The effect of direct and counter‐current flow‐through delignification on enzymatic hydrolysis of wheat straw, and flow limits due to compressibility

This article compares the processes for wheat straw lignocellulose fractionation by percolation, counter‐current progressing batch percolation and batch reaction at low NaOH‐loadings (3–6% of DM). The flow‐through processes were found to improve delignification and subsequent enzymatic saccharification, reduce NaOH‐consumption and allow reduction of thermal severity, whereas hemicellulose dissolution was unaffected. However, contrary to previous expectations, a counter‐current process did not provide additional benefits to regular percolation. The compressibility and flow properties of a straw bed were determined and used for simulation of the packing density profile and dynamic pressure in an industrial scale column. After dissolution of 30% of the straw DM by delignification, a pressure drop above 100 kPa m −1 led to clogging of the flow due to compaction of straw. Accordingly, the maximum applicable feed pressure and volumetric straw throughput was determined as a function of column height, indicating that a 10 m column can be operated at a maximum feed pressure of 530 kPa, corresponding to an operation time of 50 min and a throughput of 163 kg m −3  h −1 . Biotechnol. Bioeng. 2016;113: 2605–2613. © 2016 Wiley Periodicals, Inc.