increased bioavailability and also biodegradations of PAHs (Stringfellow and
Alvarez-Cohen 1999).
Sorption occurs also in the case of fungal mycelium, for example, in the case of
pesticides and chlorophenols (Benoit et al. 1998).
23.3.2.2 Biodegradation
Basically, aerobic degradation of organic contaminants may proceed thanks to three
different principles (Kästner 2000):
(i) Metabolic degradation of organic contaminants as a source of carbon and
energy, and their complete mineralization. Usually, the contaminant is
processed inside a cell, and microbial biomass growth occurs thanks to its
processing. CO 2 and H 2 O are released as by-products. In an ideal case, accumulation of other metabolites does not occur.
(ii) Co-metabolic degradation of organic contaminants, when an organic contaminant is degraded non-selectively by an action of enzymes (often
monooxygenases) participating in degradation of other organic sources of
carbon. It usually proceeds inside a cell too, but it can proceed also out of it,
and it often results in production of partially oxidized metabolites that are
accumulated subsequently. It does not result in biomass growth, and the
contaminant energy potential is not used.
(iii) Non-specific radical oxidation is a process that proceeds out of a cell, and is
characterized by formation of radicals as oxidation intermediates due to an
electron abstraction. Gradual secondary oxidation reactions of the primary
metabolites may follow, up to CO 2 . These processes are typical, in particular,
for ligninolytic fungi (Hofrichter 2002).
In addition to the presence of microorganisms having the proper enzymatic
properties for decomposition of organic contaminants, and ensuring availability of
the contaminants, there are several further preconditions that have to be ensured in
order that the co-composting process is efficient. One of the often neglected factors
during the direct metabolic degradation of contaminants is the fact that the contaminant must be present in a sufficient concentration in the treated material, enabling to
meet the energy needs of the degradation microorganisms and ensuring their mobility into the untreated areas of the material (Adam et al. 2014; Rein et al. 2016;
Semple et al. 2001). The moment the contaminant concentration decreases under
certain minimum limit its biodegradation stops. In real systems, biodegradation
proceeds in a dynamic state when contaminants are slowly released from sorption
places or NAPL in the direction to the relevant microorganisms degrading them. For
this reason, the microbial activity depends on the substrate flow not on its concentration. This is true, in particular, in the case of hydrophobic compounds, such as
petroleum substances, tars, and similar organic compounds when biodegradation is
usually limited by the transfer of mass (Adam et al. 2014; Bosma et al. 1997;
Marchal et al. 2013a, b; Rein et al. 2016; Volkering et al. 1992; Wick et al. 2001).
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Alvarez-Cohen 1999).
Sorption occurs also in the case of fungal mycelium, for example, in the case of
pesticides and chlorophenols (Benoit et al. 1998).
23.3.2.2 Biodegradation
Basically, aerobic degradation of organic contaminants may proceed thanks to three
different principles (Kästner 2000):
(i) Metabolic degradation of organic contaminants as a source of carbon and
energy, and their complete mineralization. Usually, the contaminant is
processed inside a cell, and microbial biomass growth occurs thanks to its
processing. CO 2 and H 2 O are released as by-products. In an ideal case, accumulation of other metabolites does not occur.
(ii) Co-metabolic degradation of organic contaminants, when an organic contaminant is degraded non-selectively by an action of enzymes (often
monooxygenases) participating in degradation of other organic sources of
carbon. It usually proceeds inside a cell too, but it can proceed also out of it,
and it often results in production of partially oxidized metabolites that are
accumulated subsequently. It does not result in biomass growth, and the
contaminant energy potential is not used.
(iii) Non-specific radical oxidation is a process that proceeds out of a cell, and is
characterized by formation of radicals as oxidation intermediates due to an
electron abstraction. Gradual secondary oxidation reactions of the primary
metabolites may follow, up to CO 2 . These processes are typical, in particular,
for ligninolytic fungi (Hofrichter 2002).
In addition to the presence of microorganisms having the proper enzymatic
properties for decomposition of organic contaminants, and ensuring availability of
the contaminants, there are several further preconditions that have to be ensured in
order that the co-composting process is efficient. One of the often neglected factors
during the direct metabolic degradation of contaminants is the fact that the contaminant must be present in a sufficient concentration in the treated material, enabling to
meet the energy needs of the degradation microorganisms and ensuring their mobility into the untreated areas of the material (Adam et al. 2014; Rein et al. 2016;
Semple et al. 2001). The moment the contaminant concentration decreases under
certain minimum limit its biodegradation stops. In real systems, biodegradation
proceeds in a dynamic state when contaminants are slowly released from sorption
places or NAPL in the direction to the relevant microorganisms degrading them. For
this reason, the microbial activity depends on the substrate flow not on its concentration. This is true, in particular, in the case of hydrophobic compounds, such as
petroleum substances, tars, and similar organic compounds when biodegradation is
usually limited by the transfer of mass (Adam et al. 2014; Bosma et al. 1997;
Marchal et al. 2013a, b; Rein et al. 2016; Volkering et al. 1992; Wick et al. 2001).
480
O. Lhotský et al.