Enhanced enzymatic hydrolysis of corncob by ultrasound-assisted soaking in aqueous ammonia pretreatment.

Ultrasound-assisted soaking in aqueous ammonia (USAA) pretreatment with 15 wt% aqueous ammonia under low temperature (~ 60 °C) and short-time (< 12 min) low-frequency (20 kHz, 60-650 W) ultrasound has been investigated for enhancement of enzymatic hydrolysis of corncob. Operational parameters of energy density (2.93-17.07 W/mL) and sonication time (0.34-11.66 min) that affect cellulose recovery, delignification, and sugar recovery yield were studied and optimized. The maximum cellulose recovery, delignification and sugar recovery yield determined at the optimum conditions (energy density 10 W/mL, sonication time 11.66 min) were 83.8, 84.7, and 77.6%, respectively. The corncob pretreated using USAA has a lower hemicellulose content (28.9% vs 31.8%), a slightly lower crystallinity index value (42.7% vs 43.7%), and a larger surface cavity diameter (> 36 μm vs < 20 μm) than that pretreated using soaking in aqueous ammonia (SAA) pretreatment. The USAA pretreatment was proved to be a reliable and effective method for corncob pretreatment.