b. Windrows: Microbial degradation of pollutants relies on periodic turning of piled
polluted soil together with added water through increased aeration and uniform
distribution of pollutants and nutrients (Barr et al. 2002). As compared to biopile,
windrows exhibit higher efficiency towards removal of hydrocarbon in soil
(Coulon et al. 2010). The use of windrow technique is more associated with the
release of greenhouse gases due to reduced aeration in anaerobic zone within
piled polluted soil (Hobson et al. 2005).
c. Bioreactor: It is a system mainly composed of batch, fed-batch, continuous and
multistage. Controlled bioaugmentation, nutrient addition, increased pollutant
bioavailability and mass transfer between pollutant and microbes facilitate efficient microbial degradation of pollutants in soil under specific set of conditions
(temperature, pH, agitation, aeration rates, and substrate and inoculum
concentrations). It is widely used in treatment of soil or water polluted with
VOCs (Table 16.3) including toluene, benzene, ethylbenzene and xylene
(Azubuike et al. 2016).
d. Land farming: It is the simplest technique owing to less equipment requirement
and low cost. It is considered under both in situ and ex situ. In former case,
bioremediation proceeds without excavation of soil when pollutants lie <1 m of
the surface of the ground and vice versa (Nikolopoulou et al. 2013). Excavated
polluted soils are treated with autochthonous microorganisms for aerobic biodegradation of pollutants (Silva-Castro et al. 2012), whereas in situ land farming is
facilitated by ploughing, addition of nutrients and irrigation to stimulate biodegradation of pollutants using autochthonous bacteria.
16.6.2.3 Bioremediation Using Microbes, Plants and Their Association
Depending upon the types of biological organisms used, bioremediation is
categorized into following:
a. Microbial Bioremediation
Microorganisms are omnipresent and considered to be the first evolved life forms
on the earth. They are versatile and tolerant towards wide range of environmental
conditions, i.e. from the small intestines of animals to frozen environments, hydrothermal vents, acidic lakes and bottoms of deep oceans (Seigle-Murandi et al. 1996).
Table 4 illustrates certain microorganisms widely used for remediation of
contaminants in soil and are resistant to adverse environmental conditions. Various
factors such as pH, temperature, soil type and texture, nutrient amendments and
oxygen significantly influence the microbial remediation process in soil (VásquezMurrieta et al. 2016; Sharma 2012). In order to thrive under extreme environmental
conditions, microorganisms exhibit certain morphological adaptation at both cellular
and colony levels (such as in shape, colour, texture, opacity, convexity, margin
appearance, etc.) (Jeanson et al. 2015). Due to their adaptability, microorganisms are
widely used for bioremediation of heavy metal(loid)s, hydrocarbons, polythenes,
food wastes, greenhouse gases, etc. (Das 2014). A large number of microbial
enzymes have been known in degradation and detoxification of organic and
16 Causes, Effects and Sustainable Approaches to Remediate Contaminated Soil
475
polluted soil together with added water through increased aeration and uniform
distribution of pollutants and nutrients (Barr et al. 2002). As compared to biopile,
windrows exhibit higher efficiency towards removal of hydrocarbon in soil
(Coulon et al. 2010). The use of windrow technique is more associated with the
release of greenhouse gases due to reduced aeration in anaerobic zone within
piled polluted soil (Hobson et al. 2005).
c. Bioreactor: It is a system mainly composed of batch, fed-batch, continuous and
multistage. Controlled bioaugmentation, nutrient addition, increased pollutant
bioavailability and mass transfer between pollutant and microbes facilitate efficient microbial degradation of pollutants in soil under specific set of conditions
(temperature, pH, agitation, aeration rates, and substrate and inoculum
concentrations). It is widely used in treatment of soil or water polluted with
VOCs (Table 16.3) including toluene, benzene, ethylbenzene and xylene
(Azubuike et al. 2016).
d. Land farming: It is the simplest technique owing to less equipment requirement
and low cost. It is considered under both in situ and ex situ. In former case,
bioremediation proceeds without excavation of soil when pollutants lie <1 m of
the surface of the ground and vice versa (Nikolopoulou et al. 2013). Excavated
polluted soils are treated with autochthonous microorganisms for aerobic biodegradation of pollutants (Silva-Castro et al. 2012), whereas in situ land farming is
facilitated by ploughing, addition of nutrients and irrigation to stimulate biodegradation of pollutants using autochthonous bacteria.
16.6.2.3 Bioremediation Using Microbes, Plants and Their Association
Depending upon the types of biological organisms used, bioremediation is
categorized into following:
a. Microbial Bioremediation
Microorganisms are omnipresent and considered to be the first evolved life forms
on the earth. They are versatile and tolerant towards wide range of environmental
conditions, i.e. from the small intestines of animals to frozen environments, hydrothermal vents, acidic lakes and bottoms of deep oceans (Seigle-Murandi et al. 1996).
Table 4 illustrates certain microorganisms widely used for remediation of
contaminants in soil and are resistant to adverse environmental conditions. Various
factors such as pH, temperature, soil type and texture, nutrient amendments and
oxygen significantly influence the microbial remediation process in soil (VásquezMurrieta et al. 2016; Sharma 2012). In order to thrive under extreme environmental
conditions, microorganisms exhibit certain morphological adaptation at both cellular
and colony levels (such as in shape, colour, texture, opacity, convexity, margin
appearance, etc.) (Jeanson et al. 2015). Due to their adaptability, microorganisms are
widely used for bioremediation of heavy metal(loid)s, hydrocarbons, polythenes,
food wastes, greenhouse gases, etc. (Das 2014). A large number of microbial
enzymes have been known in degradation and detoxification of organic and
16 Causes, Effects and Sustainable Approaches to Remediate Contaminated Soil
475