3.10 Biodigester Classification
Regarding the solids content, biodigesters are classified as
low and high solids. The presence of water defines the
concentration of solids, as it favors the activity of enzymes
and the availability of metabolites. Therefore, moisture can
be considered as a very important factor in the biodigestion
processes of organic solid waste (Leite and Lopes 2009).
In relation to the number of stages, they are classified into
one-stage, two-stage and multi-stage systems. In
double-stage biodigesters, the biodigestion of organic waste
is divided into two phases, hydrolysis and methanogenesis,
which occur in different reactors (Prosab: Basic Sanitation
Research Program 2003). In the one-stage process, all phases
occur in a single reactor (Vandevivere et al. 2002).
Multi-stage is the result of also separating the acidogenic and
the methanogenic phases, allowing the recovery of H 2 and
CH 4 , respectively (Nathao et al. 2013).
Moreover, biodigesters can be classified by the feeding
strategy as continuous or batch. In the first, the substrate
addition occurs continuously in such a way that the volume
is constant. In the intermittent feeding system, the total
volume to be digested is placed in the biodigester, and after
the digestion is complete the digested substrate removed.
3.11 Stabilization Ponds
In organic waste biodigestion systems, it is common to use a
stabilization pond after the biodigester to complete the
digestion of the substrate and generate high-quality biofertilizer. The resulting digestate has high concentrations of
phosphorus, nitrogen and potassium, which give it potential
for use as a fertilizer (Logan et al. 2019). The digestate easily
penetrates the soil and must be applied in accordance with
good agricultural practices in order to minimize the loss of
nutrients by leaching and evaporation, especially nitrogen
(Wellinger and Murphy 2013).
4 Itaipu Demonstration Unit (DU ITAIPU)
Contextualization
The Itaipu demonstration unit (DU ITAIPU) (Fig. 3) is the
result of a partnership between Itaipu Binational (IB) and the
Renewable Energies International Center [CIBiogás]. It was
built with the purpose to be explored as a proof of concept
for different organic waste treatment technologies used to
treat food waste from restaurants located in the Itaipu area.
One of the main goals is to serve as a reference and model
of studies for the implantation, operation and monitoring of
other biogas and biomethane production plants. Another
important aspect is research and development of solutions
and technologies applied to biogas production in Latin
America. Furthermore, this unit is also a place to validate
technologies and to identify technological gaps aiming the
“tropicalization” of equipment and biogas systems contributing to the productive chain in Brazil.
DU ITAIPU utilizes primary food waste from restaurants
in the Itaipu area as a source of substrates to biogas production. Eventually, external organic products are received
from different customs inspection departments, such as
Federal Police, Federal Highway Police, Department of
Federal Revenue of Brazil, Ministry of Agriculture, Livestock and Supply of Brazil, from burgling apprehensions.
These external organic products are judiciously evaluated by
Brazilian government departments and destined for the
production of biogas and biomethane. The substrate’s
diversification strategy used at DU ITAIPU is in accordance
to the Fachagentur Nachwachsende Rohstoffe [Renewable
Resources Agency] (Fachagentur Nachwachsende Rohstoffe
2010). They affirm that the biodigester’s feeding with different kinds of substrates (codigestion) is preferable than the
simple digestion. However, to reach the ideal relation
between organic matter and volumetric organic matter, it is
necessary to run tests with different mixtures of substrates.
Volatile organic compounds (VOC), according to the FNR,
are the amount of dry organic matter (DOM) allowed to be
used in the biodigester’s feeding per cubic meter of its
volume and per unit of time, expressed in kg DOM /(m
3 day).
Figure 4 presents the processing of food wastes to biogas
at DU ITAIPU. The first step in the energy conversion
process of the substrates is milling. The substrates are milled
and then discharged into a mixing chamber. After the
homogenization, the mixture is pumped to the biodigesters.
There are two CSTR at DU ITAIPU made of modular
fiberglass, an innovative product with national technology. It
is 5 m high and 10 m in diameter, with 350 m
3 total volume
for each. Regardless, the need of advanced research in the
fiberglass biodigesters technology allows geometry and
volume flexibility, besides being lighter than concrete and
steel structures, which request fewer reinforcements in the
structure foundation.
The biodigester’s feeding occurs once in a day with the
same amount of solids and liquids. Moreover, it is always
made at the same time, so there are no sudden changes in the
microorganism’s routine. There are serpentines at the
biodigester’s internal walls that allow hot water to circulate
and maintain temperature at 37 °C. Besides that, hydraulic
and mechanical agitation takes place to ensure biomass
homogenization. The hydraulic agitation is performed with
the biomass recirculation between the mixing chamber and
the biodigesters, while the mechanical agitation is performed
with a helicoidal agitator. The agitation is essential to
increase the contact area between the microorganisms and
the biomass, optimizing biogas production.
