A green pretreatment strategy using CO2 and acidogenesis liquid digestate as reagents for biomethane enhancement from corn stover

Pretreatment is a key step for the conversion of lignocellulosic biomass to biomethane via anaerobic digestion (AD). Though various chemical pretreatment strategies have been developed, most of them are costly and environmentally unfriendly, which seriously prevents them from practical applications. This study provides an innovative strategy that uses two kinds of AD byproducts, i.e., CO2 and acidogenesis liquid digestate (ALD), to replace conventional chemical reagents for pretreating corn stover. The effect of CO2-ALD pretreatment at different temperatures (35, 55, and 100 °C) on biomethane production as well as characteristics of pretreated solid and liquid products were studied. Results showed that the highest biomethane yield was obtained after using 1 Mpa CO2 in ALD at 55 °C pretreatment, which was 63.85% higher than the untreated sample. Meanwhile, CO2-ALD pretreatment could destroy the stubborn structure of lignocellulose and separate partially cellulose and hemicellulose, from the stover. The microbial community analysis indicated that this pretreatment strategy enhanced the abundance of hydrolytic bacteria and promoted the acetotrophic pathway. Further energy balance analysis proved that using 1 Mpa CO2 in ALD at 55 °C for pretreatment had the highest energy gain (Eout/Ein), which was 30.51 % higher than that without any pretreatment.