Improved Cellulosic Ethanol Titres from Highly Lignified Cotton Trash Residues Using Various Batch and Fed-Batch Process Configurations

This study investigates a fed-batch simultaneous saccharification fermentation (F-SSF) process to increase ethanol titres from highly lignified (41.6 wt.%) cotton gin trash residue. The optimal initial solid loading, enzyme dose, feed quantities and intervals to maximize substrate feed and subsequent ethanol titres were examined. Under batch SSF conditions, initial extracted cotton gin trash (ECGT) solid loadings were maximised at 19.35 wt.% and attained an ethanol titre of 23.3 g/l with a corresponding yield of 53.7%. Operating under optimised F-SSF mode, fermentations were initiated with 16.13 wt% EGCT solids followed by fresh ECGT feeds of 16.13 wt% and 12.9 wt.% at 12-h intervals. Cellulase levels were maintained at 44 FPU/g glucan throughout the fermentations. The final ethanol titre of 41 .4 g/l with a corresponding conversion rate of 70.1% was achieved after 72 h. Comparable ethanol yields of 40 g/l with 67.8% conversion were realized with lower cellulase dosing (25 FPU g/glucan) but only after extending the fermentation by 24 h.