Ethanol production from hazelnut shells through enzymatic saccharification and fermentation by low-temperature alkali pretreatment

•Hazelnut shells pretreated with NaOH at low temperature for long pretreatment time.•Effect of pretreatment conditions on the glucose recovery and ethanol production is studied.•An energy balance is established and thermal energy consumption and pretreatment energy efficiency are determined.

Low-temperature sodium hydroxide (NaOH) pretreatment, enzymatic saccharification and ethanol fermentation were evaluated for hazelnut shell cellulose to fermentable sugars and ethanol. Maximum glucose recovery (48.33 g/100 g cellulose) was achieved with 6% NaOH for 72 h and at 1/10 solid/liquid ratio. At these conditions, 41.18% of lignin was removed. The theoretical ethanol yield (ethanol produced/potential glucose in biomass) was 40.71%, overall process efficiency was 37.73 g/kg biomass, ethanol productivity and fermentation efficiency were 0.115 g/(L h) and 96.7%, respectively. Total energy consumed for the low-temperature-long-residence-time alkali process was 34.8 MJ/kg untreated hazelnut shells. Pretreatment time has a significant effect on thermal energy consumption for the low-temperature alkali process.