Optimization of Sodium Hydroxide Pretreatment Conditions to Improve Biogas Production from Asparagus Stover

Alkaline pretreatment was employed to enhance biogas production from asparagus stover with anaerobic digester in laboratory scale batch fermentation. Different pretreatment times (10, 18, 25 days), NaOH concentrations (2.5, 5, 7.5%), and water dose (20, 60, 100 mL) were tested to select the best pretreatment conditions. With response surface method (RSM) applied, the optimum pretreatment conditions were pretreatment time of 19d, NaOH concentration of 4.2%, water dose of 74 g. The biogas yield was predicted as 275.65 mL/g VS, while it was observed as 277.86 mL/g VS in the verification test, with the relative error of 0.80%. Further more, the verification tests show that contents of hemi-cellulose, cellulose and lignin after pretreatment were decreased by 65.20, 29.06 and 13.51%, respectively. The above results suggest that the effects of NaOH on degradations of hemi-cellulose and cellulose are higher than that on lignin.