micro-colonies that do not release single cells from the matrix into the soil (Costerton
and Lappin-Scott 1989). Most researchers are interested in studying the performance
of microbial transport in the porous matrix. They examined various soil types with
bacterial transport and observed that inefficiency of bacterial mobility was mostly
attributable to the extremely low hydraulic conductivity in the soil micropores
(Li et al. 1996; Silliman et al. 2001), as well as microbial community attachment
to the surface of the porous matrix (Baygents et al. 1998). Bacterial mobility can be
enhanced by the addition of surfactants or chemical modification of the bacterial
surface, which may enhance the efficacy of bacterial transport in terms of a centimeter scale to a meter scale in the porous media during the EK process. Some
investigators reported that the negative charge of microorganisms moves towards the
anode in the electrophoretic process (DeFlaun and Condee 1997; Lee and Lee 2001).
Other reports suggested the dispersal of microorganisms towards the cathode with
electro-osmotic water flow (Suni and Romantschuk 2004; Wick et al. 2004). Wick
et al. (2004) reported that the rate of bacterial transport in electrophoretic phenomena
was about 4 cm
2 /(V h) in porous media, which depended on the type of matrix and
physicochemical parameters of the microbial cell surface. They claimed that the
transport of weakly charged bacteria moved predominantly by electro-osmosis when
compared to the electrophoresis process (Wick et al. 2004). The EK transport
phenomena were inhibited when strongly charged and highly adhesive bacteria
attached to the soil surface (Wick et al. 2002). The strong affinity between microorganisms and solid matrices is partially overcome through treating the bacteria with
the non-ionic surfactant Brij 35, with up to 80% enhanced EK dispersion achieved
(Wick et al. 2004).
The electro-osmosis process can be used for mobilization of non-ionic charged
molecules such as hydrocarbons, polyaromatic hydrocarbons, PCBs, phenol, and
acetic acid contaminants in the soil matrices. Earlier, it was demonstrated that EKs
alone can remove/transport non-ionic organic molecules from soil matrix to the
cathode section. Generally, transport by electro-osmosis is a process in the range
between 1 and 10 Â 10
À9 m
2
/(VÁS) for various types of soil matrices (Casagrande
1947). However, Wick et al. (2004) calculated the transport rate of the electroosmosis process with bacteria was about 0.1–0.4 cm
2 /(VÁh). Liu et al. (1999)
experimentally observed that Escherichia coli bacteria are predominantly moved
in capillaries exclusively by the electro-osmosis process over a wide range of pH
values and an electric field strength greater than 0.3 V/cm. It can be concluded that
the mobility of bacteria or organics towards the cathode depends upon the speed of
electro-osmosis.
5.2 Degradation of Pollutants
5.2.1 Hydrocarbons
Polycyclic aromatic hydrocarbons (PAHs), which are the most important class of
pollutants, are generated by the inadequate combustion of carbon-based fuels and are
8 Electro-bioremediation: An Advanced Remediation Technology for the. . .
199
and Lappin-Scott 1989). Most researchers are interested in studying the performance
of microbial transport in the porous matrix. They examined various soil types with
bacterial transport and observed that inefficiency of bacterial mobility was mostly
attributable to the extremely low hydraulic conductivity in the soil micropores
(Li et al. 1996; Silliman et al. 2001), as well as microbial community attachment
to the surface of the porous matrix (Baygents et al. 1998). Bacterial mobility can be
enhanced by the addition of surfactants or chemical modification of the bacterial
surface, which may enhance the efficacy of bacterial transport in terms of a centimeter scale to a meter scale in the porous media during the EK process. Some
investigators reported that the negative charge of microorganisms moves towards the
anode in the electrophoretic process (DeFlaun and Condee 1997; Lee and Lee 2001).
Other reports suggested the dispersal of microorganisms towards the cathode with
electro-osmotic water flow (Suni and Romantschuk 2004; Wick et al. 2004). Wick
et al. (2004) reported that the rate of bacterial transport in electrophoretic phenomena
was about 4 cm
2 /(V h) in porous media, which depended on the type of matrix and
physicochemical parameters of the microbial cell surface. They claimed that the
transport of weakly charged bacteria moved predominantly by electro-osmosis when
compared to the electrophoresis process (Wick et al. 2004). The EK transport
phenomena were inhibited when strongly charged and highly adhesive bacteria
attached to the soil surface (Wick et al. 2002). The strong affinity between microorganisms and solid matrices is partially overcome through treating the bacteria with
the non-ionic surfactant Brij 35, with up to 80% enhanced EK dispersion achieved
(Wick et al. 2004).
The electro-osmosis process can be used for mobilization of non-ionic charged
molecules such as hydrocarbons, polyaromatic hydrocarbons, PCBs, phenol, and
acetic acid contaminants in the soil matrices. Earlier, it was demonstrated that EKs
alone can remove/transport non-ionic organic molecules from soil matrix to the
cathode section. Generally, transport by electro-osmosis is a process in the range
between 1 and 10 Â 10
À9 m
2
/(VÁS) for various types of soil matrices (Casagrande
1947). However, Wick et al. (2004) calculated the transport rate of the electroosmosis process with bacteria was about 0.1–0.4 cm
2 /(VÁh). Liu et al. (1999)
experimentally observed that Escherichia coli bacteria are predominantly moved
in capillaries exclusively by the electro-osmosis process over a wide range of pH
values and an electric field strength greater than 0.3 V/cm. It can be concluded that
the mobility of bacteria or organics towards the cathode depends upon the speed of
electro-osmosis.
5.2 Degradation of Pollutants
5.2.1 Hydrocarbons
Polycyclic aromatic hydrocarbons (PAHs), which are the most important class of
pollutants, are generated by the inadequate combustion of carbon-based fuels and are
8 Electro-bioremediation: An Advanced Remediation Technology for the. . .
199