Grantee Research Project Results
1999 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, 1998 through December 5, 1999
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 hydrophobic organic contaminants (HOCs) under conditions where aquifer solids and impermeable aggregates of such solids have been exposed to long-term contamination (aging). Furthermore, it is the objective of this research to explore the ability to predict the intrinsic rates of bioremediation of aged compounds based on sorbent and sorbate properties using a coupled desorption/biodegradation model.Progress Summary:
This research consists of abiotic and biotic batch and column studies to elucidate the effects of sorption/desorption processes on contaminant bioavailability. A summary of the research tasks that were either initiated and/or completed during the 1998-1999 grant year is provided below.Batch sorption equilibrium studies were completed using naphthalene and phenanthrene as sorbates and Borden sand, Ottawa sand, Dover orange silty-clay loam (OSCL), and Bozeman sediments as natural geosorbents. Multiple experiments were conducted to determine the time necessary to reach true equilibrium with each of the sorbent/sorbate combinations. The partition coefficient, Kd, for naphthalene and phenanthrene increased with mixing time for the Borden sand and Bozeman sediments indicating that true equilibrium was not achieved for several months. True equilibrium was achieved rapidly (less than 7 days) for Dover OSCL.
Abiotic desorption rate experiments were conducted with naphthalene and phenanthrene abiotically aged in the presence of Borden sand, Dover OSCL, and Bozeman sediments. The objective was to quantify the rate of naphthalene or phenanthrene desorption from natural geosorbents that had been previously exposed to these sorbates for different aging periods. The aging periods were 7, 30, 90, and 270 days. In addition, separate experiments were conducted with different size fractions of Borden sand and phenanthrene to ascertain the effect of particle size on the rate of desorption from these sediments. Desorption from these sediments follows the typical pattern of rapid desorption followed by much slower desorption over a prolonged period. The rate and extent of desorption is a function of aging time for the Borden sand and the Bozeman sediments, but not for the Dover OSCL sediments. These results are consistent with the hypothesis that observed aging effects (reduced bioavailability) may in part be due to mass transfer limited desorption and nonequilibrium conditions.
Model simulations were initiated using a coupled mass transfer/biodegradation model to examine the effects of desorption rate and contaminant exposure time on the bioavailability of phenanthrene. These simulations illustrate that contaminant aging can increase the time required to meet environmentally acceptable endpoints.
Batch slurry biodegradation studies with phenanthrene and Borden sand, Dover OSCL, and Bozeman sediments were initiated. These studies are being conducted for the purpose of testing coupled mass transfer/ biodegradation models using independently derived model parameters determined from batch biological degradation and abiotic equilibrium and desorption rate experiments.
Construction of 14 geosorbent columns was completed. Three column configurations have been constructed using Borden sand, Ottawa sand, and a Dover OSCL/Ottawa sand combination (a macropore column). Hydrodynamic tracer studies were completed and column breakthrough/aging/elution protocols were developed and tested.
Future Activities:
The next phase of the column investigation will consist of loading each of the experimental columns with radiolabeled and unlabeled phenanthrene. During this period, the effluent concentration of phenanthrene will be monitored. After breakthrough, each of the columns will be aged for either 210 days, 90 days, or it will be immediately eluted. At the completion of the aging period, or immediately following breakthrough, the phenanthrene in each experimental column will be desorbed abiotically by flushing it with sterile synthetic groundwater. Following these steps, the sorbent in each column will be digested and a mass balance of phenanthrene will be considered. While this experimental work is being completed, fate and transport modeling also will be ongoing.Journal Articles on this Report : 2 Displayed | Download in RIS Format
| Other project views: | All 11 publications | 3 publications in selected types | All 3 journal articles |
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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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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, 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.