Butyrate production and purification by combining dry fermentation of food waste with a microbial fuel cell.

This study developed and evaluated a high-purity butyrate producing bioprocess from food waste by combining dry fermentation (DF) with a microbial fuel cell (MFC). Acclimatization of a DF reactor with an enrichment culture resulted in high food waste degradation (VS removed, %) and butyrate production. A high VS degradation of 81%, butyrate concentration of up to 24 gCOD/L and butyrate yields of 497 gCOD/kg VS was obtained in the DF reactor. As a result, butyrate comprised 83% of all short chain fatty acids (SCFA) in the DF broth. Acetate (10%) and propionate (7%) comprised the rest of the SCFA. The butyrate composition was further purified by feeding the DF broth to a multi-electrode MFC enriched with anode respiring bacteria (ARB) such as Geobacter sp. (>55%). The ARB in the MFC removed acetate and propionate while purified butyrate was recovered in the MFC effluent. Butyrate purity in the MFC effluent reached as high as 99% at hydraulic retention time of 72 h. Along with butyrate purification, the MFC produced electric power in a range of 0.1-0.6 Wh/gCODbutyrate (or 0.01-7.85 kWh/ton of food waste), demonstrating that MFCs can be an energy-positive butyrate purification bioprocess.