSP, respectively. Higher chronic toxicity and cancer risk of VOCs were found in the SLF according to method of Risk Assessment Information System. Based on the sensitivity analysis by the Monte Carlo method, concentrations of benzene, propylene oxide, propylene, trichloroethylene, and N-nitrosodiethylamine, along with exposure duration, daily exposure time, and annual exposure frequency, significantly impacted the risk levels. We provide a scientific basis, which reflects the need for controlling and reducing gaseous pollutants from landfills, particularly rural residential landfills, which may improve rural sanitation.

Remediation of chlorinated aliphatic hydrocarbons (CAHs) contaminated site coupling groundwater recirculation well (IEG-GCW®) with a peripheral injection of soluble nutrient supplement (IEG-C-MIX) via multilevel-injection wells (IEG-MIW)

An innovative Groundwater Circulation Well (GCW) process was configured, installed, and tested for optimizing the distribution of a soluble nutrient supplement in a heterogeneous aquifer for reductive dehalogenation. This generated an in-situ bioreactor for the enhanced treatment of chlorinated aliphatic hydrocarbons (CAHs). At a site in Barcelona, Spain, trichloroethylene (TCE) concentration was found in the source area to a maximum value of up to 170 mg/L, while the degradation products like 1,2-dichloroethylene (1,2-DCE) and vinyl chloride (VC) were detected in significantly lower concentrations or were even absent. The novel system combined a vertical recirculation well (IEG-GCW®) and four multilevel injection wells (IEG-MIWs) to introduce the carbon solution into the aquifer. A 12 m deep IEG-GCW® equipped with 2 screened sections were located in the center of the 4 IEG-MIWs. The GCW induced flow moves the groundwater in an ellipsoidal recirculation cell to spread the supplements from the central GCW and from the peripheral MIWs in the aquifer body. Two multilevel sampling wells (IEG-MLSWs®) in the radius of influence (ROI) monitor the remediation process to capture hydrochemical variations along the vertical aquifer sections. A multi-source model harmonizes geological and hydrochemical information during different remediation stages, guiding the adaptation of the remediation strategy to physicochemical conditions and unmasking the decontamination mechanics induced by the remedial actions. Hydrochemical monitoring of MLWS and the stable carbon isotopic signature of cis-1,2-DCE and VC show the mobilization of secondary contamination sources triggered by recirculation during remediation, the stimulation of microbiological activity following nutrient supplement via GCW and MIWs, and the strong decrease of CAHs concentrations at different aquifer levels. Evidence from the first application at the field scale reveals a significant increase in the chloroethane biodegradation rate and short-term effectiveness of the innovative remediation strategy. GCW-MIWs synergy represents a promising strategy to degrade CAHs in a shorter period through the combination of a controllable hydraulic system, effective nutrient distribution, and the monitoring of the remediation process.

Field application of glycerol to enhance reductive dechlorination of chlorinated ethenes and its impact on microbial community

Chlorinated ethenes (CEs) are common and persistent contaminants of soil and groundwater. Their degradation is mostly driven by a process of bacterial reductive dechlorination (also called organohalide respiration) in anaerobic conditions. This study summarizes the outcomes of the long-term in-situ application of glycerol for the enhanced reductive dechlorination of CEs on a highly contaminated site. Glycerol injection resulted in an almost immediate increase in the abundance of fermentative Firmicutes, which produce essential sources of carbon (acetate) and electrons (H2) for organohalide-respiring bacteria (OHRB) and change groundwater conditions to be suitable for OHRB growth. The decreased redox potential of groundwater promoted also the proliferation of sulfate-reducing bacteria, which compete for electron donors with OHRB but at the same time support their growth by producing essential corrinoids and acetate. A considerable increase in the abundance of OHRB Dehalococcoides, concurrently with vinyl chloride (VC) reductase gene levels, was revealed by real time polymerase chain reaction (qPCR) method. Consistent with the shifts in bacterial populations, the concentrations of pollutants tetrachloroethylene and trichloroethylene decreased during the monitoring period, with rising levels of cis-1,2-dichloroethylene, VC, and most importantly, the final CE degradation products: ethene and ethane. Our study implies the importance of syntrophic bacterial interactions for successful and complete CE degradation and evaluates glycerol as convenient substrate to enhance reductive dechlorination and as an effective source of electrons for OHRB.

A quantitative study of the effects of particle' properties and environmental conditions on the electron efficiency of Pd and sulfidated nanoscale zero-valent irons

Electron efficiency (or electron selectivity, ɛe) is an important quantitative criterion for zero-valent iron treatment of organohalide contaminated groundwater. The aim of this quantitative study was the systematic exploration and comparison of the effects of the Pd/Fe and S/Fe molar ratios (i.e., [Pd/Fe] and [S/Fe]), trichloroethylene (TCE) concentrations ([TCE]), pH solution, aging time, and water matrices on the ɛe of Pd-nZVI and S-nZVI. To this end, we used TCE as a probe contaminant. The ɛe of Pd-nZVI increased and then decreased with [Pd/Fe], while that of S-nZVI increased with [S/Fe], as more hydrophobic FeS2 was formed on S-nZVI at higher [S/Fe]. The εe of S-nZVI and Pd-nZVI increased with increasing [TCE]. Specifically, the εe of S-nZVI and Pd-nZVI at [TCE] of 200 ppm increased by 24.9 % and 79.3 %, respectively, compared with that at [TCE] of 10 ppm. As the H2 evolution reaction (HER) was more sensitive to surface passivation than TCE dechlorination, the εe of S-nZVI and Pd-nZVI under alkaline conditions was higher than that under basic conditions, and increased by 11.7 % and 37.8 %, respectively, at pH 10 relative to that at pH 6. The εe also increased with the aging time of the S-nZVI and Pd-nZVI particles; the increase was by 27.2 % and 59.6 %, respectively, at aging time of 30 d compared with that of the fresh ones. The ɛe of both particles were higher in artificial groundwater (AGW) than in real groundwater (RGW). For all batch experiments, the εe of S-nZVI increased over the reaction time and tended to outperform that of Pd-nZVI, even though the εe of Pd-nZVI was higher than that of S-nZVI at the initial stage of TCE dechlorination, thereby justifying the longevity of S-nZVI.

Removal of chlorine-contaminated groundwater by two-stage ozonation and biostimulation methods.

Trichloroethene (TCE) contamination is a critical environmental hazard, and the substrate options for its biostimulated remediation are limited. This study applied an ozonation-and-biostimulation process to remove TCE from groundwater. The substrate used, denoted as Transferred Energy Element (TEE), was composed of natural organic materials and had a low viscosity (2.914cP). Ten batch experiments were conducted through the application of micro-nano bubbles (MNBs) and substrates (TEE and EOS® [emulsified oil substrate]). MNBs with an average diameter of 157.5-180.8nm effectively degraded TCE and dichloroethane within 6min. Biostimulation using the TEE substrate effectively degraded both TCE and vinyl chloride pollutants and reached a steady state after 25 days. The two-stage dechlorination procedure with MNB treatment as the first stage enhanced TCE removal via biostimulation. MNBs reduced the TCE concentration in the first 20min, but increased the chloride (Cl-) concentration over the following five days (∼80mg/L). The procedure with biostimulation as the first stage and 20min ozonation as the second stage reduced the Cl- concentration by ∼10mg/L. The Cl- concentrations rebounded after day 25 in the EOS environment. X-ray diffraction revealed that the released Na+ from the TEE settled with Cl- as minerals in the soil. The novel two-stage method for TCE removal was found to be more effective than solo MNB treatment or biostimulation.