Modeling and simulation of a tubular recycle photobioreactor for macroalgal cell suspension cultures

Photosynthetic cell suspension cultures derived from marine plants have the potential to produce biomass containing pharmacologically active metabolites within photobioreactor systems under controlled conditions. The tubular recycle photobioreactor in particular can promote the mass cultivation of photosynthetic cell suspension cultures. This photobioreactor has two sections: a coiled tubular section which illuminates the culture with a small light path, and a non-illuminated aeration tank which supplies dissolved CO 2 needed for photosynthetic biomass production. The culture is recycled between the two sections. A batch reactor model was developed to predict the cell density vs. time profile for the cultivation of photosynthetic cell suspension cultures in the tubular recycle photobioreactor. This model uniquely couples culture illumination parameters in the tubular section to interphase CO 2 mass transfer parameters in the aeration tank. Model simulations show that the tubular recycle photobioreactor is operating at saturation growth kinetics with respect to light. The model predicts a critical cell density at which photosynthetic biomass production switches from a rate-limited process to a CO 2 delivery limited process. Rate-limited growth proceeds only to this critical cell density, and then further growth is CO 2 mass transfer limited until the final cell density at complete dissolved limiting nutrient consumption is achieved. Sensitivity analyses reveal that the CO 2 mass transfer coefficient in the aeration tank, the residence time of the culture in the tubular section, the ratio of tubular section to aeration tank liquid volume, and the partial pressure of CO 2 in the aeration gas all affect the overall biomass production rate by affecting the CO 2 delivery modes to the tubular photobioreactor.