Assessing the Potential Consequences of Subsurface Bioremediation: Iron-Oxide Bioreductive Processes and the Propensity for Contaminant-Colloid Co-Transport and Media Structural Breakdown
ER-2130
Objective
The Department of Defense (DoD) is faced with the task of remediating hundreds of sites that contain groundwater contaminated with toxic metals and organics. A number of techniques have been developed for remediating contaminated sites, with bioremediation technologies being among the most attractive, based on cost and effectiveness. Bioremediation techniques generally aim to create anaerobic subsurface conditions designed to stimulate microorganisms that degrade chlorinated hydrocarbons and reduce toxic metals to sparingly soluble forms, immobilizing them in situ. Anaerobic groundwater conditions that accompany such techniques also promote microbially mediated Fe(III)-oxide mineral reduction (the most common mineral oxide of many subsurface environments) and the formation of soluble Fe(II) and secondary Fe-minerals. Since the surface charge properties and high surface area of Fe-(hydr)oxides encourage the interaction of contaminant metals with the solid phase, the microbial reduction of Fe-(hydr)oxides and the subsequent secondary solid-phase transformations may have a profound influence on contaminant mobility and bioavailability. More research is needed to understand the potential for adverse side effects associated with groundwater bioremediation technologies that induce anaerobic conditions to stimulate contaminant-degrading microorganisms.
The objective of this project is to provide new fundamental data and numerical simulations to assess the impact of bioreductive remedial processes on rates and mechanisms of colloid generation and their impacts on contaminant co-transport, as well as the propensity for irreversible changes in soil structure following bioremediation. Specific technical objectives are to (1) develop an improved understanding and predictive capability of the impacts of subsurface bioremediation on the kinetics and mechanisms of (a) media structural breakdown and loss in permeability as the result of aggregate dispersion and (b) the generation of Fe- and clay-rich colloids and secondary mineral precipitates; (2) quantify the fate and transport of colloid particles in heterogeneous subsurface media as a function of changing hydrological, geochemical, and microbiological processes and investigate the impacts of accelerated contaminant co-transport versus media pore clogging on post-bioremedial groundwater quality; and (3) develop predictive models to establish bioremedial protocols and groundwater monitoring strategies that optimize contaminant destruction and immobilization while minimizing the disruption of the subsurface media structure and the formation of mobile colloids.
Technical Approach
Laboratory-scale macroscopic fate and transport experiments will be conducted using a unique column flow technique that closely simulates the natural subsurface system. These experiments will be integrated with advanced interfacial spectroscopy techniques to quantify the impacts of time-dependent bioreduction processes on colloid generation and the formation of secondary mineral precipitates in subsurface media and investigate the impact of media structural breakdown and mineral dispersion during bioremediation processes. Numerical modeling will then be used to assess the dynamic changes in subsurface hydrological, geochemical, and microbial processes resulting from subsurface contaminant bioremediation.
Benefits
Results of this project will enable site managers to ensure remedial effectiveness while minimizing impacts to groundwater quality. Specifically, this research will provide methods to establish environmentally acceptable endpoints (EAEs) associated with bioremediation-impacted water quality issues by producing (1) scientifically defensible, peer-reviewed, publicly available databases and literature on the impacts of subsurface bioremediation on the kinetics and mechanisms of media structural breakdown and pore-clogging processes and the generation of Fe and clay-rich colloids and associated contaminants and (2) a validated model for developing bioremedial protocols and groundwater monitoring strategies that optimize contaminant destruction and immobilization without the disruption of the subsurface media structure and the formation of mobile colloids. (Anticipated Project Completion - 2014)
Points of Contact
Principal Investigator
Mr. Philip Jardine
University of Tennessee
Phone: 865-574-8058
Fax: 865-576-8646
Document Types
- Fact Sheet - Brief project summary with links to related documents and points of contact.
- Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
- Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
- Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
- Guidance - Instructional information on technical topics such as protocols and user’s guides.
- Workshop Report - Summary of workshop discussion and findings.
- Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
- Model/Software - Computer programs and applications available for download.
- Database - Digitally organized collection of data available to search and access.