Conversion of food waste to biobutanol using anaerobic digester supernatant as the fermentation medium

To overcome the challenges of water-intensive operations and expensive wastewater treatment of acetone-butanol-ethanol (ABE) fermentation, a commercial medium-free fermentation strategy utilizing food waste and anaerobic digester supernatant was proposed for butanol and biofertilizer production. Results showed the potential of digester supernatant as an alternative nutrient supplement by providing sufficient nitrogen, minerals, and buffering capacity. Clostridium sp. strain BOH3 achieved 12.2 ± 0.4 g/L biobutanol production from 60 g/L glucose in digester supernatant, surpassing the yield of 9.2 ± 1.3 g/L in mineral salts medium. Notably, strain BOH3 converted 80 g/L food waste into 14.0 ± 0.6 g/L butanol and 22.1 ± 0.7 g/L ABE solvents in digester supernatant during batch experiments, representing increases of 80% and 100% over the yields obtained in deionized water, respectively. Stable fermentation could be maintained in 2-L bioreactors without sterilization, producing 13.2 ± 0.5 g/L biobutanol and 21.2 ± 0.7 g/L ABE solvents from 80 g/L food waste amended in digester supernatant, while diluted spent fermentation broth could be utilized as a liquid fertilizer for mung bean cultivation, highlighting the potential as a valuable resource. This integrated approach effectively valorized food waste and digester supernatant while advancing fermentation processes to reduce freshwater consumption and contribute to a potentially sustainable water-energy nexus.