Methods for optimizing gas utilization

A method for optimizing the flow of gas to fermentation processes in series, the method comprising:

• a. separating a gas stream derived from at least one industrial source into a hydrogen rich stream and a hydrogen depleted stream using at least one hydrogen separation module;
• b. fermenting at least a portion of the hydrogen rich stream in a first fermentation process using at least one reactor comprising a liquid nutrient medium containing a culture of one or more C1-fixing microorganism to produce a first fermentation product;
• and
• c. fermenting at least a portion of the hydrogen depleted stream in a second fermentation process comprising at least one reactor comprising a liquid nutrient medium containing a culture of one or more C1-fixing microorganism to produce a second fermentation product,
• wherein at least a portion of the first fermentation product is passed to the second fermentation process;
• and wherein the hydrogen rich stream comprises H2 and CO at a H2 to CO ratio from 2:1 to 5:1 and the hydrogen depleted stream comprises H2 and CO at a H2 to CO ratio from 0.05:1 to less than 2:1.