Using Plants to Remediate Petroleum Contaminated Soil - Project Renewal
EPA Grant Number: X83-2428-01Title: “Using Plants to Remediate Petroleum Contaminated Soil - Project Renewal”
Investigators:
Greg Thoma, Dept. of Chemical Engineering, 3202 Bell Engineering, University of Arkansas, Fayetteville, AR 72701, (479) 575‑7374, gthoma@uark.edu
Susan Ziegler, Dept. of Biological Sciences, 416 Science Building, University of Arkansas, Fayetteville, AR 72701, (479) 575-6342, susanz@uark.edu
Duane Wolf, Dept. of Crop, Soil, and Environmental Sci., 115 Plant Sciences, University of Arkansas, Fayetteville, AR 72701, (479) 575‑5739, dwolf@uark.edu
Institutions: University of Arkansas
EPA Project Officer: Bala Krishnan
Project Period: 11/1/2005 – 10/31/2006
Project Amount: $133,030
Research Category: Phytoremediation
Abstract
Description:
This project is an evaluation of phytoremediation, using grass, as a low cost approach to cleanup oil-contaminated soils
Objective:
The broad objectives proposed for the fourth year are as follows:
1. To assess the role of plants in enhancing biodegradation of recalcitrant components of the crude oil through continuation of the field study.
2. To elucidate the microbial community components responsible for the degradation of specific contaminants during phytoremediation through a series of greenhouse experiments involving the use of 13C tracers.
3. To evaluate, in-situ, the spatial extent of the rhizosphere through the use of a recently developed inclined-plate mini-rhizotron technique. This has been shown to be an important parameter in the modeling.
4. To extend the mathematical model to account for temperature effects on degradation rates associated with the presence or absence of vegetation and to validate it with additional datasets.
Approach:
We will use a combination of field, growth chamber, and laboratory studies to evaluate phytoremediation. The field study is a continuation of work previously funded through IPEC.
Field study: Continued sample collection is required to determine the ultimate effectiveness, elucidate treatment differences, and develop and test an approach to rapidly detect the effectiveness of phytoremediation at other sites. Therefore, we will continue to work with Shuler Drilling, who has provided sites for evaluation of phytoremediation techniques. Our initial design for the field study included sufficient plots for 6 years of semiannual sampling. We will continue to evaluate the field site where samples will be collected to assess plant parameters, microbial community structure, and TPH and biomarker concentrations.
Greenhouse studies: Our findings suggest phytoremediation reduces petroleum contaminant levels through microbial degradation in the rhizosphere. However, detailed knowledge of the microbial ecology of the rhizosphere is still lacking. This will be investigated through a series of mechanistic greenhouse studies. In these experiments 13C-labeled phenanthrene and pyrene will be adsorbed to Bio-Sep® beads placed in the soil then later extracted and analyzed for microbial d13CPLFA. Biomarkers can be more efficiently extracted from Bio-Sep® beads than from soil and provide measures of viable biomass and microbial community composition. Experiments involving compound-specific stable isotopic, and analyses of microbial biomarkers will confirm the presence of hydrocarbon-degrading microbes and will relate the composition of active hydrocarbon degraders to the observed rates of hydrocarbon degradation.
Modeling and Rhizotron Studies: Both the laboratory and field work will provide data for validation of the mathematical model. Our knowledge of the extent of the rhizosphere in undisturbed systems is sparse. We propose a series of experiments using inclined quartz plate rhizotrons with digital image analysis of the root system to quantify, in-situ, the extent of root influence. A fluorescent surrogate, phenanthrene, on the rhizotron plate will allow assessment of the rhizosphere extent around the root surface, as defined by enhanced contaminant degradation, using acquired digital images. This information regarding the extent of the rhizosphere will be important in defining reasonable ranges for important model parameters.
Expected Results:
The results from this study will provide initial information sufficient to begin designing coherent management strategies for phytoremediation systems. The proposed field and greenhouse studies will be used to identify the main factors impacting phytoremediation efficacy through the assessment of degrader population levels, primary microbial group(s) responsible for the degradation of contaminants, and the biodegradation kinetics for those contaminants.
The field study will evaluate the influence of plants and amendments on remediating crude oil contaminated soils under field conditions. Collection of time-series data will provide a significant dataset for model validation for individual components of the TPH. The greenhouse data on degradation of phenanthrene or pyrene will be useful in the extension of the model to predict the efficacy of phytoremediation at other sites. The El Dorado, AR field study site is one of 12 RTDF Phytoremediation Working Group sites. The data collected from all of the sites will be available for validation and verification of the model.
Results from the greenhouse/growth chamber studies will allow us to address the importance of the indigenous microbial population on the potential success of phytoremediation at different sites. We will identify which group(s) of microorganisms is/are responsible for hydrocarbon degradation providing a significant step forward in terms providing information necessary for making decisions regarding the agronomic management of phytoremediation systems. The benefits of this research include establishing the knowledge base necessary to provide guidance at the field scale regarding the enhancement of the microbial activity required to degrade the contaminants. We anticipate that the results from this study will provide information sufficient to begin providing design guidance based on underlying mechanistic processes for effective on-site management of phytoremediation systems.
Key Words:
Rhizosphere; rhizodegradation; species selection; Arkansas; South Central United States