Biomedical Engineering Reference
In-Depth Information
and much work has yet to be done to better understand and consequently cap-
italize on the existing potential.
5.7 Conclusions and Outlook
Biofilms can have a significant influence on hydrodynamics and thus on mass
transport in porous media. Biofilm growth quickly induces heterogeneity into
even highly uniform porous media and the dynamics of biofilm development
are—at this point—somewhat unpredictable owing to the influence biofilm
growth and hydrodynamics have on each other. Hydrodynamics, nutrient
availability, physicochemical conditions (e.g., temperature, pH), presence (or
production) of inhibitory or stimulating compounds, community composition
and structure are only some of the factors that have been shown to influence
the development of biofilms in porous media. The interplay of hydrodynamics
and biofilm growth leads to an oscillatory behavior, which appears to reach a
pseudosteady state at certain scales in time and space. The ability to predict
the size of these relevant scales remains a challenge.
In general, porous media permeability and porosity decrease during biofilm
formation while dispersivity generally increases. Although rarely observed,
opposite effects might also occur.
The immense beneficial (and detrimental) potential of porous media
biofilms has led to the development of large-scale technologies, such as sub-
surface biofilm barriers and biofilm reactors, as well as strategies on how to
control biofilms in porous media environments (e.g., around injection wells
where excessive biofilm growth is undesirable).
Owing to the challenges of studying porous media biofilms in detail, a
number of these developments have been based more or less on science-based
understanding. The (mostly microscale) research summarized in this chapter
has been designed to develop the fundamental knowledge necessary to develop
science-based engineering strategies for porous media biofilm technologies.
Even without a complete understanding of biofilm processes in porous
media, the potential of promoting subsurface biofilm growth for benefit has
been widely acknowledged and technology development in the areas of oil
production, contaminant remediation, carbon sequestration, soil stabilization,
and waste treatment proves its economic potential.
The widely accepted inherent resistance of biofilm organisms to environ-
mental stresses has made biofilm barriers an attractive strategy. Even exposure
for extended periods of time to toxins; absence of nutrientsl; low water poten-
tial; highly saline, acidic, or basic conditions; and supercritical carbon dioxide
have been shown to affect biofilm barriers in porous media only slightly (Stur-
man et al. 1995; Warwood et al
.
1995; Cunningham et al. 1997; Dennis and
Turner 1998; Bouwer et al. 2000; Hiebert et al. 2001; Cunningham et al. 2003;
Komlos et al. 2004; Mitchell et al. 2008a,b, 2009).
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