THESIS
2018
xx, 115 pages : illustrations (some color) ; 30 cm
Abstract
Water scarcity has become a global issue that has forced many communities to seek
alternative water resources. Seawater, covering a majority of the earth’s surface, is one such
resource. In Hong Kong, seawater has been used directly for toilet flushing since the 1950s’,
and now seawater toilet flushing (SWTF) serves 80% of the residents, with the remaining 20%
still using freshwater. Even though SWTF can save 20-30% percent of water used in an urban
area, its environmental impacts need to be clarified before it is introduced to other water
stressed areas. No quantitative analysis has been conducted to evaluate the geographic
conditions for its extensive application. Life cycle assessment (LCA) is regarded as a
promising method to evaluate environmental impacts for urban water sy...[
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Water scarcity has become a global issue that has forced many communities to seek
alternative water resources. Seawater, covering a majority of the earth’s surface, is one such
resource. In Hong Kong, seawater has been used directly for toilet flushing since the 1950s’,
and now seawater toilet flushing (SWTF) serves 80% of the residents, with the remaining 20%
still using freshwater. Even though SWTF can save 20-30% percent of water used in an urban
area, its environmental impacts need to be clarified before it is introduced to other water
stressed areas. No quantitative analysis has been conducted to evaluate the geographic
conditions for its extensive application. Life cycle assessment (LCA) is regarded as a
promising method to evaluate environmental impacts for urban water systems. Improving the
LCA method will help to obtain more accurate environmental impacts. This research,
therefore, used the two most widely known LCA methods of Process-based LCA (PRO-LCA)
and Economic Input-Output LCA (EIO-LCA) to assess feasible alternative water resources
and compare these two methods in urban water systems. By comparing the environmental
impacts of urban water systems using several different water resources, both LCA results
suggest that SWTF is more environmentally friendly than other alternative water resources
for the rest of 20% Hong Kong residents who are still using freshwater to flush toilets. Global
sensitivity analysis is developed to simulate the impact of geographic factors, illustrating that
the most influential factors are effective population density and seaside distance. After
estimating the most sensitive factors in coastal areas, it demonstrates that SWTF is more
environmentally friendly regardless of population density and more economical for areas
with a population density above 17500 persons/km
2. Comparing PRO-LCA with EIO-LCA,
the environmental impact generated by EIO-LCA is 1.4 times greater than that from
PRO-LCA. That is due to truncation error in PRO-LCA. However, while the input data for
EIO-LCA is averaged to 42 sectors, it is not as detailed as in EIO-LCA. Thus the hybrid LCA
considering the shortcomings of these two methods is suggested to further improve the
environmental results in the future work.
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