Laboratory evaluation of a prospective remediation method for PCB-contaminated paint

Background: Paint laden with polychlorinated biphenyls (PCBs) often acts as a point source for environmental contamination. It is advantageous to address contaminated paint before the PCBs transport to surrounding media; however, current disposal methods of painted material introduce a variety of complications. Previous work demonstrates that PCBs can be broken down at ambient temperatures and pressures through a degradation process involving magnesium metal and acidified ethanol. This report is an extension of that work by describing the development of a delivery system for said reaction in preparation for a field test. Two treatment options including the Activated Metal Treatment System (AMTS) and the Non-Metal Treatment System (NMTS) remove and degrade PCBs from painted surfaces. Findings: AMTS decreased the Aroclor® concentration of a solution by more than 97% within 120 minutes and the Aroclor® concentration of industrial paint chips by up to 98% over three weeks. After removing up to 76% of PCBs on a painted surface after seven days, NMTS also removed trace amounts of PCBs in the paint’s concrete substrate. The evaporation rate of the solvent (ethanol) from the treatment system was reduced when the application area was increased. The solvent system’s ability to remove more than 90% of PCBs was maintained after losing 36% of its mass to solvent evaporation. Conclusions: The delivery systems, AMTS and NMTS, are able to support the hydrodechlorination reaction necessary for PCB degradation and are therefore attractive options for further studies regarding the remediation of contaminated painted surfaces

Direct Comparison Of Flipping In The Large Lecture Environment

Very large lecture-based classes are a commonly used teaching mode at high-population universities. To ascertain the effectiveness of ?flipping the classroom? in these classes, a study focused on the change in the presentation mode: in-person lectures versus recorded lectures posted online with problem solving during class time. The study involved two very large classes (320 and 415 students) of second-semester general chemistry students taught by the same instructor. One class was taught in the traditional lecture format normally used within the department with example problems posted online. The other class was taught using a flipped protocol and those students accessed all lectures online with class time devoted to instructor-led examples and small group problem solving. Final grades were compared between the two groups and results showed that students in the flipped class had a greater percentage of high grades (?A? and ?B? grades) compared to the control group. The control group had more ?C? or average grades but the two groups had almost identical percentages of low grades (?D? and ?F?). This suggests that the average performing students were aided by this teaching method compared to the traditional teaching format. Surveys that were administered to each class at the end of the semester revealed that students in the flipped class found the online instruction valuable; 86% watched at least some recorded lectures more than once and 68% responded that they would take another class using this teaching method. The control class expressed a high evaluation of the in-class instruction but did not express a high evaluation of the example problems and slides (without recorded lecture) provided online

Reductive degradation of oxygenated polycyclic aromatic hydrocarbons using an activated magnesium/co-solvent system

This study evaluates the capability of zero-valent magnesium and a protic co-solvent to promote the degradation of oxygenated polycyclic aromatic hydrocarbons compounds, specifically 9-fluorenone, 9,10-anthraquinone, 7,12-benz(a)anthraquionone, and 7H-benz(de)anthracene-7-one. At room temperature conditions, greater than 86% degradation efficiency is observed after 24h of reaction time for a mixture containing 0.05g of magnesium and four selected oxygenated aromatic hydrocarbons with 250mgL-1 concentrations. It is noted that glacial acetic acid is needed as an activator for the degradation reaction to proceed. It is also presumed that the acid removes oxide and hydroxide species from the magnesium surface. With the GC-MS analysis of the reaction products, possible reductive pathways are suggested. Furthermore, this study is the first report on the degradation of these emerging contaminants and it is proposed that the magnesium-powder/protic-solvent system is a promising low-cost reagent and may allow for the future development of an economic and environmentally-friendly remediation application. © 2013 Elsevier Ltd

Comparative Study For The Removal And Destruction Of Pentachlorophenol Using Activated Magnesium Treatment Systems

