title: 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.
authors.affiliation: Bioprocess Engineering, Wageningen University, PO Box 8129, 6700EV Wageningen, The Netherlands. carsten.vejrazka@gmail.com
authors.forename: Carsten
authors.initials: C
authors.lastname: Vejrazka
authors.forename: Marcel
authors.initials: M
authors.lastname: Janssen
authors.forename: Mathieu
authors.initials: M
authors.lastname: Streefland
authors.forename: René H
authors.initials: RH
authors.lastname: Wijffels
mesh_terms: D018533:Biomass; D019149:Bioreactors; D016825:Chlamydomonas reinhardtii / Q000254:growth & development / Q000502:physiology* / Q000528:radiation effects*; D008027:Light; D010788:Photosynthesis