Enhanced anaerobic digestion performance of corn stalk pretreated with freezing-thawing and ammonia: An experimental and theoretical study

Pretreatment is one of effective methods for improving biodegradability and biomethane production from lignocellulosic materials such as corn stalk (CS). In this study, a pretreatment technology combing freezing-thawing with ammonia was proposed. The effects of freezing and thawing (-20 degrees C and 20 degrees C) with ammonia (NH3) addition on anaerobic digestion (AD) performance of CS were investigated. The microscopic interaction mechanisms on CS structural destruction during pretreatment was also revealed by quantum chemistry calculation and molecular dynamics. The experimental results showed that among all pretreatment conditions, the CS pretreated by -20 degrees C and 20 degrees C with NH3 achieved the highest biomethane yield (283 mL.g(vs)(-1)) and volatile solid (VS) removal rate (60.6%), which were 54.6% and 40.0% higher than those of untreated CS, respectively. The surface structure of CS and functional groups in the lignocellulose structure were found to be destructed severely. The theoretical calculation results indicated that the damage to the crystalline cellulose was attributed to the external hydrogen bonds (H6s) formed between water or NH3 and cellulose, thereby leading to the destruction of the HBs networks inside the cellulose after pretreatment with freezing-thawing and ammonia. The findings showed that this combining pretreatment is one of promising methods for its greatly increasing biomethane production from CS, and also has great potential of being used for biomethane production from other lignocellulosic materials. (C) 2019 Published by Elsevier Ltd.