Evaluation of gas supply configurations for microbial product formation involving multiple gaseous substrates

Background: Gaseous substrates such as O₂ and CO₂ are often required in fermentation processes. However, a simple methodology to compare different gas supply strategies using gaseous substrates from different sources is missing. Results: In this study, we present a methodology to identify and theoretically compare different configurations to supply mixtures of gaseous compounds to fermentations that consume these gases. For the different configurations that were identified, all gas flow rates can be calculated in terms of other process parameters such as optimal concentrations of the gaseous compounds in the liquid phase, top pressures of the fermentation, and consumption/production rates. The approach is demonstrated for fumaric acid fermentation with Rhizopus delemar, which consumes O₂ and can theoretically produce or consume CO₂. Three different gas supply configurations were identified: Air supplemented with O₂, a mixture of O₂ and CO₂, and air supplemented with CO₂. All three configurations lead to gas supply costs in the same order of magnitude. O₂ and CO₂ prices and consumption rates determine which configuration is best. However, the overall production costs will not be dominated by the gas costs, but by the glucose costs. Conclusions: The presented methodology enables a simple way to identify and compare different gas supply strategies for fermentations that require more than one gaseous substrate. This includes the costs for compression of gases. Other substrate costs are easily added for overall process optimization.