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Maximum photosynthetic yield of green microalgae in photobioreactors.

Zijffers JW, Schippers KJ, Zheng K, Janssen M, Tramper J, Wijffels RH - Mar. Biotechnol. (2010)

Bottom Line: Using the model of Pirt (New Phytol 102:3-37, 1986), a biomass yield on light energy of 0.78 and 0.75 g mol photons⁻¹ and a maintenance requirement of 0.0133 and 0.0068 mol photons g⁻¹ h⁻¹ were found for D. tertiolecta and C. sorokiniana, respectively.The observed yield decreases steeply at low light supply rates, and according to this model, this is related to the increase of the amount of useable light energy diverted to biomass maintenance.Consequently, for the design of a photobioreactor, we should maintain a relatively high specific light supply rate.

View Article: PubMed Central - PubMed

Affiliation: Bioprocess Engineering, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.

ABSTRACT
The biomass yield on light energy of Dunaliella tertiolecta and Chlorella sorokiniana was investigated in a 1.25- and 2.15-cm light path panel photobioreactor at constant ingoing photon flux density (930 µmol photons m⁻² s⁻¹). At the optimal combination of biomass density and dilution rate, equal biomass yields on light energy were observed for both light paths for both microalgae. The observed biomass yield on light energy appeared to be based on a constant intrinsic biomass yield and a constant maintenance energy requirement per gram biomass. Using the model of Pirt (New Phytol 102:3-37, 1986), a biomass yield on light energy of 0.78 and 0.75 g mol photons⁻¹ and a maintenance requirement of 0.0133 and 0.0068 mol photons g⁻¹ h⁻¹ were found for D. tertiolecta and C. sorokiniana, respectively. The observed yield decreases steeply at low light supply rates, and according to this model, this is related to the increase of the amount of useable light energy diverted to biomass maintenance. With this study, we demonstrated that the observed biomass yield on light in short light path bioreactors at high biomass densities decreases because maintenance requirements are relatively high at these conditions. All our experimental data for the two strains tested could be described by the physiological models of Pirt (New Phytol 102:3-37, 1986). Consequently, for the design of a photobioreactor, we should maintain a relatively high specific light supply rate. A process with high biomass densities and high yields at high light intensities can only be obtained in short light path photobioreactors.

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Observed biomass yield on light energy during the Dunaliella tertiolecta cultivations. Squares: 1.25 cm light path; circles: 2.15 cm light path; triangles: 3 cm light path (Barbosa et al. 2005). Error bars represent standard errors from the mean
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Fig5: Observed biomass yield on light energy during the Dunaliella tertiolecta cultivations. Squares: 1.25 cm light path; circles: 2.15 cm light path; triangles: 3 cm light path (Barbosa et al. 2005). Error bars represent standard errors from the mean

Mentions: The biomass yield on light was calculated with Eq. 4 and plotted as a function of the light supply rate (the amount of light available per amount of biomass) as calculated with Eq. 5. In Figs. 5 and 6, the observed biomass yield on light energy as a function of the light supply rate at the different light paths are shown for D. tertiolecta and C. sorokiniana cultivations, respectively. In Fig. 5, we also added the data for D. tertiolecta in a photobioreactor with a light path of 3 cm from Barbosa et al. (2005) At higher photon flux densities, a relatively constant yield between 0.6 and 0.8 g/mol photons is obtained for all cases. At lower photon flux densities, i.e., at higher biomass concentrations, the yield drops considerably. At a given light supply rate, the highest biomass concentration is present in the 1.25-cm light path reactor and the lowest in the 3-cm light path reactor, leading to different light penetration depths in the reactors but the observed yields as a function of light supply rate in the different photobioreactors are independent of the light path used. The different biomass concentrations in the different biooreactors result in different light gradients and different exposure patterns of the algae to the light, ranging from an exposure to a steep gradient in the 1.25-cm reactor to an exposure to a more gradual gradient in the 3-cm reactor. Apparently, this gradient and the corresponding light exposure pattern does not influence the biomass yield in these reactors since the biomass yield observed at a given specific light supply rate was equal for all three reactors.Fig. 5


Maximum photosynthetic yield of green microalgae in photobioreactors.

