Towards a better understanding of the role of mechanics in enzymatic degradation of plant biomass

For any industrial biorefining process based on enzymatic degradation of insoluble plant biomass to be economically feasible, the enzymatic hydrolysis step needs to take place at high solids loading. However, absence of free water during saccharification limits the rate of hydrolysis, so it is essential to achieve liquefaction during the initial phase of the hydrolysis. Mechanical forces acting on fibers during enzymatic breakdown of biomass have been shown to play a vital role in liquefaction, reducing the particle size dramatically. Specifically, it has been found that the longest dimension of the particles, i.e. the length, decreases as elongated particles break into shorter segments. Further, it has been shown that liquefaction rate is faster when saccharification takes place in a horizontal rotating reactor where agitation is based on gravity, so-called free fall hydrolysis. These findings suggest that reactor configuration and operation conditions are key to process optimization. Nevertheless, knowledge about the influence of these parameters on liquefaction rate and saccharification yield is limited. This study attempts to improve the fundamental understanding of the interrelation between mechanical and biological degradation mechanisms of insoluble plant biomass during free fall hydrolysis. Results show that both reactor parameters (i.e. reactor dimensions) and enzymatic hydrolysis conditions (i.e. enzyme loading and dry matter content) affect the rate of liquefaction and saccharification, and that these effects are furthermore confounded.