Adsorption Of Trichloroethylene Research Articles

Highly efficient bioregeneration of high temperature-pyrolyzed biochar after trichloroethylene adsorption through biodegradation of Dehalococcoides

Biochars was widely employed to immobilize chlorinated aliphatic hydrocarbons (CAHs) in groundwater. Biodegradation of adsorbed CAHs may be able to regenerate biochars, but was scarcely explored. In this study, therefore, biodegradation of trichloroethylene (TCE) adsorbed on a biochar prepared at 700 °C (WBC700) by Dehalococcoides mccartyi 195 (Dhc 195) was investigated. Aqueous TCE was completely degraded to ethene by Dhc 195 within 28 days, while 87.5 % of WBC700-adsorbed TCE was degraded to ethene within 63 days. The slower biodegradation of WBC700-adsorbed TCE could be attributed to its lower accessibility to Dhc 195 caused by the steric effects of WBC700. The adsorption capacity of WBC700 for TCE remained 80.4 % after five adsorption-bioregeneration cycles, indicating that the microbial degradation could be a highly efficient method to regenerate biochars. The microbial degradation was mainly through the electron transfer from Dhc 195 to TCE mediated by biochars as electron conductor or shuttle, but was not assisted by desorption or extracellular redox active species. Compared with biodegradation of aqueous TCE, the biodegradation of WBC700-adsorbed TCE by Dhc 195 had a wider pH tolerance and required more VB12, due to the buffer effect and adsorption of WBC700, respectively. The obtained results could provide a cost-effective method of biochar regeneration for CAHs removal in groundwater.

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.

Tandem supported Pt and ZSM-5 catalyst with separated catalytic functions for promoting multicomponent VOCs oxidation

The painting and electronics industries simultaneously release aromatic compounds and chlorinated organics. The development of catalysts with synergistic control of these pollutants is of great significance to achieve air purification. However, developing active catalysts while maintaining good chlorine resistance remain a huge challenge due to the difficulty of the trade-off between the redox properties and acidity and the production of polychlorinated byproducts. Herein, we introduce a novel tandem PtSn/CeO2&Mn/ZSM-5 catalyst and investigate its catalytic performance for multicomponent volatile organic compounds (VOCs) oxidation. The two individual catalysts, PtSn/CeO2 and Mn/ZSM-5, were used to catalyze two distinct sequential reactions. PtSn/CeO2 catalyzed toluene oxidation to produce CO2 and H2O. Meanwhile, the introduction of SnOx favored the adsorption of trichloroethylene (TCE) molecules that prevented Pt sites from chlorine poisoning and possibly converted adsorbed TCE into intermediates, which were subsequently oxidized deeply by the nearby Mn/ZSM-5. This approach resulted in a remarkable oxidation efficiency for toluene (T90 = 296 °C) and TCE (T90 = 384 °C), with fewer unexpected toxic byproducts (chlorobenzene and 4-chlorotoluene). Furthermore, the tandem catalyst possessed excellent chlorine and water resistances. In conclusion, the above findings provide new insights into the design and/or syntheses of advanced catalysts for widespread VOCs pollution control.

Synergistic action of ferrate and biochar in the removal of trichloroethylene from water: Little biochar addition, large ferrate activity improvement

Ferrate (Fe(VI)) is strongly considered an efficient green oxidant for degrading organic pollutants in groundwater. However, overdosage is often used to achieve the desired efficiency, resulting in adverse effects on the groundwater quality and the ecological environment and high costs. This study aimed to enhance the removal of trichloroethylene (TCE) using Fe(VI) by investigating the synergistic action of a ferrate-biochar system. 1 h into the reaction, the TCE degradation rate had increased from 18.7% to 96.0% and the K2FeO4 concentration had increased from 1 mM to 25 mM. The pH strongly influenced the TCE degradation by K2FeO4 by affecting the stability, species, and consequent oxidation capacity of K2FeO4. Co-existing metal cations in the solution could enhance the K2FeO4 self-decay by facilitating the electron transfer process. Biochar addition significantly enhanced TCE removal by K2FeO4 (up to 4.4 times) compared with the combined removal via individual oxidation and adsorption systems. Significant enhancement comparable to that of a high 16 mM Fe(VI) dosage was obtained with 666 mg/L biochar and 5 mM Fe(VI). The enhancement mechanisms by which biochar addition enhanced the TCE removal by K2FeO4 included the oxidation process by prior to TCE adsorption onto biochar, an enhanced electron transfer of Fe(VI) reduction by the biochar functional group, and an enhanced adsorption capacity of biochar owing to its peroxidation by Fe(VI). Thus, compared to individual and excessive chemical oxidation, the ferrate-biochar composite system provides a promising strategy for improving the TCE removal efficiency with lower oxidant consumption and less negative ecological impacts.

