Abstract: Photobioreactors according to embodiments of the present invention deliver nutrient gas intermittently to the photobioreactor media. In some embodiments, one or more gases are delivered according to a duty cycle or timing pattern. According to some embodiments, algae is grown in a photobioreactor using intermittent introduction of carbon dioxide. In other embodiments, carbon dioxide is supplied to algae grown in a photobioreactor in whole or in part from a head space above the media of the photobioreactor.

Abstract: A top reference photobioreactor system according to an embodiment of the present invention includes a flexible floating photobioreactor having a buoyancy tube filled with a gas that is less dense, and a ballast tube filled with a substance, such as saltwater, that is more dense, than the liquid in which the photobioreactor floats. A top reference photobioreactor method according to an embodiment of the present invention includes controlling a depth of the top reference photobioreactor by controlling a volume and/or density of ballast in the ballast tube and/or by controlling a volume and/or density of gas in the buoyancy tube.

Abstract: A top reference photobioreactor system according to an embodiment of the present invention includes a flexible floating photobioreactor having a buoyancy tube filled with a gas that is less dense, and a ballast tube filled with a substance, such as saltwater, that is more dense, than the liquid in which the photobioreactor floats. A top reference photobioreactor method according to an embodiment of the present invention includes controlling a depth of the top reference photobioreactor by controlling a volume and/or density of ballast in the ballast tube and/or by controlling a volume and/or density of gas in the buoyancy tube.