Natural freezing-thawing pretreatment of corn stalk for enhancing anaerobic digestion performance

[Display omitted] •Natural freezing-thawing pretreatment was proposed for CS pretreatment.•The optimal pretreatment time and ratio were 21d and 1:6, respectively.•The highest biomethane yield was 40.5% higher than that of the untreated.•The predominant archaeal at genus level was Methanobacterium (54.0%). Natural freezing-thawing (NFT) was proposed as a low energy input and alternative pretreatment method for high biomethane production from corn stalk (CS) by anaerobic digestion (AD). The CS was pretreated by freezing-thawing in winter season using different pretreatment time periods (7d, 14d, 21d and 28d) and solid-to-liquid ratios (1:2, 1:4, 1:6, 1:8 and 1:10). The results showed that CS pretreated for 21d coupled with a solid-to-liquid ratio of 1:6 achieved the best result among all pretreatment conditions. In this case, the biomethane yield and VS removal rate of CS reached the highest values of 253 mL·gvs−1 and 58.6%, respectively, which were 40.5% and 27.4% higher than that of the untreated. It was also found that the predominant bacterial and archaeal at genus level in AD were Clostridium_sensu_stricto_1 (36.1%) and Methanobacterium (54.0%), respectively. This study provided that NFT is a simple pretreatment strategy for efficient AD bioconversion of CS to biomethane.