Remediation of groundwater contaminated with trichloroethylene (TCE) using a long-lasting persulfate/biochar barrier

Groundwater contamination by chlorinated solvents causes potential threats to water resources and human health. Therefore, it is important to develop effective technologies to remediate contaminated groundwater. This study uses biodegradable hydrophilic polymers, hydroxypropyl methylcellulose (HPMC), hydroxyethyl cellulose (HEC) and polyvinyl pyrrolidone (PVP) as binders to manufacture persulfate (PS) tablets for the sustained release of persulfate to treat trichloroethylene (TCE) in groundwater. The release time for different tablets decreases in the order: HPMC (8–15 days) > HEC (7–8 days) > PVP (2–5 days). The efficiency with which persulfate is released is: HPMC (73–79%) > HEC (60–72%) > PVP (12–31%). HPMC is the optimal binder for the manufacture of persulfate tablets and persulfate is released from a tablet of HPMC/PS ratio (wt/wt) of 4/3 for 15 days at a release rate of 1127 mg/day. HPMC/PS/biochar (BC) ratios (wt/wt/wt) between 1/1/0.02 and 1/1/0.0333 are suitable for PS/BC tablets. PS/BC tablets release persulfate for 9–11 days at release rates of 1243 to 1073 mg/day. The addition of too much biochar weakens the structure of the tablets, which results in a rapid release of persulfate. TCE is oxidized by a PS tablet with an efficiency of 85% and a PS/BC tablet eliminates more TCE, with a removal efficiency of 100%, due to oxidation and adsorption during the 15 days of reaction. Oxidation is the predominant mechanism for TCE elimination by a PS/BC tablet. The adsorption of TCE by BC fits well with the pseudo-second-order kinetics and the pseudo-first-order kinetics, which describes the removal of TCE by PS and PS/BC tablets. The results of this study show that a PS/BC tablet can be used in a permeable reactive barrier for long-term passive remediation of groundwater.

Unveiling the role of biochar in simultaneous removal of hexavalent chromium and trichloroethylene by biochar supported nanoscale zero-valent iron

The simultaneous removal of hexavalent chromium (Cr(VI)) and Trichloroethylene (TCE) is facing great challenges, and the influences of the biochar on their removal by nanoscale zero-valent iron (nZVI) are poorly understood and seldom addressed in the literature. The rice straw pyrolysis at 700 °C (RS700) and their supported nZVI composites were investigated on the removal of Cr(VI) and TCE by batch experiments. The surface area and chromium bonding state of biochar supported nZVI with and without Cr(VI)-TCE loading were analyzed by Brunauer-Emmett-Teller analysis and X-ray photoelectron spectroscopy. In single pollutants system, the highest removal amounts of Cr(VI) and TCE were observed in RS700-HF-nZVI (76.36 mg/g) and RS700-HF (32.32 mg/g), respectively. The Cr(VI) removal was attributed to the reduction by Fe(II) with the adsorption by biochar primarily controlling the TCE removal. The mutual inhibition was revealed in simultaneous removal of Cr(VI) and TCE, in which the reduction of Cr(VI) was decreased due to the adsorption of Fe(II) by biochar, while the TCE adsorption was primarily inhibited owing to the blockage of surface pores of biochar supported nZVI by chromium‑iron oxides. Therefore, biochar supported nZVI could be potentially used for the combined contaminated groundwater remediation, but the mutual inhibition should be evaluated.

