Enzymatic saccharification of pretreated wheat straw: Comparison of solids-recycling, sequential hydrolysis and batch hydrolysis

•Solids-recycling at steady state was compared to sequential and batch hydrolysis.•Volumetric productivity was increased by solids-recycling and sequential hydrolysis.•Solids-recycling is a method for product removal rather than enzyme recycling.•Solids-recycling requires less unit operations than sequential hydrolysis.•A solids-recycle process was modeled, based on a geometrical series.

In the enzymatic hydrolysis of lignocellulose materials, the recycling of the solid residue has previously been considered within the context of enzyme recycling. In this study, a steady state investigation of a solids-recycling process was made with pretreated wheat straw and compared to sequential and batch hydrolysis at constant reaction times, substrate feed and liquid and enzyme consumption. Compared to batch hydrolysis, the recycling and sequential processes showed roughly equal hydrolysis yields, while the volumetric productivity was significantly increased. In the 72 h process the improvement was 90% due to an increased reaction consistency, while the solids feed was 16% of the total process constituents. The improvement resulted primarily from product removal, which was equally efficient in solids-recycling and sequential hydrolysis processes. No evidence of accumulation of enzymes beyond the accumulation of the substrate was found in recycling. A mathematical model of solids-recycling was constructed, based on a geometrical series.