Effect of design dark fraction on the loss of biomass productivities in photobioreactors.

Design dark fraction reflects the unlit part of a microalgal culture system, as for example a hydraulic loop used for temperature or pH regulation, or a circulating pump for mixing purposes. This study investigates the impact of design dark fraction on photosynthetic biomass productivity of the eukaryotic microalgae Chlorella vulgaris. The effect of the volume of the dark fraction and the residence time spent in this dark fraction was investigated with two different nitrogen sources (N-NH4+, N-NO3-). Results showed a decrease of biomass productivity when the volume of the dark fraction and the dark residence time increased. Up to 47% loss of biomass productivity could be reached for a design dark fraction [Formula: see text] = 30% of the total culture system volume. This loss was explained as a result of metabolic reactions related to an increase of respiration activity or a decrease of photosynthetic activity in the cells.

Screening of freshwater and seawater microalgae strains in fully controlled photobioreactors for biodiesel production.

Strain selection is one of the primary hurdles facing cost-effective microalgal biodiesel production. Indeed, the strain used affects both upstream and downstream biodiesel production processes. This study presents a screening procedure that considers the most significant criteria in microalgal biodiesel production including TAG production and wet extraction and recovery of TAGs. Fourteen freshwater and seawater strains were investigated. Large variation was observed between the strains in all the screening criteria. The overall screening procedure ultimately led to the identification of Parachlorella kessleri UTEX2229 and Nannochloropsis gaditana CCMP527 as the best freshwater and seawater strains, respectively. They featured the largest areal TAG productivity equal to 2.7×10(-3) and 2.3×10(-3)kgm(-2)d(-1), respectively. These two strains also displayed encouraging cell fragility in a high pressure bead milling process with 69% and 98% cell disruption at 1750bar making them remarkable strains for TAG extraction in wet environment.

Development and validation of a screening procedure of microalgae for biodiesel production: application to the genus of marine microalgae Nannochloropsis.

Nannochloropsis has emerged as a promising alga for biodiesel production. However, the genus consists of 6 species and hundreds of strains making strain selection a challenge. Furthermore, oil productivity is instrumental to economic viability of any algal strain for industrial production, which is dependent on growth rate and oil content. In most cases, these two parameters have been studied independently. Thus, the goal of this study is to provide a combined method for evaluating strain performance in specially designed photobioreactors together with an in-depth lipidomic analyses. The nine strains of Nannochloropsis tested showed considerable variations in productivity and lipidomics highlighting the importance of strain selection. Finally, Nannochloropsis gaditana CCMP527 and Nannochloropsis salina CCMP537 emerged as the two most promising strains, with an oil content of 37 and 27 dry wt% after 11-day nitrogen starvation, respectively, resulting in TAG productivity of 13×10(-3) and 18×10(-3) kg m(-3) d(-1), respectively.

Kinetic modeling of light limitation and sulfur deprivation effects in the induction of hydrogen production with Chlamydomonas reinhardtii. Part II: Definition of model-based protocols and experimental validation.

Photosynthetic hydrogen production under light by the green microalga Chlamydomonas reinhardtii was investigated in a torus-shaped PBR in sulfur-deprived conditions. Culture conditions, represented by the dry biomass concentration of the inoculum, sulfate concentration, and incident photon flux density (PFD), were optimized based on a previously published model (Fouchard et al., 2009. Biotechnol Bioeng 102:232-245). This allowed a strictly autotrophic production, whereas the sulfur-deprived protocol is usually applied in photoheterotrophic conditions. Experimental results combined with additional information from kinetic simulations emphasize effects of sulfur deprivation and light attenuation in the PBR in inducing anoxia and hydrogen production. A broad range of PFD was tested (up to 500 µmol photons m(-2) s(-1) ). Maximum hydrogen productivities were 1.0 ± 0.2 mL H2 /h/L (or 25 ± 5 mL H2 /m(2) h) and 3.1 mL ± 0.4 H2 /h L (or 77.5 ± 10 mL H2 /m(2) h), at 110 and 500 µmol photons m(-2) s(-1) , respectively. These values approached a maximum specific productivity of approximately 1.9 mL ± 0.4 H2 /h/g of biomass dry weight, clearly indicative of a limitation in cell capacity to produce hydrogen. The efficiency of the process and further optimizations are discussed.