Production of sugars from grass silage after steam explosion or soaking in aqueous ammonia

Grass is an underutilized potential feedstock for lignocellulosic sugar production for biorefinery applications and can be stabilized by ensiling for year-round supply. This study compared soaking in aqueous ammonia and steam explosion with dilute acid as pretreatments for enzymatic saccharification of grass silage. Both treatments led to high hydrolysability of the silage carbohydrates. An ammonia loading of 10% per DM was sufficient in an overnight soaking at 90 °C whereas the maximum yield from steam explosion treatment was obtained with 1% acid loading at 190 °C for 10 min. The soluble carbohydrates of silage had to be removed by washing before pretreatment as otherwise severe degradation of sugars was observed. The use of an acid catalyst only had a small effect for total yield in steam explosion, but increased monomerization and degradation of hemicellulosic sugars during pretreatment. Considering the surplus potential of grass production in Europe, grass silage was found to be a very prominent feedstock for lignocellulosic sugar production.