Methods for controlling acetoclastic microorganisms in acetogenic syngas fermentation processes

A continuous process for the anaerobic bioconversion of a gas substrate comprising carbon monoxide, hydrogen and carbon dioxide in an aqueous fermentation broth containing microorganisms suitable for converting said substrate to oxygenated organic compound and, optionally, containing acetoclastic microorganisms, which process comprises:

• continuously contacting said gas substrate with said aqueous broth under acidic, anaerobic fermentation conditions to bioconvert gas substrate to acetogenic oxygenated organic compound and provide an oxygenated organic compound-containing broth and a depleted gas phase;
• continuously withdrawing the depleted gas phase from said broth;
• continuously or intermittently withdrawing a portion of said broth for recovery of said oxygenated organic compound, said withdrawal being sufficient to maintain the oxygenated organic compound in said broth below a concentration that unduly adversely affects the acetogenic microorganisms, in which process the partial pressure of carbon dioxide in the depleted gas phase from the broth is continuously or intermittently at a partial pressure of less than about 2 kPa.

A continuous, syntrophic process for the anaerobic bioconversion of a gas substrate comprising carbon monoxide, hydrogen and carbon dioxide in an aqueous fermentation broth containing a mixture of acetoclastic microorganisms and acetogenic microorganisms suitable for converting said substrate to a mixture of oxygenated organic compounds, which process comprises:

• continuously contacting said gas substrate with said broth under acidic, anaerobic fermentation conditions to bioconvert syntrophicly gas substrate to said mixture of oxygenated organic compounds and provide an oxygenated organic compounds-containing broth and a depleted gas phase;
• continuously withdrawing the depleted gas phase from said aqueous broth;
• and continuously or intermittently withdrawing a portion of said broth for recovery of said oxygenated organic compounds, said withdrawal being sufficient to maintain the oxygenated organic compounds in said broth below a concentration that unduly adversely affects the acetoclastic microorganisms and acetogenic microorganisms, in which process the partial pressure of carbon dioxide in the depleted gas phase from the broth is continuously or intermittently controlled to provide a desired mixture of oxygenated organic compounds in said broth.