Session: Mobile Magnetic Resonance and Lowfield MR I - L-001

In-situ detection of subsurface biofilm using low-field NMR-a field study

C. Kirkland¹*, M.P. Herrling², R. Hiebert¹, A.T. Bender¹, E. Grunewald³, D.O. Walsh³, S.L. Codd¹

1. Center for Biofilm Engineering, Montana State University, Bozeman, Montana, United States
2. Chair of Water Chemistry and Water Technology, Karlsruhe Institute of Technology, Karlsruhe, Germany
3. Vista Clara, Inc., Mukilteo, Washington, United States

Subsurface biofilms are central to bioremediation of chemical contaminants in soil and groundwater whereby micro-organisms degrade or sequester environmental pollutants. [1] Conventional methods to monitor subsurface biofilm growth are indirect, destructive, and potentially hazardous. Previous laboratory research conducted at MSU has indicated that low-field NMR is sensitive to biofilm growth in porous media, where biofilm contributes a polymer gel-like phase and enhances T₂ relaxation. [2] [3] Here we show that a small-diameter NMR well logging tool [4] can detect biofilm accumulation in the subsurface. T₂ relaxation distributions were measured over a 17 day experimental period by two NMR probes, operating at approximately 275kHz and 400kHz, installed in 4-inch (10.2 cm) wells in an engineered field testing site. The mean log T₂ relaxation times were reduced by 62% and 43%, respectively, while biofilm was cultivated in the soil surrounding each well. Biofilm growth was confirmed by bleaching and flushing the wells and observing the NMR signal's return to baseline. This result provides a direct and non-invasive method to spatio-temporally monitor biofilm accumulation in the subsurface.

T2 distribution for ~275kHz well (a) and ~400kHz well (b) at inoculation (short dash line), during biofilm growth (solid lines), and after flushing and bleaching each well (dash-dot lines).

References:

[1] Cunningham, A. B.; Sharp, R. R.; Hiebert, R.; James, G., (2003), Subsurface biofilm barriers for the containment and remediation of contaminated groundwater.
[2] Kirkland, C. M.; Hiebert, R.; Phillips, A.; Grunewald, E.; Walsh, D. O.; Seymour, J. D.; Codd, S. L., (2015), Biofilm detection in a model well-bore environment using low-field NMR. , Groundwater Monitoring and Remediation (accepted)
[3] Sanderlin, A. B.; Vogt, S. J.; Grunewald, E.; Bergin, B. A.; Codd, S. L., (2013), Biofilm detection in natural unconsolidated porous media using a low-field magnetic resonance system.
[4] Walsh, D.; Turner, P.; Grunewald, E.; Zhang, H.; Butler, J. J.; Reboulet, E.; Knobbe, S.; Christy, T.; Lane, J. W.; Johnson, C. D.; Munday, T.; Fitzpatrick, A., (2013), A small-diameter NMR logging tool for groundwater investigations.