providing a gaseous substrate comprising CO₂ to a bioreactor, wherein the gaseous substrate has a CO to CO₂ ratio of less than about 0.3;

providing acetogenic bacteria and medium to the bioreactor to provide a fermentation broth;

providing sodium ions to the bioreactor through one or more sodium ion sources;

fermenting the gaseous substrate with the acetogenic bacteria in the fermentation broth to produce one or more organic acids; and

controlling a butyric acid to an acetic acid ratio by controlling the pH of the fermentation broth;

wherein a ratio of the butyric acid to acetic acid concentration increases when the pH of the fermentation broth decreases, and the ratio of butyric acid to acetic acid concentration decreases when the pH of the fermentation broth increases,

wherein the acetogenic bacteria includes a sodium translocating ATPase that is active during fermentation in the bioreactor,

wherein the sodium ions are provided so that Na⁺ is maintained between 1000 to 11000 ppm (g/g) in the fermentation broth, and

wherein the process provides a CO₂ conversion rate of about 75 to about 100%.