Application of flashing blue-red LED to boost microalgae biomass productivity and energy efficiency in continuous photobioreactors

Flashing light is a promising strategy to increase light penetration in microalgal cultures, even though its actual advantage is still a matter of discussion, in particular in batch cultures. In this work, we demonstrated that the cultivation of Arthrospira maxima in steady-state continuous photobioreactors under high frequencies (up to 3700 Hz) of red-and-blue LED light pulses resulted in an increased productivity with respect to the control, carried out under continuous light. Pulse duration between 10 and 1000 μs and pulses intensity up to 70,000 μmol m−2 s−1 were tested at different values of integral light intensities and residence times. At both 120 and 300 μmol m−2 s−1 of integral light an increase of biomass concentration under light periods between 100 and 200 μs was observed. By managing the pulse intensity at a constant light period of 100 μs, biomass concentration can be up to three times higher than the control, but only if the residence time is properly set. Thus, residence time is one of the main variables affecting productivity under pulsed light. Finally, even though the efficiency of the LED apparatus under pulsed regime was lower than in continuous regime, the loss was compensated by the increase of productivity under certain conditions.