Abstract: A method to produce high density microalgae having high lipid concentration in mass culture including the steps of inoculating a vessel with microalgae at mid-log phase to a depth greater than 25 cm. Then culturing the microalgae to a preselected target density threshold, bringing the microalgae to stationary phase, manipulating growth parameters to maximize lipid concentration and harvesting the vessel.

Abstract: A device for circulating a liquid media in a vessel includes a gas infusion tube having a leading end immersed in the liquid media and a trailing end in fluid communication with a remote air pump. A diffuser is secured to the leading end of the gas infusion tube. The lumen of an outer tube receives the gas infusion tube and the diffuser. The outer tube has a leading end disposed in spaced relation to a bottom wall of the vessel and has a trailing end substantially flush with a level of the liquid media. A plurality of circumferentially spaced openings are formed in the trailing end of the outer tube or in a cap secured to the trailing end. Bubbles are emitted from the diffuser, entraining the liquid media so that it follows a toroidal path of travel that maximizes cell growth.