The maximum rate of biogas production at 75.8 mL · min–1 by the application of 45 g VS · L–1 · d–1 (which is
equal to 0.135 kg VS · d–1), with the assumption of constant production rate, is equivalent as 808.6 L biogas kg–1 VS
90 L-1 working volume. This amount could be converted to 8.9 L biogas kg–1 VS · L–1 working volume. As a
comparison, Zhu et al. [15] studied the effect of NaOH pretreatment on corn stover and obtained a maximum
accumulative yield of 372.4 L kg–1 VS by 5.0 % NaOH in 40 d of batch process at 2.0 L fermentation. This value
was equal to 4.66 L biogas kg–1 VS · d–1 · L–1 of fermentation.