Effect of sequential pretreatment combinations on the composition and enzymatic hydrolysis of hazelnut shells.

Hazelnut shells, a high lignin containing biomass, were subjected to individual and sequential liquid hot water (LHW), alkaline (AP) and dilute acid pretreatments (DAP). Among the single pretreatments, LHW demonstrated the highest cellulose recovery of 98.1%, DAP resulted in the highest hemicellulose solubilization of 56.0%, and AP of the highest lignin removal of 49.6%. Employing two-step pretreatment on hazelnut shells, in general, demonstrated an enhanced action of the second pretreatment; therefore, the sequence of the pretreatment methods had a significant impact on both substrate characteristics and enzymatic hydrolysis efficiency of biomass. In terms of delignification, AP-LHW achieved 60.7% lignin removal, while LHW-DAP showed the highest hemicellulose removal of 93.8% and DAP-LHW resulted in the highest cellulose recovery of 94.0%. Structural properties of raw and pretreated hazelnut shells were observed by FTIR. The maximum glucose recovery of 54.9% was observed in DAP-LHW pretreated samples. For this pretreatment combination, almost 1.8 MJ total energy was required to recover 10.2 g glucose. The findings indicated that complete removal of the physical barrier of lignin and hemicellulose might not be essential; partial relocation of lignin and alteration of cellulose structure may also be efficient in increasing the sugar recovery from the lignocellulosic biomass.

Bioethanol production from pistachio (pistacia vera L.) shells applying ozone pretreatment and subsequent enzymatic hydrolysis.

Pistachio (pistacia vera L.) is a lignocellulosic raw material. One of the most pistachio produced three countries in the World is Turkey and Sanliurfa is the city that most pistachio production in Turkey. As a result of this production, a large amount of pistachio waste is generated. Therefore, this study was conducted considering the abundant pistachio waste and furthermore, the effects of ozone and combined (ozone and hot water) pretreatments for bioethanol production from pistachio shells were investigated. Initially, the ozone and combined pretreatments were applied to the pistachio shells. It has been observed that applying the combined pretreatment provides better lignin removal than only ozone pretreatment and on the other hand, the ozone pretreatment provides better lignin removal than the hot water pretreatment. Scanning electron microscopy (SEM) images of pretreated and untreated pistachio shells were compared. Enzyme activity was measured, and 30-60 FPU enzyme loading was applied in an enzymatic hydrolysis. The enzymatic hydrolysis was applied to obtain fermentable sugar from the pistachio shells after pretreatments. As a result of enzymatic hydrolysis, 2.34-8.24 g/L reducing sugar was obtained. On the other hand, 1.21-2.33 g/L ethanol concentration was obtained end of the fermentation process. Fermentation efficiency was calculated between 42% and 55%. As a result, this study showed that combined pretreatment was more effective than the single pretreatment in the ethanol production process.