Photobioreactors for mass production of microalgae

Industrial exploitation of microalgae for feed, food, and biofuel production is currently limited by several factors, among which those connected with large-scale cultivation are of the greatest importance. Photobioreactors (closed systems for algae cultivation) suffer from high energy expenditures (mixing, cooling, and embodied energy), while open ponds have a more favorable energy balance. However, cultures in large-scale open ponds have a considerable water footprint, are unstable and maintaining selected strains in these systems for long periods is difficult. In the last years, thanks to the renewed interest in microalgae as feedstock for biofuels, many new photobioreactor designs have been proposed, most of them aiming at reducing costs. Besides improvements of the classic tubular and flat panel designs, some new concepts have been proposed, like hybrid systems combining open ponds and photobioreactors, and floating photobioreactors, which aim at exploiting water bodies instead of land for algae cultivation.