A liquid foam-bed photobioreactor for microalgae production

Microalgae are promising sources for the production of food, feed, bulk chemicals and biofuels. Currently, the production of bulk commodities from algal biomass is not yet feasible due to high costs and energy demand of microalgae production processes. In order to reduce the costs and energy demand of microalgae cultivation, a liquid foam-bed photobioreactor was developed. Such a liquid foam-bed photobioreactor has several advantages over traditional photobioreactors. For example, the foam-bed photobioreactor allows for increased biomass concentration, thereby reducing harvesting costs. Furthermore, less energy is required for gassing because of the low pressure in the reactor, and the transfer of carbon dioxide to the microalgae culture is faster and more efficient due to improved gas-liquid contact. This new photobioreactor design relies on continuous foam formation and foam breaking, and therefore several foam breaking techniques and reactor configurations were experimentally evaluated. In addition, our experiments revealed that Pluronic F68 is a suitable foam stabilizing agent for the foam-bed photobioreactor. We showed experimentally the feasibility and potential of such a foam-bed photobioreactor: we maintained > 20 g L-1 biomass density during continuous reactor operation, and we achieved 57 g m-2 d-1 areal biomass productivity. Our calculations show that the energy requirements of microalgae production can be reduced ten-fold when a foam-bed photobioreactor is used instead of a traditional flat panel photobioreactor.