Flashing light effects on CO2 absorption by microalgae grown on a biofilm photobioreactor

The effect of flashing light and continuous light from red light emitting diodes on the photosynthetic activity of microalgae biofilms was investigated. In contrast to suspended microalgae cultures, biofilm-based microalgae photobioreactors allow a uniform exposure of the microalgae to incident radiation throughout the period of microalgae cultivation. In this work, multi-species microalgae biofilms were produced in a biofilm photobioreactor to be subsequently taken to an ad-hoc laboratory for biofilm light emitting diodes trials. Continuous light and flashing light at three light/dark frequencies: 0.1, 1 and 10 kHz and four light fractions: 5, 25, 50, and 75% were tested on microalgae biofilms. All flashing light experiments resulted in higher net photosynthetic activity of microalgae biofilms than the continuous light; the highest increase was obtained for 10 kHz frequency at 5% light fraction, for which the net photosynthetic activity was 7-times the continuous light (51 μmol photons m− 2 s− 1). Over the whole experiment, the quantum yield varied from 0.014 (at 10 kHz & 1 kHz, 766 μmol photons m− 2 s− 1) to 0.161 (at 10 kHz, 51 μmol photons m− 2 s− 1); the latter value was much higher than the theoretical maximum one, estimated at 0.125 μmol CO2 μmol photons− 1. Some hypotheses for this finding were raised, which would require further investigation.