Abiotic Degradation of Chlorinated Hydrocarbons (CHCs) with Zero-valent Magnesium (ZVM) and Zero-valent Palladium Bimetallic (Pd/Mg)-reductant PDF Download
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Author: Fang Yu Publisher: ISBN: Category : Chlorohydrocarbons Languages : en Pages : 71
Book Description
Chlorinated hydrocarbons (CHCs) in groundwater can be treated by monometallic and bimetallic metal reductants through abiotic degradation. The breakdown of CHC is achieved by gaining electrons from those reductants and removing chlorines from CHC molecules to transform the CHCs into less chlorinated compounds. As a proven technology in groundwater treatment, permeable reactive barriers (PRBs) have been used to passively treat contaminated groundwater, in which granular metals can be used as reactive materials. This study explored the abiotic degradation of CHCs by zero-valent magnesium (ZVM) and bimetallic palladium/magnesium (Pd/Mg) reductants. Different CHCs (carbon tetrachloride, chloroform, dichloromethane (DCM), 1,2-dichloroethane (1,2-DCA), 1,1,2-trichloroethane (1,1,2-TCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,2-dichloropropane (1,2-DCP), and 1,2,3-Trichloropropane (1,2,3-TCP) were chosen as target contaminants. Results showed that even with its high reduction potential, ZVM did not treat CHCs effectively due to corrosion of Mg by water, which formed Mg (OH)2(s) precipitate on the metal surface and prevented further reaction. Such inhibition can be reduced by lowering pH conditions. However, in the presence of Pd, CHCs were removed at a much faster rate at neutral pH conditions. Hydrocarbons were produced as sole products, which indicated complete degradation of CHCs by Pd/Mg. Recalcitrant CHCs such as DCM, 1, 1,2-TCA, 1,2-DCP and 1,2,3-TCP were found to be effectively degraded by Pd/Mg. No significant effect of Pd loading on CHC degradation was observed, while the degradation was accelerated by increasing the Mg loading.
Author: Fang Yu Publisher: ISBN: Category : Chlorohydrocarbons Languages : en Pages : 71
Book Description
Chlorinated hydrocarbons (CHCs) in groundwater can be treated by monometallic and bimetallic metal reductants through abiotic degradation. The breakdown of CHC is achieved by gaining electrons from those reductants and removing chlorines from CHC molecules to transform the CHCs into less chlorinated compounds. As a proven technology in groundwater treatment, permeable reactive barriers (PRBs) have been used to passively treat contaminated groundwater, in which granular metals can be used as reactive materials. This study explored the abiotic degradation of CHCs by zero-valent magnesium (ZVM) and bimetallic palladium/magnesium (Pd/Mg) reductants. Different CHCs (carbon tetrachloride, chloroform, dichloromethane (DCM), 1,2-dichloroethane (1,2-DCA), 1,1,2-trichloroethane (1,1,2-TCA), 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA), 1,2-dichloropropane (1,2-DCP), and 1,2,3-Trichloropropane (1,2,3-TCP) were chosen as target contaminants. Results showed that even with its high reduction potential, ZVM did not treat CHCs effectively due to corrosion of Mg by water, which formed Mg (OH)2(s) precipitate on the metal surface and prevented further reaction. Such inhibition can be reduced by lowering pH conditions. However, in the presence of Pd, CHCs were removed at a much faster rate at neutral pH conditions. Hydrocarbons were produced as sole products, which indicated complete degradation of CHCs by Pd/Mg. Recalcitrant CHCs such as DCM, 1, 1,2-TCA, 1,2-DCP and 1,2,3-TCP were found to be effectively degraded by Pd/Mg. No significant effect of Pd loading on CHC degradation was observed, while the degradation was accelerated by increasing the Mg loading.
Author: Andrew Franze Publisher: ISBN: Category : Bioremediation Languages : en Pages : 89
Book Description
Nanoscale zero valent iron (nZVI) is a remediation technology that can be used to treat chlorinated hydrocarbons (CHCs) in contaminated aquifers. Nanoparticles remain mobile in water and can be transported with groundwater flow to contaminated zones. However, due to magnetic and van der Waals forces, unstabilized nZVI agglomerates. Carboxymethylcellulose (CMC) was used as a polyelectrolyte stabilizer in this study. nZVI serves as an electron donor and can dechlorinate CHCs. nZVI reactivity with CHCs can be enhanced by addition of a secondary metal catalyst. This study evaluates the potential of copper amended nZVI (Cu-nZVI) to degrade select CHCs. The objective of this study was to characterize degradation of select CHCs in batch reactors with regard to degradation kinetics and degradation byproduct distributions. The following CHCs were studied: CF, 1,1,2,2-TeCA, 1,1,1-TCA, 1,1,2-TCA, PCE, TCE, cis-DCE, trans-DCE, and 1,2,3-TCP. Degradation kinetics were quantified using a pseudo first-order rate constant (kobs). Initial degradation of CHCs was reported separately from later degradation, which occurred after 0.5 hr. The change in reaction kinetics with time could be caused by particle aging. The effect of Cu loading and nZVI concentration was evaluated with CF degradation. Increasing Cu loading or nZVI concentrations yielded faster degradation rates. Increasing Cu loading systematically increased methane byproduct production. The loss of reactivity with CF after 0.5 hr was greater for nZVI when compared to Cu-nZVI. Degradation kinetics were faster and byproduct distribution was more favorable for Cu-nZVI than nZVI for all CHCs studied. Cu-nZVI outperformed most other bimetallic nZVI reductants reported in the literature for CF and chlorinated ethanes treatment. Cu-nZVI invokes a-elimination of CF and 1,l,1-TCA, which produces reactive carbene intermediates capable of degrading into benign products such as methane, ethane, and ethene. Cu-nZVI also showed potential for 1,2,3-TCP remediation. However, Cu-nZVI was particularly ineffective at degrading chlorinated ethenes. Chlorinated ethene degradation pathways and mechanisms induced by Cu-nZVI were not clearly identified. Particle longevity experiments showed that reactivity with 1,1,1-TCA decreases as particles age. Unstable Cu-nZVI particles showed a slow linear decline in reactivity with time, whereas CMC stabilized Cu-nZVI particles showed a rapid power function decline in reactivity with time. The unstable particles were 12-fold faster compared to stablized particles 24 hr after particle synthesis. Even with declines in reactivity, 1,1,1-TCA was rapidly degraded (over a few hours) by both stable and unstable Cu-nZVI seven days after particle synthesis. Cu-nZVI hydrogen production was minor and was limited to occurring immediately after particle synthesis. Cu-nZVI shows great potential for treating certain CHCs.
