Effect of enzyme and substrate dosing strategies on mixing and hydrolysis of old corrugated cardboard

Enzymatic hydrolysis is one of the key steps in biofuel production from lignocellulosic material. High consistency of biomass slurry in the hydrolysis step improves the economics and energy efficiency of biofuel processes. However, it has been shown that the high consistency also decreases the hydrolysis yield and affects the rheology of hydrolysis slurry. In this study, mixing related effects on the hydrolysis of old corrugated cardboard have been studied in two different scales. Results from small pressure tube scale studies show that the dosing order of enzyme and substrate (16 % (w/v)) affect both hydrolysis rate and yield. The best result was achieved by the addition of all enzyme to dilute hydrolysis slurry with subsequent stepwise addition of the substrate (52.8 ± 1.2 % yield). The highest initial rate was achieved by adding the enzyme into the vessel before substrate. Further studies in a scale of a stirred-tank reactor showed that enzyme addition before substrate is advantageous mainly due to the mixing behavior of hydrolysis slurry at high substrate consistencies (>15 % (w/v)). The dosing of substrate before enzyme resulted in thick slurry that could not be kept in full motion within the first hours of hydrolysis. Full motion was reached by the dosing of the enzyme before substrate followed by the dosing of substrate within an hour after the enzyme. The effect of the dosing order on hydrolysis yield at high consistency in the studied reactor scale is negligible.