Production of bioethanol from Opuntia ficus-indica using Saccharomyces cerevisiae and Water Kefir following an autohydrolysis pretreatment

Abstract

This study investigates the conversion of Opuntia ficus-indica waste (pears, peels, and seeds) into bioethanol. The research was done in two steps. The first objective of this work was to evaluate the optimal conditions of autohydrolysis pretreatment (AP) on these lignocellulosic materials. Experimentation involved assessing various temperatures (121 °C, 150 °C, and 180 °C) against a fixed solid-to-liquid ratio of 1:10. The Response Surface Methodology was employed for this optimization process. The highest glucose and saccharose concentrations, 0.251 mol/l and 2.81 mol/l, respectively, were observed at 150 °C over 15 min. The second part of this study focused on fermenting the pretreated biomass to maximize ethanol concentration after autohydrolysis. Both water kefir and Saccharomyces cerevisiae were employed separately and combined to assess their effectiveness in fermenting the pretreated biomass to maximize ethanol concentration. This fermentation was conducted at 30 °C with a solution-yeast ferment ratio of 70:30. The most efficacious fermentation condition was observed with a pretreatment at 121 °C for 15 min using water kefir, which resulted in an ethanol concentration of 16%. This process highlights the potential of cactus pear waste in cellulosic ethanol production, offering a sustainable energy source and a solution for agricultural waste management.