Light optimization and management technologies for increasing algal bioreactors efficiency

Illumination in microalgae cultivation is a key factor for the achievement of target biomass productivity, and it is strongly influenced by operating variables of the plant. Traditionally, autotrophic microalgae cultivation at mid to large scale is carried out in outdoor open ponds, exploiting sun radiation. This approach often suffers from low photosynthetic efficiencies and low productivities limiting the spread of the microalgae market, which struggle to develop and to ensure the productivity required by an increasing bio-based industrial demand. This chapter is focused on strategies for managing light utilization and improving efficiency under both natural and artificial light. Outdoor cultivation technologies such as sunlight concentrators, spectral converters, and photovoltaics are discussed, among others. The aim is to avoid excessive stress and culture damages due to peak radiation and simultaneously produce electricity to increase the overall process efficiency. For what concerns the artificial light, the improvement in solid-state lighting technologies, represents an alternative to produce high amount of algae biomass, even though artificial lighting increases both capital and operating costs. The minimization of energy losses is then required to curtail the running costs of the system and can be obtained with two main approaches: focusing on spectral matching between the light source and the microalgae absorption; careful management of the reactor operation. The main outcome is that a low light intensity should be used to increase the energy conversion efficiency, carefully assessing the light compensation point. The use of flashing light also represents a viable approach to be considered.