hydrogen yield (Fig. 5B). Almost no methane was produced in PGSF
and PGS-T-F, while the PFS-F and PFS-T-F showed the potential to
produce methane. This result indicates that hydrogen was not consumed
by methanogens in PGS-F and PGS-T-F, resulting in the
accumulation of hydrogen. In PFS-F, methane began to appear on
day 3, and continued to increase over the following days. However,
low-temperature thermal pretreatment was not conducive to
methane production because of the inhibition of methanogens
(Guo et al., 2010). It should be noted that the methane yield in
PFS-F and PFS-T-F was very low. This can be attributed to the short
fermentation time (7 days). In addition, the pH values in the PFS-F
and PFS-T-F reactors decreased to 5.9–6.3 after one day of fermentation,
and then stabilized in this range (Fig. S5), which was not
suitable for methane production (Chen et al., 2007). Further investigation
is need for the biogas production, especially for hydrogen
production from PGS.