Fig (Ficus carica) is a sugar-rich lignocellulosic fruit, making it an excellent biomass candidate for biofuels. Metals are important precursors in biochemical transformation pathways and also play major roles in microbial metabolism when present in the appropriate concentrations. In this study, the effects of cations (Co²⁺, Cu²⁺, Mn⁺, Fe²⁺, Na⁺, Mg²⁺, Zn²⁺, Ca²⁺, K⁺, Mo³⁺, B³⁺) on ABE (acetone-butanol-ethanol) fermentation, organic acids, and biohydrogen production with fig as biomass was done using Plackett-Burman statistical design. Mo³⁺ and Na⁺ were the most significant elements favoring acetone, butanol, and ethanol production. Mo³⁺ and Fe²⁺ strongly supported organic acids (acetic and butyric acid production) while Fe²⁺, Zn²⁺, Ca²⁺, K⁺, and Mo³⁺ favored hydrogen production rates. In our study, Mo³⁺, an unreported element from previous studies, was found to be highly influential in the ABE fermentation process and H₂ production. Optimization studies were conducted within the ranges of the significant cations on responses tested in our study achieving ABE (6.3, 5.03, and 1.6 g L⁻¹, respectively), acetic and butyric acids (6.9 and 3.9 g L⁻¹, respectively) and hydrogen production rate (51.5 ml H₂ L⁻¹ h⁻¹).

Graphical abstract