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 LEDbased
PBR possible. We have calculated theoretical values
of gas mass transfer requirements and light-intensity
requirements 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 x
lo9 cells/mL (more than 6.6% v/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. 0
1994 John Wiley & Sons, Inc.