Indirect methods for characterization of carbon dioxide levels in fermentation broth

Various factors which influence dissolved carbon dioxide levels were indire ctly evaluated in pilot scale and laboratory studies. For pilot stale studi es, off-gas carbon dioxide (percentage in exit air) was measured using a ma ss spectrometer and then its potential impact on dissolved carbon dioxide c oncentrations qualitatively examined. Greater volumetric air flowrates redu ced off-gas carbon dioxide levels more effectively at lower airflow ranges and thus lowered expected dissolved carbon dioxide levels through gas strip ping. Lower broth pH values decreased off-gas carbon dioxide levels but inc reased expected dissolved carbon dioxide levels due to the pH-dependence of the gas/liquid carbon dioxide equilibrium. While back-pressure increases h ad an insignificant effect on off-gas carbon dioxide levels, they directly affected expected dissolved carbon dioxide levels according to Henry's law. Laboratory studies, conducted using both uninoculated and inoculated ferme ntation media, quantified the response of the media to pH changes with bica rbonate addition, specifically its buffering capacity. This effect then was related qualitatively to expected dissolved carbon dioxide levels. Higher dissolved carbon dioxide levels, as demonstrated by reduced pH changes with bicarbonate addition, thus would be expected for salt solutions of increas ed ionic strength and higher protein content media. In addition, pH changes with greater bicarbonate additions declined for fermentation samples taken over the course of a one week cultivation, most likely due to the higher p rotein content associated with biomass growth. The presence of weak acids/b ases initially in the media or formed as metabolic by products, as well as the concentration bf buffering ions such as phosphate, also were believed t o be important contributing elements to the buffering: capacity of the solu tion.