In the present research, municipal solid waste incineration (MSWI) bottom ash (BA) residues from three incinerators (N, K, and R) in Japan were collected for hydrogen gas generation purpose. The samples were split into four particle size fractions: (1) d ≤ 0.6, (2) 0.6 ≤ d ≤ 1.0, (3) 1.0 ≤ d ≤ 2.0, and (4) 2.0 ≤ d ≤ 4.75 mm for the characterization of metal aluminum, the relationship between the present metal aluminum and hydrogen gas production, and the influence of external metal aluminum on the enhancement of hydrogen gas. The batch experiments were performed for each BA fraction under agitated (200 rpm) and non-agitated conditions at 40 °C for 20 days. The highest amount of hydrogen gas (cumulative) was collected under agitation condition that was 39.4, 10.0, and 8.4 L/kg of dry ash for N2, R2, and K2 (all fraction 2), respectively. To take the benefit of the BA high alkalinity (with initial pH over 12), 0.1 and 1 g of household aluminum foil were added to the fractions 2 and 3. A Significantly larger amount of hydrogen gas was collected from each test. For 0.1 g of aluminum foil, the cumulative amount of gas was in the range of 62 to 78 L/kg of dry ash and for 1 g of aluminum foil the cumulative amount of hydrogen was in the range of 119–126 L/kg of dry ash. This indicated that the hydrogen gas yield was significantly a function of supplementary aluminum and the intrinsic alkaline environment of the BA residues rather than ash source or particle size.
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