Modeling fixed bed bioreactors for isopropanol and butanol production using Clostridium beijerinckii DSM 6423 immobilized on polyurethane foams

Abstract

Isopropanol-butanol fermentation carried out by C. beijerinckii can be improved by immobilizing cells in a fixed bed bioreactor. In this study, a fixed bed bioreactor was developed using polyurethane foams as a solid support for biofilm growth. The dilution rate was increased over time to follow biofilm development while avoiding solvent accumulation within the bioreactor. A phenomenological model was designed and successfully described batch and continuous fixed bed bioreactor dynamics. The parameters regarding biofilm detachment and attachment were estimated using a bioreactor design allowing biofilm sampling during a continuous fermentation. This last experiment was operated during 550 h and reached a maximum productivity of 1.5 g.L −1.h −1. The model prediction capacity was tested by describing a continuous fermentation in a fixed bed bioreactor column over 800 h. This latter bioreactor enabled a maximum productivity of 2.5 g.L −1 h −1 in 650 h of continuous fermentation. A high solvent concentration (13.5 g.L −1) with a butanol concentration close to the toxicity threshold (7.5 g.L −1) was obtained during the fermentation process. The process enhanced the isopropanol butanol fermentation productivity. The model properly described the batch fermentation and the immobilized cells fermentation. However, a 20% difference between experimental and modeled data was observed. Therefore, the model should be improved to better described such fermentation systems.