A Sustainable Strategy for the Conversion of Industrial Citrus Fruit Waste into Bioethanol
Rossella Vadalà, Giovanna Lo Vecchio, Rossana Rando, Michelangelo Leonardi, Nicola Cicero, Rosaria Costa
Abstract
The present study focused on the development of a methodology for the production of ethanol from the fermentation of waste resulting from citrus fruit processing. The experimental design included a number of steps, each optimized to make the whole process cost-effective, energy-saving, and ecofriendly. Particular emphasis was given to the pretreatment of citrus waste (CW), which was carried out through a combination of physical means, namely milling, heating, sonication, and microwave irradiation. Following this, an enzymatic hydrolysis was performed by loading a mix of enzymes, i.e., cellulase, pectinase, and β-glucosidase. Different combinations and concentrations were assayed with respect to the effective degree of saccharification. Afterwards, the hydrolysate was transferred to a bioreactor, added with nutrients and inoculated with two yeast strains, i.e., Saccharomyces cerevisiae and Saccharomyces bayanus. Fermentation lasted 48 h, leading to an amount of 40.1 g·L−1 ethanol. The process involved an extra step of fed batch that allowed the entire potential productivity of CW to be exploited by yielding 52.3 g·L−1 ethanol at a rate of 1.09 g·L−1·h−1. In accord with previously published data, this investigation has proven to be successful in reaching its prefixed objectives of sustainability.