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Chapter 70 : Transport of Microorganisms in the Terrestrial Subsurface: In Situ and Laboratory Methods
This chapter describes and discusses laboratory and field techniques for studying microbial transport behavior in aquifer materials and model porous media. Changes in ionic strength (I) during transport studies may occur inadvertently as a result of using halides as conservative tracers and may lead to density-induced sinking of the tracer cloud. Substantive increases in I as a result of injection of high concentrations of halide tracers can also result in overestimations of microbial attachment. In order to differentiate "test" microorganisms from indigenous subsurface populations and/or from other inadvertently introduced populations, microorganisms used in laboratory or in situ transport tests are typically labeled a priori with a stable tag. Other methods of labeling microorganisms for use in in situ and column transport studies have involved the use of stable isotopes ratio mass spectrometry (IRMS). The characteristics of the conservative tracer breakthrough curve can then be used comparatively to determine some of the major transport parameters exhibited by the introduced microorganisms. Most controlled field investigations of subsurface microbial transport are conducted on limited spatial scales relative to the scales of interest to those concerned with pathogen transport to water supply wells, with microbially enhanced oil recovery from petroleum reservoirs, and with the feasibility of using introduced bacteria for aquifer restoration.
Integrated field and laboratory experimental approach to investigating transport behavior of microorganisms in ground-water environments.
Schematic representation of a hollow-fiber-type tangential-flow filtration device modified for on-site concentration of indigenous microorganisms from groundwater. Modified from Kuwabara and Harvey ( 137 ) with permission from the Journal of Environmental Quality.
Dimensionless concentration histories for bacteria and bromide transported downgradient through aquifers from the point of coinjection. (A) Natural-gradient test in a well-sorted, sandy aquifer in Cape Cod, Mass. (reprinted from reference 23 with permission from Wiley-Liss). (B) Forced-gradient test in a fractured, granite aquifer at Chalk River Laboratory, Ontario, Canada (redrawn from reference 39 with permission from the publisher of Water Science and Technology).
Schematic depiction of experimental designs for small- to intermediate-scale injection and recovery investigations examining microbial transport behavior in aquifers (modified from reference 23 with permission from Wiley Liss, Inc.). (A) Divergent, forced gradient; (B) convergent, forced gradient; (C) doublet cell, forced gradient; (D) natural gradient.
Experimental apparatuses for conducting laboratory-scale studies of microbial transport behavior in saturated subsurface media. (A) Upflow column at a slight incline to the horizontal employing a pressure-sensitive, high-precision piston pump to supply a constant head. (B) Experimental setup for examining microbial transport behavior through consolidated materials under static conditions. (Reproduced from D. G. Jewett et al., J. Contam. Hydrol. 36:73–89, 1999 [ 115 ], © 1999, with permission from Elsevier.) (C) Experimental apparatus for assessing bacterial transport in porous media as a function of water content. (Modified from reference 113 with permission from the American Society for Microbiology.) (D) Experimental setup for evaluating the effect of porous media on the effective random motility and chemotactic sensitivity coefficients. (Reprinted from reference 14 with permission from the American Society for Microbiology.)