Scale-up of algal bioreactors for renewable resource production

While microalgae can be easily cultivated in highly controlled laboratory environments, achieving good productivity at large-scale remains challenging. Photobioreactors (PBRs) are cultivation systems that allow the algal culture to develop in a closed and highly regulated environment, leading to increased nutritional and metabolic efficiency and resulting in increased biomass output per unit of substrate. PBRs are multiphase reactors, and their efficient operation requires achieving residence times within distinct reactor zones that guarantee good mass transfer, the best distribution and release, possibly on top of optimal light/dark cycles. Design considerations for PBRs include reactor shape, structure, concentration profiles, and operating mode. While most chemical reactor scale-ups nowadays involve physically based multiscale models, a complete simulation considering all phenomena affecting PBRs and their performance remains challenging and is often avoided. Due to possible design faults, the PBRs restricted scalability makes often uneconomical to employ them in very large-scale units for microalgae production. The approach discussed in this chapter uses the Buckingham -theorem to carry out the PBRs scale-up. It involves defining the main dimensionless groups, computing their values at the laboratory scale, and keep these values during scale-up at pilot and industrial scale. This approach remains valid also during the change of shape of the reactor. The key is to carefully tune the parameters of the more complex reactor adopted at the largest scale within the identified ranges of the operating variables.