Method and algal growth system for autotrophic algal growth

A method for autotrophic algal growth, the method comprising:

• circulating an algae-containing reaction medium between a light reactor zone and a dark reactor zone of an internal reaction volume of an algal growth reactor;
• during the circulating, adding to the reaction medium nutrients for algal growth in the reaction medium, the nutrient comprising at least a nitrogen nutrient;
• during the circulating, irradiating the reaction medium in the light reactor zone with photosynthetically active radiation for absorption by algae in the algae-containing medium for algal photosynthesis;
• and
• during the circulating, maintaining a first residence time of the reaction medium in the dark reactor zone of at least 0.2 second and a second residence time of the reaction medium in the light reactor zone of not more than 5 milliseconds;
• and wherein:
• a ratio of the first residence time to the second residence time is at least 100:1;
• the circulating comprises sparging gas into the reaction medium at a gas velocity of at least 2 meters per second;
• the sparging comprises introducing the gas into the reaction medium from gas delivery ports having a maximum cross-dimension perpendicular to a direction of flow in a range of from 2 microns to 200 microns;
• and
• during the circulating, the dark reactor zone contains a first volume of the reaction medium and the light reactor zone contains a second volume of the reaction medium, wherein a ratio of the first volume to the second volume is at least 5:1.

A method for autotrophic algal growth, the method comprising:

• circulating an algae-containing reaction medium between a light reactor zone and a dark reactor zone of an internal reaction volume of an algal growth reactor;
• during the circulating, adding to the reaction medium nutrients for algal growth in the reaction medium, the nutrient comprising at least a nitrogen nutrient;
• during the circulating, irradiating the reaction medium in the light reactor zone with photosynthetically active radiation for absorption by algae in the algae-containing medium for algal photosynthesis;
• during the circulating, maintaining a first residence time of the reaction medium in the dark reactor zone of at least 0.2 second and a second residence time of the reaction medium in the light reactor zone of not more than 5 milliseconds;
• and
• during the irradiating, fluorometrically monitoring the reaction medium and adjusting at least one operating parameter of the reactor in response to a change in a monitored fluorometric property of the reaction medium, wherein the adjusting comprises decreasing residence time of reaction medium in the light reactor zone in response to an increase in monitored fluorescence of the reaction medium during the fluorometric monitoring.

An algal growth system for autotrophic algal growth, comprising:

• an algal growth reactor with an internal reaction volume to receive and contain algae-containing reaction medium during autotrophic algal growth;
• the reactor comprising a first reactor portion including a first portion of the internal reaction volume to provide a dark reactor zone for the reaction medium during autotrophic algal growth;
• the reactor comprising a second reactor portion including a second portion of the internal reaction volume to provide a light reactor zone for the reaction medium during autotrophic algal growth;
• a light transmissive path in optical communication with the second portion of the internal reaction volume to provide photosynthetically active radiation from a light source to the light reactor zone of the second portion of the internal reaction volume to be absorbed by biomass in the second portion of the internal reaction volume during autotrophic algal growth;
• a ratio of the volume of the first portion of the internal reaction volume to the volume of the second portion of the internal reaction volume of at least 5:1;
• and
• a liquid circulation system to circulate the reaction medium during autotrophic algal growth between the dark reactor zone in the first portion of the internal reaction volume and the light reactor zone in the second portion of the internal reaction volume, the liquid circulation system comprising a gas sparge system to sparge pressurized gas into the internal reaction volume between the first portion and the second portion of the internal reaction volume to drive circulation of the reaction medium between the dark reactor zone in the first portion of the internal reaction volume and the light reactor zone in the second portion of the internal reaction volume during autotrophic algal growth;
• and wherein:
• the gas sparge system comprises a plurality of gas delivery ports to deliver compressed gas into the internal reaction volume between the first portion and the second portion of the internal reaction volume;
• the gas delivery ports have a maximum cross-dimension perpendicular to a direction of flow of gas from the gas delivery ports in a range from 2 microns to 200 microns;
• and
• the gas sparge system includes an array of the gas delivery ports at a density of the gas delivery ports of from 200 to 20,000 of the ports per square meter.