Scale-Up-Bioreactor Design and Culture Optimization

Tubular and the flat plate are the two most common general designs of microalgal photobioreactors. Desired photobioreactors for microalgal mass production have effective liquid mixing to promote nutrients mixing and gas mass transfer; have adequate surface area for light capture; prevent significant accumulation of oxygen; allow for ease of scale-up; and have low material and maintenance costs, among others. The higher, more stable productivity, the markedly reduced incidence of significant culture contamination, and the greater land- and water-use efficiencies constitute the principal reasons why photobioreactors are considered favorable for the scaled-up production of microalgal biomass for biofuel production compared with open raceways. The principal goal of the photobioreactor scale-up process is to ensure that the desired level of microalgal productivity is maintained as the volume of production transitions from small laboratory scale to intermediate pilot scale, all the way to the large industrial scale. This necessitates that the characteristic hydrodynamic conditions (e.g., degree of mixing) and the accompanying environmental conditions (e.g., lighting) of the specific type of photobioreactor used are maintained or appropriately adjusted with increasing production volume to maintain the desired level of microalgal productivity. The scale-up process of cultivating a specific algal species in a specific photobioreactor is thus the stage-by-stage optimization or reoptimization of the culture with the goal of ensuring that the desired level of microalgal productivity is maintained with each increase in scale.