The results reveal that the biogas option is economically feasible
with a positive energy balance. The result also shows that, compared
with the biogas option, the current landfill approach of controllingwater hyacinth proliferation is not a good social investment because
it has two major disadvantages. First, the biomass of water hyacinth
is not used but disposed as a waste. Second, the emission of landfill
gas is neglected because it eventually enters the atmosphere due to
a lack of gas capture system, and thus increases GHG stock in the
atmosphere. We cannot draw a conclusion on the economic justification
of the current practice, say, as compared with “do nothing”,
because the avoided loss from the control of water hyacinth proliferation
was not estimated. However, the emission of landfill gas
deserves attention. Therefore, the biogas option is a good alternative
to the current landfill approach because the emission of methane
can be avoided and the biomass of water hyacinth is used.
Moreover, the biogas option is desirable in terms of energy
performance. For disposing 11,004.2 tons of water hyacinth, this
option has an energy gain of 5.3 TJ while the landfill approach has
an energy loss of 162.9 GJ.