Modeling of immobilized cell reactor for propionic acid fermentation

A novel recycle batch immobilized cell bioreactor for propionate production from whey lactose

Recycle batch fermentations using immobilized cells of Propionibacterium acidipropionici were studied for propionate production from whey permeate, de-lactose whey permeate, and acid whey. Cells were immobilized in a spirally wound fibrous sheet packed in a 0.5-L column reactor, which was connected to a 5-L stirred tank batch fermentor with recirculation. The immobilized cells bioreactor served as a breeder for these recycle batch fermentations. High fermentation rates and conversions were obtained with these whey media without nutrient supplementation. It took approximately 55 h to ferment whey permeate containing approximately 45 g/L lactose to approximately 20 g/L propionic acid. Higher propionate concentrations can be produced with various concentrated whey media containing more lactose. The highest propionic acid concentration obtained with the recycle batch reactor was 65 g/L, which is much higher than the normal maximum concentration of 35 to 45 g/L reported in the literature. The volumetric productivity ranged from 0.22 g/L x h to 0.47 g/L x h, depending on the propionate concentration and whey medium used. The corresponding specific cell productivity was 0.033 to 0.07 g/L x g cell. The productivity increased to 0.68 g/L x h when whey permeate was supplemented with 1% (w/v) yeast extract. Compared with conventional batch fermentation, the recycle batch fermentation with the immobilized cell bioreactor allows faster fermentation, produces a higher concentration of product, and can be run continually without significant downtime. The process also produced similar fermentation results with nonsterile whey media.

Use and engineering aspects of immobilized cells in biotechnology

A short review of the research in the past two years (1990-1991) on immobilized whole cells, such as microbial, plant, and animal cells, is presented including a discussion from an engineering point of view. Recent works concerning the intraparticle mass transfer effect on immobilized microbial cells by the authors and their co-workers are also introduced. Finally, future prospects of the immobilized cell system will be discussed.