Project Abstract

Evaluation and Modeling of Subsurface Biobarrier Formation and Persistence

Principal Investigators

A.B. Cunningham
Montana State University
E-mail: al_c@erc.montana.edu

B.M. Chen
University of Wyoming

Goal

The overall goal of this project is to understand factors which promote or retard biomass accumulation in porous media with an intent to apply such understanding toward prediction and beneficial manipulation of permeability and mass transport properties.

Rationale

A concept which appears promising in the manipulation of biological and chemical processes for remediation of subsurface hazardous waste sites is the creation of biobarriers for containment and remediation of soil and groundwater contaminated with organics and heavy metals. Biobarriers are formed by stimulating growth of microbial biomass so as to plug the free pore space flow paths through porous media, thereby reducing permeability and mass transport. Selective plugging of permeable strata is currently being explored as a means of preventing contaminant migration of groundwater contaminants from hazardous waste sites. Penetration of bacteria through porous media varies between extensive penetration of ultramicrobacteria and formation of plugging biofilms on the proximal formations by well-fed cells of the same organisms. Investigators will attempt to use simple nutritional differences to deliver bacteria to any location in the subsurface environment to resuscitate and either plug the formation or carry out specific biodegradation.

Approach

Test organisms will include a Klebsiella pneumoniae as well as these same bacteria starved for ultramicrobacteria size. Experimental objectives will be carried out using a series of flowing packed- bed reactors including flat plate flow cells and packed columns. Procedures will be developed for applying bacterial inoculum, along with subsequent resuscitation with nutrients, so as to produce controlled reduction of porous media permeability and dissolved oxygen transport. Researchers will quantify and model temporal and spatial variability in the biofilm accumulation (and mass transport) using bioluminescence. Finally, a mathematical model for biofilm accumulation and corresponding permeability and dissolved oxygen gradients in porous media will be developed and evaluated.

Status

This project is on schedule and no major difficulties are anticipated. Investigators have determined quantitative relationships that describe biomass accumulation and corresponding mass transport properties in saturated porous media. Methods for controlling biobarrier thickness, longevity, and degree of permeability reduction have been established. The efficacy of using biobarriers to create and maintain anaerobic conditions has been assessed. Funding from a major oil company has been obtained for a pilot project that will test the feasibility of installing a biobarrier at a field site to control hydrocarbons leaching from the groundwater system into a nearby river. A radial flow lysimeter was constructed to simulate field conditions in preparation for this demonstration project. Efforts to refine our modeling techniques will continue. This project is in its third year.

Clients/Users

This project will be of interest the U.S. Department of Energy, U.S. Department of Defense, environmental contractors, regulators, and those in the petroleum industry.

Keywords

Biofilms, hydraulic conductivity, ultramicrobacteria, waste containment, barriers.