Adsorption of chlorinated hydrocarbons onto non-activated biochars: Biochar physicochemical characteristics and governing factors

Pyrolysis of biomass is the carbonization process where biomass is processed into biochar (BC) and the characteristics of BC like surface area, hydrophilicity, carbon content etc., are determined by the carbonization process. Trichloroethylene (TCE) and tetrachloroethylene (PCE) are chlorinated hydrocarbons that are used for metal degreasing and found in groundwater. In this study, six lignocellulosic feedstocks were gathered to produce BCs through pyrolysis in an argon atmosphere at temperatures between 300 °C and 900 °C. TCE and PCE batch adsorption tests were conducted for 72 h to generate Freundlich and Langmuir isotherm profiles. The results showed that as the pyrolysis temperature increased, hydrophilicity, surface area, and carbon content of all the BCs increased. Among the six examined feedstocks, the BC produced from walnut shells showed better results than other feedstocks with a microporous area of 37.91 m2/g, Qmax of 194 mg/g for TCE, and KF of 133 mg/g for PCE.

Oil shale kerogen-derived adsorbents and their application to trichloroethylene adsorption from aqueous solutions

This paper examines microporous oil shale kerogen-derived semicokes as potential sorbents for environmental cleanup applications. This carbonaceous residue (“semicoke”) left behind during the processing of oil shale kerogen is the main source of adsorptive potential in the processed oil shale. The surface area and porosity of model microporous semicokes were determined using N2 and CO2 adsorption techniques. The model semicoke material had a BET surface area of 494 m2/g of char (net of the minerals), which could be increased by mild thermal activation in the air at 698 K (425 °C) to 857 m2/g-char. The semicokes were tested as potential sorbents by measuring their efficacy at removing trichloroethylene (TCE) from aqueous solutions at 295 K in the concentration range from about 0.1 to 7 mg/L. TCE adsorption isotherms were determined for seven different sorbents – the model semicoke, the air-activated model semicoke, raw unprocessed oil shale, three commercially prepared semicokes, and, for reference, a commercial granulated activated carbon. The present results show that the kerogen-derived carbons have TCE adsorptive capacity values which are comparable to those of a commercial activated carbon (e.g., 70 mg/g-C). The results pointed to the importance of a particular micropore size range for adsorption. While air activation increased the pore volume and surface area of the materials as measured by nitrogen and carbon dioxide, this did not result in an increase in adsorptive capacity for TCE. The critical pore size appears to be in the range of 0.5–0.8 nm.

Batch and Continuous Flow Treatment Studies of Trichloroethylene Contaminated in Water by Silver and Cerium Doped Zinc Oxide Adsorption and Photocatalysis

The development of photocatalytic treatment in continuous flow systems to be more practical is challenging. This research aimed to study batch and continuous flow treatment of trichloroethylene (TCE) contaminated in water by silver and cerium doped zinc oxide (0.005Ag-0.005Ce-ZnO) visible light driven photocatalyst. This catalyst was selected to represent the green route synthesis with simplicity and ease of upscaling. The 0.005Ag-0.005Ce-ZnO powder was synthesized using sticky rice flour as a template. Mechanical coating of the 0.005Ag-0.005Ce-ZnO powder on activated alumina (Al2O3) beads was done to improve the appropriate packing in the fixed bed columns. Characterization of 0.005Ag-0.005Ce-ZnO showed a higher response to visible light and smaller crystallite size compared to zinc oxide synthesized with the same method. Using sticky rice starch as a template increased the uniform distribution of the elements. The photocatalytic batch test over 0.005Ag-0.005Ce-ZnO powder, 0.30 g/100 mL, could remove TCE up to 80% in 180 min. The decrease of TCE via photocatalysis compared to volatilization, adsorption, and photolysis presented the predominance of photocatalysis. Langmuir-Hinshelwood kinetics described that the decrease of TCE more depended on the reaction than adsorption. In addition, the TCE degradation steadily remained at 80-90% along the run of 0.005Ag-0.005Ce-ZnO@Al2O3 photocatalysis under visible light from both warm white lamps and sunlight in the continuous flow system. Besides photocatalysis, TCE adsorption on 0.005Ag-0.005Ce-ZnO@Al2O3 packed in the columns showed significant results. Our findings presented the possibility of applying the photocatalytic continuous flow system to remove TCE in industrial wastewater.

A first-principles study of the adsorption of trichloroethylene on vacancy-defected graphene decorated by Cu and/or Ni dimers

The adsorption behavior of trichloroethylene (TCE) on vacancy-defected graphene (VG) decorated by Cu2/Ni2/CuNi dimers (VG-Cu2/Ni2/CuNi) was studied by using first-principles calculation. Results showed that decorating with Cu2/Ni2/CuNi could increase the adsorption performance of VG, thus forming chemical adsorption between TCE and VG-Cu2/Ni2/CuNi. Furthermore, when VG was decorated by CuNi dimer in the configuration of VG-CuNi-2, the substrate exhibited the largest adsorption energy and charge transfer amount with TCE upon its adsorption. After TCE was adsorbed on VG-CuNi-2, the electrical conductivity of the substrate was increased significantly. Therefore, VG-CuNi-2 could be used as a sensing material to detect TCE molecules.

