Methane concentration of the biogas from each sample is presented
in Fig. 2. The initial methane concentration from pretreated
water hyacinth samples was 15–35% until the fourth day, but there
was no methane produced from untreated sample. On the 16th
day, treatments of 100 C for 120 min, 120 C for 120 min and
120 C for 60 min resulted in higher methane concentration of
65%, 68% and 60%, respectively, compared to the untreated water
hyacinth with 53%. Treatments at 140 C for 120 min and at
120 C for 240 min resulted in the highest methane concentration
of 35% and 32%, respectively. However, after 7 days the methane
concentration dropped to 15% and 10%, respectively, and no further
methane was produced. The result indicates that the pretreatments
of 140 C for 120 min and at 120 C for 240 min against
the anaerobic digestion.
3.3. Solvents recovery
In the present work, separation processes were observed to
compare separation speed which follows the order DMA DMSO
> [Bmim]Cl/DMA [Bmim]Cl/DMSO > [Emim]Ac/DMA [Emim]-
Ac/DMSO > [Emim]Ac[Bmim]Cl. The recovery rates for DMAC,
DMSO, [Emim]Ac and [Bmim]Cl were 96%, 95%, 92%, and 90%,
respectively. This result was in accordance with the order of the
separation speed, which indicated that separation speed of ABS
could reflect its separation ability.