Comparison of pretreatment effects on sugar release, energy efficiency and the reuse of effluents

Abstract

The effect of ultrasonic, alkali and acid pretreatments and their combination on saccharification was investigated, and the impact of the liquid fractions, obtained after the enzymatic hydrolysis of pretreated biomasses, on seed germination was evaluated. Mechanical deconstruction of biomass coupled to chemical and/or physical pretreatments was found to enhance the cellulose to glucose conversion yields for both barley and bean straws. The highest conversion yield of 86% was obtained by ultrasonication coupled to alkaline pretreatment of bean straw, corresponding to 171 mg of glucose/g TS. The maximum conversion yield (48 %) for barley straw was obtained with NaOH pretreatment accounting for approximately 140 mg/gTS. The highest energy efficiency was obtained with NaOH pretreatment (1.7 kg glucose /kWh and 1.9 kg glucose /kWh for barley and bean straws respectively). Therefore, NaOH pretreatment appears the most suitable for an efficient release of glucose from the studied biomasses. As for the effect of the liquid fractions of hydrolysis on seed germination, the diluted effluents (3 %) were found to enhance tomato seeds germination, especially in the case of barley straw, by 17–50 %. This work suggests the valorization of liquid fractions and their reuse for agriculture, which is an option to be considered especially in the context of scarce water resources. Finally, the selected pretreatments based on energy efficiency and environmental impact will be developed at pilot and industrial scale for objective to develop a local and regional bioeconomy. • Alkaline and Alkaline combined with US had the highest impact on enzymatic hydrolysis. • Ball milling has further improved the yields of sugars achieved after pretreatments. • Alkaline pretreatment was the most energy efficient for biomass saccharification. • Effluents from pretreatments had no negative effect on tomato seeds germination.