Valorization of Contaminated Ficus Carica Fruit Residues for Biohythane Production by Consolidated Anaerobic Dark Fermentation

Abstract

The quest for a reliable, eco-friendly, and sustainable alternative energy source has led to the ex-ploration of utilizing inexpensive organic waste as a substrate for biofuel production. This study focuses on the sequential biohydrogen and biomethane productions with the side products of organic acids and solvents from the contaminated fruit of Ficus carica through consolidated bioprocessing at mesophilic conditions (37 °C). The research involved the extraction of fermentable sugar from dried fruit of F. carica with an average particle diameter of 275 µm at 100 °C for 1 h which results in 45% sugar recovery from 50 g/L fig residue. Consolidated batch dark fermentation was conducted in sealed 310-mL capacity serum bottles with a working volume of 200 mL, containing fig fruit waste at an initial substrate concentration ranging from 10 g/L to 25 g/L. Total gas volume, hydrogen, total sugar, organic acid, and solvent concentrations were monitored daily. Fermentation setup with an initial fruit waste concentration of 10 g/L, corresponding to a sugar concentration of 5 g/L, re-sulted in high volumetric hydrogen production rate of 110.50 mL/L·day. Acetic and butyric acids were the dominant organic acids determined in all the experimental setup and their concentration increases as fermentation time progressed. Acetone was consistently detected in all setups. Subse-quently, in studies of methane production under mesophilic conditions, residual acetic acid from hydrogen production was used and adjusted to three different initial total acetic acid concentra-tions—1.5, 3, and 6 g/L—with methanogen-containing anaerobic sludge serving as the inoculum. Methane production was observed only at an initial concentration of 1.5 g/L, resulting in a cumula-tive methane volume of 174 mL. The results underscore consolidated bioprocessing as an effective approach for producing biohydrogen, biomethane, organic acids, and solvents from sugar-rich F. carica fruit.