Using Plants to Remediate Petroleum-Contaminated Soil

Period Covered by Report:
Date of Report:
EPA Grant Number: R827015-01-0
Title: Using Plants to Remediate Petroleum-Contaminated Soil
Investigators: Greg Thoma, Duane Wolf, Craig Beyrouty
Institutions: University of Arkansas
EPA Project Officer: Bala Krishnan
Project Period: September 1, 1999 to August 31, 2000 (N/C Ext. to June 3 0, 2001)
Project Amount: $134,949
Research Category: Phytoremediation

Description:

Objective(s) of the Research Project:

1. To conduct greenhouse studies to screen plants for their ability to germinate and grow in weathered crude oil-contaminated soil with or without amendments.

2. To survey and collect plant species currently growing on contaminated sites and screen the plants and rhizosphere microorganisms for their ability to enhance biodegradation of petroleum contaminants.

3. To conduct an on-site field study to evaluate likely combinations of plants and management systems to enhance phytoremediation of weathered crude oil-contaminated sites.

4. To develop a model that can be used to summarize and aid in the interpretation of experimental data collected in both the laboratory and field during the first experimental season.

Progress Summary/Accomplishments:

This report covers the Dec. 1, 2000 to February 28, 2001 period and summarizes our current IPEC phytoremediation studies that consist of an on-site field project in southern Arkansas, greenhouse studies, and a mathematical modeling project.

Field Study

The field site in El Dorado, AR is located in a bermed area that is the site of an intentional spill in 1997 by vandals. The experimental plots consist of four replicates of the following treatments: (1) nonvegetated-nonfertilized control, (2) fescue-ryegrass-alfalfa + fertilizer, and (3) fescue-bermudagrass + fertilizer. Each field plot has 12 microplots ('soil socks') that contain homogenized soil that allow monitoring of the field treatments, on a smaller scale, with less effect of field variability of the contaminant levels.

On 10-12 July 2000, 6 months after establishment of vegetation at the site, soil and plant samples were collected from the plots. Plant shoot biomass and root biomass, length, surface area, and volume for each of the treatments were determined. All plant species appeared to be exhibiting adequate plant growth. The Total Petroleum Hydrocarbon (TPH) and biomarker (hopane) analyses of the soil samples collected 6 months after plot establishment (t=6) are currently being conducted.

A percent plant cover evaluation of the plots was attempted February 25, 2001, but was unsuccessful due to flood conditions that prevented the researchers from reaching the field site.

An additional survey was conducted to identify plant species currently growing on petroleum-contaminated sites near the El Dorado, AR field site. Plants that were observed to be growing at the various sites included bermudagrass (Cynodon dactylon L.), yellow nutsedge (Cyperus esculentus L.), fall panicum (Panicum dichotomiflorum Michx.), brome grass (Bromus spp.), and witchgrass (Panicum capillare L.).

Greenhouse Study

Total Petroleum Hydrocarbon analysis was completed on soil samples following the greenhouse study where plants were grown in oil-contaminated soil amended with and without inorganic and organic amendments. The initial TPH concentration was 9% by weight. The amendments included broiler litter, papermill sludge, hardwood sawdust + inorganic fertilizer, and inorganic fertilizer. The samples were extracted in accordance with EPA Method 3540C and TPH concentration determined gravimetrically (Table 1).

Table 1. Total Petroleum Hydrocarbon (TPH) concentrations in soil amended with inorganic or organic amendments following 14-week greenhouse study.

Mathematical Model

We have identified the source of the instability in the model solution as resulting from simulations in which the soil becomes 'root-bound' and the calculated volume of soil remaining as 'bulk' drops to zero (or in extreme cases, negative values). We are correcting the acceptable ranges of certain parameters (particularly the ratio of rhizosphere to root volume) that influence this behavior. We have preliminary models of the root growth and senescence functions for annual and perennial species that more closely mimic the expected growth patterns. In particular, we have functions that can be used to simulate the root growth patterns expected when cool- season -> warm-season -> cool-season species are planted successively in a single year. We are testing the L-system analysis code to be sure that segment orientation (for single segments) does not affect the computed results, and that the overlap of the rhizosphere is calculated correctly for adjacent, parallel segments.

Publications/Presentations:

Abstracts and titles that have been submitted for presentation as posters or presentations in the future include:

Thoma, G.J., T.B. Lam, D.C. Wolf, and C.A. Beyrouty. 2001. A Mathematical Model of Phytoremediation of Crude Oil-Contaminated Soils. In The Sixth International In Situ and On-Site Bioremediation Symposium, San Diego, CA. 4-7 June 2001. Battelle, Columbus, OH.

W.D. Kirkpatrick, White, P.M., G.J. Thoma, D.C. Wolf, C.M. Reynolds, and E.E. Gbur. 2001. Plant response to N addition in petroleum-contaminated soil. In 2001 Agronomy abstracts. ASA, Madison, WI. (submitted)

White, P.M., W.D. Kirkpatrick, G.J. Thoma, D.C. Wolf, C.M. Reynolds, and E.E. Gbur. 2001. Field study to evaluate phytoremediation of petroleum-contaminated soil. In 2001 Agronomy abstracts. ASA, Madison, WI. (submitted)

Supplemental Keywords:

Arkansas (AR), petroleum, phytoremediation, EPA Region 6, rhizosphere