From this point of view, utilization of compost is ideal for biodegradation of these
substances as it comprises bigger particles of slowly biologically degradable substrates, humic acids, and other complicated biomolecules. Moreover, mixing contaminated soils with organic substrates results in increasing the mass flow of the
contaminants partially thanks to the actual mechanical processing of the material, but
also thanks to the temperature growth and the increase of the concentration gradient,
which often results in destruction of the interfaces between the phases preventing
mass transfers. Destruction of the interfaces by mixing and adding organic substances results in the increase in biological availability, and thus in much quicker
degradation of the organic contaminants (Kästner and Miltner 2016).
The addition of organic substrates to the contaminated materials in the course of
co-composting usually also provides sufficient amounts of primary substrates and
nutrients for the co-metabolic processes (Alburquerque et al. 2009; Chen et al. 2015;
Gandolfi et al. 2010; Megharaj et al. 2011) that depend, in addition to the mass flow
of the contaminant, also on the mass flow of these substances. The addition of
organic substrates to the soil increases nitrogen and phosphorus concentrations and
at the same time considerably improves the environmental properties of the
decontaminated material thanks to the change of its structure, the increase in the
pore volume, and the increase in the ability to absorb water. This is essential for
ensuring sufficient transport of gases through the decontaminated material in order
that the degradation microorganisms have sufficient oxygen supply and, simultaneously, the CO 2 accumulation does not occur. At the same time, sufficient water
concentration is ensured too, which is generally necessary for the growth of microorganisms (Potts 1994). One often neglected fact during composting is the production of water as a final product of the microbial metabolism. In certain cases (for
example, during composting of a grass substrate without addition of a bulking agent)
this may result in oversaturating the material with water within the course of the
process, which further prevents efficient exchange of gases, and causes CO 2 accumulation and O 2 deficiency. On the other hand, in the case of too dry or intensively
ventilated materials, the water production is positive. The addition of an organic
substrate may, because of its buffering capacity, also act as acidity regulation
(Gandolfi et al. 2010; Zhang et al. 2011). Hernández et al. (2015) proved that the
positive effects of the addition of an organic substrate on the activity of the microbial
communities are long-term. Specifically, they persisted for more than 5 years in his
studies.
Positive changes caused by organic substrate additions to the contaminated
materials are often designated as the so-called “matrix effect” that is caused by the
above-described mechanisms, such as addition of primary organic substrates, solubilization of the contaminants, and also changes of the material structure (Haderlein
et al. 2001; Marchal et al. 2013a, b; Mayer et al. 2005; Ortega-Calvo and SaizJimenez 1998; Puglisi et al. 2007; Smith et al. 2011). In addition to that, the matrix
effect may manifest itself through the fact that it results in the desorption of the
organic contaminants from the soil material, with subsequent sorption to biologically
degradable solid organic substrates. Subsequently, in the course of the degradation
of these organic substrates, the contaminants adsorbed on them are degraded too. In
23 Composting Practices for the Remediation of Matrices Contaminated by. . .
481
substances as it comprises bigger particles of slowly biologically degradable substrates, humic acids, and other complicated biomolecules. Moreover, mixing contaminated soils with organic substrates results in increasing the mass flow of the
contaminants partially thanks to the actual mechanical processing of the material, but
also thanks to the temperature growth and the increase of the concentration gradient,
which often results in destruction of the interfaces between the phases preventing
mass transfers. Destruction of the interfaces by mixing and adding organic substances results in the increase in biological availability, and thus in much quicker
degradation of the organic contaminants (Kästner and Miltner 2016).
The addition of organic substrates to the contaminated materials in the course of
co-composting usually also provides sufficient amounts of primary substrates and
nutrients for the co-metabolic processes (Alburquerque et al. 2009; Chen et al. 2015;
Gandolfi et al. 2010; Megharaj et al. 2011) that depend, in addition to the mass flow
of the contaminant, also on the mass flow of these substances. The addition of
organic substrates to the soil increases nitrogen and phosphorus concentrations and
at the same time considerably improves the environmental properties of the
decontaminated material thanks to the change of its structure, the increase in the
pore volume, and the increase in the ability to absorb water. This is essential for
ensuring sufficient transport of gases through the decontaminated material in order
that the degradation microorganisms have sufficient oxygen supply and, simultaneously, the CO 2 accumulation does not occur. At the same time, sufficient water
concentration is ensured too, which is generally necessary for the growth of microorganisms (Potts 1994). One often neglected fact during composting is the production of water as a final product of the microbial metabolism. In certain cases (for
example, during composting of a grass substrate without addition of a bulking agent)
this may result in oversaturating the material with water within the course of the
process, which further prevents efficient exchange of gases, and causes CO 2 accumulation and O 2 deficiency. On the other hand, in the case of too dry or intensively
ventilated materials, the water production is positive. The addition of an organic
substrate may, because of its buffering capacity, also act as acidity regulation
(Gandolfi et al. 2010; Zhang et al. 2011). Hernández et al. (2015) proved that the
positive effects of the addition of an organic substrate on the activity of the microbial
communities are long-term. Specifically, they persisted for more than 5 years in his
studies.
Positive changes caused by organic substrate additions to the contaminated
materials are often designated as the so-called “matrix effect” that is caused by the
above-described mechanisms, such as addition of primary organic substrates, solubilization of the contaminants, and also changes of the material structure (Haderlein
et al. 2001; Marchal et al. 2013a, b; Mayer et al. 2005; Ortega-Calvo and SaizJimenez 1998; Puglisi et al. 2007; Smith et al. 2011). In addition to that, the matrix
effect may manifest itself through the fact that it results in the desorption of the
organic contaminants from the soil material, with subsequent sorption to biologically
degradable solid organic substrates. Subsequently, in the course of the degradation
of these organic substrates, the contaminants adsorbed on them are degraded too. In
23 Composting Practices for the Remediation of Matrices Contaminated by. . .
481