Influence of Biofilms on Porous Media Hydrodynamics - Porous Media: Applications in Biological Systems and Biotechnology - page 181

environmental and industrial processes as well as the control of detrimental
biofilms in medicine and industry. Hence, a number of experimental systems
and approaches have been developed to study biofilms in porous media.
5.3 Experimental Systems and Techniques for
the Investigation of Biofilms in Porous Media
The direct observation of biofilm processes in porous media is challenging due
to the irregular shape and opaque nature of most porous media. However,
for the development of effective porous media biofilm technologies it is often
necessary to observe the spatial and temporal distribution and activity of
biofilm cells as well as of the EPS.
A number of reactor designs can be imagined for the investigation of biofilm
processes in porous media, and the exact design of laboratory (and industrial)
scale reactors will depend on the goal of each study or application. In addition,
the mere existence of biofilm cells does not necessarily correlate with metabolic
activity since it has been shown that a large portion of biofilm cells can be
basically metabolically inactive (Mclean et al . 1999; Hunt et al . 2004; Werner
et al . 2004; Sharp et al . 2005; Rani et al . 2007; Kim et al . 2009). The activity of
biofilm organisms is governed by a number of mass transfer processes, such as
the transport of solvents and solutes into reactors, the possible mass transfer
from the gaseous to the liquid phase (e.g., for oxygen as an electron acceptor),
the mass transfer of solutes from the liquid phase to the biofilm surface, and
simultaneous reaction, diffusion, as well as the sorption of solutes within the
biofilm and the supporting porous medium (Mclean et al . 1999).
The remainder of this chapter will mostly focus on approaches for better
understanding the influence of biofilms on porous media porosity, permeability,
and hydrodynamics. It should be kept in mind that the activity of microor-
ganisms in porous media will ultimately determine the success of advanced
biofilm technologies, and, activity measurements should be utilized as much as
possible. However, spatially and temporally resolved measurements of biofilm
activity are a challenge even in the absence of porous media.
Approaches for measuring biofilm activity include, but are not limited to,
traditional microbiological culturing techniques (e.g., plate counts and most
probable number techniques), substrate consumption measurements, enzyme
assays to assess specific activities, and molecular techniques, such as mRNA
(messenger ribonucleic acid) measurements, gene-specific quantitative PCR
(polymerase chain reaction), and reporter gene constructs. The interested
reader is referred to past (e.g., Fletcher 1979; Poulsen et al . 1993; Lazarova
and Manem 1995; Dorn et al . 2004; Teal et al . 2006; Stewart and Franklin
2008; Lenz et al . 2008) and future literature evaluating techniques suitable for
activity assessments in porous media environments. A recent review article by