HR: 0800h
AN: H51F-0432    [Abstracts]
TI: The Impact of Biofilms on the Process of Back Diffusion From a Contaminated Rock Matrix
AU: * Yungwirth, G A
EM: grace@civil.queensu.ca
AF: Department of Civil Engineering, Queen's University, Ellis Hall , Kingston, ON K7L3N6 Canada
AU: Novakowski, K S
EM: kent@ce.queensu.ca
AF: Department of Civil Engineering, Queen's University, Ellis Hall , Kingston, ON K7L3N6 Canada
AU: Ross, N
EM: nross@genie.uottawa.ca
AF: Department of Chemical Engineering, University of Ottawa, 161 Louis Pasteur, Ottawa, ON K1N6N5 Canada
AB: Groundwater remediation in fractured rock settings is complicated by the diffusion of contaminants into the rock matrix and the subsequent back diffusion into the fractures. The process of back diffusion, in particular, leads to extended periods of low-level contamination in the fracture network that persists long after the source area is hydraulically or otherwise removed. In such a case, we hypothesize that back diffusion could be limited by growing a biofilm which coats the rock fracture surface and potentially invades the rock micropores. This would effectively sequester the contamination potentially in perpetuity. To explore the viability of this concept, diffusion experiments were conducted in which the effect of biofilm growth on diffusion through thin (0.8 to 1.2 cm) slices of dolostone core obtained from the Lockport Formation, Southern Ontario, was investigated. The experiments were conducted using a double-cell method, in which the core slices were encapsulated inside Teflon coated hydraulic hose, fitted with ultra high molecular weight polyethylene endcaps having stainless steel sample ports. Diffusion was established across the core slice by spiking one reservoir with a conservative tracer and monitoring the tracer arrival in the reservoir located on the other side of the coupon. The experiments were conducted both in the presence and absence of a biofilm. Biofilm was grown on the rock coupons in a separate bath before the coupons were transferred to the apparatus for the diffusion experiments. Microbial populations indigenous to the groundwater used in the bath were stimulated to form the biofilm with the addition of a beef extract and peptone nutrient broth in 1g/L concentration. The extent of biofilm growth was monitored using a modified Dubois et al (1956) colorimetric method for sugar determination. Results were simulated using an analytical model that was developed for the geometry of the diffusion experiments. Governing equations for the model are based on a cylindrical coordinate system where one equation was developed for the rock and another for the biofilm. The solution was found using the Laplace Transform method. Preliminary results show substantial biofilm growth, confirming that the method of biofilm stimulation is viable. Preliminary analysis of data from the diffusion experiments shows the impact of biofilm presence on back diffusion to be profound.
DE: 0418 Bioremediation
DE: 1831 Groundwater quality
DE: 1847 Modeling
SC: Hydrology [H]
MN: Fall Meeting 2005