words, biologically stable products are rich in recalcitrant organic compounds and
have low C:N ratio (Tambone et al. 2009). Biological stability of organic waste
influences the quality of fertilizer or amendment. Organic matter stabilization relies
on the mineralization of easily biodegradable substrates through anaerobic digestion
or composting. Heavy organic fractions such as lignin like compounds as well as
lipids (Tambone et al. 2009) and steroids are partially accumulated during this
process (Tambone et al. 2010). Further stabilization leads to transformation of
heavy fraction into simple compounds like polyphenols, reducing sugars, amino
acids or fatty acids, which are mineralized or repolymerized into precursors of humic
substances (Qi et al. 2012). Many approaches have been tested to measure the
biological stability of organic matter, among which respirometric approaches
(Ponsá et al. 2008), like dynamic respiration index (DRI) and specific oxygen uptake
rate test (SOUR test), get the most of acceptance (Barrena et al. 2009). Within
alternative methods of biological stability measurement, anaerobic biogas production was recognized as the most representative (Ponsá et al. 2008; Barrena et al.
2009).
Composted digestate has higher biological stability due to further reduction of
easily biodegradable substances. In the maturation phase of digestate composting,
low microbial activity was also observed (Bustamante et al. 2013). Furthermore,
composted digestate showed values of pH, total volatile solids (TVS), and C:N ratio
similar to those of mature compost (Abdullahi et al. 2008). The complex implications after addition of stabilized organic matter to soil are presented in Fig. 5.4.
Stable organic matter has been proved to enhance the level of hydrocarbons
degradation in higher degree than low stable matter (Sayara et al. 2010a, b). The
reason relies in the high availability of nutrients impacting microbial activity and low
content of bioavailable carbon (Tambone et al. 2010; Torres-Climent et al. 2015). In
case of non-stabilized organic amendments the easily biodegradable substrates may
constitute the preferential carbon source and limit the degradation rate of the
contaminants (Sayara et al. 2010a). In stable organic matter, the easily biodegradable
substances have already been decomposed and microorganisms are forced to use the
contaminant as a carbon source. Stable matter has also high nutrient status defined
as N, P, K concentrations in bioavailable forms (Scaglia et al. 2014). High nutrients
status of digestate is ensured by anaerobic conditions, during which mineralization
of organic matter leads to preservation and concentration of nutrients (Tambone
et al. 2010). Nutrient availability to microorganisms is driven by soil chemical
properties like pH or redox potential, which change after application of the digestate.
Thus, modified conditions of soil environment will affect not only the soil nutrient
status but direct and indirect consequence will have an influence on the activity and
composition of the microbial community (Gómez-Brandón et al. 2016).
Stable amendment is an organic matrix rich in complex molecules like humic
acids, which can contribute to SOM turnover and to the maintenance of soil humus
balance (Tambone et al. 2009). The fraction of humic acids dissolved in soil–water
solution has been found to act as a carrier of organic compounds (Smith et al. 2009).
Therefore, addition of composted digestate to the weathered contaminated soils may
increase the bioavailability of hydrophobic substances, like TPH, which enables
5 Potential Use of Waste-to-Bioenergy By-Products in Bioremediation of Total. . .
259
have low C:N ratio (Tambone et al. 2009). Biological stability of organic waste
influences the quality of fertilizer or amendment. Organic matter stabilization relies
on the mineralization of easily biodegradable substrates through anaerobic digestion
or composting. Heavy organic fractions such as lignin like compounds as well as
lipids (Tambone et al. 2009) and steroids are partially accumulated during this
process (Tambone et al. 2010). Further stabilization leads to transformation of
heavy fraction into simple compounds like polyphenols, reducing sugars, amino
acids or fatty acids, which are mineralized or repolymerized into precursors of humic
substances (Qi et al. 2012). Many approaches have been tested to measure the
biological stability of organic matter, among which respirometric approaches
(Ponsá et al. 2008), like dynamic respiration index (DRI) and specific oxygen uptake
rate test (SOUR test), get the most of acceptance (Barrena et al. 2009). Within
alternative methods of biological stability measurement, anaerobic biogas production was recognized as the most representative (Ponsá et al. 2008; Barrena et al.
2009).
Composted digestate has higher biological stability due to further reduction of
easily biodegradable substances. In the maturation phase of digestate composting,
low microbial activity was also observed (Bustamante et al. 2013). Furthermore,
composted digestate showed values of pH, total volatile solids (TVS), and C:N ratio
similar to those of mature compost (Abdullahi et al. 2008). The complex implications after addition of stabilized organic matter to soil are presented in Fig. 5.4.
Stable organic matter has been proved to enhance the level of hydrocarbons
degradation in higher degree than low stable matter (Sayara et al. 2010a, b). The
reason relies in the high availability of nutrients impacting microbial activity and low
content of bioavailable carbon (Tambone et al. 2010; Torres-Climent et al. 2015). In
case of non-stabilized organic amendments the easily biodegradable substrates may
constitute the preferential carbon source and limit the degradation rate of the
contaminants (Sayara et al. 2010a). In stable organic matter, the easily biodegradable
substances have already been decomposed and microorganisms are forced to use the
contaminant as a carbon source. Stable matter has also high nutrient status defined
as N, P, K concentrations in bioavailable forms (Scaglia et al. 2014). High nutrients
status of digestate is ensured by anaerobic conditions, during which mineralization
of organic matter leads to preservation and concentration of nutrients (Tambone
et al. 2010). Nutrient availability to microorganisms is driven by soil chemical
properties like pH or redox potential, which change after application of the digestate.
Thus, modified conditions of soil environment will affect not only the soil nutrient
status but direct and indirect consequence will have an influence on the activity and
composition of the microbial community (Gómez-Brandón et al. 2016).
Stable amendment is an organic matrix rich in complex molecules like humic
acids, which can contribute to SOM turnover and to the maintenance of soil humus
balance (Tambone et al. 2009). The fraction of humic acids dissolved in soil–water
solution has been found to act as a carrier of organic compounds (Smith et al. 2009).
Therefore, addition of composted digestate to the weathered contaminated soils may
increase the bioavailability of hydrophobic substances, like TPH, which enables
5 Potential Use of Waste-to-Bioenergy By-Products in Bioremediation of Total. . .
259