Processes and systems for culturing algae

A process to culture algae by controlling algae age and/or maintaining aerobic conditions in an algal growth system, the process comprising:

• feeding an aquaculture medium including microorganisms capable of phototaxis into at least one algal aquaculture zone, wherein the microorganisms include algae;
• exposing the aquaculture medium to one or more light sources in an illumination zone of the at least one algal aquaculture zone, wherein the entirety of the illumination zone has a width to depth ratio from about 100:0.5 to about 1:1;
• allowing the microorganisms capable of phototaxis to move toward the one or more light sources in the aquaculture medium, thereby forming an upper layer containing the microorganisms capable of phototaxis and a lower layer in the illumination zone, wherein the upper layer is 1 to 100 mm deep;
• separating at least part of the upper layer from at least the lower layer in a separation zone;
• and
• transferring at least part of the microorganisms capable of phototaxis of the upper layer from the separation zone to a harvesting zone.