Al–Fe pillared bentonite−Fe3O4–CaO2 nanocomposite for efficient adsorption and degradation of trichloroethylene

The agglomeration of magnetic nanoparticles significantly affects their catalytic efficiency, and the reduction of oxidant dosage is crucial for the practical application of heterogeneous catalysis from the perspective of cost and environmental friendliness. Al–Fe pillared bentonite−Fe3O4–CaO2 nanocomposite (PB@Fe3O4–CaO2) was synthesized in this study to form a heterogeneous catalytic system, and trichloroethylene (TCE) was used as the target contaminant because of its universality and volatility. The adsorption of TCE in the PB@Fe3O4–CaO2 system reached 63.9% under the condition of release inhibition of H2O2 from CaO2, and the value decreased to 28.2% and 29.8% under conditions favoring H2O2 release owing to the efficient catalytic degradation of TCE (68.0% and 65.4%, respectively). A higher systematic pH would result in a significant decrease in the TCE removal efficiency in the PB@Fe3O4–CaO2 system owing to the decrease in the yield of H2O2 and the tendency toward O2 generation. The co-existing inorganic anions and cations also resulted in a decrease in the efficiency of TCE removal, which was attributed to the generation of weak free radicals and promote the aggregation of the catalyst, respectively. Although the adsorption effect was 50.9% for TCE removal in actual groundwater, the degradation efficiency of TCE in the PB@Fe3O4–CaO2 system (41.9%) was approximately the same as that of the PB@Fe3O4/H2O2 system (40.9%) considering TCE volatilization. This research provides a material for the efficient adsorption and degradation of trichloroethylene without the need for the exogenous addition of oxidants.

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.

Adsorption and reduction of trichloroethylene by sulfidated nanoscale zerovalent iron (S-nZVI) supported by Mg(OH)2.

Sulfidated nanoscale zerovalent iron (S-nZVI) supported on a flower spherical Mg(OH)2 with different Mg/Fe ration were successfully synthesized. The synthesized materials were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS). The results showed that S-nZVI particles were well dispersed on the petals of the flower spherical Mg(OH)2. The influence of factors, including the initial solution pH, Mg/Fe, S/Fe were studied. The trichloroethylene (TCE) adsorption data on Mg(OH)2 and S-nZVI @Mg(OH)2 fit well to a Langmuir isotherm model, and the maximum adsorption of S-nZVI @Mg(OH)2 was 253.55mg/g, which was 2.6-fold of S-nZVI. Meanwhile, the S-nZVI @Mg(OH)2 composite expanded the pH selection range of S-nZVI from 2 to 11. Cycling experiments showed that removal rate was 58.3% for the 5th cycle. TCE removal was due to synergistic action of reduction coupled with adsorption. During this process, 65.43% of total remove TCE from ion chromatography data was reduced and 34.57% of total remove TCE was adsorbed finally. At the same time, adsorption favors reduction. These observations indicated that the S-nZVI @Mg(OH)2 can be considered as potential adsorbents to remove TCE for environment remediation.

Unveiling the positive effect of mineral induced natural organic matter (NOM) on catalyst properties and catalytic dechlorination performance: An experiment and DFT study

Herein, we report the significant effects of natural organic matter contained in natural zeolite (Z-NOM) on the physicochemical characteristics of a Ni/Fe@natural zeolite (NF@NZ) catalyst and its decontamination performance toward the dechlorination of trichloroethylene (TCE). Z-NOM predominantly consists of humic-like substances and has demonstrable utility in the synthesis of bimetallic catalysts. Compared to NF@NZ600C (devoid of Z-NOM), NF@NZ had increased dispersibility and mobility and showed significant enhancement in the catalytic dechlorination of TCE owing to the encapsulation of Ni0/Fe0 nanoparticles by Z-NOM. The results of corrosion experiments, spectroscopic analyses, and H2 production experiments confirmed that Ni0 acted as an efficient cocatalyst with Fe0 to enhance the dechlorination of TCE to ethane, and Z-NOM-capped Ni0 showed improved adsorption of TCE and atomic hydrogen on their reactive sites and oxidation resistance. The density functional theory (DFT) studies have substantiated the improved adsorption of TCE due to the presence of NOM (especially by COOH structure) and the enhanced charge density at the Ni site in the Ni/Fe bimetal alloy for the stronger adsorption of hydrogen atoms that ultimately enhanced the TCE reduction reaction. These findings illustrate the efficiency of NOM containing natural minerals toward the synthesis of bimetallic catalysts for practical applications.

