order to preserve these positive effects of adding the organic substrate to the
contaminated materials, it is necessary to ensure the presence of a minimum amount
of the organic substrate in the final mixture. This minimum amount is usually
10–50% of fresh weight, wherein preserving moisture and oxygen contents at
suitable levels is no less important (Antizar-Ladislao et al. 2004; Li et al. 2010;
Megharaj et al. 2011).
Naturally, the organic substrate having been added to the contaminated materials
should also contain a high amount of microbial biomass, and, in particular, specific
microorganisms that are able to degrade the target contaminants. Thus, from this
point of view, this is bioaugmentation of the contaminated materials with proper
degradation microorganisms. For example, Gandolfi et al. (2010) proved in his study
that the organic substrate addition to the contaminated soil caused transfer from
Alphaproteobacteria and Gammaproteobacteria to Bacteroidetes and Firmicutes.
The size of the microbial communities is usually estimated on the basis of cultivation
tests and/or by means of analysis of phospholipid fatty acids (PLFAs) (Adam et al.
2015; Covino et al. 2016; Gandolfi et al. 2010; Puglisi et al. 2007). On the other
hand, organic substrate additions, and the improvement of conditions for microbial
biomass growth resulting from them, also naturally support the increase in activity of
microorganisms that were already present in the contaminated material before the
addition. Moreover, these microorganisms usually have suitable degradation mechanisms at their disposal due to the long-term contaminant presence. Thus, from this
point of view, the support of the original microorganisms may be more important
than the bioaugmentation with new species, in some cases.
23.3.2.3 Microbial Communities
As described above, a wide spectrum of microorganisms is present in the compost in
the course of the composting process, and thus the organic substrate addition usually
results in significant increase in organic pollutant biodegradation potential in the
contaminated materials (Dees and Ghiorse 2001; Loick et al. 2009; Thummes et al.
2007). Moreover, the composition of the microbial communities changes greatly in
the course of the composting process, depending on the temperature and available
organic substrates in particular. A number of lists of specific bacteria and fungi that
are able to degrade specific organic contaminants, particularly PAHs, have already
been published (Antizar-Ladislao et al. 2004; Cerniglia 1984, 1992; Heitkamp and
Cerniglia 1989; Cerniglia and Sutherland 2010; Juhasz and Naidu 2000; Loick et al.
2009; Lu et al. 2011; Peng et al. 2008), showing the biodiversity of these biodegradation potentials. On the other hand, the lists are usually very general and do not
deal with degradation of organic contaminants in specific conditions in the course of
co-composting. There are only few studies describing in detail the development of
microbial communities in the course of the co-composting process. An in-vessel
composting bioremediation of pyrene-4,5,9,1013 C 4 and unlabeled pyrene spiked
soil amended with fresh wastes was investigated by Peng et al. (2013), DNA-based
stable isotope probing (SIP) of active bacteria was involved as well. The highest
482
O. Lhotský et al.
contaminated materials, it is necessary to ensure the presence of a minimum amount
of the organic substrate in the final mixture. This minimum amount is usually
10–50% of fresh weight, wherein preserving moisture and oxygen contents at
suitable levels is no less important (Antizar-Ladislao et al. 2004; Li et al. 2010;
Megharaj et al. 2011).
Naturally, the organic substrate having been added to the contaminated materials
should also contain a high amount of microbial biomass, and, in particular, specific
microorganisms that are able to degrade the target contaminants. Thus, from this
point of view, this is bioaugmentation of the contaminated materials with proper
degradation microorganisms. For example, Gandolfi et al. (2010) proved in his study
that the organic substrate addition to the contaminated soil caused transfer from
Alphaproteobacteria and Gammaproteobacteria to Bacteroidetes and Firmicutes.
The size of the microbial communities is usually estimated on the basis of cultivation
tests and/or by means of analysis of phospholipid fatty acids (PLFAs) (Adam et al.
2015; Covino et al. 2016; Gandolfi et al. 2010; Puglisi et al. 2007). On the other
hand, organic substrate additions, and the improvement of conditions for microbial
biomass growth resulting from them, also naturally support the increase in activity of
microorganisms that were already present in the contaminated material before the
addition. Moreover, these microorganisms usually have suitable degradation mechanisms at their disposal due to the long-term contaminant presence. Thus, from this
point of view, the support of the original microorganisms may be more important
than the bioaugmentation with new species, in some cases.
23.3.2.3 Microbial Communities
As described above, a wide spectrum of microorganisms is present in the compost in
the course of the composting process, and thus the organic substrate addition usually
results in significant increase in organic pollutant biodegradation potential in the
contaminated materials (Dees and Ghiorse 2001; Loick et al. 2009; Thummes et al.
2007). Moreover, the composition of the microbial communities changes greatly in
the course of the composting process, depending on the temperature and available
organic substrates in particular. A number of lists of specific bacteria and fungi that
are able to degrade specific organic contaminants, particularly PAHs, have already
been published (Antizar-Ladislao et al. 2004; Cerniglia 1984, 1992; Heitkamp and
Cerniglia 1989; Cerniglia and Sutherland 2010; Juhasz and Naidu 2000; Loick et al.
2009; Lu et al. 2011; Peng et al. 2008), showing the biodiversity of these biodegradation potentials. On the other hand, the lists are usually very general and do not
deal with degradation of organic contaminants in specific conditions in the course of
co-composting. There are only few studies describing in detail the development of
microbial communities in the course of the co-composting process. An in-vessel
composting bioremediation of pyrene-4,5,9,1013 C 4 and unlabeled pyrene spiked
soil amended with fresh wastes was investigated by Peng et al. (2013), DNA-based
stable isotope probing (SIP) of active bacteria was involved as well. The highest
482
O. Lhotský et al.