Effects of grinding processes on enzymatic degradation of wheat straw.

The effectiveness of wheat straw fine to ultra-fine grindings at pilot scale was studied. The produced powders were characterised by their particle-size distribution (laser diffraction), crystallinity (WAXS) and enzymatic degradability (Trichoderma reesei enzymatic cocktail). A large range of wheat-straw powders was produced: from coarse (median particle size ∼800 µm) to fine particles (∼50 µm) using sieve-based grindings, then ultra-fine particles ∼20 µm by jet milling and ∼10 µm by ball milling. The wheat straw degradability was enhanced by the decrease of particle size until a limit: ∼100 µm, up to 36% total carbohydrate and 40% glucose hydrolysis yields. Ball milling samples overcame this limit up to 46% total carbohydrate and 72% glucose yields as a consequence of cellulose crystallinity reduction (from 22% to 13%). Ball milling appeared to be an effective pretreatment with similar glucose yield and superior carbohydrate yield compared to steam explosion pretreatment.