LED-based photobioreactor systems were designed, constructed,
and tested to achieve high-density photoautotrophic
algal cultures. These PBR used LED emitting at 680
nm as the sole light source. The LED units were located
internally for direct illumination and could emit the photosynthetic
photon flux of up to 50 mW/cm2. By introducing
(1) internal sparging (which improves overall light utilization),
(2) on-line ultrafiltration (supplying medium components
semicontinuously while removing any secondary metabolites),
(3) higher light intensity (increasing the number
of LED per illumination area), and (4) a shorter light path,
both the highest cell concentration (more than 2 X lo9
cells/mL) and the highest total cell volume fraction (more
than 6.6% v/v) were achieved. By modifying these four
factors, the oxygen production rate in the final PBR was
increased almost 5-fold from the initial PBR, giving the
maximal oxygen production rate of 10 mmol oxygedL culture/
h. Further challenges are to improve light distribution
and continuously perfuse fresh medium of the proper composition
to reach the stated goal of a SOPR of 100 fmol/
cell/h at a cell concentration of 1 * lo9 cells/mL.