Pretreatment of pistachio (Pistacia vera) shells using Deep Eutectic Solvents (DES) for the production of second-generation bioethanol

Bioethanol production from lignocellulosic biomass offers a sustainable alternative to fossil fuels, mitigating environmental challenges such as climate change and air pollution. Traditional pretreatment methods involving acid and alkali treatments pose risks due to wastewater discharge. This study investigates the use of Deep Eutectic Solvent (DES), specifically choline-chloride-based DES, for the pretreatment of pistachio shell biomass. The optimal pretreatment conditions were determined, and the pretreated biomass was characterized and compared to its untreated counterpart. XRD analysis revealed an increase in crystallinity index (CrI%) to around 27–28% post-pretreatment, compared to 21% in untreated biomass. For production of bioethanol, the samples were subjected to Simultaneous Saccharification and Fermentation (SSF) and Separate Hydrolysis and Fermentation (SHF) using Aspergillus niger cellulase and Saccharomyces cerevisiae . The enzymatic hydrolysis of 1:2 Cch/CA 2h-pretreated biomass produced the highest reducing sugar concentration, about 24 g/L.The ethanol concentrations obtained from the sample pretreated with 1:2 Cch/CA for 2 h were 28.60 g/L (SHF) and 29.82 g/L (SSF) after 72 h of fermentation. This was more than the ethanol obtained from the untreated sample (22 g/L). This study demonstrates the promising potential of DES pretreatment for efficient bioethanol production from lignocellulosic biomass.