Chlorophenols are highly toxic, environmentally-persistent compounds which have been classified as probable human carcinogens by the United States Environmental Protection Agency. Due to the high toxicity of these compounds, it is necessary to treat water and soils with concentrations of chlorophenols above the detection limit set by regulatory agencies. The aim of this work is to demonstrate the capabilities of using ball-milled magnesium for the dechlorination of PCP. Comparison of dechlorination processes were performed in an attempt to determine the most effective system for degradation of PCP to phenol. Three systems with powerful capabilities of treatment were studied: ball-milled zero-valent magnesium (ZVMg), ball-milled zero-valent magnesium carbon (ZVMg/C), and ball-milled zero-valent magnesium with palladium (ZVMg/Pd). In addition to measuring PCP disappearance, all byproducts were identified and quantified for each degradation system. The results of these studies indicate that all three of the systems degrade PCP within 30 min. The most rapid and complete PCP dechlorination is achieved using ball-milled Mg/Pd and a matrix consisting of at least 0.02 g Mg0/mL ethanol, and 10 μL acetic acid/mL ethanol, in which case 20 ng/μL of PCP was dechlorinated to chlorophenols in approximately 15 min with complete dechlorination achieved in six days. Carbon mass balances of 90.16% for Mg, 94.76% (Mg/C) and 97.05% (Mg/Pd) verify dechlorination was responsible for declining concentrations of PCP. The reactions of PCP degradation and phenol formation were found to follow pseudo-first order kinetics for all systems. Further work will consist of optimization and development of field-scale applications

Multivariate evaluation and optimization of an activated-magnesium/co-solvent system for the reductive degradation of polycyclic aromatic hydrocarbons

The present study evaluates the capability of an activated-magnesium metal and protic co-solvents to promote the reductive degradation of three different polycyclic aromatic hydrocarbons, specifically pyrene, benzo[k]fluoranthene and benzo[g,h,i]perylene. Multivariate analyses demonstrated that the kinetics of degradation was affected by several experimental factors such as magnesium loading, acid addition and solubility of the compounds. It was determined that an acid activator is needed for the degradation reaction to proceed and it is also noted that the use of a 1:1 ethanol/ethyl lactate co-solvent is ideal for the complete dissolution of all three compounds with concentrations varying from 200 to 275mgL-1. The experimental results also indicate that, at room temperature conditions, only 0.05-0.1g of magnesium is required in order to achieve greater than 93% degradation efficiency after 24h of reaction. This methodology is attractive and may allow for the development of an economic and environmentally friendly field application for the remediation of other polycyclic aromatic hydrocarbons. © 2013 Elsevier B.V

Reductive Degradation Of Oxygenated Polycyclic Aromatic Hydrocarbons Using An Activated Magnesium/Co-Solvent System

This study evaluates the capability of zero-valent magnesium and a protic co-solvent to promote the degradation of oxygenated polycyclic aromatic hydrocarbons compounds, specifically 9-fluorenone, 9,10-anthraquinone, 7,12-benz(a)anthraquionone, and 7H-benz(de)anthracene-7-one. At room temperature conditions, greater than 86% degradation efficiency is observed after 24h of reaction time for a mixture containing 0.05g of magnesium and four selected oxygenated aromatic hydrocarbons with 250mgL-1 concentrations. It is noted that glacial acetic acid is needed as an activator for the degradation reaction to proceed. It is also presumed that the acid removes oxide and hydroxide species from the magnesium surface. With the GC-MS analysis of the reaction products, possible reductive pathways are suggested. Furthermore, this study is the first report on the degradation of these emerging contaminants and it is proposed that the magnesium-powder/protic-solvent system is a promising low-cost reagent and may allow for the future development of an economic and environmentally-friendly remediation application. © 2013 Elsevier Ltd

Multivariate Evaluation And Optimization Of An Activated-Magnesium/Co-Solvent System For The Reductive Degradation Of Polycyclic Aromatic Hydrocarbons

