Intrinsic Bioremediation/Natural Attenuation Bioremediation relies on the natural environmental conditions and behaviour of soil microorganisms and plants that
are indigenous. It occurs without human intervention other than monitoring. The
techniques are widely used to treat hydrocarbons, dyes, chlorinated solvents and
metal(loid)s at polluted sites (Roy et al. 2015; Frascari et al. 2015).
Enhanced In Situ Bioremediation Intrinsic bioremediation is enhanced by some
additive agents for effective remediation of polluted sites. This includes bioventing,
bioslurping, biosparging and phytoremediation (Azubuike et al. 2016).
a. Bioventing: It involves controlled stimulation of airflow by supplying oxygen to
unsaturated zone (vadose) in order to increase microbial activities. Besides, soil
amendments are used to supply moisture and nutrients for enhanced bioremediation of pollutants rendering them into a harmless form (Philp and Atlas 2005).
b. Slurping: The technique is the combination of vacuum-enhanced pumping,
extraction of soil vapour and bioventing for indirect provision of oxygen for
contaminant biodegradation (Gidarakos and Aivalioti 2007). It is effectively used
in remediation of volatile and semi-volatile organic pollutants in soil (Table 16.3).
The technique is not suitable for soil with low permeability.
c. Biosparging: Unlike bioventing, air is injected into the saturated zone of soil
subsurface which causes skyward movement of VOCs into the unsaturated zone
to stimulate bioremediation process. The effectiveness of the technique proportionally depends upon soil permeability and pollutant biodegradability (Philp and
Atlas 2005).
d. Phytoremediation: The technique relies on the use of plants’ interaction with
physical, chemical and biological factors at polluted sites to mitigate the toxic
effects of pollutants (Azubuike et al. 2016; Sarma et al. 2021).
16.6.2.2 Ex Situ Bioremediation
Ex situ bioremediation techniques implicate excavation of polluted soils from
contaminated sites and its subsequent transportation to another site for treatment.
The techniques are usually preferred after envisaging the type of pollutant, depth and
degree of pollution, geology of the polluted site, geographical location and the cost
of treatment (Philp and Atlas 2005). Following ex situ bioremediation techniques
are:
a. Biopile: It is a bioremediation technology where excavated soils are amended
with nutrient to form a compost piles and enclosed for further treatments. The
entire setup composed of a treatment bed, aeration, irrigation and a leachate
collection system. An aeration and irrigation system is buried under the soil to
pass through air and nutrients. Moreover, pH, oxygen, heat and nutrients are
controlled factors to enhance biodegradation. The biopile technique is mainly
applicable to polluted sites having VOCs with low molecular weight (Whelan
et al. 2015). In the process, airstream-containing VOCs when leave the soil are
treated to remove or destroy before being discharged into the atmosphere.
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M. Gautam et al.
are indigenous. It occurs without human intervention other than monitoring. The
techniques are widely used to treat hydrocarbons, dyes, chlorinated solvents and
metal(loid)s at polluted sites (Roy et al. 2015; Frascari et al. 2015).
Enhanced In Situ Bioremediation Intrinsic bioremediation is enhanced by some
additive agents for effective remediation of polluted sites. This includes bioventing,
bioslurping, biosparging and phytoremediation (Azubuike et al. 2016).
a. Bioventing: It involves controlled stimulation of airflow by supplying oxygen to
unsaturated zone (vadose) in order to increase microbial activities. Besides, soil
amendments are used to supply moisture and nutrients for enhanced bioremediation of pollutants rendering them into a harmless form (Philp and Atlas 2005).
b. Slurping: The technique is the combination of vacuum-enhanced pumping,
extraction of soil vapour and bioventing for indirect provision of oxygen for
contaminant biodegradation (Gidarakos and Aivalioti 2007). It is effectively used
in remediation of volatile and semi-volatile organic pollutants in soil (Table 16.3).
The technique is not suitable for soil with low permeability.
c. Biosparging: Unlike bioventing, air is injected into the saturated zone of soil
subsurface which causes skyward movement of VOCs into the unsaturated zone
to stimulate bioremediation process. The effectiveness of the technique proportionally depends upon soil permeability and pollutant biodegradability (Philp and
Atlas 2005).
d. Phytoremediation: The technique relies on the use of plants’ interaction with
physical, chemical and biological factors at polluted sites to mitigate the toxic
effects of pollutants (Azubuike et al. 2016; Sarma et al. 2021).
16.6.2.2 Ex Situ Bioremediation
Ex situ bioremediation techniques implicate excavation of polluted soils from
contaminated sites and its subsequent transportation to another site for treatment.
The techniques are usually preferred after envisaging the type of pollutant, depth and
degree of pollution, geology of the polluted site, geographical location and the cost
of treatment (Philp and Atlas 2005). Following ex situ bioremediation techniques
are:
a. Biopile: It is a bioremediation technology where excavated soils are amended
with nutrient to form a compost piles and enclosed for further treatments. The
entire setup composed of a treatment bed, aeration, irrigation and a leachate
collection system. An aeration and irrigation system is buried under the soil to
pass through air and nutrients. Moreover, pH, oxygen, heat and nutrients are
controlled factors to enhance biodegradation. The biopile technique is mainly
applicable to polluted sites having VOCs with low molecular weight (Whelan
et al. 2015). In the process, airstream-containing VOCs when leave the soil are
treated to remove or destroy before being discharged into the atmosphere.
474
M. Gautam et al.