development of microbial communities. The growth of microorganisms is boosted
by the presence of the organic substrates, and the co-metabolic, besides metabolic,
degradation of pollutants is achieved through the various temperature-dependent
stages of the composting process. Co-composting has been performed in windrows,
static piles, and as in-vessel (Antizar-Ladislao et al. 2004).
The process of co-composting is altogether very similar to the process of conventional biowaste composting, with bio-oxidation reactions causing a prompt
increase in the temperature and attainment of the thermophilic conditions, followed
by cooling and maturation phases. Thermophilic conditions represent the fingerprint
feature of co-composting. Spontaneous thermogenesis marks in fact the difference
between co-composting and other bioremediation approaches (e.g., land farming or
biopiles), where the addition of amendments/bulking agents does not cause the
temperature to rise above 40–45
C. Due to this fact, the discussion concerning
the usefulness of attaining such temperatures for the sake of the contaminant removal
has been open for several years. On the one hand, the increase in the temperature
during the composting process could potentially support the biodegradation of the
contaminants, particularly with regard to lipophilic compounds (e.g., high molecular
weight polycyclic aromatic hydrocarbons—PAHs) that tend to be adsorbed on soil
organic matter; therefore, a consistent rise in the temperature might facilitate desorption kinetics from the organic matter to water and, in turn, biodegradation by
microbial consortia as a result of the increased contaminant bioavailability
(Margesin and Schinner 2001; Wong et al. 2004; Viamajala et al. 2007). On the
other hand, the thermophilic stage represents an ecological bottleneck because
oxygen solubility tends to decrease when the temperature increases, and most
microbes, including contaminant-degrading microbes, cannot grow when the temperature rises above 55–60
C (Antizar-Ladislao et al. 2005, 2006).
23.3.1 Regulatory Conditions
Regulatory limits and targets connected with remediation of contaminated soil
significantly differ in each country. Contaminant concentrations in soil acceptable
in certain countries may far exceed the acceptability limits in other ones. The
situation concerning the approach to the actual process of composting of biologically
degradable waste is similar. Requirements for composting plants, composting process parameters as well as for the treated biologically degradable waste differ in
individual countries. A trend towards unification of the regulations may be seen
within the EU currently, however, the situation is still relatively unclear.
Figure 23.4 summarizes the rules that have to be taken into account in the various
phases of utilization of contaminated waste composting. Part A concerns regulatory
limits for contaminant concentrations in soil and other materials to be
decontaminated. Part B relates to regulations concerning organic substrates. Utilization of co-composting is possible only in the case that the conditions given in the
decision tree are met (Antizar-Ladislao 2010).
23 Composting Practices for the Remediation of Matrices Contaminated by. . .
477
by the presence of the organic substrates, and the co-metabolic, besides metabolic,
degradation of pollutants is achieved through the various temperature-dependent
stages of the composting process. Co-composting has been performed in windrows,
static piles, and as in-vessel (Antizar-Ladislao et al. 2004).
The process of co-composting is altogether very similar to the process of conventional biowaste composting, with bio-oxidation reactions causing a prompt
increase in the temperature and attainment of the thermophilic conditions, followed
by cooling and maturation phases. Thermophilic conditions represent the fingerprint
feature of co-composting. Spontaneous thermogenesis marks in fact the difference
between co-composting and other bioremediation approaches (e.g., land farming or
biopiles), where the addition of amendments/bulking agents does not cause the
temperature to rise above 40–45
C. Due to this fact, the discussion concerning
the usefulness of attaining such temperatures for the sake of the contaminant removal
has been open for several years. On the one hand, the increase in the temperature
during the composting process could potentially support the biodegradation of the
contaminants, particularly with regard to lipophilic compounds (e.g., high molecular
weight polycyclic aromatic hydrocarbons—PAHs) that tend to be adsorbed on soil
organic matter; therefore, a consistent rise in the temperature might facilitate desorption kinetics from the organic matter to water and, in turn, biodegradation by
microbial consortia as a result of the increased contaminant bioavailability
(Margesin and Schinner 2001; Wong et al. 2004; Viamajala et al. 2007). On the
other hand, the thermophilic stage represents an ecological bottleneck because
oxygen solubility tends to decrease when the temperature increases, and most
microbes, including contaminant-degrading microbes, cannot grow when the temperature rises above 55–60
C (Antizar-Ladislao et al. 2005, 2006).
23.3.1 Regulatory Conditions
Regulatory limits and targets connected with remediation of contaminated soil
significantly differ in each country. Contaminant concentrations in soil acceptable
in certain countries may far exceed the acceptability limits in other ones. The
situation concerning the approach to the actual process of composting of biologically
degradable waste is similar. Requirements for composting plants, composting process parameters as well as for the treated biologically degradable waste differ in
individual countries. A trend towards unification of the regulations may be seen
within the EU currently, however, the situation is still relatively unclear.
Figure 23.4 summarizes the rules that have to be taken into account in the various
phases of utilization of contaminated waste composting. Part A concerns regulatory
limits for contaminant concentrations in soil and other materials to be
decontaminated. Part B relates to regulations concerning organic substrates. Utilization of co-composting is possible only in the case that the conditions given in the
decision tree are met (Antizar-Ladislao 2010).
23 Composting Practices for the Remediation of Matrices Contaminated by. . .
477