Ethanol production from olive stones using different process strategies

Abstract

In this work, olive stone is used as a lignocellulosic raw material for ethanol production. In order to optimise the ethanol production yield, three different process strategies are studied considering the different streams produced in a sequential pretreatment of olive stone with dilute sulfuric acid/steam explosion (SE), which has been previously tested and demonstrated to be an effective fractionation strategy for olive stone biomass. Strategy 1 features fermentation with E. coli SL100 of the mixture of the detoxified prehydrolysate from the dilute sulfuric acid stage and the enzymatic hydrolysate of WIS and detoxified SE liquid fractions. Strategy 2 consists of fermentation with E. coli SL100 separately from the prehydrolysate and the enzymatic hydrolysate of WIS and detoxified SE liquid fractions. Strategy 3 considers fermentation with E. coli SL100 of the prehydrolysate from the acid stage and presaccharification and simultaneous saccharification and fermentation with S. cerevisiae “Ethanol Red” of WIS and detoxified SE liquid fractions. Strategies 2 and 3 reach a similar ethanol production of ~162 kg/t, which is the highest ethanol yield reported so far from olive stones. The latter strategy uses two different microorganisms that allow an ethanol concentration close to 30 g/L.