Effects of Alkaline Pretreatment with Sodium Hydroxide with and Without Anthraquinone on the Enzymatic Hydrolysis of Corncob and Corn Stover and Ethanol Production

The efficient bioconversion of lignocellulose into fermentable sugars is a key focus in the biofuel production. For that, alkaline pretreatments, particularly with sodium hydroxide (NaOH) and anthraquinone (AQ), have been explored for the enhancement of enzymatic saccharification. This study compared the effects of pretreatments with diluted NaOH (1%) in association or not with AQ (NaOH 1% + AQ 0.15%) on the hydrolysis of corn cob (CC) and corn stover (CS) and bioethanol production. Both methods effectively preserved the cellulosic fraction in pretreated CC and CS. However, NaOH pretreated CC exhibited the maximum delignification rate (72.19%). Enzymatic hydrolyses were carried out with 10% solids and variable enzyme loadings (5.0, 12.5, and 20 FPU/g cellulose) of Cellic CTEC 3 in order to optimize the sugar release. No significant difference in the total reducing sugar (TRS) was observed between the saccharifications performed with 12.5 and 20 FPU/g cellulose. Then, the enzyme loading of 12.5 FPU/g cellulose was selected for the hydrolysis in fed-batch mode (10 to 30% solids). The strategy of gradual substrate addition provided superior TRS production, with a maximum concentration of 67.90 g/L in NaOH pretreated CC hydrolysate. Elevated concentrations of glucose were also obtained in the fed-batch saccharifications of NaOH pretreated CC and CS (around 50 g/L), with low formation of inhibitors. The NaOH pretreated hydrolysates also resulted in elevated ethanol production, with maximum yields of 66.69% in CC and 77.27% in CS. These findings highlight the potential of NaOH-based pretreatments as a viable approach for the conversion of lignocellulosic biomasses in bioethanol.