Physisorption of trichloroethylene and tetrachloroethylene on novel zeta arsenene nanotubes – A first-principles study

The structural stability of novel ζ-arsenene nanotubes (ζ-AsNT) is studied based on the density functional theory framework and is used as a base material for the detection of trichloroethylene and tetrachloroethylene vapours. The formation energy of ζ-AsNT is found to be −4.321 eV/atom and the energy band gap is 0.304 eV. Besides, the changes in the electronic properties of ζ-AsNT are explored with regard to the projected density of states, charge transfer, and electron density difference. The bandgap energy decreases for hollow site orientation to 0.205 and 0.204 eV for trichloroethylene and tetrachloroethylene vapours and increases for the valley and top site orientations. The adsorption energies were maximum for the valley site orientation of target molecules onto ζ-AsNT (01.165 and −1.513 eV for trichloroethylene and tetrachloroethylene, respectively). Moreover, the target vapours trichloroethylene and tetrachloroethylene are physisorbed on ζ-AsNT enabling the recycling of base substrate for continuous operation. The average energy gap changes vary from 18 to 32.9% depending on adsorption sites. The variation in the average energy gap owing to adsorption of trichloroethylene and tetrachloroethylene indicates the chemo-sensing nature of ζ-AsNT. The current report lays the inroads in the development of a new sensing element for the detection of chloroethylene molecules.

A Polyhydroxybutyrate (PHB)-Biochar Reactor for the Adsorption and Biodegradation of Trichloroethylene: Design and Startup Phase.

In this work, polyhydroxy butyrate (PHB) and biochar from pine wood (PWB) are used in a mini-pilot scale biological reactor (11.3 L of geometric volume) for trichloroethylene (TCE) removal (80 mgTCE/day and 6 L/day of flow rate). The PHB-biochar reactor was realized with two sequential reactive areas to simulate a multi-reactive permeable barrier. The PHB acts as an electron donor source in the first “fermentative” area. First, the thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses were performed. The PHB-powder and pellets have different purity (96% and 93% w/w) and thermal properties. These characteristics may affect the biodegradability of the biopolymer. In the second reactive zone, the PWB works as a Dehalococcoides support and adsorption material since its affinity for chlorinated compounds and the positive effect of the “coupled adsorption and biodegradation” process has been already verified. A specific dechlorinating enriched culture has been inoculated in the PWB zone to realize a coupled adsorption and biodegradation process. Organic acids were revealed since the beginning of the test, and during the monitoring period the reductive dichlorination anaerobic pathway was observed in the first zone; no chlorinated compounds were detected in the effluent thanks to the PWB adsorption capacity.

Equilibrium and thermodynamic study of trichloroethylene adsorption on activated carbon in a fluidized bed and its thermal regeneration

AbstractVolatile organic compounds (VOC), used as solvents in industries, are major sources of air pollution. Trichloroethylene (TCE) is a chlorinated VOC widely used in industries. TCE vapours are toxic in nature and adversely affect human health and the surrounding environment when exposed over the threshold limit value for a long duration. Adsorption of TCE vapours using activated carbon as an adsorbent in a fluidized bed and its thermal regeneration is a viable, effective, and economic technology for its separation from air. However, before designing such a system, the equilibrium and thermodynamic study of the adsorption of TCE vapour on activated carbon is important. In this study, the dynamic adsorption of TCE vapour was carried out in a fluidized bed using nitrogen as the carrier gas. The effect of operating conditions, including particle size of activated carbon (212–710 μm), flowrate of nitrogen (carrier gas), adsorption temperature (303–353 K), and the concentration of TCE vapour in nitrogen at the inlet (25–85 mg/L) on the adsorption capacity of TCE on the fluidized bed of activated carbon, was examined. The experimental results obtained were analyzed using the Langmuir and Freundlich adsorption isotherms. The thermodynamic study showed that the adsorption of TCE was spontaneous, exothermic, and physical in nature. The effect of regeneration temperature and purge gas flowrate on the renewal of used activated carbon was also studied.

