Performance and stability of Amberlite™ IRA-67 ion exchange resin for product extraction and pH control during homolactic fermentation of corn stover sugars

• Bacillus culture used for non-sterile lactic acid fermentation of biomass sugars.
• Extractive fermentation of lactic acid with ion exchange resin was conducted.
• 1.33-Fold increase in productivity observed over traditional fed batch fermentation.
• Fermentation pH was controlled using ion exchange resin to extract product.
• Resin capacity for acid was stable over 100 days of fermentation on corn stover.

A thermotolerant, mixed culture with Bacillus coagulans as a dominating bacterium was grown for production of lactic acid. Acid extraction using Amberlite™ IRA-67 weak base resin in a recirculation loop with a fermentation vessel was implemented to maximize culture productivity by maintaining a concentration of lactic acid below 20 g/L. Productivity of this fermentation was found to be 1.3-fold higher than a control fed-batch process. Characterization of the resin through isotherm analysis produced data that fit well (R2 > 0.99) to both Langmuir and Redlich–Petersen models with a Langmuir monolayer loading of 203.8 mg acid/g resin. Resin stability was tested over 108 days of fermentation on corn stover hydrolysate. During this fermentation, resin capacities for lactic and acetic acid were on average 112.2 mg/g and 19.6 mg/g, respectively, with no statistical evidence for change lactic acid capacity after reuse. However, acetic acid capacity on average dropped 4.9% per reuse.