Microbial Enhanced Dissolution of DNAPL in a Three-Dimensional Fracture Network

Wednesday, April 22, 2009: 4:35 p.m.
Agave Ballroom (Hilton Tucson El Conquistador Golf & Tennis Resort )
Peggy Altman , Environmental Science and Engineering, Colorado School of Mines, Golden, CO
Kaneen Elizabeth Christensen , Environmental Science and Engineering, Colorado School of Mines, Golden, CO
Jared King , Environmental Science and Engineering, Colorado School of Mines, Golden, CO
John McCray, Ph.D. , Environmental Science and Engineering, Colorado School of Mines, Golden, CO
Charles E. Schaefer, Ph.D. , Shaw Environmental and Infrastructure Inc., Lawrenceville, NJ
Bioaugmentation of dense non-aqueous phase liquid (DNAPL) present in fractured bedrock settings is dramatically different from bioaugmentation in porous media. While microbe transport and reaction kinetics have been widely studied in porous media, little research has been done to characterize microbes in fractured settings.  Accurate characterization of microbial degradation kinetics and transport in a fractured network setting yield more efficient application of bioremediation techniques in field settings.  This research investigates the dissolution behavior of tetrachloroethylene (PCE) DNAPL in the presence of microbial degradation of aqueous phase PCE, in a three dimensional (3-D) fractured sandstone bench-scale experiment. Dissolution behavior was characterized in the presence and absence of microbial amendments. Experiments are conducted using Dehalococcoides sp. (DHC) and microbial kinetics, transport, and DNAPL dissolution will also be evaluated as a function of (DHC) inoculation dosage.  Microbial reaction kinetics inferred from effluent breakthrough curves, when compared to those of static batch studies, provide a guide for understanding and improving field-scale bioremediation efforts. In addition to reaction kinetics, the transport and delivery of microbes is affected by complex flow characteristics of a fracture network.  Conservative tracer testing highlighted the importance of dead-end fractures, or no flow regions, to fracture systems.  The affect of these no flow regions on delivery and transport of microbes will also be discussed.   Preliminary results from a discrete fracture experimental setup have shown that a DHC concentration of 1 x 106 cell/L yields an effective PCE-to-ethene first-order dechlorination rate constant of 4 x 10 /hr, which correlates well with rates measured in soil columns without DNAPL present.  Results also indicate that re-augmenting the system with a higher DHC dosage yields measureable DHC growth, leading to increased ethane concentrations.  The results of 3-D fracture network experimental runs will be compared to those of the discrete fracture experiments.