water hyacinth, the supernatant mainly containing the solvent was
removed and placed to 25 C. 30.0 g K3PO4 was added into the
solution, vibrated by a vortex mixer (XW-80A, Jingke, Inc., China),
and placed over night.
2.6. Analytical methods
Cellulose, hemicelluloses and lignin contents of the pretreated
or untreated water hyacinth species were determined according
to NREL procedures (Sluiter et al., 2008). Biogas production was
measured by water displacement. Methane and carbon dioxide
were analyzed using a gas chromatograph (GC 9560, Huaai Inc.,
Shanghai, China) equipped with a thermal conductivity detector.
The gas samples were analyzed twice in a week. The concentration
of ILs and K3PO4 in the upper and lower phases were analyzed by
an ion chromatography (Basic IC 792, Methohm, Switzerland)
equipped with electric conductivity detector. Karl-Fisher titration
was used to measure the water content in all samples. The weight
fractions of co-solvents were calculated by material balance
method.