Environmental Engineering Reference
In-Depth Information
6.1.1 Industrial Applications of Biofilms
While removing biofilms has been one of the great industrial challenges, biofilms
have also found many applications. For instance, biofilms have been successfully
used in waste and water treatment due to their advantages over the use of suspended
bacteria [9]. Biofilms have the ability to support a variety of microbial populations
at various locations within the biofilm. Thus, diversity of microorganisms in the
biofilm can induce degradation of different organic substances [1, 9]. Biofilms also
have high microorganism populations in a small unit volume. This enables high
substrate removal rates, making it possible to build small, effective reactors [9].
In soil bioremediation of xenobiotic compounds, field scale permeable reactive
barriers using biofilms have been tested for the treatment of contaminated ground-
water [10]. In biobarrier systems for contaminated soil and groundwater, the biofilm
EPS plays an important role in the sorption of organic pollutants [11]. Hydrophobic
organic compound (HOC) sorption is the primary chemical process in subsurface
aquifer systems [12, 13] and is important for stable operation of engineered biore-
mediation systems. Therefore, an increased biomass and the EPS content of the
biofilm can create a strong affinity for HOCs.
Due to the increased sorption capacity, the biofilm EPS can trap organic com-
pounds in the groundwater; the adsorbed organic compounds can then be desorbed
and diffused out from the EPS, permitting subsequent degradation of the HOCs by
the attached microorganisms in the biofilm matrix. The increased mass of HOCs
sorbed to the biofilm matrix can also induce an increase in the number of degraders
present. A stable removal of HOC may be achieved through entrapment and simulta-
neous degradation of HOC in biofilm. In addition to the sorption capacity of biofilm,
recent studies observed direct biofilm growth on toxic chemical crystals (pyrene and
phenanthrene) without any other available carbon source [14-16]. In this aspect,
formation and structure of the biofilm is crucial for the soil and groundwater reme-
diation [10]. However, biofilm formation in a subsurface aquifer has sometimes
produced an adverse effect. Currently, most studies have focused on the removal
of HOC through the biobarrier [17-19] and the mass transport mechanisms, and
structural forms of the biofilm exposed to the HOC are not well understood.
6.1.2 Biofilms in Environmental Systems
Biofilm formation and development in natural and industrial systems solely depend
on electron donors (organic substrates) and electron acceptors (oxygen, nitrate and
sulfate). Thus, monitoring and controlling the electron donors and acceptors is one
of the approaches used to control biofilms in both natural and industrial systems.
Recent developments in the field of molecular biology are beginning to enable
scientists to study the spatial distribution, diversity, and activity of microorganisms
in biofilms [20]. Along with molecular tools, microelectrode techniques have been
applied for
in situ
measurement of chemical transport in biofilms [21, 22]. Initially,
