The LED based Phototbioreactor system were designed, constructed and implemented to achieve photoautotrophic algal culture. The PBR used GaALAs LEd emitting red light at 660 nm as the monochromatic illumination source. The LEd units were located internally for direct illuminating the culture volume uniformly at light intensities of 25 W.M~-2/.unit. Uniform light distribution is achieved throughout the reactor without iuterfering with the flow pattern required to keep the cells in suspension. The prototype photobioreactor system was operated both in batch and in contiunous mode and was controlled by light intensity as well as mode (continuous or intermittent). At the dilution rate of 0.25 day~-1 under continuous operation, the optimal productivity was 1.052 g.L~-1 d~-1 for biomass concentration. Therefore a protoype PBR used GaALAs red LED arrays units as internal illumination source with short light delivery path and coverage of the photosynthetic absorption narrow spectrum indicated that LEDS are perhaps the optimal light source for PBRs.
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