Study and mathematical modeling of the production of propionic acid by Propionibacterium acidipropionici immobilized in a stirred tank fermentor

A mathematical model was developed that describes production of propionic a cid by fermentation of sweet whey with Propionibacterium acidipropionici im mobilized in calcium polygalacturonate beads in a fermentor-type stirred ta nk. This mathematical model is constituted by a partial differential equati ons system, which fits consumption, production, growth and internal diffusi on rates in the support. Fermentation was experimentally studied with free cells and immobilized cells, effective diffusivities of lactose and propion ic acid were estimated in the support, and typical parameters of the model were obtained by nonlinear regression of the experimental data. The varianc e analysis shows that the combination of mu (max) and K-d parameters is the source of variation most significative, also they were found to be the mos t sensitive parameters of the model. Finally, an effectiveness factor was c alculated in order to assess the effect of mass transfer on the overall rea ction rate observed.