Author: Md Abu Raihan Chowdhury Publisher: ISBN: Category : Chlorohydrocarbons Languages : en Pages : 64
Book Description
Nanoscale Zero Valent Iron (NZVI) has shown limited effectiveness in degrading chlorinated hydrocarbons (CHCs), like 1,1,1-Trichloroethane (1,1,1-TCA) and Trichloroethene (TCE), in aqueous solution. A rapid agglomeration behavior of NZVI particles due to van der waals and magnetic forces can negatively impact its overall effectiveness due to increase in particle size, and decline in CHC degradation kinetics. Different support materials, such as clays and activated carbon, have been used to stabilize NZVI particle and reduce agglomeration in aqueous solution. In this bench-scale study, NZVI supported on Powdered Activated Charcoal (PAC) was selected to prepare a composite, called PAC/NZVI, for a more effective treatment of 1,1,1-TCA and TCE in aqueous solution. The study shows that PAC/NZVI has both adsorption and degradation capability toward 1,1,1-TCA and TCE. PAC exhibited high porosity to accommodate NZVI as a suitable support in order to keep NZVI in suspension in aqueous medium and to minimize agglomeration. Bench-scale experiments with variable concentrations of PAC (0.1{u2013}0.8 g/L) and NZVI (0.2{u2013}0.6 g/L) showed that PAC/NZVI composite can be highly efficient in rapid 1,1,1-TCA removal by adsorption, and effective in overall degradation leading to production of non-chlorinated daughter products. Increase in PAC concentration in the composite was correlated with greater removal of 1,1,1-TCA by sorption whereas lower PAC concentration yielded greater degradation kinetics and higher byproduct yields. PAC/NZVI was found to be active for more than three months presumably because NZVI embedded within hydrophobic pore spaces of PAC did not get oxidized. Cu amendment to NZVI as a secondary/catalysts metal showed faster degradation and higher byproduct yields.
Author: Shirin Ghahghaei Nezamabadi Publisher: ISBN: Category : Environmental sciences Languages : en Pages : 92
Book Description
Nanoscale zero-valent iron (nZVI) injections have proven to be a promising approach for the remediation of aquifers contaminated by chlorinated organic pollutants. This study compares the efficacy of nZVI in sulfidated and unamended forms in degrading selected chlorinated hyrocarbons (CHCs). Results show that nZVI amended with iron monosulfide (FeS) increases the rate of dechlorination of CT, CF and 1,1,1-TCA compared to that by unamended nZVI. The focus of this research was to characterize degradation kinetics and degradation byproduct distributions of CT, CF and 1,1,1-TCA by nZVI coated by iron monosulfide, which is represented as nZVI/FeS. To prevent nZVI particles from agglomerating, carboxymethylcellulose (CMC) was used as a stabilizer in all experiments. Results indicated that the nZVI/FeS system was faster and produced less toxic byproducts than nZVI for all CHCs studied. a-elimination in nZVI/FeS system was an important degradation pathway for CF and 1,l,1-TCA: it produces reactive carbene intermediates capable of degrading into benign products such as methane, ethane, and ethene. The effect of sulfide loading on degradation was evaluated with all CHCs studied. Regardless of CHC type, the rate constant (kobs) increased with increasing sulfide loading, reaching the highest amount at 1 wt% sulfide, and then decreased with higher sulfide loading. An additional study focused on the effects of varying of the concentration of nZVI and CMC, and particle longevity on the degradation of 1,1,1-TCA in the nZVI/FeS system with 1 wt.% sulfide. Particle longevity experiments showed that reactivity with 1,1,1-TCA decreases as particles age. nZVI/FeS particles showed a rapid power function decline in reactivity with time. Increasing the amount of iron-reducing chemical during nZVI/FeS synthesis improved reactivity by 43%. The addition of a polyelectrolyte stabilizer at an optimized concentration of 4.0 g/L further increased nZVI/FeS reactivity by 350%. nZVI/FeS shows great potential for treating certain CHCs.
Author: Fang Yu
Author: Fang Yu
Author: Andrew Franze
Author: Christopher Scott Cushman
Author: Md Abu Raihan Chowdhury
Author: Punam Patel
Author: Shirin Ghahghaei Nezamabadi