A liquid foam-bed photobioreactor for microalgae production

•Proof of principle of a foam-bed photobioreactor for microalgae cultivation.•A method for continuous foam breaking was established.•Chlorella cultures survive shear stress linked to bubble formation and burst.•A growth rate of 0.1 h−1 was achieved for Chlorella sorokiniana.

A novel concept of cultivating microalgae in liquid foam was developed with the intention of reducing biomass production costs. This cost reduction is based on reduced harvesting costs due to high biomass densities, and reduced energy requirements due to improved mass transfer and lower pressure drop in the foam-bed photobioreactor. Foam generation could be controlled by adding foaming agents and employing homogenous gas distribution at the bottom of the photobioreactor. In order to refresh the gas phase entrapped in the bubbles, and ensure sufficient CO2 for microalgal growth, different foam break-up methods were evaluated. A packed bed filled with large hydrophobic beads resulted in efficient foam break-up at minimal pressure drop. It was shown that microalgae (Chlorella sorokiniana) can grow in the liquid channels of liquid foams stabilised by the protein Bovine Serum Albumin, and that the culture can withstand the physical processes of foam formation and foam break-up. An average growth rate of 0.10 h−1 was observed. The quantum yield of photosystem II photochemistry remained maximal during the reactor runs, indicating that photosynthesis was not impaired. The results obtained show that cultivation of microalgae in liquid foams is a promising new concept.