Dual-frequency ultrasound combined with alkali pretreatment of corn stalk for enhanced biogas production.

To solve the problem of standing wave produced by single-frequency ultrasonic pretreatment, the dual-frequency ultrasound was applied to pretreat the corn stalk. In this paper, the mechanism of dual-frequency ultrasound was studied, and digital simulation results showed that the cavitation of dual-frequency ultrasound was more violent than that of single-frequency ultrasound, and its energy was more efficient. The anaerobic fermentation of corn stalk that was pretreated by dual-frequency ultrasound combined with alkali (Group 1) lasted for 53 days. The results showed that the cumulative biogas yield of Group 1 was 11.1%, 28.2% and 56.6% respectively higher than that of single-frequency ultrasound combined with alkali pretreatment (Group 2), alkali pretreatment (Group 3) and without pretreatment (Group 4). The TS removal rate of Group1 was 9.9%, 25.0% and 71.4% respectively higher than that of other pretreatment samples, and the VS removal rate was 7.4%, 28.9% and 77.1% respectively higher than that of other group samples. The net energy of Group 1 was 32.2%, 114.9% and 19.7% higher than that of Group 2, Group 3 and Group 4. [ABSTRACT FROM AUTHOR]