Photosynthetic efficiency of Chlamydomonas reinhardtii in attenuated, flashing light

Abstract

As a result of mixing and light attenuation, algae in a photobioreactor (PBR) alternate between light and dark zones and, therefore, experience variations in photon flux density (PFD). These variations in PFD are called light/dark (L/D) cycles. The objective of this study was to determine how these L/D cycles affect biomass yield on light energy in microalgae cultivation. For our work, we used controlled, short light path, laboratory, turbidostat-operated PBRs equipped with a LED light source for square-wave L/D cycles with frequencies from 1 to 100 Hz. Biomass density was adjusted that the PFD leaving the PBR was equal to the compensation point of photosynthesis. Algae were acclimated to a sub-saturating incident PFD of 220 µmol m(-2) s(-1) for continuous light. Using a duty cycle of 0.5, we observed that L/D cycles of 1 and 10 Hz resulted on average in a 10% lower biomass yield, but L/D cycles of 100 Hz resulted on average in a 35% higher biomass yield than the yield obtained in continuous light. Our results show that interaction of L/D cycle frequency, culture density and incident PFD play a role in overall PBR productivity. Hence, appropriate L/D cycle setting by mixing strategy appears as a possible way to reduce the effect that dark zone exposure impinges on biomass yield in microalgae cultivation. The results may find application in optimization of outdoor PBR design to maximize biomass yields.

Microalgae production in a biofilm photobioreactor

“…The model was also validated for Chlamydomonas reinhardtii based on seven chemostat experiments (Kliphuis et al 2011a), 22 turbidostat experiments (de Mooij et al 2014;Kliphuis et al 2011c;Takache et al 2012;Vejrazka et al 2011;Vejrazka et al 2012) and three Batch experiments (Jacobi 2013;Takache et al 2012). All experiments utilized for validation were performed in flat plate photobioreactors or a similar design.…”

“…Zijffers et al (Zijffers et al 2010), Mooij et al (de Mooij et al 2014), Takache et al (Takache et al 2012), and Vejrazka (Vejrazka et al 2011;Vejrazka et al 2012) measured the real specific absorption coefficients (Appendix 4.B). When evaluating the datasets separately, they all indicate photo acclimation, however, when combined, no trend was observed.…”

“…In the case of Vejrazka et al (Vejrazka et al 2011;Vejrazka et al 2012), the light intensity ranges from 30% of the average in the corners to 140% of the average in the center of the reactor (FMT150, PSI, Czech Republic). All other datasets do not report the light distribution over the illuminated surface.…”

“…It is possible that these species exhibit different growth characteristics. The strain used by Vejrazka et al (Vejrazka et al 2011;Vejrazka et al 2012), for example, is a wild type which carries mutations in the nitrate reducing genes and can only grow on ammonium.…”

“…The reported a x were weighted to the light source used for cultivation by Zijffers et al and, therefore, were recalculated to the non-weighted a x . The a x for C. reinhardtii is based on five studies (de Mooij et al 2014;Fouchard et al 2009;Takache et al 2012;Vejrazka et al 2011;Vejrazka et al 2012). An overview of the a x found in literature is depicted in (Dubinsky et al 1986).…”