AbstractThe effect of biomass loading from 50 to 200 g/L on enzymatic hydrolysis was studied using switchgrass samples pretreated by dilute acid and hypochlorite-alkaline methods. It was confirmed that an increase of initial loading of the pretreated biomass leads to a decrease of enzymatic digestibility, probably due to difficulty of mass transfer of cellulolytic enzymes in the high-viscous substrate slurry and also because of an inhibiting effect of the formed sugars. An additional sharp problem connected with enzymatic hydrolysis at the high-solids loading is absorption and retention of liquid hydrolysate by residual non-hydrolyzed biomass that causes diminution of the available volume (Va) of the sugar solution and decreases productivity of the saccharification process. To optimize the high-solids enzymatic hydrolysis, the maximal amount of the formed sugars was determined Am = Cm x Va,m , where Cm is maximal concentration of the sugar solution and Va,m is maximal available volume. Such an approach makes it possible to find the optimal conditions for the hydrolysis: optimal biomass loading and hydrolysis time. After enzymatic hydrolysis at these optimal conditions, the low-lignified biomass pretreated by hypochlorite-alkaline method displayed much more available volume of sugar solution and higher digestibility characteristics than the cellolignin obtained by acidic pretreatment of the initial biomass sample.