Development of equipment and procedures for the safe operation of aerobic bacterial bioprocesses in the presence of bulk amounts of flammable organic solvents

Many pseudomonads and other bacteria can grow on aliphatic and aromatic hydrocarbons that occur in the environment. We are examining the potential of such organisms as biocatalysts for the oxidation of a variety of substituted aliphatic and aromatic compounds. In order to attain a high production rate of oxidation products via such biotransformations, we have focused on two-liquid phase culture systems. In these systems cells are grown in liquid media consisting of an aqueous phase containing water soluble growth substrates and droplets of a water immiscible organic solvent containing bioconversion substrates and products. For industrial applications of such two-liquid phase processes, it is mandatory that these systems can be operated efficiently and safely. Therefore, the danger of an explosive atmosphere within the reactor, when using flammable organic solvents as substrates or products under aerobic conditions, must be considered. We have analyzed in detail four strategies to safely operate two-liquid phase cultivations. These include reducing the flammability of the organic solvent, operating within an explosion proof reactor, maintaining the operating pressure above a minimum level or maintaining the oxygen concentration within the reactor headspace and exhaust below a critical value. We conclude that technical means are available to operate two-liquid phase bioprocesses safely and efficiently.