| abstract |
A two-stage continuous microbiological process for the production of solvents such as acetone, butanol and ethanol, comprises culturing an acid- and solvent-producing microorganism under acid-producing conditions in a first vessel, wherein the pH and the flow of fresh media are controlled by a pH auxostat, transferring a portion of the culture into a second vessel or vessels; and culturing the same microorganism under solvent-producing conditions in the second vessel(s). Preferably, this is an acetone, butanol and ethanol (ABE) fermentation process using solventogenic Clostridia, such as Clostridium beijerinckii. In the first (acidogenic) stage, the culture vessel is fed with fresh growth media at dilution rates that support fast growth and acid production. The culture flows into the second (solventogenic) stage, which is a separate culture vessel or vessels, designed to provide the culture with sufficient residence time to convert acids into solvents. A system for use in such methods comprises a first vessel suitable for acidogenic growth of the microorganism, in fluid communication with a second vessel suitable for solventogenic growth of the microorganism, and a pH auxostat which is capable of controlling the pH of the first vessel. |