Ethanol production from glucose and xylose obtained from steam exploded water-extracted olive tree pruning using phosphoric acid as catalyst

• Steam explosion of olive tree pruning using H3PO4 was evaluated for the first time.
• High enzymatic hydrolysis and SSF yields were obtained with pretreated material.
• Glucose and xylose from olive tree pruning are jointly fermented for the first time.
• Ion-exchange resins resulted in ethanol yield similar to xylose control fermentations.
• About 160 g of ethanol from kg of olive tree pruning could be obtained.

In this work, the effect of phosphoric acid (1% w/w) in steam explosion pretreatment of water extracted olive tree pruning at 175 °C and 195 °C was evaluated. The objective is to produce ethanol from all sugars (mainly glucose and xylose) contained in the pretreated material. The water insoluble fraction obtained after pretreatment was used as substrate in a simultaneous saccharification and fermentation (SSF) process by a commercial strain of Saccharomyces cerevisiae. The liquid fraction, containing mainly xylose, was detoxified by alkali and ion-exchange resin and then fermented by the xylose fermenting yeast Scheffersomyces stipitis. Ethanol yields reached in a SSF process were close to 80% when using 15% (w/w) substrate consistency and about 70% of theoretical when using prehydrolysates detoxified by ion-exchange resins. Considering sugars recovery and ethanol yields about 160 g of ethanol from kg of water extracted olive tree pruning could be obtained.