Photobioreactors with internal illumination - A survey and comparison.

The idea of internally illuminated photobioreactors has existed since the 1990s and various systems were developed since. Recently, the interest in these systems has been on the rise again, due to the increased production of and research on high-value products and recombinant proteins from microalgae and plant cell cultures. While promising results in lab-scale have been achieved, the potential of photoautotrophic or mixotrophic production of these compounds is limited due to the lack of scalable photobioreactors, which could be overcome by internally illuminated systems. In this article, we review different internally illuminated photobioreactors from the last two decades and classify them into two major groups. The photobioreactors are compared based on the ratio of illuminated surface-to-culture volume and the occupied volume by internal light-emitting elements, and possible obstacles, challenges and future trends are discussed. Looking forward, new technologies and smaller light sources have improved the potential of internally illuminated photobioreactors with internal light sources and will enable these technologies to compete with systems with internal light guides, but only a few of these systems have currently achieved a relevant scale.