Effects of Light Quality Adjustment in Microalgal Cultivation: Flashing Light and Wavelength Shifts in Photobioreactor Design

The distribution of light within a microalgal culture and the choice of the best wavelengths are considered the most critical aspects in the scale-up of microalgal culture. Several studies have investigated these features, resulting in a substantial body of literature that analyzes the effects in terms of an increase in biomass production or shift in its composition. This work addresses two types of light quality adjustments: the application of flashing light and shifts in light wavelength. The effects on microalgal culture are examined. Later, the application of these light features to photobioreactor design is described. Specifically, three kinds of photobioreactors are examined: (1) reactors designed to minimize light gradients, (2) reactors where the geometry produces a flashing light effect on the cells and (3) reactors that use filters to obtain a shift in the sunlight wavelength. The results showed that both the effect of flashing lights and wavelength shift strongly depends on various parameters such as the alga taken into consideration, the light intensity, the agitation type, growth medium, light intensity and temperature and, regarding the flashing light also, the frequency and the duty cycle. Despite all these specific differences, this work aims to resume and provide specific instruments for choosing operational parameters in microalgal cultivation and in photobioreactor design to achieve targeted outcomes, such as an increase in biomass production or in high-value compound accumulation.