Enzyme Recycling by Adsorption during Hydrolysis of Oxygen-Delignified Wheat Straw

Enzyme recycling by adsorption from supernatant to fresh substrate is a promising strategy to reduce enzyme expenses and the production cost of lignocellulosic ethanol. The study was performed using oxygen-delignified wheat straw, and the effect of lignin content, enzyme loading, and hydrolysis time on recycling was determined. The percent of recycled cellulases, 0-35% of initial cellulase loading, increased with increasing enzyme loading and hydrolysis time but decreased with increasing lignin content. Cellulose conversions of 10-71% were achieved during the second hydrolysis round using only recycled cellulases indicating the existence of a highly active subset of enzymes. To achieve constant production of sugars during enzyme recycling, fresh cellulases were loaded before the second hydrolysis round to match the cellulase loading used in the first round. Subsequently, similar glucose, xylose, and protein concentrations were obtained at the end of the first and second rounds for all conditions. Recycling mass balances were developed to support future techno-economic analyses to determine the impact of enzyme recycling on the cost of ethanol.