Pretreatment Optimization of Corn Stover with Subsequent Enzymatic Hydrolysis for Polyhydroxybutyrate (PHB) Production

Polyhydroxybutyrate (PHB) is considered a potential substitute for conventional, non-biodegradable petroleum-based plastics. However, high production cost has been a major drawback to the commercialization of PHB. The use of low-cost lignocellulosic agricultural residues such as corn stover, together with an effective pretreatment method, can reduce production costs. In this study, optimization of pretreatment methods for corn stover – namely, steam explosion and sequential steam explosion–dilute acid pretreatment – was done to maximize the concentration of reducing sugars in the hydrolysate obtained after enzymatic saccharification. Response surface methodology (RSM)-designed experiments showed that steam explosion temperature had the highest impact on reducing sugar production for both pretreatment methods. Optimum conditions for steam explosion pretreatment were 220.9 °C steam explosion temperature and 11.2 min residence time, yielding a hydrolysate with 9.67 g/L (64.50% yield) of reducing sugars after saccharification. For the sequential pretreatment, 9.14 g/L of reducing sugars (60.93% yield) was produced from the optimum conditions of 224.8 °C steam explosion temperature, 144.2 °C dilute acid temperature, 43.8 min reaction time, and 5% w/v acid concentration. Dilute acid pretreatment significantly decreased the reducing sugar yield after the steam explosion by 5.5%, probably due to the degradation of reducing sugars, making steam explosion sufficient in the pretreatment of corn stover. More importantly, PHB was produced using the hydrolysate from steam-exploded corn stover, with a maximum concentration of 1.81 g/L after 24 h of bacterial fermentation. Therefore, the steam explosion was proven effective in producing sugar-rich hydrolysates from corn stover for PHB production.