The grinding of lignocellulose materials into small particles increases the surface area and allows subsequent enzyme or acid treatment to hydrolyse the cellulose. The pro­cess requires a considerable energy input and is not as effective as other treatments.

Ammonia explosion

The lignocellulose is milled and the ground lignocellulose, with a moisture content of 15-30%, is placed in a pressure vessel with ammonia (1-2 kg/kg biomass) at pressures of 12 atmospheres for 30 min. No sugars are released but the hemicellulose and cel­lulose are opened up to enzymatic digestion.

Acid treatment

Acid treatment can use sulfuric, hydrochloric, nitric and phosphoric acids although sulfuric is used most widely. Acid treatment converts the hemicellulose to sugar (xylose) (80-95%) and furfural, and increases cellulose digestibility. The treatment time is short (minutes), and depending on the substrate between 80 and 95% of the hemicellulose sugar can be recovered.