High‐density algal photobioreactors using light‐emitting diodes

Lack of high‐density algal photobioreactors (PBR) has been a limitation in exploiting the biotechnological potential of algae. Recent developments of highly efficient light‐emitting diodes (LED using gallium aluminum arsenide chips) have made the development of a small LED‐based PBR possible. We have calculated theoretical values of gas mass transfer requirements and light‐intensity requirement to support high‐density algal cultures for the 680 nm monochromatic red light from LED as a light source. A prototype PBR has been designed based on these calculations. A cell concentration of more than 2 × 10⁹ cells/mL (more than 6.6% v%sol;v), cell doubling times as low as 12 h, and an oxygen production rate as high as 10 mmol oxygen/L culture/h were achieved using on‐line ultrafiltration to periodically provide fresh medium. © 1994 John Wiley & Sons, Inc.