Zijffers JW, Schippers KJ, Zheng K, Janssen M, Tramper J, Wijffels RH - Mar. Biotechnol. (2010)

Observed biomass yield on light energy during the Dunaliella tertiolecta cultivations. Squares: 1.25 cm light path; circles: 2.15 cm light path; triangles: 3 cm light path (Barbosa et al. 2005). Error bars represent standard errors from the mean
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2991169&req=5

Fig5: Observed biomass yield on light energy during the Dunaliella tertiolecta cultivations. Squares: 1.25 cm light path; circles: 2.15 cm light path; triangles: 3 cm light path (Barbosa et al. 2005). Error bars represent standard errors from the mean
Mentions: The biomass yield on light was calculated with Eq. 4 and plotted as a function of the light supply rate (the amount of light available per amount of biomass) as calculated with Eq. 5. In Figs. 5 and 6, the observed biomass yield on light energy as a function of the light supply rate at the different light paths are shown for D. tertiolecta and C. sorokiniana cultivations, respectively. In Fig. 5, we also added the data for D. tertiolecta in a photobioreactor with a light path of 3 cm from Barbosa et al. (2005) At higher photon flux densities, a relatively constant yield between 0.6 and 0.8 g/mol photons is obtained for all cases. At lower photon flux densities, i.e., at higher biomass concentrations, the yield drops considerably. At a given light supply rate, the highest biomass concentration is present in the 1.25-cm light path reactor and the lowest in the 3-cm light path reactor, leading to different light penetration depths in the reactors but the observed yields as a function of light supply rate in the different photobioreactors are independent of the light path used. The different biomass concentrations in the different biooreactors result in different light gradients and different exposure patterns of the algae to the light, ranging from an exposure to a steep gradient in the 1.25-cm reactor to an exposure to a more gradual gradient in the 3-cm reactor. Apparently, this gradient and the corresponding light exposure pattern does not influence the biomass yield in these reactors since the biomass yield observed at a given specific light supply rate was equal for all three reactors.Fig. 5

Bottom Line: Using the model of Pirt (New Phytol 102:3-37, 1986), a biomass yield on light energy of 0.78 and 0.75 g mol photons⁻¹ and a maintenance requirement of 0.0133 and 0.0068 mol photons g⁻¹ h⁻¹ were found for D. tertiolecta and C. sorokiniana, respectively.The observed yield decreases steeply at low light supply rates, and according to this model, this is related to the increase of the amount of useable light energy diverted to biomass maintenance.Consequently, for the design of a photobioreactor, we should maintain a relatively high specific light supply rate.

View Article: PubMed Central - PubMed

Affiliation: Bioprocess Engineering, Wageningen University, P.O. Box 8129, 6700 EV Wageningen, The Netherlands.

ABSTRACT
The biomass yield on light energy of Dunaliella tertiolecta and Chlorella sorokiniana was investigated in a 1.25- and 2.15-cm light path panel photobioreactor at constant ingoing photon flux density (930 µmol photons m⁻² s⁻¹). At the optimal combination of biomass density and dilution rate, equal biomass yields on light energy were observed for both light paths for both microalgae. The observed biomass yield on light energy appeared to be based on a constant intrinsic biomass yield and a constant maintenance energy requirement per gram biomass. Using the model of Pirt (New Phytol 102:3-37, 1986), a biomass yield on light energy of 0.78 and 0.75 g mol photons⁻¹ and a maintenance requirement of 0.0133 and 0.0068 mol photons g⁻¹ h⁻¹ were found for D. tertiolecta and C. sorokiniana, respectively. The observed yield decreases steeply at low light supply rates, and according to this model, this is related to the increase of the amount of useable light energy diverted to biomass maintenance. With this study, we demonstrated that the observed biomass yield on light in short light path bioreactors at high biomass densities decreases because maintenance requirements are relatively high at these conditions. All our experimental data for the two strains tested could be described by the physiological models of Pirt (New Phytol 102:3-37, 1986). Consequently, for the design of a photobioreactor, we should maintain a relatively high specific light supply rate. A process with high biomass densities and high yields at high light intensities can only be obtained in short light path photobioreactors.

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