Mesophilic–hydrothermal–thermophilic (M–H–T) digestion of green corn straw

•Mesophilic–hydrothermal–thermophilic digestion (M–H–T) of green corn straw was studied.•Maximum CH4 yield of M–H–T was 20.44% higher than that of mesophilic digestion.•Enhancement of the M–H–T process was analyzed.•The M–H–T process coupled with co-generation of heat and power is proposed.

Mesophilic–hydrothermal (80–160 °C, 30 min)–thermophilic (M–H–T) digestion and control tests of mesophilic (M), thermophilic (T), hydrothermal–mesophilic (H–M), and mesophilic–thermophilic digestion (M–T) of green corn straw were conducted for a 20-day fermentation period. The results indicate that M–H–T is an efficient method to improve methane production. A maximum methane yield of 371.74 mL/g volatile solid was obtained by the M (3 days)–H (140 °C)–T (17 days) process, which was 20.44%, 16.55%, 31.44%, and 14.31% higher than the yields of the M, T, 140–M, and M–T processes. The enhanced methane production was attributed to (1) the improved hemicellulose degradation and lignin disorganization; (2) prevention of the degradation of soluble sugar, easily hydrolyzed hemicellulose and cellulose into furfural and methylfurfural; and (3) lack of formation of Maillard reaction products during initial hydrothermal treatment.

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