processes were used to remove toxic substance present in the contaminated environment. In the biological process, microbial consortia utilized the contaminants in
the soil, which act as bacterial inoculum in so-called bio-augmentation.
Bio-stimulation states that the enhancement of biodegradation by autochthonous
bacteria in soil could be increased by the addition of nutrients. A significant number
of studies have reported the degradation of polyaromatic hydrocarbon-polluted soil
in laboratory experiments (Qin et al. 2015; Wick et al. 2004, 2007, 2010).
Every technique has its own merits and demerits, and bioremediation also has
some limitations. Before using the bioremediation process, initial assessment of the
soil is needed. The bioremediation treatment process depends highly on the availability of nutrients, moisture content, pH, and permeability and temperature of the
soil matrix. Geller (1991) observed that carbon (C), nitrogen (N), and phosphorus
(P) are the main nutrients for microbial cell growth and its activity. The approximate
ratio of 250:10:3 for C:N:P is suitable for microbial growth, but this ratio is most
often not found at contaminated field sites. Sometimes higher N values at the soil site
also cause microbial inhibition. The growth of microorganisms requires favorable
pH condition and also requires a suitable temperature at which microbes can survive,
in the range 20
C to 30
C. Some chemicals are highly resistant to the bioremediation process, for example, heavy metals, radioactive materials, and some chlorinated compounds such as polychlorinated biphenyls (PCBs). The biological process
of contamination may produce secondary toxic metabolism that affects the environment. Bioremediation is a slow process and is site specific: a small-scale study
should be done before implementing this technology at the pilot scale. The bioremediation process can also be combined with the mechanical treatment of the soil,
which stimulates the process. Thus, the bacteria move in the entire soil matrix to
encounter pollutants, but this action is not feasible for the remediation of entire,
heterogeneous sites; the desired remediation cannot be achieved within economically acceptable timeframes (Harms and Wick 2006). Different research articles
cover the treatment of polyaromatic hydrocarbons in contaminated soil by autochthonous microorganisms, but no studies are available on the treatment of reactive
dye in contaminated soil by bioremediation. Tailored design and easy application in
the field are necessary for the successful removal of dyes.
4 Biotransformation of Contaminants
The biotransformation of contaminants is the alteration of environmentally persistent
organic/inorganic contaminants into easily degradable substances using microorganism activity. The gain of energy resulting from microorganism growth and maintenance in organic pollutants is called the biotransformation process. The degradation
reaction is mainly the result of physiological coupling of the redox process. In the
redox process, reduction and oxidation reactions occur within a cell. In general,
electrons are transferred from one compound (called the electron donor or oxidation)
to an electron-accepting compound (called the electron acceptor or reduction). Many
authors (Tiehm and Schmidt 2007; Wiedemeier 1999) have reported that,
8 Electro-bioremediation: An Advanced Remediation Technology for the. . .
197
the soil, which act as bacterial inoculum in so-called bio-augmentation.
Bio-stimulation states that the enhancement of biodegradation by autochthonous
bacteria in soil could be increased by the addition of nutrients. A significant number
of studies have reported the degradation of polyaromatic hydrocarbon-polluted soil
in laboratory experiments (Qin et al. 2015; Wick et al. 2004, 2007, 2010).
Every technique has its own merits and demerits, and bioremediation also has
some limitations. Before using the bioremediation process, initial assessment of the
soil is needed. The bioremediation treatment process depends highly on the availability of nutrients, moisture content, pH, and permeability and temperature of the
soil matrix. Geller (1991) observed that carbon (C), nitrogen (N), and phosphorus
(P) are the main nutrients for microbial cell growth and its activity. The approximate
ratio of 250:10:3 for C:N:P is suitable for microbial growth, but this ratio is most
often not found at contaminated field sites. Sometimes higher N values at the soil site
also cause microbial inhibition. The growth of microorganisms requires favorable
pH condition and also requires a suitable temperature at which microbes can survive,
in the range 20
C to 30
C. Some chemicals are highly resistant to the bioremediation process, for example, heavy metals, radioactive materials, and some chlorinated compounds such as polychlorinated biphenyls (PCBs). The biological process
of contamination may produce secondary toxic metabolism that affects the environment. Bioremediation is a slow process and is site specific: a small-scale study
should be done before implementing this technology at the pilot scale. The bioremediation process can also be combined with the mechanical treatment of the soil,
which stimulates the process. Thus, the bacteria move in the entire soil matrix to
encounter pollutants, but this action is not feasible for the remediation of entire,
heterogeneous sites; the desired remediation cannot be achieved within economically acceptable timeframes (Harms and Wick 2006). Different research articles
cover the treatment of polyaromatic hydrocarbons in contaminated soil by autochthonous microorganisms, but no studies are available on the treatment of reactive
dye in contaminated soil by bioremediation. Tailored design and easy application in
the field are necessary for the successful removal of dyes.
4 Biotransformation of Contaminants
The biotransformation of contaminants is the alteration of environmentally persistent
organic/inorganic contaminants into easily degradable substances using microorganism activity. The gain of energy resulting from microorganism growth and maintenance in organic pollutants is called the biotransformation process. The degradation
reaction is mainly the result of physiological coupling of the redox process. In the
redox process, reduction and oxidation reactions occur within a cell. In general,
electrons are transferred from one compound (called the electron donor or oxidation)
to an electron-accepting compound (called the electron acceptor or reduction). Many
authors (Tiehm and Schmidt 2007; Wiedemeier 1999) have reported that,
8 Electro-bioremediation: An Advanced Remediation Technology for the. . .
197