Given the total starch in the cassava residues was converted into ethanol according to the theoretical yield (0.511 g ethanol/g starch) during the Co-SSF process, the theoretical ethanol increase was only 0.77 g/L, far less than the total ethanol increase 5.5 g/L with cellulase addition. Therefore, it is reasonable to conclude that most of the ethanol increased after cellulase addition was from the glucose released from cellulose.