102
E. B. Sydney et al.
Regarding the solids content, biodigesters are classified as
low and high solids. The presence of water defines the
concentration of solids, as it favors the activity of enzymes
and the availability of metabolites. Therefore, moisture can
be considered as a very important factor in the biodigestion
processes of organic solid waste (Leite and Lopes 2009).
In relation to the number of stages, they are classified into
one-stage, two-stage and multi-stage systems. In
double-stage biodigesters, the biodigestion of organic waste
is divided into two phases, hydrolysis and methanogenesis,
which occur in different reactors (Prosab: Basic Sanitation
Research Program 2003). In the one-stage process, all phases
occur in a single reactor (Vandevivere et al. 2002).
Multi-stage is the result of also separating the acidogenic and
the methanogenic phases, allowing the recovery of H 2 and
CH 4 , respectively (Nathao et al. 2013).
Moreover, biodigesters can be classified by the feeding
strategy as continuous or batch. In the first, the substrate
addition occurs continuously in such a way that the volume
is constant. In the intermittent feeding system, the total
volume to be digested is placed in the biodigester, and after
the digestion is complete the digested substrate removed.
3.11 Stabilization Ponds
In organic waste biodigestion systems, it is common to use a
stabilization pond after the biodigester to complete the
digestion of the substrate and generate high-quality biofertilizer. The resulting digestate has high concentrations of
phosphorus, nitrogen and potassium, which give it potential
for use as a fertilizer (Logan et al. 2019). The digestate easily
penetrates the soil and must be applied in accordance with
good agricultural practices in order to minimize the loss of
nutrients by leaching and evaporation, especially nitrogen
(Wellinger and Murphy 2013).
4 Itaipu Demonstration Unit (DU ITAIPU)
Contextualization
The Itaipu demonstration unit (DU ITAIPU) (Fig. 3) is the
result of a partnership between Itaipu Binational (IB) and the
Renewable Energies International Center [CIBiogás]. It was
built with the purpose to be explored as a proof of concept
for different organic waste treatment technologies used to
treat food waste from restaurants located in the Itaipu area.
One of the main goals is to serve as a reference and model
of studies for the implantation, operation and monitoring of
other biogas and biomethane production plants. Another
important aspect is research and development of solutions
and technologies applied to biogas production in Latin
America. Furthermore, this unit is also a place to validate
technologies and to identify technological gaps aiming the
“tropicalization” of equipment and biogas systems contributing to the productive chain in Brazil.
DU ITAIPU utilizes primary food waste from restaurants
in the Itaipu area as a source of substrates to biogas production. Eventually, external organic products are received
from different customs inspection departments, such as
Federal Police, Federal Highway Police, Department of
Federal Revenue of Brazil, Ministry of Agriculture, Livestock and Supply of Brazil, from burgling apprehensions.
These external organic products are judiciously evaluated by
Brazilian government departments and destined for the
production of biogas and biomethane. The substrate’s
diversification strategy used at DU ITAIPU is in accordance
to the Fachagentur Nachwachsende Rohstoffe [Renewable
Resources Agency] (Fachagentur Nachwachsende Rohstoffe
2010). They affirm that the biodigester’s feeding with different kinds of substrates (codigestion) is preferable than the
simple digestion. However, to reach the ideal relation
between organic matter and volumetric organic matter, it is
necessary to run tests with different mixtures of substrates.
Volatile organic compounds (VOC), according to the FNR,
are the amount of dry organic matter (DOM) allowed to be
used in the biodigester’s feeding per cubic meter of its
volume and per unit of time, expressed in kg DOM /(m
3 day).
Figure 4 presents the processing of food wastes to biogas
at DU ITAIPU. The first step in the energy conversion
process of the substrates is milling. The substrates are milled
and then discharged into a mixing chamber. After the
homogenization, the mixture is pumped to the biodigesters.
There are two CSTR at DU ITAIPU made of modular
fiberglass, an innovative product with national technology. It
is 5 m high and 10 m in diameter, with 350 m
3 total volume
for each. Regardless, the need of advanced research in the
fiberglass biodigesters technology allows geometry and
volume flexibility, besides being lighter than concrete and
steel structures, which request fewer reinforcements in the
structure foundation.
The biodigester’s feeding occurs once in a day with the
same amount of solids and liquids. Moreover, it is always
made at the same time, so there are no sudden changes in the
microorganism’s routine. There are serpentines at the
biodigester’s internal walls that allow hot water to circulate
and maintain temperature at 37 °C. Besides that, hydraulic
and mechanical agitation takes place to ensure biomass
homogenization. The hydraulic agitation is performed with
the biomass recirculation between the mixing chamber and
the biodigesters, while the mechanical agitation is performed
with a helicoidal agitator. The agitation is essential to
increase the contact area between the microorganisms and
the biomass, optimizing biogas production.
102
E. B. Sydney et al.