Mechanical treatment is done by grinding, mixing and sieving, to remove
non-degradable materials such as metals, plastics, glass and stones, which
gives good conditions for the biological treatment of compostable materials
(Das and Adholeya 2012). High substrate levels in composts can lead to
co-metabolism of organic contaminants (Niti et al. 2013).
(f) Windrow: Soils with added amendments are layered in the form of long piles
known as windrows. At first, the polluted soils are removed from the site, which
is then screened for removing big rocks and waste debris. This soil is then
shifted to a composting pad for providing containment and safety from extreme
weather conditions. Modifications are used for bulking agents such as straw,
alfalfa, manure, agricultural wastes or wood chips as well as a supplementary
source of carbon (Niti et al. 2013). Bioremediation is further enhanced by
preparing a thorough mixture of the windrow by periodic turning and a commercially available windrow turning machine (Niti et al. 2013; Azubuike et al.
2016). This periodical turning of contaminated soil, along with water addition,
enhances aeration, homogeneous distribution of contaminants, nutrients and
degradative activities of microbes, thus increasing the bioremediation rate
(Azubuike et al. 2016). Factors such as humidity, pH, temperature and
concentrations of explosives are monitored. The windrows are removed, and
the compost is taken to the final disposal area, at the end of the composting
period (Niti et al. 2013).
(g) Biostimulation: In this process, the naturally occurring microbial population is
managed to monitor and provide an environment that optimizes the growth of
microbes and their activity (Agwu and Kalu 2012). In this process, nutrients of
the soil, minerals present in traces, acceptors or donors of electrons and several
limiting factors as well as amendments are added to enhance the biotransformation of a broad range of pollutants occurring in the contaminated soil (Niti et al.
2013; Banik et al. 2014).
(h) Bioaugmentation: This approach includes the application of specific strains or
microbial consortia either indigenous or exogenous to the polluted sites that
target only specific domain of chemical compounds (Agwu and Kalu 2012; Das
and Adholeya 2012; Shah 2017). Two points limit the usage of microbial
cultures added in this method:
(i) Exogenous cultures have to compete with a native population of microbes
for the sustainability of useful microbes to complete the process.
(ii) Native microbes are efficient degraders, and long-term exposure of these
microbes to biodegradable waste is well managed by the native microflora
(Das and Adholeya 2012).
Bioaugmentation is generally paired with the process of biostimulation by the
addition of an optimal amount of water, nutrients and oxygen where the site is
polluted; it increases the action of microbes added or enhancing co-metabolism (Niti
et al. 2013).
15 The Role of Microorganisms in Remediation of Environmental Contaminants
429
non-degradable materials such as metals, plastics, glass and stones, which
gives good conditions for the biological treatment of compostable materials
(Das and Adholeya 2012). High substrate levels in composts can lead to
co-metabolism of organic contaminants (Niti et al. 2013).
(f) Windrow: Soils with added amendments are layered in the form of long piles
known as windrows. At first, the polluted soils are removed from the site, which
is then screened for removing big rocks and waste debris. This soil is then
shifted to a composting pad for providing containment and safety from extreme
weather conditions. Modifications are used for bulking agents such as straw,
alfalfa, manure, agricultural wastes or wood chips as well as a supplementary
source of carbon (Niti et al. 2013). Bioremediation is further enhanced by
preparing a thorough mixture of the windrow by periodic turning and a commercially available windrow turning machine (Niti et al. 2013; Azubuike et al.
2016). This periodical turning of contaminated soil, along with water addition,
enhances aeration, homogeneous distribution of contaminants, nutrients and
degradative activities of microbes, thus increasing the bioremediation rate
(Azubuike et al. 2016). Factors such as humidity, pH, temperature and
concentrations of explosives are monitored. The windrows are removed, and
the compost is taken to the final disposal area, at the end of the composting
period (Niti et al. 2013).
(g) Biostimulation: In this process, the naturally occurring microbial population is
managed to monitor and provide an environment that optimizes the growth of
microbes and their activity (Agwu and Kalu 2012). In this process, nutrients of
the soil, minerals present in traces, acceptors or donors of electrons and several
limiting factors as well as amendments are added to enhance the biotransformation of a broad range of pollutants occurring in the contaminated soil (Niti et al.
2013; Banik et al. 2014).
(h) Bioaugmentation: This approach includes the application of specific strains or
microbial consortia either indigenous or exogenous to the polluted sites that
target only specific domain of chemical compounds (Agwu and Kalu 2012; Das
and Adholeya 2012; Shah 2017). Two points limit the usage of microbial
cultures added in this method:
(i) Exogenous cultures have to compete with a native population of microbes
for the sustainability of useful microbes to complete the process.
(ii) Native microbes are efficient degraders, and long-term exposure of these
microbes to biodegradable waste is well managed by the native microflora
(Das and Adholeya 2012).
Bioaugmentation is generally paired with the process of biostimulation by the
addition of an optimal amount of water, nutrients and oxygen where the site is
polluted; it increases the action of microbes added or enhancing co-metabolism (Niti
et al. 2013).
15 The Role of Microorganisms in Remediation of Environmental Contaminants
429