comparison to low stable matter. This is an important factor while considering the
potential of ground and surface water contamination. Leaching of nutrients to
ground water and runoff to surface water contribute to the decrease of the environmental and economic value of organic matter field application. Fertilization accelerates undesirable eutrophication process of surface water as well as generates extra
costs of ground water decontamination in purpose of drinking water supply.
Stabilization of organic matter also reduces odor production (Barrena et al. 2009)
and emission of greenhouse gases, which is meaningful during application in open
composting piles. Nevertheless, as digestates contain high concentration of ammonium, which was released and accumulated in anaerobic conditions, e.g., during
protein hydrolysis, thus aerobic posttreatment due to nitrogen transformations may
lead to ammonia, nitrate, and nitrous oxide emission. Ammonium oxidized to nitrate
consumes oxygen and due to the production of proton may potentially contribute to
the acidification of compost. During composting of digestate up to 42% of nitrogen
may be lost as a consequence of NH 3 volatilization (Tambone et al. 2015). This
process is favored by forced aeration, elevated temperatures, and slightly alkaline pH
(Bustamante et al. 2012; Tambone et al. 2015). Ammonia volatilization may represent up to 92% of total nitrogen losses during the composting of digestate and this
process is favored by alkaline pH (Tambone et al. 2015). Release of nitrous oxide
(N 2 O) is mainly associated to incomplete nitrification phenomena occurring in the
second phase of composting, after thermophilic phase, when the temperature is
lower and oxygen is more available (Trémier et al. 2013). Although, composting
is an aerobic process, it is hard to ensure homogenous aeration within all the pile and
local anaerobic zones may appear, which eventually may lead to methane production
(Trémier et al. 2013).
5.3.4 Pathogen Content in Digestate Before and After
Composting
Agricultural wastes such as animal manures or slurries are well-known for pathogenicity (Stevens et al. 2003). To ensure the quality of organic wastes, different
methods of pretreatment may be applied including composting or anaerobic digestion, e.g., thermophilic or mesophilic. Although high temperatures during thermophilic anaerobic digestion (50–65
C) ensure better final parameters of treated matter
in comparison with mesophilic conditions (35–38
C), the amount of biogas
resulting from mesophilic anaerobic digestion (MAD) is significantly higher,
which makes this process more economically reasonable (Scaglia et al. 2014). To
prepare mesophilic digestate for land application according to mentioned European
guidelines (EEC 2008), subsequent composting should be applied (Ponsá et al.
2008; Scaglia et al. 2014).
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A. Gielnik et al.
potential of ground and surface water contamination. Leaching of nutrients to
ground water and runoff to surface water contribute to the decrease of the environmental and economic value of organic matter field application. Fertilization accelerates undesirable eutrophication process of surface water as well as generates extra
costs of ground water decontamination in purpose of drinking water supply.
Stabilization of organic matter also reduces odor production (Barrena et al. 2009)
and emission of greenhouse gases, which is meaningful during application in open
composting piles. Nevertheless, as digestates contain high concentration of ammonium, which was released and accumulated in anaerobic conditions, e.g., during
protein hydrolysis, thus aerobic posttreatment due to nitrogen transformations may
lead to ammonia, nitrate, and nitrous oxide emission. Ammonium oxidized to nitrate
consumes oxygen and due to the production of proton may potentially contribute to
the acidification of compost. During composting of digestate up to 42% of nitrogen
may be lost as a consequence of NH 3 volatilization (Tambone et al. 2015). This
process is favored by forced aeration, elevated temperatures, and slightly alkaline pH
(Bustamante et al. 2012; Tambone et al. 2015). Ammonia volatilization may represent up to 92% of total nitrogen losses during the composting of digestate and this
process is favored by alkaline pH (Tambone et al. 2015). Release of nitrous oxide
(N 2 O) is mainly associated to incomplete nitrification phenomena occurring in the
second phase of composting, after thermophilic phase, when the temperature is
lower and oxygen is more available (Trémier et al. 2013). Although, composting
is an aerobic process, it is hard to ensure homogenous aeration within all the pile and
local anaerobic zones may appear, which eventually may lead to methane production
(Trémier et al. 2013).
5.3.4 Pathogen Content in Digestate Before and After
Composting
Agricultural wastes such as animal manures or slurries are well-known for pathogenicity (Stevens et al. 2003). To ensure the quality of organic wastes, different
methods of pretreatment may be applied including composting or anaerobic digestion, e.g., thermophilic or mesophilic. Although high temperatures during thermophilic anaerobic digestion (50–65
C) ensure better final parameters of treated matter
in comparison with mesophilic conditions (35–38
C), the amount of biogas
resulting from mesophilic anaerobic digestion (MAD) is significantly higher,
which makes this process more economically reasonable (Scaglia et al. 2014). To
prepare mesophilic digestate for land application according to mentioned European
guidelines (EEC 2008), subsequent composting should be applied (Ponsá et al.
2008; Scaglia et al. 2014).
262
A. Gielnik et al.