Ultrasonic induced mechanoacoustic effect on delignification of rice straw for cost effective biopretreatment and biomethane recovery

The mass transfer limitation of biopretreatment (BAC) of rice straw biomass can be improved by a delignification process prior to BAC for energy efficient biomethane recovery. In the present study, rice straw biomass was subjected to delignification by ultrasonic homogenization. As a result, a higher lignin removal efficiency of 70.28% was achieved at an optimal biomass to water medium ratio of 0.02 (w/v) and a specific energy input of 450 kJ per kg TS. Delignification can increase the accessibility of cellulose present in the rice straw to biopretreatment. The delignified and biopretreated rice straw (Delign-BAC) sample was more efficient with a chemical oxygen demand (COD) solubilization of 35% than BAC with 21% solubilization and the control (untreated sample) with 3.2% solubilization. The lignin content of the Delign-BAC sample was 0.3 g L−1 and it did not lead to the inhibition of methanogenesis with a specific methane production of 165.5 mL per g VS. Economic analysis exposed that Delign-BAC gained a profitable net profit (68.62 USD per ton) with a cost benefit ratio (1.23) higher than that of BAC (−22.912 USD ton and 0.62).