compost, some microorganisms like Bacillus spp., Enterobacter spp.,
Flavobacterium balustinum, Pseudomonas spp., Streptomyces spp., and fungi also
play an important role as biocontrol agents (Bertoldi 2010). In the study of Tambone
et al. (2015), composted digestates originating from three different feedstocks such
as pig slurry, energy crops, and agro-industrial residues were examined in terms of
pathogen content. E. coli and Salmonella were not detected even when temperature
during composting did not reach the threshold of 50
C and oscillated between
25 and 35
C. Bustamante et al. (2013) also investigated the impact of composting
on biological quality of digestates. Pig slurry digestate was mixed with bulking
agents to improve the structure and porosity of mixture. During the first week of the
process the temperature exceeded 50
C in all the tested mixtures with maximum
value of 65
C, which indicates that thermophilic phases of composting have been
reached. Three out of five composted mixtures showed low level of pathogens such
as E. coli and S. faecalis and absence of Salmonella. Therefore, limits required by
European Union guidelines (European Commission, Biological Treatment of
Biowaste 2001) according to the compost quality were fulfilled. In another study
(Bustamante et al. 2012) sanitation of the piles with sole digestate and digestate
amended with bulking agent was evaluated. In all piles, elevated temperature was
observed reaching the values above 50
C, which indicates intensive microbial
proliferation and occurrence of biooxidative phase. The pile without addition of
bulking agent showed longer duration of thermophilic phase, which might be caused
by slowing down of bacterial activity caused by addition of bulking agent. Notwithstanding, the sanitation effect occurred in all the samples as manifested by the lack of
Salmonella, lack or low levels of E. coli and low colony forming unit (CFU) values
of total coliform. All of the tested pathogenic factors were low, within the limits
provided by European Union guidelines and legislation (European Commission,
Biological Treatment of Biowaste 2001). The studies of the composting of digestate
mixed with bulking agent indicate a good sanitation effect, encouraging further
studies with the use of contaminated soil.
5.3.5 Organic Contaminants and Trace Elements Content
in Digestate
Organic matter used in the process of bioremediation should not contain substances,
which could additionally contaminate the treated soil. However, in most available
organic residues, raw and pretreated, some extent of organic micropollutants may
be present. The amount and type of organic micropollutants in digestate are related
to initial content in the feedstock. Organic residues originating from animal production like manures or slurry may contain elevated concentrations of veterinary
products, e.g., antibiotics. In municipal sewage sludge contaminants like personal
care products, pharmaceuticals, oestrogens, surfactants, or phthalates are often
detected (Stasinakis 2012). During anaerobic digestion, the amount of organic
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A. Gielnik et al.
Flavobacterium balustinum, Pseudomonas spp., Streptomyces spp., and fungi also
play an important role as biocontrol agents (Bertoldi 2010). In the study of Tambone
et al. (2015), composted digestates originating from three different feedstocks such
as pig slurry, energy crops, and agro-industrial residues were examined in terms of
pathogen content. E. coli and Salmonella were not detected even when temperature
during composting did not reach the threshold of 50
C and oscillated between
25 and 35
C. Bustamante et al. (2013) also investigated the impact of composting
on biological quality of digestates. Pig slurry digestate was mixed with bulking
agents to improve the structure and porosity of mixture. During the first week of the
process the temperature exceeded 50
C in all the tested mixtures with maximum
value of 65
C, which indicates that thermophilic phases of composting have been
reached. Three out of five composted mixtures showed low level of pathogens such
as E. coli and S. faecalis and absence of Salmonella. Therefore, limits required by
European Union guidelines (European Commission, Biological Treatment of
Biowaste 2001) according to the compost quality were fulfilled. In another study
(Bustamante et al. 2012) sanitation of the piles with sole digestate and digestate
amended with bulking agent was evaluated. In all piles, elevated temperature was
observed reaching the values above 50
C, which indicates intensive microbial
proliferation and occurrence of biooxidative phase. The pile without addition of
bulking agent showed longer duration of thermophilic phase, which might be caused
by slowing down of bacterial activity caused by addition of bulking agent. Notwithstanding, the sanitation effect occurred in all the samples as manifested by the lack of
Salmonella, lack or low levels of E. coli and low colony forming unit (CFU) values
of total coliform. All of the tested pathogenic factors were low, within the limits
provided by European Union guidelines and legislation (European Commission,
Biological Treatment of Biowaste 2001). The studies of the composting of digestate
mixed with bulking agent indicate a good sanitation effect, encouraging further
studies with the use of contaminated soil.
5.3.5 Organic Contaminants and Trace Elements Content
in Digestate
Organic matter used in the process of bioremediation should not contain substances,
which could additionally contaminate the treated soil. However, in most available
organic residues, raw and pretreated, some extent of organic micropollutants may
be present. The amount and type of organic micropollutants in digestate are related
to initial content in the feedstock. Organic residues originating from animal production like manures or slurry may contain elevated concentrations of veterinary
products, e.g., antibiotics. In municipal sewage sludge contaminants like personal
care products, pharmaceuticals, oestrogens, surfactants, or phthalates are often
detected (Stasinakis 2012). During anaerobic digestion, the amount of organic
264
A. Gielnik et al.