Enhanced corn-stover fermentation for biogas production by NaOH pretreatment with CaO additive and ultrasound

Abstract

Corn stover provides a great potential of bioenergy and biomaterial production through biorefinery, rather than being discarded as solid wastes. Appropriate pretreatments can enhance the biodegradability and digestion efficiency of lignocellulosics, and NaOH pretreatment is considered as an effective method. However, most NaOH pretreatments are usually performed at high temperatures (>100 °C) and over a long reaction time (∼days). In this study, we utilize both CaO-additive and ultrasound technique to improve the cost-effectiveness of NaOH pretreatment of corn stover at relatively low temperatures for a short treatment time. We first evaluate the effect of CaO/ultrasound-assisted NaOH pretreatment on the properties of corn stover, and then determine the performance of subsequent biogas production. We also estimate the costs and benefits of the entire biogas production processes. The results indicated that the developed CaO-and-ultrasound-assisted NaOH pretreatment could effectively improve the lignin conversion to 60% and promote the biogas production through anaerobic digestion to over 500 mL per gram of total solids. The benefit-cost ratio of the proposed pretreatment was estimated as 1.39–1.65, suggesting that the combination of ultrasound and CaO addition should result in a higher lignin conversion, and thus enhance the cost-effectiveness of biogas production. • NaOH pretreatment was enhanced by ultrasound and CaO additive at mild conditions. • Lignin conversion was improved to 60% by ultrasound-CaO-NaOH pretreatment. • The biogas production through anaerobic fermentation increased to over 500 mL/g-TS. • Ultrasound significantly ( p < 0.05) enhanced lignin conversion and biogas production. • The maximum B/C ratio of ultrasound-and-CaO-assisted NaOH pretreatment was 1.65.