High reaction rate continuous bioconversion process in a tubular reactor with narrow residence time distributions for the production of lactic acid

The subject of the work was the microbial bioconversion of whey ultrafiltration permeate giving lactic acid as the reaction product. The purpose of the work was to design a tubular reaction system, characterized by a narrow residence time distribution, with very high reaction rates. The process is further characterized by cell recycling and its continuous operation. In a tubular reactor, gradients occur in the concentration of the substrate and of the reaction product along the direction of the flow. Inhibition of the microbial activity by the reaction product is therefore restricted to a very low level at the end of the reactor. Hence, the productivity of the process is accelerated in comparison to conventional continuous reaction systems. In this study, a stirred tank cascade with cell recycling has been used for the experiments which was equivalent to a tubular reactor, as far as the residence time behavior is concerned.