Adsorption of trichloroethylene on common indoor materials studied using a combined inverse gas chromatography and frequency response technique

Building materials can act as sinks and sources of volatile organic compounds (VOCs) which are indoor air contaminants. A knowledge of the dynamics of VOC sorption processes on building materials is needed in order to fully understand how these compounds can influence indoor air quality, and thus, their potential for influencing human health. In the current work, a combination of classical inverse gas chromatography (IGC) and frequency response (FR) technique was used to investigate the sorptive partition and diffusion coefficients of trichloroethylene (TCE) on building materials. This is a compound of considerable interest in many indoor air environments, particularly those impacted by vapor intrusion processes, and the TCE also serves as a model VOC for demonstrating the method. Six typical indoor materials (carpet, cotton, cinderblock, printer paper, polyethylene, drywall) were selected to demonstrate the technique. A selected building material was packed into a stainless-steel column and exposed to a low-concentration TCE flow applied in a sinusoidal temporal pattern at room temperature (22 ℃). In this case, cinderblock showed the highest sorption uptakes (6209 ng TCE/g material-ppbv TCE) and the slowest sorption rates (7.3 × 10−10 m2/s) among tested materials. The results from the FR-IGC method are compared to other conventionally obtained results and agree well.

Pyridinic nitrogen enables dechlorination of trichloroethylene to acetylene by green rust: Performance, mechanism and applications

Carbonous materials were found to catalyze the dechlorination of trichloroethylene (TCE) by green rust (GR), but the catalytic mechanism was not fully understood. We have developed a facile ball milling method to synthesize N-doped graphene (NG) with various N species, catalyzing fast dechlorination of TCE to acetylene by GR with the highest acetylene production rate of ~0.1 d−1. The adsorption of TCE onto NG is mainly derived from the graphene region of NG, and high pyridinic N is essential for the enhanced TCE reduction by GR. Oxygen species did not enhance the TCE reduction in GR/NG system. High dechlorination rates are correlated to a high amount of defect in NG and a high electron conductivity of NG. Pyridinic N has the highest adsorption energy for TCE among all the N species, which leads to the highest catalytic performance. High electrochemically active surface area resulted from the high content of pyridinic N facilitate the NG-catalyzed dechlorination. The acetylene production rate in real groundwater is still around one-third of that in ultrapure water. This work not only reveals the catalytic mechanism of NG-catalyzed dechlorination by GR, but also provide a feasible approach for practical remediations of TCE-contaminated groundwater using GR-NG mixture.

Coupled Adsorption and Biodegradation of Trichloroethylene on Biochar from Pine Wood Wastes: A Combined Approach for a Sustainable Bioremediation Strategy.

Towards chlorinated solvents, the effectiveness of the remediation strategy can be improved by combining a biological approach (e.g., anaerobic reductive dechlorination) with chemical/physical treatments (e.g., adsorption). A coupled adsorption and biodegradation (CAB) process for trichloroethylene (TCE) removal is proposed in a biofilm–biochar reactor (BBR) to assess whether biochar from pine wood (PWB) can support a dechlorinating biofilm by combining the TCE (100 µM) adsorption. The BBR operated for eight months in parallel with a biofilm reactor (BR)—no PWB (biological process alone), and with an abiotic biochar reactor (ABR)—no dechlorinating biofilm (only an adsorption mechanism). Two flow rates were investigated. Compared to the BR, which resulted in a TCE removal of 86.9 ± 11.9% and 78.73 ± 19.79%, the BBR demonstrated that PWB effectively adsorbs TCE and slows down the release of its intermediates. The elimination of TCE was quantitative, with 99.61 ± 0.79% and 99.87 ± 0.51% TCE removal. Interestingly, the biomarker of the reductive dechlorination process, Dehalococcoides mccartyi, was found in the BRR (9.2 × 105 16S rRNA gene copies/g), together with the specific genes tceA, bvcA, and vcrA (8.16 × 106, 1.28 × 105, and 8.01 × 103 gene copies/g, respectively). This study suggests the feasibility of biochar to support the reductive dechlorination of D. mccartyi, opening new frontiers for field-scale applications.