Mechanical Pretreatment Options on Biofuel Biomass Feedstock Discussing on Biomass Grindability Index Relating to Particle Size reduction—A Review

Mechanical pretreatment methods are the first steps imposed on biomass feedstocks for the production of various types of biofuels. The goal of this review article is to provide information on the varying mechanical pretreatment methods for instance mechanical-physical, combined-mechanical, thermal–mechanical and irradiation-mechanical pretreatments, pertaining to particle size reduction. Included in this short review is the grindability index as well as various types of biomass feedstock for biofuel production. Biomass grindability index \({(GI}_{VUK})\), defined as the grinding efficiency in milling technique (comminution), is scarcely reported for various mechanical pretreatment methods particularly for biofuels. Thus, it is crucially needed to be promoted. \({GI}_{VUK}\) which is calculated based on mass, fine particle fractions and energy requirements is presented. The \({GI}_{VUK}\) based on mass (I_E) is higher than that based on volume (I_Ev) and work index (I_w), indicating the importance of particle size reductions. Lastly, in this review, variety of biomass feedstocks available for biofuel production undergoing mechanical pretreatment is presented.