PHOTOBIOREACTOR DESIGN - MIXING, CARBON UTILIZATION, AND OXYGEN ACCUMULATION

Photobioreactor design and operation are discussed in terms of mixing, carbon utilization, and the accumulation of photosynthetically produced oxygen. The open raceway pond is the primary type of reactor considered; however small diameter (1-5 cm) horizontal glass tubular reactors are compared to ponds in several respects. Open ponds have greater CO//2 storage capacity than tubular reactors because of their greater culture volume per square meter. However, after recarbonation, open ponds tend to desorb CO//2 to the atmosphere. Thus ponds must be operated at higher pH and lower alkalinity than would be possible with tubular reactors if cost of carbon is a constraint. The major advantage of enclosed reactors lies in the potential for aseptic operation, given a product value which justifies the expense. For most products of algal mass cultivation, open ponds are the only feasible photobioreactor design capable of meeting the economic and operating requirements.