Availability and saccharification of starchy biowastes for bioethanol production in the Kingdom of Saudi Arabia

Abstract Bioenergy has received a great interest because of increase in oil price, rapid depletion of fossil fuels, global climate change, and environmental pollution. However, cheap, and fermentable sugar-rich substrates represent a challenge that face production of biofuel on commercial scale. Therefore, this study offers a reliable solution for sustainability of biofuel production by recycling cheap resource (starchy biowaste) that is abundant in Kingdom of Saudi Arabia (KSA). To achieve the goal of this study, we applied different hydrolysis protocols to obtain a high quantity of fermentable sugars from starchy biowaste collected from restaurants as meal leftover. The results approved that starchy biowastes are abundant in the KSA; with the size of the residue per meal ranging from 149 to 5218 g, and starchy materials, mostly waste rice (WR), representing 72.5%. The saccharification of thermochemically pre-treated WR, carried out using an α-amylase and glucoamylase mixture for 4 h, was the most effective technique amongst all the pre-treatment methods, and produced the highest glucose concentration, i.e. 430.6 g/kg WR. Among five yeast isolates that were tested for their ability to produce ethanol from pre-treated WR via fermentation, Kluyveromyces marxianus KKU-RDI-11 and Pichia kudriavzevii KKU-RDI-18 produced the highest bioethanol concentrations, i.e. 15.44 g/L and 15.62 g/L, respectively. This study recommends application of our technique and the fermentative yeasts on the industrial and commercial scale in KSA, for production of biofuel and recycling of starchy waste materials from restaurants.