Influence of Biofilms on Porous Media Hydrodynamics - Porous Media: Applications in Biological Systems and Biotechnology - page 205

minerals are the most frequently described inorganic constituents of biofilms
in porous media (Mclean et al . 1997; Cooke et al . 2005). The precipitation
of minerals can result in semipermanent to permanent encrustation of biofilm
cells or clogging of certain areas in a porous medium. These effects might or
might not be desirable depending on the goal of a given application.
The following sections will summarize a few biofilm technologies in porous
media in detail and discuss research and development needs associated with
the further development of these technologies.
5.6.1 Subsurface Biofilm Barriers for the Control
and Remediation of Contaminated Groundwater
Subsurface biofilm barriers are engineered structures developed through the
growth and activity of microorganisms in soils. The establishment of perme-
able, impermeable, and semipermeable biofilm barriers has been proposed for
the control and remediation of contaminated soil and groundwater (Cunning-
ham et al . 1997; Waybrant et al . 1998; Benner et al . 1999; Hiebert et al . 2001;
Nyman et al . 2002; Ludwig et al . 2002; Cunningham et al . 2003; Komlos et al .
2004).
The establishment of low-permeability biofilm barriers (Figure 5.9) has
been the focus of a number of research and development efforts. These barri-
ers are designed to provide maximum reduction of permeability by promoting
thick biofilm growth to either reduce the flow of groundwater through certain
areas of the subsurface or direct groundwater into a certain direction (e.g.,
an area where treatment occurs). Maximum permeability reduction is usually
obtained by promoting the production of copious amounts of EPS by indige-
nous microorganisms or through bioaugmentation with organisms known to
produce copious amounts of EPS.
These barriers have been shown to reduce porous media permeabil-
ity by several orders of magnitude (Cunningham et al . 1997, 2003; Ross
et al . 1998, 2007; Hiebert et al . 2001; Komlos et al . 2004). More recently,
the biofilm-promoted precipitation of carbonate minerals has been proposed
to be advantageous for long-term biofilm barrier stability (Gerlach et al .
2009).
In addition, these subsurface biofilm barriers have been shown to effec-
tively remove solutes. The consumption of soluble electron acceptors such as
oxygen as well as the removal of contaminants of concern such as nitrate
(Hiebert et al . 2001; Cunningham et al . 2003) has been shown. Cunning-
ham et al . (2003) described the establishment of a nitrate-remediating biofilm
barrier in a 130 ft wide, 180 ft long, 21 ft deep test cell. Starved cells of Pseu-
domonas fluorescens strain CPC211a were injected and biofilm growth was
stimulated through the injection of a growth nutrient mixture composed of
molasses, nitrate, and other additives. The biofilm barrier reduced the soil
hydraulic conductivity by 99% from an initial value of 0.042 cm/sec and reli-
ably reduced nitrate concentrations by 93% or more from an initial value