Extraction of bioethanol from fermentation broth and valorization of the vinasse for biogas production

Abstract

An effective ethanol extraction from fermentation broths and further utilization of the waste streams for biogas production can enhance the overall efficiency of the biorefinery process. In the present study, ethanol was extracted from a fermentation broth by liquid-liquid extraction (LLE) after ultrafiltration. Thereafter, the vinasse was subjected to batch and continuous anaerobic digestion (AD). Batch AD was carried out at inoculum-to-substrate ratios (ISR) of 0.1, 0.2 and 0.3 (gVS/gCOD), while continuous AD was carried out at hydraulic retention times (HRT) of 2, 3 and 5 days as well as at organic loading rates (OLR) of 2, 5 and 7 gCOD/L/day. Results showed that during ultrafiltration, fouling mechanism was primarily due to the formation of a cake layer on the surface of the membrane. LLE efficiency was 97.13% with an ethanol purity of 98.84%. During the batch AD, the highest cumulative biomethane potential of 236.43 mL/gCOD (± 13) was obtained at an ISR of 0.2 (gVS/gCOD). During the continuous AD, both OLR and HRT significantly affected biogas and biomethane production with the highest biogas yield being 415.50 mL/gCOD at an HRT of 5 days and OLR of 2 gCOD/L/day.