A Mild Thermal Pre-treatment of the Organic Fraction of Municipal Wastes Allows High Ethanol Production by Direct Solid-state Fermentation

Abstract

A solid standard mixture (SSM) representing the annual composition of fresh fruits and vegetables residues generated at the Supply Center in Mexico City was used for bioethanol production. This type of residues allows bioethanol production with a single thermal pre-treatment instead of hard thermochemical or enzymatic treatments. The release of fermentable carbohydrates from the SSM by a mild thermal pretreatment was firstly optimized. After that, mixed and single cultures of Saccharomyces cerevisiae, Scheffersomyces stipitis, and Schwanniomyces occidentalis were evaluated for bioethanol production. The maximum ethanol production, 282.61 ± 13.09 L ethanol per ton of dry matter (DM), was reached using a severity factor (SF) of 2.35 and a mixed culture composed of Saccharomyces cerevisiae, Scheffersomyces stipitis, and Schwanniomyces occidentalis. The improved lab scale conditions were evaluated in a pilot scale (18 Kg) stirred bioreactor with an SF of 2.35 and the mixed culture, obtaining 245.72 ± 17.76 L ethanol per ton DM. The obtained results demonstrate for the first time the use of fresh fruits and vegetables residues for bioethanol production under solid-state culture conditions without any thermochemical or enzymatic pre-treatment.