commercially used for cultivation of Agaricus bisporus and consists of chopped
wheat straw, chicken manure, and gypsum (Šašek et al. 2003). The raw material was
obtained from a local company producing spent mushroom substrate. The compost
(400 kg wet weight) was mixed with 120 kg of dry contaminated soil. The ratio of
contaminated soil to compost was approximately 1:1 (dry weight basis). The samples were analysed after a cooling phase (6–8 weeks) and after another 14 and
42 weeks of maturation.
The second experiment (Treatment 2) was conducted outdoors in garden
composters with a waterproof bottom tray and a total working volume of 400 L.
Two different organic co-substrates were used as bulking agents in two independent
variants of Treatment 2, namely fresh GC originated from the garden of the Institute
of Microbiology and BL (described above). BL was pre-wetted with tap water in a
ratio of 1:2.2 (w/w), while GC was used as provided. The two composters were filled
in a multi-stratum fashion, overlapping layers of either BL or GC (14 kg wet weight)
with layers of CTW (5 kg, 3 cm in size) until an overall weight of 128 kg (13 layers)
was achieved within each of the reaction vessel. In both cases, the overall initial
moisture content was approximately 60% w/w. The samples for chemical analyses
were collected during the mild-thermophilic (day 5), the mesophilic/cooling phase
(days 12 and 40), and the maturation phase (days 140 and 240).
Analytical Procedure The evaluation of the PAHs extraction and quantification
procedures used in Treatment 1 has been published by Cajthaml and Šašek (2005).
The obtained data were recalculated according to the content of the soil in the
samples (soil/substrate mixture) using the amount of ash after combustion at
650
C as an internal standard.
All of the extractions and quantifications of PAHs in Treatment 2 were performed
according to Covino et al. (2016). To calculate the amount of CTW in the collected
samples of non-homogenous mixture of CTW and co-substrate, heavy metals such
as Co and Pb were used as internal standards because of their presence only in CTW.
Contrary to Treatment 1, the ash as an internal standard was not usable in the case of
CTW. The metals were determined after total acid digestion and atomic absorption
spectrometry conducted by Analytical Laboratories, Plzeň (Czech Republic)
according to ISO 8288:1986 (ISO 1986) and EN 13657:2002 (CEN 2002).
The bioaccessible fraction of PAHs, which represents the portion of the target
chemical that is bioavailable for biotransformation processes in soils (Hawthorne
and Grabanski 2000), was estimated using a combination of sequential mild SFE and
by calculating the slow- and fast-release (F) fractions. The SFE extractor (Labio, a.s.,
Czech Republic) operated at 50
C and 200 bar (Cajthaml and Šašek 2005; Covino
et al. 2016). Three parallel samples (1 g) underwent sequential supercritical CO 2
extraction over the time range 0–200 min, and the fractions (collected after 5, 10,
20, 40, 60, 80, 120, 160, and 200 min) were analysed separately to complete the
desorption-kinetic profiles. The so-called “F-fraction” is usually assumed to be
25 Field Study IX: Pilot-Scale Composting of PAH-Contaminated. . .
529
wheat straw, chicken manure, and gypsum (Šašek et al. 2003). The raw material was
obtained from a local company producing spent mushroom substrate. The compost
(400 kg wet weight) was mixed with 120 kg of dry contaminated soil. The ratio of
contaminated soil to compost was approximately 1:1 (dry weight basis). The samples were analysed after a cooling phase (6–8 weeks) and after another 14 and
42 weeks of maturation.
The second experiment (Treatment 2) was conducted outdoors in garden
composters with a waterproof bottom tray and a total working volume of 400 L.
Two different organic co-substrates were used as bulking agents in two independent
variants of Treatment 2, namely fresh GC originated from the garden of the Institute
of Microbiology and BL (described above). BL was pre-wetted with tap water in a
ratio of 1:2.2 (w/w), while GC was used as provided. The two composters were filled
in a multi-stratum fashion, overlapping layers of either BL or GC (14 kg wet weight)
with layers of CTW (5 kg, 3 cm in size) until an overall weight of 128 kg (13 layers)
was achieved within each of the reaction vessel. In both cases, the overall initial
moisture content was approximately 60% w/w. The samples for chemical analyses
were collected during the mild-thermophilic (day 5), the mesophilic/cooling phase
(days 12 and 40), and the maturation phase (days 140 and 240).
Analytical Procedure The evaluation of the PAHs extraction and quantification
procedures used in Treatment 1 has been published by Cajthaml and Šašek (2005).
The obtained data were recalculated according to the content of the soil in the
samples (soil/substrate mixture) using the amount of ash after combustion at
650
C as an internal standard.
All of the extractions and quantifications of PAHs in Treatment 2 were performed
according to Covino et al. (2016). To calculate the amount of CTW in the collected
samples of non-homogenous mixture of CTW and co-substrate, heavy metals such
as Co and Pb were used as internal standards because of their presence only in CTW.
Contrary to Treatment 1, the ash as an internal standard was not usable in the case of
CTW. The metals were determined after total acid digestion and atomic absorption
spectrometry conducted by Analytical Laboratories, Plzeň (Czech Republic)
according to ISO 8288:1986 (ISO 1986) and EN 13657:2002 (CEN 2002).
The bioaccessible fraction of PAHs, which represents the portion of the target
chemical that is bioavailable for biotransformation processes in soils (Hawthorne
and Grabanski 2000), was estimated using a combination of sequential mild SFE and
by calculating the slow- and fast-release (F) fractions. The SFE extractor (Labio, a.s.,
Czech Republic) operated at 50
C and 200 bar (Cajthaml and Šašek 2005; Covino
et al. 2016). Three parallel samples (1 g) underwent sequential supercritical CO 2
extraction over the time range 0–200 min, and the fractions (collected after 5, 10,
20, 40, 60, 80, 120, 160, and 200 min) were analysed separately to complete the
desorption-kinetic profiles. The so-called “F-fraction” is usually assumed to be
25 Field Study IX: Pilot-Scale Composting of PAH-Contaminated. . .
529