Minimizing inhibitors during pretreatment while maximizing sugar production in enzymatic hydrolysis through a two-stage hydrothermal pretreatment

Hydrothermal pretreatment has shown a great promise in biochemical conversion process improving sugar recovery of enzymatic hydrolysis due to its green and simple process features. However, there is very a little useful data on its impact on the generation of inhibitors retarding the subsequent enzymatic hydrolysis. In this investigation, three two-stage hydrothermal pretreatments with different severities combined with physical refining (PFI mill beating) were performed on wheat straw followed by enzymatic hydrolysis to evaluate its impact on sugar recovery and inhibitor generation. The pretreatment that was combined with first stage (120 °C, 30 min) and second stage (150 °C, 20 min) was defined as pretreatment II in this study. And the sample treated by pretreatment II achieved the highest total sugars recovery of 66 %, while generated a relative low level of inhibitors. However, the sample that was treated by less severe treatment defined as pretreatment I or more severe treatment defined as pretreatment III obtained lower total sugars recovery. The results suggested that the two-stage hydrothermal pretreatment should be operated in the following way to diminish inhibitors and enhance the total sugar recovery: the first stage should be performed at low temperature with an extended residence time, while the second stage should be completed at high temperature with a short residence time.