Enzyme recirculation in saccharification of lignocellulosic materials

Steam-exploded aspen wood and wheat straw were enzymically hydrolysed for 2 days when sugar yields of 53% and 49% were obtained. Removal of hydrolysate after 1 day and continued hydrolysis for a further 24 h increased the yields to 67 and 56%, respectively. After hydrolysis, 50% or more of the enzymes was adsorbed on the solid residue with the remainder in solution along with the hydrolysate. Enzymes in the hydrolysate were easily recovered by a few minutes contact with a plug of new substrate. A small quantity of sugar is also adsorbed, but ≈90% passes through the substrate plug. We propose here a simple technique for recirculating the enzymes attached to the solid residue, thereby improving significantly the total enzyme recovery and sugar yield per enzyme unit. An enzyme recovery factor, ERF, was calculated on the basis of sugar yields obtained with recovered enzyme and was compared with the initial amount of enzyme. ERF values of 0.79 and 0.73 were obtained with steam-exploded aspen wood and wheat straw, respectively. Various aspects associated with the adsorption of enzymes in the hydrolysate onto new substrate and the extent to which sugars are bound to the substrate and residue are discussed.