The present study evaluates the capability of an activated-magnesium metal and protic co-solvents to promote the reductive degradation of three different polycyclic aromatic hydrocarbons, specifically pyrene, benzo[k]fluoranthene and benzo[g,h,i]perylene. Multivariate analyses demonstrated that the kinetics of degradation was affected by several experimental factors such as magnesium loading, acid addition and solubility of the compounds. It was determined that an acid activator is needed for the degradation reaction to proceed and it is also noted that the use of a 1:1 ethanol/ethyl lactate co-solvent is ideal for the complete dissolution of all three compounds with concentrations varying from 200 to 275mgL-1. The experimental results also indicate that, at room temperature conditions, only 0.05-0.1g of magnesium is required in order to achieve greater than 93% degradation efficiency after 24h of reaction. This methodology is attractive and may allow for the development of an economic and environmentally friendly field application for the remediation of other polycyclic aromatic hydrocarbons. © 2013 Elsevier B.V

Mechanistic And Computational Studies Of Pcb 151 Dechlorination By Zero Valent Magnesium For Field Remediation Optimization

Polychlorinated biphenyls (PCBs) are banned in the U.S. but are persistent in the environment; current regulations provide an urgent need to remediate PCBs in a cost-effective way. In prior work, a novel method of degradation of PCBs via hydrodehalogenation with ball milled zero-valent magnesium and activated carbon showed promising results even with water present in the system. In this research, a detailed study of the byproducts formed in the dechlorination process for PCB 151 (used as an example of hexa-chlorinated PCB) and a study of the mechanism involved in this reaction via density functional theory (DFT) computations are presented. It was demonstrated that these reactions are exothermic and involved two transition states, the formation of the ionic transition state being the rate limiting step of the reaction. The torsion angle of the PCB congeners was also shown to be an extremely important factor to be able to use activated carbon as part of the remediation process

Remediation of Chlorinated Alkanes by Vitamin B12 and Zero-Valent Iron

Chlorinated alkanes were heavily used in a wide range of industrial applications including as degreasers, paint strippers, chemical intermediates, and soil fumigants. These compounds are an environmental concern due to the adverse health effects associated with them and have been detected in environmental matrices including soils and groundwater. Chlorinated alkanes are recalcitrant, and current remediation methods that employ zero-valent iron (ZVI) are unable to directly dehalogenate these compounds, limiting the available approaches for in situ remediation of these widely utilized chemicals. This study employed a novel approach for the remediation of 1,2,3-trichloropropane (TCP), 1,2-dichloropropane (1,2-DCP), 1,3-dichloropropane (1,3-DCP), 1-chloropropane (1-CP), and 1,2-dichloroethane (1,2-DCA) in the presence of ZVI and vitamin B12, a naturally occurring electron mediator. Batch reactions were performed in order to determine a kinetic model for the associated degradation mechanisms. Dechlorination byproducts were confirmed through gas chromatography-mass spectrometry (GC-MS) coupled to a purge and trap. Free chloride was quantified by ion chromatography (IC) utilizing suppressed conductivity detection. In the absence of vitamin B12, reductive dechlorination of chlorinated alkanes was observed to not occur when exposed to only reactive ZVI particles (<5 μm). However, in the presence of ZVI combined with vitamin B12, complete reductive dechlorination was observed and followed a pseudo-first-order reaction

Indirect Determination Of Hydroxyl Radicals In Fine Particle Mist Generated From An Odor Control Technology Via Hplc

Size distribution analysis of microsized water particle mist generated from an odor control technology showed the majority of particles to be in the low micron range. The indirect detection and determination of hydroxyl radicals generated by their reaction with benzene to produce phenol was performed through UV-Vis spectrophotometry (UV-Vis) and high performance liquid chromatography (HPLC). These techniques gave verification of the presence of hydroxyl radical species in the water samples collected via this odor control technology. This technology is currently being utilized at various wastewater treatment plants. © 2013 Copyright 2013 International Ozone Association