Improvements in Biobutanol Fermentation and Their Impacts on Distillation Energy Consumption and Wastewater Generation

In the conventional fermentation process to obtain butanol (a novel biofuel), product-induced toxicity results in a product stream with low concentration of butanol (similar to 13 g/L) and limits the concentration of the sugar solution to less than 60 g/L. As a result, steam-consuming operations such as mash sterilization, downstream product recovery (distillation), and wastewater treatment are energy-intensive and important economic drawbacks. Based on the correlation between energy consumption of the distillation unit and butanol concentration in the fermentation beer, the present research points out that improvements in biobutanol processing intended to increase the concentration of butanol in the beer should have a minimum target of 36 g/L. Moreover, due to the dramatic effect of butanol concentration on the wastewater footprint, the volume of the effluent stream can be reduced by 60% (from 72 to 29 L stillage/L butanol) if the minimum concentration target is reached instead of the usual butanol titer of 13 g/L. These correlations were used as the basis to discuss the impacts of today's research works (genetic strain improvement, utilization of lignocellulosic biomass feedstock, and development of new process technologies) on the energy consumption for complete dehydration of butanol and on wastewater generation.