It is impossible to present the natural attenuation and the
treatment of all types of pollution; the chosen examples are
representative of major pollutions affecting the environment, and for a given type of pollution, only few examples
of treatments described in the scientific literature will be
presented.
16.2 Preventive and Bioremediation
Treatments
The aim is to exploit the degradation capabilities of
microorganisms by implementing ways that will increase
and accelerate the natural process of biodegradation. For
example, wastewater treatment plants reproduce, under controlled conditions, processes that occur in the environment.
The composting process is based on the acceleration of the
humification of organic residues into natural humic
substances* as it occurs in soils.
The acceleration and amplification of the biodegradation
process are obtained by inputs of nutrients, electron acceptors
(oxygen, nitrate, sulfate, etc.), and/or microorganisms (pure
strains, consortium*, communities, genetically modified
organisms, GMO*) whose metabolic capabilities are specifically adapted to the biodegradation of the treated pollutant.
16.2.1 Microorganisms as Bioremediation
Agents
Overall, there are five possibilities of using microorganisms
in preventive treatments and bioremediation: biostimulation,
bioaugmentation, rhizostimulation, bioleaching, and
bioimmobilization.
16.2.1.1 Biostimulation
Biostimulation is based on the stimulation of the activity of
natural communities on the polluted site by adding the
following:
(i) Nutrients (e.g., nitrogen, phosphorus) (Prince 1993)
(ii) Electron acceptors (oxygen for aerobic biodegradation,
nitrate or sulfate for anaerobic biodegradation)
(Cunningham et al. 2001)
(iii) Surfactants* of chemical or biological origin which
will increase the bioavailability of the more hydrophobic pollutants (hydrocarbons, PCBs, etc.) (Iwamoto and
Nasu 2001; Ron and Rosenberg 2002; Lawniczak et al.
2013).
Ideally, the goal is to suppress the action of any limiting
factor for biodegradation, allowing a maximal activity of
microorganisms.
16.2.1.2 Bioaugmentation
Bioaugmentation is based on the input of microorganisms
capable of degrading the pollutant in the polluted area
(Timmis and Pieper 1999; Sayler and Ripp 2000; Gentry
et al. 2004; El Fantroussi and Agathos 2005; Thompson et al.
2005). The strains used are indigenous strains which are
isolated from the polluted site and selected in laboratory
conditions according to the pollutant; after growth (usually
in a bioreactor), microorganisms are then reinjected on site
in the polluted area.
It is also possible to make use of genetically modified
microorganisms (GMMs). A.M. Chakrabarty was the first to
file a patent in 1971 for a GMM capable of degrading
alkanes and aromatic hydrocarbons after transfer of plasmids
of three different strains in a strain of Pseudomonas. Potentially, GMMs can optimize the biodegradation of a pollutant:
by increasing degradation rates, by creating new biodegradation pathways, and by broadening the range of
biodegraded substrates. However, the introduction of
GMMs in a natural environment is subject to stringent
laws, which severely limits their use. In general, the greatest
difficulty in using bioaugmentation techniques is the competition between introduced and indigenous microorganisms.
16.2.1.3 Rhizostimulation
Many plants grow in the presence of a pollutant that can extract,
accumulate, transform, or eliminate (Pilon-Smits 2005). In the
case of rhizodegradation, the pollutant is degraded by enzymes
released by the plant roots or by phytostimulation of
microorganisms associated with the rhizosphere (cf. Sect. 11.
3.6) (Gerhardt et al. 2009). Hydrocarbons (e.g., PAHs) and
PCBs are organic compounds that are degraded in the rhizosphere. This treatment, which lasts for several years, is a lowcost treatment because the energy source is provided by the sun
that ensures photosynthetic processes. It also offers a landscape
which is esthetically acceptable.
16.2.1.4 Bioleaching
Bioleaching corresponds to solubilization by microorganisms and to leaching by entrainment in the aqueous
phase of pollutants (ores, heavy metals, phosphorus, etc.)
fixed or trapped in a solid matrix (cf. Sect. 16.9.2).
