Biochar and activated carbon enhance ethanol conversion and selectivity to caproic acid by Clostridium kluyveri

Syngas from biomass or steel mills can be fermented into a dilute stream of ethanol and acetic acid, which requires energy intensive distillation for product recovery. This can be circumvented by selective secondary fermentation of the syngas fermentation effluent to caproic acid as easier recoverable platform chemical with Clostridium kluyveri. Here, we explore the impact of biochar and activated carbon on this process. Changes during the fermentation with biochar or activated carbon were monitored, different doses were tested and the recyclability of biochar and activated carbon was assessed. Biochar decreased the lag phase and increased the caproic acid production rate (up to 0.50 g.L-1.h(-1)). Upon recycling for subsequent fermentation, biochar retained this property largely. Activated carbon addition, especially at high dose, could potentially increase the conversion and selectivity towards caproic acid to 14.15 g.L-1 (control: 11.01 g.L-1) and 92% (control: 84%), respectively.

Automated summary

The study found that the addition of biochar and activated carbon in the secondary fermentation of syngas fermentation effluent can increase caproic acid production and selectivity. Biochar performs well in reducing the lag phase and increasing yield, with good recyclability. Activated carbon, especially at high doses, can enhance the conversion rate and selectivity towards caproic acid.