Extraction of Bioethanol from Fermentation Broth of Cocoa Pod Husks and Downstream Processing of the Vinasse for Biogas Production

Abstract

Extraction from fermentation broths is an integral part of ethanol biorefinery. During extraction, as much as 17 litres of vinasse is generated per litre of ethanol produced. Vinasse, the liquid waste from ethanol production, has the potential to cause devastating effect on the environment if not properly disposed. One way of treating vinasse is by reducing its organic components through anaerobic digestion (AD). In this study, ethanol was extracted from a fermentation broth of cocoa pod husks by liquid-liquid extraction (LLE) and batch AD of the waste stream was carried out for biogas production. Operation parameters for LLE were varied using a batch process after which continuous operation was carried out based on the determined parameters. Since substrate-to-inoculum ratio (S/R) can affect biomethane yield, it was varied at 0.5, 1.0, 1.5, 2.0 and 2.5 (gCOD basis) for the AD process using the automatic biomethane potential test system. Three kinetic models were used to fit the experimental biomethane potential from each reactor. Results show that a distribution coefficient, percentage efficiency and selectivity of 37.49, 89.27% and 109 respectively were obtained for ethanol during LLE. A maximum biomethane potential of 328 mL/gCOD was obtained at a S/R of 2.0. Although all models gave a reasonably good fit to the experimental data, the dual pool model gave the best fit.