(Semi) continuous operation. The ADM1 has been used to represent the AD of
microalgae by tweaking the original ADM1 with the inclusion of the Contois
equation instead of the first-order equation to represent the hydrolysis step (Mairet
et al. 2011). The Contois equation takes into account both the particulate material
and the microbial population responsible for this process, while the first-order
equation only considers the particulate substrate concentration. The model outperformed the original ADM1 with experimental data from a digester operating for
140 d. An interesting application in this study was the representation of the
semi-continuous feeding mode by considering successive batch reactor operations
changing the initial conditions for each daily pulses. Moreover, another study tested
the same modified ADM1 above-mentioned in an integrated system of wastewater
treatment and AD of microalgae (Passos et al. 2015). In this work, the authors
found that an appropriate characterisation of the microalgae composition was of
paramount importance in order to have a proper model performance due to population changes over time (in particular, the variations in the inert and organic
content of the biomass). In addition, a reduced mechanistic 3-reaction model,
obtained after principal component analysis, was developed and calibrated with the
ADM1 (Mairet et al. 2012). The model was composed of a double hydrolysis
reaction to describe the production of volatile fatty acids and a methanogenic
reaction. The performance of this model was quite similar to the same simulation
results obtained with the ADM1 model, despite its complexity was much lower.
Batch operation. Batch tests, namely biochemical methane potential
(BMP) assays, are widely used to assess the kinetics of biodegradation of different
substrate. From this test, many parameters such as the hydrolysis coefficient or the
inert fraction of the microalgae may be determined when a proper kinetic expression is used (Donoso-Bravo et al. 2010). The first-order model has been a popular
option to draw parameters by fitting the accumulated biogas production (Eq. 1).
B t
ð Þ ¼ B max ð1 À e
Àk h Ãt
Þ
ð 1Þ
This has been done using as a substrate a residual microalgae (i.e. after lipids
extraction) (Neumann et al. 2015) or raw microalgae (Fernández-Rodríguez et al.
2014). Some of the values found up-to-date in literature are shown in Table 5.
Moreover, the synergism in the co-digestion of microalgae with waste-activated
sludge was assessed by the application of a first-order equation to describe the
hydrolysis reaction and the Monod equation to model the methanogenesis (Lee
et al. 2017). To our knowledge, the Contois equation has not been yet used to
describe the performance of BMP assays.
Global approaches. Apart from the classic modelling application in continuous
or batch mode, other new approaches such as the global WWTP plant-wide model
that aims at representing an integrated process have been recently developed. This
approach intends to implement a model-based on nonlinear programming to evaluate the best configuration of a microalgae-based biorefinery in which AD is also
incorporated (Rizwan et al. 2015).
12 Biofuels from Microalgae: Biomethane
259
microalgae by tweaking the original ADM1 with the inclusion of the Contois
equation instead of the first-order equation to represent the hydrolysis step (Mairet
et al. 2011). The Contois equation takes into account both the particulate material
and the microbial population responsible for this process, while the first-order
equation only considers the particulate substrate concentration. The model outperformed the original ADM1 with experimental data from a digester operating for
140 d. An interesting application in this study was the representation of the
semi-continuous feeding mode by considering successive batch reactor operations
changing the initial conditions for each daily pulses. Moreover, another study tested
the same modified ADM1 above-mentioned in an integrated system of wastewater
treatment and AD of microalgae (Passos et al. 2015). In this work, the authors
found that an appropriate characterisation of the microalgae composition was of
paramount importance in order to have a proper model performance due to population changes over time (in particular, the variations in the inert and organic
content of the biomass). In addition, a reduced mechanistic 3-reaction model,
obtained after principal component analysis, was developed and calibrated with the
ADM1 (Mairet et al. 2012). The model was composed of a double hydrolysis
reaction to describe the production of volatile fatty acids and a methanogenic
reaction. The performance of this model was quite similar to the same simulation
results obtained with the ADM1 model, despite its complexity was much lower.
Batch operation. Batch tests, namely biochemical methane potential
(BMP) assays, are widely used to assess the kinetics of biodegradation of different
substrate. From this test, many parameters such as the hydrolysis coefficient or the
inert fraction of the microalgae may be determined when a proper kinetic expression is used (Donoso-Bravo et al. 2010). The first-order model has been a popular
option to draw parameters by fitting the accumulated biogas production (Eq. 1).
B t
ð Þ ¼ B max ð1 À e
Àk h Ãt
Þ
ð 1Þ
This has been done using as a substrate a residual microalgae (i.e. after lipids
extraction) (Neumann et al. 2015) or raw microalgae (Fernández-Rodríguez et al.
2014). Some of the values found up-to-date in literature are shown in Table 5.
Moreover, the synergism in the co-digestion of microalgae with waste-activated
sludge was assessed by the application of a first-order equation to describe the
hydrolysis reaction and the Monod equation to model the methanogenesis (Lee
et al. 2017). To our knowledge, the Contois equation has not been yet used to
describe the performance of BMP assays.
Global approaches. Apart from the classic modelling application in continuous
or batch mode, other new approaches such as the global WWTP plant-wide model
that aims at representing an integrated process have been recently developed. This
approach intends to implement a model-based on nonlinear programming to evaluate the best configuration of a microalgae-based biorefinery in which AD is also
incorporated (Rizwan et al. 2015).
12 Biofuels from Microalgae: Biomethane
259