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Gas chromatography and gateway sensors for on‐line state estimation of complex fermentations (butanol‐acetone fermentation)

A fermentation system has been designed to demonstrate the use of gas chromatography (GC) for on‐line monitoring of the butanol‐acetone and other complex saccharolytic fermentations. Tangential flow ultrafiltration was used to sterilely and continuously obtain a cell‐free filtrate from the fermentation broth for on‐line GC analysis of butanol, butyrate, acetate, acetone, ethanol, and acetoin. The liquid injection system consists of a phosphoric acid contactor, a slider‐type injection valve, and a heater to address the difficulties (ghosting) encountered in the analysis of carboxylic acids. The fermentation headspace gas was also analyzed by on‐line GC for nitrogen and carbon dioxide, while hydrogen was measured by difference. Raw chromatographic data were analyzed by a chromatography data system. Both raw and processed data were transmitted to a VAX 11/750 computer for further processing (using the fermentation equation) and archiving. The fermentation equation, which has recently been derived and tested on completed fermentation data, was also found to be valid during transient fermentations and thus useful as a gateway sensor for calculating various fermentation parameters on‐line. Such parameters include glucose concentration and gas composition, as well as a number of unobservable parameters (such as YATP, excess ATP, and NAD reduced by FdH2), which characterize the state of the fermentation.