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Tan, Swee Ngin
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The use of incineration to treat our local municipal solid waste has reduced our waste volume considerably, and thus led to a significant decrease in our need for landfill space. However, the current method of disposal of the various incinerator residues at our offshore Pulau Semakau landfill has also given rise to several issues. These include the potential leaching of harmful heavy metals and metalloids into our waterways which could give rise to a myriad of potential environmental and health problems. The 20-year limited life span of Pulau Semakau also provides the need for proper characterisation of these ashes to establish procedures that could help reduce their potential impact, and also to provide an avenue for their potential downstream applications. This study aims to evaluate the physicochemical characteristics of two main incinerator ashes, air pollution control (APC) and electrostatic precipitator (ESP), and to investigate their heavy metal and metalloid leaching behaviour under various pH conditions. APC ash was found to have a lower bulk density (0.56 g/cm3) compared to ESP ash (0.85 g/cm3) possibly due to its higher moisture content which was more than three times that of ESP ash, and was also seen to have a monomodal particle size distribution (~10 μm) while ESP ash had a bimodal size distribution (~10 and 200 μm). The leaching results obtained in this work were analysed with respect to landfill guidelines set by the United Kingdom Environment Agency (EBPRI11507B). Leaching at the natural pH of the ashes showed that amongst the heavy metals and metalloid (Arsenic, Cadmium, Chromium, Copper, Lead, Mercury, Nickel, Zinc) tested, only Pb levels in APC ash (1019 mg/kg) was found to exceed the guidelines (50 mg/kg) by more than 20 times, while all other analytes in both ashes were found to be within acceptable limits, with APC ash having more Cu, Pb, Ni and Zn compared to ESP ash. It was also discovered that acidic conditions promoted heavy metal and metalloid leaching, with high leaching observed especially with Cd, Cu, Pb, Zn, while basic conditions generally limit leaching, except for amphoteric analytes such as As, Cr, Pb and Zn which showed leaching at alkaline pH as well. Generally, a pH of 9 seems to be the most ideal pH at which the leaching of nearly all the tested elements was suppressed. These results can hence be useful in developing methods in which these pollutants could be removed prior to their disposal or use in applications, thereby reducing their potential environmental impact.
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TD883 Gan
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Appears in Collections:Master of Science (Life Sciences)

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