Efficient utilization of high irradiance for production of photoautotropic cell mass: a survey

Abstract

For mass production of microalgae outdoors to be justified as a significant commercial entity, solar energy should be utilized at a much higher efficiency, yielding greatly increased photosynthetic productivity than presently obtained. Development of photobioreactors to provide an answer for this challenge rests at the root and the very future of this biotechnology. Most available Photobioreactors yield increased volumetric outputs of cell mass, but the areal yield which relates to the photosynthetic efficiency is rather similar to that obtained in the basically inefficient open raceway, the most prevalent commercial reactor today. The key for efficient utilization of the super saturating solar irradiance existing outdoors rests in distributing it, in effect, to as large a number of cells per given volume in as high a frequency as possible. This unfolds the design principles underlying efficient utilization of high irradiance for photoautotrophic production of cell mass: Reactors should be maximally exposed to sun light, have a narrow light-path coupled with a safe mixing system designed to create fast, turbulent streaming for moving the algal cells in and out of the photic volume at maximal frequency. Reactors designed along these principles may support ultrahigh cell densities resulting in high volumetric as well as areal yields, hopefully expanding thereby the economic basis of microalgal biotechnology.