CONTINUOUS CELL-RECYCLE PROCESS FOR L-CARNITINE PRODUCTION - PERFORMANCE, ENGINEERING AND DOWNSTREAM PROCESSING ASPECTS COMPARED WITH DISCONTINUOUS-PROCESSES

For the biotransformation of gamma-butyrobetaine into L-carnitine, a chemostat with cell-recycling and a fed-batch process were developed and compared. Different cell recycling systems were tried at the pilot plant scale: crossflow filter, rotating filter and centrifuge. With respect to microbial performance, media composition, technical reliability and contamination problems, the cell recycling system was the crucial part of the continuous biotransformation plant. The residence time in the cell recycling system, most likely due to limiting oxygen concentrations, also played an important role. The experiences, made during continuous operation runs of up to 700 h in a 450 l bioreactor, are discussed and compared with the performance of a fed-batch process, which turned out to have a lower volumetric productivity, but a better quality of the product solution. The effect of continuous and discontinuous operation on the downstream processing will be outlined.