Pretreatment of wheat straw with Potassium Hydroxide for Increasing the Enzymatic and Microbial Degradability

Wheat straw, as an abundant agricultural residue, is a potential feedstock for biofuel production. Alkaline pretreatment has proved to be a promising treatment for enhancing biodegradability of wheat straw. The objective of this research was to develop a lignocellulosic pretreatment method that would require low energy input and initial capital investment, and result in minimal sugar degradation and formation of inhibitory compounds. Potassium hydroxide (KOH) was used as the treatment chemical due to its recovery value as plant nutrient. Various concentrations (0.2% to 5%) of KOH were tested for pretreatment of wheat straw at 10% total solid content, 20°C temperature and atmospheric pressure. The highest lignin removal of 55% was achieved by the pretreatment with 5% KOH. Reducing sugar yield via enzymatic hydrolysis increased from 16.5% to 57.5% when KOH concentration increased from 0.2% to 2% and then leveled off. The biogas production via anaerobic digestion showed that the wheat straw with 3% KOH pretreatment had highest biogas yield of 547 ml/gVS and methane yield of 310 ml/gVS. The biogas yield increased from 263 to 493 ml/gVS when KOH concentration increased from 0.2% to 2%. As KOH concentrations exceeded 2%, biogas yield increases were small. Considering chemical costs needed for increasing biogas yields, a 2% KOH concentration is recommended as having the highest benefit to cost ratio for this wheat straw pretreatment. Mass balance and economic considerations for application of low severity KOH pretreatment under different conditions were also evaluated.