Fermentation process for the production of lipids

A method for producing at least one lipid product from CO2 and H2, the method comprising:

• i. receiving a gaseous substrate comprising at least CO2 and H2 in a first bioreactor containing a culture of at least one first microorganism in a first liquid nutrient medium and fermenting the gaseous substrate to produce acetate product in a first fermentation broth;
• ii. passing at least a portion of the first fermentation broth to a second bioreactor containing a culture of at least one second microorganism in a second liquid nutrient medium, where the second microorganism is not the same as the first microorganism and is selected from Scenedesmus, Thraustochytrium, Japonochytrium, Aplanochytrium, Elina, and Labyrinthula, and fermenting the acetate product to produce at least one lipid product in a second fermentation broth;
• iii. obtaining a tail gas comprising at least CO2 and O2 from the second bioreactor;
• and
• iv. separating at least a portion of the O2 from the tail gas and recycling at least a portion of the reminder of the tail gas to the first bioreactor.