Field Air Analysis With Solid Phase Microextraction

Current methods and field data for air sampling and analysis with solid phase microextraction (SPME) using spot and time-weighted average (TWA) modes were presented. These methods included BTEX, formaldehyde, and total VOC analysis in residential and occupational air. Recent developments in field air sampling with SPME included the theory of rapid air sampling and diffusion-based quantification of VOC in air with adsorptive SPME fiber coatings. This methodology is the fastest VOC air sampling method based on extraction. Novel portable devices were designed and tested to apply this concept to living plant aroma and VOC in occupational air. In addition, SPME fibers were used for sampling and analysis of aerosols and airborne particulate matter from several sources. Experiments were also completed to determine the feasibility of single particle matrix investigations with SPME fibers and Raman micro spectra copy measurements. New experiments are currently conducted to apply the rapid SPME sampling to agricultural odors. Advantages and challenges associated with field air analysis with SPME were discussed.4111310131

Chromate reduction in highly alkaline groundwater by zerovalent iron: Implications for its use in a permeable reactive barrier

It is not currently known if the widely used reaction of zerovalent iron (ZVI) and Cr(VI) can be used in a permeable reactive barrier (PRB) to immobilize Cr leaching from hyperalkaline chromite ore processing residue (COPR). This study compares Cr(VI) removal from COPR leachate and chromate solution by ZVI at high pH. Cr(VI) removal occurs more rapidly from the chromate solution than from COPR leachate. The reaction is first order with respect to both [Cr(VI)] and the iron surface area, but iron surface reactivity is lost to the reaction. Buffering pH downward produces little change in the removal rate or the specific capacity of iron until acidic conditions are reached. SEM and XPS analyses confirm that reaction products accumulate on the iron surface in both liquors, but that other surface precipitates also form in COPR leachate. Leachate from highly alkaline COPR contains Ca, Si, and Al that precipitate on the iron surface and significantly reduce the specific capacity of iron to reduce Cr(VI). This study suggests that, although Cr(VI) reduction by ZVI will occur at hyperalkaline pH, other solutes present in COPR leachate will limit the design life of a PRB

Understanding pH effects on trichloroethylene and perchloroethylene adsorption to iron in permeable reactive barriers for groundwater remediation

Metallic iron filings are becoming increasing used in permeable reactive barriers for remediating groundwater contaminated by chlorinated solvents. Understanding solution pH effects on rates of reductive dechlorination in permeable reactive barriers is essential for designing remediation systems that can meet treatment objectives under conditions of varying groundwater properties. The objective of this research was to investigate how the solution pH value affects adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) on metallic iron surfaces. Because adsorption is first required before reductive dechlorination can occur, pH effects on halocarbon adsorption energies may explain pH effects on dechlorination rates. Adsorption energies for TCE and PCE were calculated via molecular mechanics simulations using the Universal force field and a self-consistent reaction field charge equilibration scheme. A range in solution pH values was simulated by varying the amount of atomic hydrogen adsorbed on the iron. The potential energies associated TCE and PCE complexes were dominated by electrostatic interactions, and complex formation with the surface was found to result in significant electron transfer from the iron to the adsorbed halocarbons. Adsorbed atomic hydrogen was found to lower the energies of TCE complexes more than those for PCE. Attractions between atomic hydrogen and iron atoms were more favorable when TCE versus PCE was adsorbed to the iron surface. These two findings are consistent with the experimental observation that changes in solution pH affect TCE reaction rates more than those for PCE