High-rate continuous production of lactic acid by Lactobacillus rhamnosus in a two-stage membrane cell-recycle bioreactor

It is important to produce L(+)-lactic acid at the lowest cost possible for lactic acid to become a candidate monomer material for promising biodegrad able polylactic acid. In an effort to develop a high-rate bioreactor that p rovides high productivity along with a high concentration of lactic acid, t he performance of membrane cell-recycle bioreactor (MCRB) was investigated via experimental studies and simulation optimization. Due to greatly increa sed cell density, high lactic acid productivity, 21.6 g L-1 h(-1), was obta ined in the reactor. The lactic acid concentration, however, could not be i ncreased higher than 83 g/L. When an additional continuous stirred tank rea ctor (CSTR) was attached next to the MCRB a higher lactic acid concentratio n of 87 g/L was produced at significant productivity expense. When the two MCRBs were connected in series, 92 g/L lactic acid could be produced with a productivity of 57 g L-1 h(-1),the highest productivity among the reports of L(+)-lactic acid that obtained lactic acid concentration higher than 85 g/L using glucose substrate. Additionally, the investigation of lactic acid fermentation kinetics resulted in a successful model that represents the c haracteristics of lactic acid fermentation by Lactobacillus rhamnosus. The model was found to be applicable to most of the existing data with MCRBs an d was in good agreement with Levenspiel's product-inhibition model, and the Luedeking-Piret equation for product-formation kinetics appeared to be eff ective in representing the fermentation kinetics. There was a distinctive d ifference in the production potential of cells (cell-density-related parame ter in Luedeking-Piret equation) as lactic acid concentration increases ove r 55 g/L, and this finding led to a more precise estimation of bioreactor p erformance. (C) 2001 John Wiley & Sons, Inc.