Grantee Research Project Results

1998 Progress Report: Bioavailability of Aromatic Hydrocarbons in Saturated Porous Media: The Effects of Chemical Aging and Mass Transfer

EPA Grant Number: R825406
Title: 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, 1997 through December 5, 1998
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 primary objective 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). Research objectives are being met through a series of abiotic and biotic batch and column studies designed to elucidate the effects of sorption/desorption processes on contaminant bioavailability.

Progress Summary:

A summary of the research tasks that were initiated and completed during the Second Year (Dec. 1997 - Dec. 1998) is provided below.

Batch sorption equilibrium studies were conducted using naphthalene and phenanthrene as sorbates and Borden sand, Ottawa sand, Dover aquitard solids (orange silty-clay loam, OSCL), and Bozeman sediments as natural geosorbents. Dover aquifer solids (dark gray silt loam, DGSL) were also studied and considered for use, but were dropped from further consideration owing to the oxygen demand of the sorbent which complicated the biotic analysis. Sorption equilibrium studies were conducted at incubation times of 7, 30, 90 and 210 days for all natural geosorbents except Dover OSCL. The studies with Dover OSCL have been initiated but not completed. Sorption rate studies were conducted using naphthalene and phenanthrene and Dover OSCL solids, Bozeman sediments, Ottawa sand, and Borden sand.
Sorption rate studies were conducted using naphthalene and phenanthrene and Dover OSCL, Bozeman sediments, Ottawa sand, and Borden sand.
Experimental protocols were evaluated for batch aging/desorption rate studies. Methods evaluated included bottle point dilution and Tenax extraction.
Batch abiotic aging followed by biotic 14C mineralization studies were conducted with naphthalene and phenanthrene in the presence of Borden sand, Ottawa sand, Dover OSCL, and Bozeman sediments.
Construction of 14 geosorbent columns was undertaken. Three column configurations have been constructed using Borden sand, Ottawa sand and a Dover OSCL/Ottawa sand combination (a macropore column). The geosorbents used in the respective column arrangements were previously characterized, and pertinent characterization results were summarized in the first (1996-1997) Annual Report.

Batch sorption equilibrium studies were evaluated using linear and nonlinear (Freundlich) sorption isotherm models. Study results indicate that sorption equilibrium was not reached with naphthalene and phenanthrene after 210 days of incubation with Borden sand. Sorption of these compounds was minimal with combusted Ottawa sand. Sorption to Bozeman sediments was rapid and equilibrium was reached in approximately 7 days. Results from long-term sorption studies with Dover OSCL solids are not available at this time. Sorption rate study results were consistent with trends observed during the batch equilibrium studies. Biphasic sorption was observed with rapid initial uptake of naphthalene and phenanthrene in the presence of the geosorbents. Continued slow uptake of naphthalene and phenanthrene was observed with Borden sand for a period of several months. Batch aging/ mineralization studies in the presence of Ottawa sand, Borden sand, Dover OSCL solids and Bozeman sediments were undertaken to evaluate the affect of contaminant exposure time on the initial mineralization rates of naphthalene and phenanthrene. Aging periods investigated included 1, 7, 30 90, 210, and 270 days. Initial mineralization rates were quantified and are summarized in Table 1.

Table 1. Initial naphthalene and phenanthrene mineralization rates as a function of aging time
(numbers in parenthesis represent standard deviation)

Geosorbent	Initial Naphthalene Mineralization Rate (%/hr.)
	1-day	7-day	30- day	270-day
Ottawa sand	8. 46 (1.75)	-	6.46 (1.42)	4.88 (0.67)
Borden sand	3.74 (0.29)	3.46 (0.21)	3.04 (0.32)	2.02 (0.22)
Dover OSCL	-	3.72 (0.35)	3.04 (0.55)	0.32 (0.004)
Geosorbent	Initial Phenanthrene Mineralization Rate (%/hr.)
	7-day	30-day	210-day
Dover OSCL	0.454 (0.008)	0.621 (0.169)	0.610 (0.066)
Bozeman sediment	1.141 (0.177)	0.512 (0. 063)	0.270 (0.009)
Borden sand	0.620 (0.118)	0.319 (0.037)	0.294 (0.176)

For naphthalene, the initial mineralization rates decrease with increasing aging time for all geosorbents. Initial phenanthrene mineralization rates declined with increased aging time for Borden and Bozeman sediments but this trend was not realized for Dover OSCL solids, consistent with an apparently rapid particle scale equilibrium for this material. Initial naphthalene and phenanthrene mineralization rates in liquid cultures were two to 30 times greater than observed in the slurry systems when comparing systems with equivalent initial contaminant mass. These data illustrate that the presence of solids and contaminant exposure time can impact the rate of biodegradation of hydrophobic nonpolar contaminants such as naphthalene and phenanthrene in the presence of natural geosorbents under saturated conditions.

Tracer studies have been performed on representative sediment columns by injecting tritiated water, in the form of a Dirac pulse. In association with column setup, experimental column breakthrough and elution times have been estimated using various numerical transport and reaction models written in FORTRAN code.

Future Activities:

Future work will include batch desorption rate studies, long-term isotherm experiments with naphthalene and phenanthrene using Dover OSCL solids, fate and transport modeling and column breakthrough, aging, elution, and biodegradation experiments.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Publications Views
Other project views:	All 11 publications	3 publications in selected types	All 3 journal articles

Publications
Type	Citation	Project	Document Sources
Journal Article	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
Journal Article	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, 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, transport

Progress and Final Reports:

Original Abstract

The 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.