Influence of Biofilms on Porous Media Hydrodynamics - Porous Media: Applications in Biological Systems and Biotechnology - page 184

with thin layers of porous media (sand, glass beads, or similar). Depending on
their size and optical quality, these reactors allow for direct optical or micro-
scopic observations of biofilm formation and mass transport (see Figure 5.3 for
examples). Capillary flowcells also allow for direct microscopic interrogations
and are sometimes used to represent single pores.
While there are no review articles available, which summarize use and oper-
ation of reactors for the investigation of biofilm formation in porous media,
there are reviews and special issues available related to the possibilities of
visualizing colloid transport in porous media, such as a recent special section
in Water Resources Research (2006, Vol. 42, Issue 12) and, in specific, an
article by Ochiai et al . (2006).
The challenges in both fields—colloid transport and biofilm formation
in porous media—are similar: (1) Aqueous phase measurements are simply
not sucient to completely understand the fundamental microscale processes
affecting colloid transport or biofilm development and (2) The direct obser-
vation of microscale processes is complicated because of the opaque nature of
porous media.
Nevertheless, a fairly large body of literature on the influence of biofilm
formation on porous media hydrodynamics is available and will be described
in the next section. Such studies generally rely on measurements of differences
in hydraulic head, flow rate, and (particulate or dissolved, reactive or nonreac-
tive) tracer through characteristics, sometimes combined with direct, real-time
observation of biofilm distribution in columns, capillaries, network models,
or larger lysimeter-like (two-dimensional/quasi three-dimensional) reactors
(Paulsen et al . 1997; Sharp et al . 1999a; Rinck-Pfeiffer et al . 2000; Yarwood
et al . 2002; Thullner et al . 2002a; VanGulck and Rowe 2004; Sharp et al . 2005;
Arnon et al . 2005a; Yarwood et al . 2006; Castegnier et al . 2006; Seki et al .
2006; Ross et al . 2007; Rees et al . 2007).
More recently, with the broader availability of computer-controlled
microscale fabrication opportunities, microscale reactors have been devel-
oped and employed in our and other laboratories, which allow for signifi-
cantly improved possibilities for the noninvasive observation of reactive trans-
port processes in porous media model reactors (Wan et al . 1994; Dupin and
McCarty 1999; Kim and Fogler 2000; Nambi et al . 2003; Knutson et al . 2005;
Willingham et al . 2008; and Figure 5.4).
Larger scale laboratory studies have also been conducted, mostly as precur-
sors to field-scale demonstrations (Figure 5.5). In general, it has been observed
that the increased complexity of two- or pseudo-three-dimensional systems
can result in lesser permeability reductions, presumably due to the possi-
bility of flow around biofilm- or mineral-clogged areas (Cunningham et al .
1997, 2003; Kildsgaard and Engesgaard 2001; Thullner et al . 2002a; Seki et al .
2006). Direct observations and simulations clearly show diverted flow around
biofilm-clogged areas (Thullner et al . 2002a; Seki et al . 2006).