For T1 and T2, the peak value of reducing
sugar concentration attained to 45.3 g L−1 and 50.8 g L−1, respectively,
on hours 12, which was higher than those (45 g L−1 and
42 g L−1) obtained by SSF and SSCF (simultaneous saccharification
and cofermentation), respectively, in batch mode reported by Kang
et al. [26], possibly because of more ash existing in the paper mill
sludge used in the latter paper; but for T3, the peak value was only
17.8 g L−1 on hours 24; the main reason was that there was no nutrient
solution in T3 compared with T1 and T2. Compared T1 with T3,
all initial conditions were the same except that the nutrient solution
was added in reactor T1, but not for reactor T3 (Table 2), and
the reducing sugar concentrations and ethanol yields in reactor T1
was much higher than those in reactor T3 during the SSF (Fig. 1
and Fig. 2).