total costs depend on numerous factors like the area of contaminated site, the soil
characteristics, the physicochemical properties of the contaminants as well as depth
and the age of the contamination (Saterbak et al. 1999).
Bioremediation is based on the natural capabilities of microorganisms to break
down hydrocarbons combined with application of methods that allow the enhancement of microbial activity and consequently degradation efficiency. Biodegradation
of organic contaminants may occur in aerobic and anaerobic conditions. Aerobic
methods are more widespread and well-studied (Zappi et al. 1996; Robles-González
et al. 2008; Baboshin and Golovleva 2012). The main bioremediation technologies
includes in situ and ex situ treatments. In situ aerobic techniques are simple processes based on nutrient application and air or oxygen injection to soil. In contrast to
ex situ treatments, in situ methods do not include excavation or transport of
contaminated soil. The most important ex situ technologies include landfarming,
composting in biopiles, and treatment in slurry bioreactors (Robles-González et al.
2008). In this chapter, the potential use of the solid digestate which is an anaerobic
digestion by-product, in composting strategy for the cleanup of TPH-contaminated
soils is reviewed.
The main challenge in the design of a bioremediation strategy is to determine the
main factors which limit microbial activity and select appropriate treatment conditions (Fuentes et al. 2014). The limiting factors likely to occur on a contaminated site
can refer to the physical, chemical, or biological aspects. The biological factors that
limit biodegradation may include low activity and density of indigenous bacteria and
fungi as well as interactions between TPH degrading agents and other organisms,
e.g., prokaryotic predation by viruses or heterotrophic nanoflagellates (HNF) (Sauret
et al. 2015). Among the physicochemical aspects, the low bioavailability and
bioaccessibility of the contaminants, insufficient level of soil aeration, water content,
and inadequate level of bioavailable nutrients in soil are the most often listed
(Fuentes et al. 2014). Bioavailable compounds are able to cross the plasma membrane of microorganisms while bioaccessibility describes the possibility of physical
contact with the contaminant (Aemig et al. 2016). A non-bioaccessible compound
may occur in bioavailable form but due to entrapment in the complex of other
complex organic molecules being out of reach for bacteria (Aemig et al. 2016).
The design of a bioremediation strategy should be preceded by proper analysis
and adjusted to each case, as each soil is unique. The analysis of soil structure should
include texture characterization, since granulometry may influence the bioavailability of the contaminant and thus the biodegradation efficiency. It has been observed
that soils characterized by high clay and silt content are more problematic for
remediation purposes in comparison with a sandy soil due to stronger sorption
phenomena as well low permeability which limits fluid flow and affects mass
transfer (Yeh and Young 2003). TPHs may also be adsorbed or trapped into soil
organic matter and the degree of sorption is correlated with the total content of SOM
in the soil (Nishiwaki et al. 2012). The characteristics and age of the contamination
are also important features of contaminated soils. Over time, organic contaminants
are more strongly bound to the soil matrix, resulting in a lower bioavailability and
therefore lower microbial uptake. In this case, the use of surface-active substances
246
A. Gielnik et al.
characteristics, the physicochemical properties of the contaminants as well as depth
and the age of the contamination (Saterbak et al. 1999).
Bioremediation is based on the natural capabilities of microorganisms to break
down hydrocarbons combined with application of methods that allow the enhancement of microbial activity and consequently degradation efficiency. Biodegradation
of organic contaminants may occur in aerobic and anaerobic conditions. Aerobic
methods are more widespread and well-studied (Zappi et al. 1996; Robles-González
et al. 2008; Baboshin and Golovleva 2012). The main bioremediation technologies
includes in situ and ex situ treatments. In situ aerobic techniques are simple processes based on nutrient application and air or oxygen injection to soil. In contrast to
ex situ treatments, in situ methods do not include excavation or transport of
contaminated soil. The most important ex situ technologies include landfarming,
composting in biopiles, and treatment in slurry bioreactors (Robles-González et al.
2008). In this chapter, the potential use of the solid digestate which is an anaerobic
digestion by-product, in composting strategy for the cleanup of TPH-contaminated
soils is reviewed.
The main challenge in the design of a bioremediation strategy is to determine the
main factors which limit microbial activity and select appropriate treatment conditions (Fuentes et al. 2014). The limiting factors likely to occur on a contaminated site
can refer to the physical, chemical, or biological aspects. The biological factors that
limit biodegradation may include low activity and density of indigenous bacteria and
fungi as well as interactions between TPH degrading agents and other organisms,
e.g., prokaryotic predation by viruses or heterotrophic nanoflagellates (HNF) (Sauret
et al. 2015). Among the physicochemical aspects, the low bioavailability and
bioaccessibility of the contaminants, insufficient level of soil aeration, water content,
and inadequate level of bioavailable nutrients in soil are the most often listed
(Fuentes et al. 2014). Bioavailable compounds are able to cross the plasma membrane of microorganisms while bioaccessibility describes the possibility of physical
contact with the contaminant (Aemig et al. 2016). A non-bioaccessible compound
may occur in bioavailable form but due to entrapment in the complex of other
complex organic molecules being out of reach for bacteria (Aemig et al. 2016).
The design of a bioremediation strategy should be preceded by proper analysis
and adjusted to each case, as each soil is unique. The analysis of soil structure should
include texture characterization, since granulometry may influence the bioavailability of the contaminant and thus the biodegradation efficiency. It has been observed
that soils characterized by high clay and silt content are more problematic for
remediation purposes in comparison with a sandy soil due to stronger sorption
phenomena as well low permeability which limits fluid flow and affects mass
transfer (Yeh and Young 2003). TPHs may also be adsorbed or trapped into soil
organic matter and the degree of sorption is correlated with the total content of SOM
in the soil (Nishiwaki et al. 2012). The characteristics and age of the contamination
are also important features of contaminated soils. Over time, organic contaminants
are more strongly bound to the soil matrix, resulting in a lower bioavailability and
therefore lower microbial uptake. In this case, the use of surface-active substances
246
A. Gielnik et al.