Grantee Research Project Results
2000 Progress Report: Bioavailability of Aromatic Hydrocarbons in Saturated Porous Media: The Effects of Chemical Aging and Mass Transfer
EPA Grant Number: R825406Title: Bioavailability of Aromatic Hydrocarbons in Saturated Porous Media: The Effects of Chemical Aging and Mass Transfer
Investigators: Bouwer, Edward J. , Ball, William P.
Institution: The Johns Hopkins University
EPA Project Officer: Chung, Serena
Project Period: December 6, 1996 through December 5, 1999 (Extended to December 5, 2001)
Project Period Covered by this Report: December 6, 1999 through December 5, 2000
Project Amount: $439,725
RFA: Environmental Fate and Treatment of Toxics and Hazardous Wastes (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management , Safer Chemicals
Objective:
The purpose of this research is to evaluate, quantify, and model the effects of sorption/desorption processes and diffusional mass transfer on the biodegradation of polynuclear aromatic hydrocarbons (PAHs) in sediment/water systems, and under "aged" conditions, i.e., under conditions where the solids have been exposed to high aqueous concentration of contaminants for long time (up to several years). A further objective is to develop and evaluate means of mathematically simulating and predicting rates of bioremediation from aged sediments, using independent estimates of bacterial activity, sorption isotherms, and desorption mass transfer rates. A guiding hypothesis of the research has been that desorption rates often control overall rates of biodegradation and that these rates are in turn determined by both the nature of intrasorbent diffusion (effective coefficient and diffusion length scale) and the initial contaminant concentration gradient within the sorbent. In this context, "aging" effects on the biodegradation rate of PAHs are an expected result of time-variant physical distributions of contaminant within the sorbent.Progress Summary:
This research has involved abiotic and biotic experimental efforts as well as associated modeling efforts and data interpretation. Experimental efforts have included batch biodegradation, sorption, and desorption studies as well as column-based transport experiments through packed beds of the various sediments. A summary of the research tasks that were either initiated and/or completed during the 1999-2000 grant year (no-cost extension period) is provided below:- Biotic studies of the mineralization of 14 sup>C-labeled phenanthrene were conducted with sediments that had been abiotically "aged" for 900 days. These studies supplemented previous mineralization studies at other aging periods, as conducted during the 1997-1998 grant year.
- Batch sorption equilibrium studies were completed for naphthalene and phenanthrene with pulverized Borden sand. The sorption equilibrium studies were conducted at mixing times up to 30 days. They provide comparable results for sorption with unaltered sand and longer periods of equilibrium.
- Desorption rate studies were completed with phenanthrene and naphthalene as sorbates and Borden sand, Dover AFB orange silty clay loam aquitard material ("OSCL"), and Bozeman sediments as natural geosorbents. These geosorbents were abiotically aged in the presence of naphthalene or phenanthrene for a period of 900 days prior to initiation of desorption rate experiments. This work supplemented previous work completed during the 1998-1999 grant year for aging periods up to 270 days.
- Tracer studies were performed on some of the 14 sediment-filled HPLC columns that have been aged for approximately 2 years in the presence of synthetic groundwater. For the two materials evaluated (OSCL/macropore and Ottawa sand materials), results indicate no substantial change in hydrodynamic properties over this 2-year period.
- Experimental columns of three sorbent types (OSCL/ macropore, Borden sand, Ottawa sand) were subjected to the " breakthrough" and subsequent continuous feed ("aging") of synthetic groundwater containing a uniform aqueous concentration of 14C-labeled phenanthrene. Initial breakthrough effluent data were monitored. One column has already been subjected to elution by clean synthetic groundwater, following an aging period of 90 days. The remaining columns will be subjected to aging periods between 90 days and 1 year, and then eluted with clean water. This will be accomplished in the coming year.
- Some difficulties with the experimental column setup were identified and addressed. These difficulties included the following: (1) unsteady phenanthrene concentrations from generator columns, (2) retardation of phenanthrene in the stainless steel tubing used to sample soil columns, and (3) variability and bias in the sampling of column effluent concentrations, owing to unanticipated "carry over" effects with the automated sample collector. Because none of these experimental concerns have been reported previously in the literature, their nature and resolution should be of interest to the research community and future publication is intended. (Note: Although these difficulties do not compromise the integrity of our "aged" columns, they do complicate the interpretation of early breakthrough and elution data. New experiments are being performed to provide comparison with some of the early results.)
Future Activities:
In the coming year, two experimental columns will be subjected to aging periods between 90 days and 1 year, and then eluted with clean water. Although the difficulties with the experimental column setup that were identified do not compromise the integrity of our "aged" columns, they do complicate the interpretation of early breakthrough and elution data. Therefore, new experiments will be performed to provide comparison with some of the early results.Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 11 publications | 3 publications in selected types | All 3 journal articles |
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Type | Citation | ||
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Xia G, Ball WP. Adsorption-partitioning uptake of nine low-polarity organic chemicals on a natural sorbent. Environmental Science & Technology 1999;33(2):262-269. |
R825406 (1998) R825406 (1999) R825406 (2000) R825406 (Final) |
not available |
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Xia GS, Ball WP. Polanyi-based models for the competitive sorption of low-polarity organic contaminants on a natural sorbent. Environmental Science & Technology 2000;34(7):1246-1253. |
R825406 (2000) R825406 (Final) |
not available |
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Zhang WX, Bouwer EJ, Ball WP. Bioavailability of hydrophobic organic contaminants: Effects and implications of sorption-related mass transfer on bioremediation. Ground Water Monitoring and Remediation 1998;18(1):126-138. |
R825406 (1997) R825406 (1998) R825406 (1999) R825406 (2000) R825406 (Final) |
not available |
Supplemental Keywords:
bioavailability, sorption, mass transfer, aging, intrinsic bioremediation, polynuclear aromatic hydrocarbons, PAHs., Scientific Discipline, Toxics, Waste, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, National Recommended Water Quality, Environmental Chemistry, HAPS, Chemistry, Fate & Transport, Bioremediation, Ecological Risk Assessment, fate and transport, hydrocarbon, bioremediation model, Naphthalene, aquifer sediments, biodegradation, field studies, sorption kinetics, chemical speciation, saturated porous material, adsorption, chemical transport, kinetic studies, mass transfer, soils, toxicity, contaminants in soil, hazardous waste cleanup, soil characterization, saturated porous media, 1, 2-Dichlorobenzene, environmental toxicant, harmful environmental agents, mobility, aging, biodegradation of hydrophobic organic contaminants, contaminated aquifers, Phenanthrene, groundwater, hydrocarbon desorption kinetics, transportProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.