16 Applied Microbial Ecology and Bioremediation
661
treatment of all types of pollution; the chosen examples are
representative of major pollutions affecting the environment, and for a given type of pollution, only few examples
of treatments described in the scientific literature will be
presented.
16.2 Preventive and Bioremediation
Treatments
The aim is to exploit the degradation capabilities of
microorganisms by implementing ways that will increase
and accelerate the natural process of biodegradation. For
example, wastewater treatment plants reproduce, under controlled conditions, processes that occur in the environment.
The composting process is based on the acceleration of the
humification of organic residues into natural humic
substances* as it occurs in soils.
The acceleration and amplification of the biodegradation
process are obtained by inputs of nutrients, electron acceptors
(oxygen, nitrate, sulfate, etc.), and/or microorganisms (pure
strains, consortium*, communities, genetically modified
organisms, GMO*) whose metabolic capabilities are specifically adapted to the biodegradation of the treated pollutant.
16.2.1 Microorganisms as Bioremediation
Agents
Overall, there are five possibilities of using microorganisms
in preventive treatments and bioremediation: biostimulation,
bioaugmentation, rhizostimulation, bioleaching, and
bioimmobilization.
16.2.1.1 Biostimulation
Biostimulation is based on the stimulation of the activity of
natural communities on the polluted site by adding the
following:
(i) Nutrients (e.g., nitrogen, phosphorus) (Prince 1993)
(ii) Electron acceptors (oxygen for aerobic biodegradation,
nitrate or sulfate for anaerobic biodegradation)
(Cunningham et al. 2001)
(iii) Surfactants* of chemical or biological origin which
will increase the bioavailability of the more hydrophobic pollutants (hydrocarbons, PCBs, etc.) (Iwamoto and
Nasu 2001; Ron and Rosenberg 2002; Lawniczak et al.
2013).
Ideally, the goal is to suppress the action of any limiting
factor for biodegradation, allowing a maximal activity of
microorganisms.
16.2.1.2 Bioaugmentation
Bioaugmentation is based on the input of microorganisms
capable of degrading the pollutant in the polluted area
(Timmis and Pieper 1999; Sayler and Ripp 2000; Gentry
et al. 2004; El Fantroussi and Agathos 2005; Thompson et al.
2005). The strains used are indigenous strains which are
isolated from the polluted site and selected in laboratory
conditions according to the pollutant; after growth (usually
in a bioreactor), microorganisms are then reinjected on site
in the polluted area.
It is also possible to make use of genetically modified
microorganisms (GMMs). A.M. Chakrabarty was the first to
file a patent in 1971 for a GMM capable of degrading
alkanes and aromatic hydrocarbons after transfer of plasmids
of three different strains in a strain of Pseudomonas. Potentially, GMMs can optimize the biodegradation of a pollutant:
by increasing degradation rates, by creating new biodegradation pathways, and by broadening the range of
biodegraded substrates. However, the introduction of
GMMs in a natural environment is subject to stringent
laws, which severely limits their use. In general, the greatest
difficulty in using bioaugmentation techniques is the competition between introduced and indigenous microorganisms.
16.2.1.3 Rhizostimulation
Many plants grow in the presence of a pollutant that can extract,
accumulate, transform, or eliminate (Pilon-Smits 2005). In the
case of rhizodegradation, the pollutant is degraded by enzymes
released by the plant roots or by phytostimulation of
microorganisms associated with the rhizosphere (cf. Sect. 11.
3.6) (Gerhardt et al. 2009). Hydrocarbons (e.g., PAHs) and
PCBs are organic compounds that are degraded in the rhizosphere. This treatment, which lasts for several years, is a lowcost treatment because the energy source is provided by the sun
that ensures photosynthetic processes. It also offers a landscape
which is esthetically acceptable.
16.2.1.4 Bioleaching
Bioleaching corresponds to solubilization by microorganisms and to leaching by entrainment in the aqueous
phase of pollutants (ores, heavy metals, phosphorus, etc.)
fixed or trapped in a solid matrix (cf. Sect. 16.9.2).
16 Applied Microbial Ecology and Bioremediation
661