a b s t r a c t
The production of biofuels based on microalgae as feedstock is associated with a high demand of nutrients,
mostly nitrogen and phosphorus. The integration of microalgae growth with anaerobic digestion can
significantly improve the economic and energy balance of such a promising platform technology. However,
the lack of information about the fundamental mass and energy balances of this integrated process
restricts its full scale implementation. This study quantified both the mass (carbon, nitrogen and phosphorus)
and energy balances in the integrated process of Chlorella sorokiniana cultivation (under photoautotrophic
and mixotrophic conditions) coupled with anaerobic digestion in batch mode in order to
properly design the microalgae growth-anaerobic digestion process and minimize the overall microalgae
cultivation costs. Under fully photoautotrophic growth, the productivity during the microalgae exponential
growth phase was 147 g/m3 d, with an overall photosynthetic efficiency of 7.4%. The productivity of
the mixotrophically-grown microalgae was 165 g/m3 d. However, the photosynthetic activity of C. sorokiniana
decreased at increasing glucose concentrations in the tested range (180–440 g/m3). During the
anaerobic digestion of photoautotrophically-grown microalgae 55 ± 1% of the initial carbon present in
the biomass was hydrolyzed (15 ± 1% to C-CO2 and 33 ± 1% to C-CH4). The potential recovery of the N
and P present in the biomass accounted for 59 ± 2% as N-NHþ4
and 89 ± 2% as P-PO3
4 , respectively. During
the anaerobic digestion of mixotrophically-grown microalgae, 46 ± 1% of the initial carbon as biomass
was hydrolyzed (14 ± 1% to C-CO2 and 36 ± 1% to C-CH4) with a nutrient recovery of 70 ± 3% as N-NHþ4
and 77 ± 2% as P-PO3
4 . The energy recovery from the chemical energy fixed as biomass under photoautotrophic
and mixotrophic conditions was 48% and 61%, respectively, and decreased to 3.5% when
referred to the total energy available during the growth stage.
a b s t r a c t
The production of biofuels based on microalgae as feedstock is associated with a high demand of nutrients,
mostly nitrogen and phosphorus. The integration of microalgae growth with anaerobic digestion can
significantly improve the economic and energy balance of such a promising platform technology. However,
the lack of information about the fundamental mass and energy balances of this integrated process
restricts its full scale implementation. This study quantified both the mass (carbon, nitrogen and phosphorus)
and energy balances in the integrated process of Chlorella sorokiniana cultivation (under photoautotrophic
and mixotrophic conditions) coupled with anaerobic digestion in batch mode in order to
properly design the microalgae growth-anaerobic digestion process and minimize the overall microalgae
cultivation costs. Under fully photoautotrophic growth, the productivity during the microalgae exponential
growth phase was 147 g/m3 d, with an overall photosynthetic efficiency of 7.4%. The productivity of
the mixotrophically-grown microalgae was 165 g/m3 d. However, the photosynthetic activity of C. sorokiniana
decreased at increasing glucose concentrations in the tested range (180–440 g/m3). During the
anaerobic digestion of photoautotrophically-grown microalgae 55 ± 1% of the initial carbon present in
the biomass was hydrolyzed (15 ± 1% to C-CO2 and 33 ± 1% to C-CH4). The potential recovery of the N
and P present in the biomass accounted for 59 ± 2% as N-NHþ4
and 89 ± 2% as P-PO3
4 , respectively. During
the anaerobic digestion of mixotrophically-grown microalgae, 46 ± 1% of the initial carbon as biomass
was hydrolyzed (14 ± 1% to C-CO2 and 36 ± 1% to C-CH4) with a nutrient recovery of 70 ± 3% as N-NHþ4
and 77 ± 2% as P-PO3
4 . The energy recovery from the chemical energy fixed as biomass under photoautotrophic
and mixotrophic conditions was 48% and 61%, respectively, and decreased to 3.5% when
referred to the total energy available during the growth stage.
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