Epsilon Archive for Student Projects

Abstract

As a small and land scarce country, effective waste management is of
outmost importance in Singapore. In this study the production of biogas
through anaerobic digestion from the organic fraction of municipal solid
waste (OFMSW) was compared to incineration of the waste. At the moment
almost all of the OFMSW in Singapore is incinerated. Three different
scenarios were compared to the reference scenario (incineration): one with a
large scale biogas plant that can treat half of all OFMSW in Singapore, one
with a medium scale biogas plant about 15 times smaller than the large one
and one with a small scale biogas plant that can treat waste from e.g. a
shopping center or a food center.

By using life cycle assessment (LCA) the different scenarios were compared
in terms of global warming potential (GWP), acidification, eutrophication,
energy use and land use. Two alternatives for utilization of the biogas were
also compared through LCA, generation of electricity and the use of the
biogas in heavy vehicles.

From an environmental perspective production of biogas is a better way to
treat OFMSW than incineration. When biogas is used for electricity
generation the impact on GWP decreased about 80-130 CO2-eq/ton
compared to the incineration scenario and also has lower impact on
acidification and eutrophication. The result also showed that the use of the
gas as a vehicle fuel gives about the same impact on GWP as when the gas
is used to generate electricity but a much lower impact on both acidification
and eutrophication. In terms of scale, the medium and large scale plants
have less environmental impact than the small scale plant when the gas is
used as a vehicle fuel. When the gas is used to generate electricity, the small
scale scenario had higher GWP but lower acidification and eutrophication.

The prevention of leakage of biogas during production and upgrading is
crucial for the environmental impact on GWP. A leakage of only a few
percent of the produced gas will lead to a loss of all the gain in saved green
house gas emissions.