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The fabrication of conductive carbon nanomaterial has attracted extensive research due to its promising potential in energy application. However, the conventional fabrication methods, e.g. chemical vapour deposition, are expensive due to high energy consumption, which makes it both economically and environmentally unsustainable. The concept of using carbonaceous waste as a precursor for growing carbon nanomaterial has recently been explored. By using carbonaceous waste, the fabrication of conductive carbon will be more sustainable. In this work, a carbonaceous waste has the potential to be a precursor for the fabrication of conductive carbon nanomaterial. Our previous characterisation work showed that the carbonaceous waste had a nano-particle size distribution and possessed conductive property. Due to its inherent nano-particle size, no further size reduction is required. However, the carbonaceous waste had to be leached to remove the toxic heavy metal. After leaching, the conductive property decreased slightly. This work explores the use of hydrothermal treatment of the leached sample at low temperature to modify the surface area and surface functional groups, so as to enhance the conductive property of the carbonaceous waste. The capacitance of the treated carbonaceous residue was also analysed.

Batch and column tests were conducted on untreated incineration bottom ash (IBA) samples from two incineration plants in Singapore, using seawater as the leachant. The main objective of this study was to investigate the change in the leaching behavior of certain elements (i.e. As, Cd, Cr, Cu, Ni, Pb, Sb, Se and Zn) when IBA comes into contact with seawater. Such an investigation using seawater as leachant was not commonly carried out when investigating leaching behavior in IBA. The leaching tests were then carried out on the same IBA samples using DI water, as a comparison. Lower level of leaching was observed for Pb and Zn when seawater was used as the leachant. Cr and Sb showed significant cumulative release at Liquid-to-Solids (L/S) ratio 5 in the seawater column leaching. The influence of Dissolved Organic Carbon (DOC) on Cu leaching seems to decrease after L/S 2 when using seawater in the column test. Although the leaching behavior of IBA was affected when seawater was used, for the column test, there was no significant difference during the initial release when compared to DI water. The initial L/S fractions collected were important as the low L/S ratios represent the pore water concentration and the maximum output in an actual application. The results from this study would be useful for the future study on using IBA in marine applications.

The management of solid waste has become increasingly challenging with the accelerated growth in residency in Singapore. Alternative utilization, such as high temperature thermal energy storage material, valorizes the waste to the status of a new resource, thereby reducing the need of virgin material and ensuring sustainability. In Singapore, coal is co-fired with biomass and the coal/biomass fly ash is partially reused and the rest is landfilled. This research evaluated two different fabrication routes: conventional sintering and plasma processing. The novelty of this study is that unlike most studies whereby plasma arc is used to melt the ash at high temperature, in this study, a 13.56 MHz radio frequency plasma is used to control discharge parameters through in-situ diagnostics of active species density and temperatures. This allows for high throughput and uniform processing. An optimized plasma process could potentially reduce the total number of processing phases, with a lower energy budget for processing, while increasing the controllability of the processes to achieve the desired material properties. The chemical composition, and the thermal properties such as specific heat capacity, energy density and thermal conductivity of the ceramics made from coal/biomass fly ash were evaluated. Experimental evaluation shows that the radio frequency plasma processed coal/biomass fly ash samples were found to improve the thermal properties of coal/biomass fly ash in general. It is hypothesized that the mechanism of improvement from radio frequency plasma was due to the incorporation of hydrogen into the material and the conversion of mineralogical composition (i.e. quartz) which gave rise to the better performance. In conclusion, this study has shown the potential of using coal/biomass fly ash as thermal energy storage material through innovative process such as radio frequency plasma discharge.

Alkaline activated materials such as geopolymers and cementitious materials derived from pozzolanic reactions offer several advantages over the currently widely used Portland cement, especially in terms of environmental sustainability and physiochemical properties. However due to the need of an alkaline activator, such as NaOH or KOH, which result in high production cost and requires skilled personnel, they have not been deeply explored and put to use. Here in this study, wood fly ash, a by product of wood combustion is used as an alternative source of alkaline activator for producing such alkaline activated materials along with coal fly ash, where the resulting geopolymer-cementitious hybrid (GCH) was characterized physico-chemically through electron microscopy, BET, FTIR, XRF & XRD. However, the leaching of heavy metals from the wood fly ash could potentially pose an environmental concern. Therefore, the focus of this study is to reduce the leachability factor of wood fly ash involved in the alkaline activated process and to understand the effects of various factors (i.e. water-to-ash ratio (w/a), method of curing, type of alkaline activator and ash sieving) on the leaching process, through factorial experimental analysis. The leaching patterns of various elements such as Pb, Zn, Cr, As. Hg, Se were studied along with the contributing factors and results showed that the dominant factor was the type of alkaline activator (i.e. Wood Fly Ash versus Na2SiO3). By comparing the leaching data to Denmark's leaching criteria, the best performing GCH sample was found to be 0.3DI_p_s (0.3 represents the w/a ratio, "p" denotes that samples were precured and "s" denotes sieving).

Incineration is one of the methods in providing an efficient management of the municipal solid waste problem. At the same time, the energy released during the combustion of the waste can be harnessed for heat and generation of electricity. While there is potential for improved harnessing of electricity, the high chloride and sulphate content found in the waste limited the steam temperature to the current 400°C due to corrosion issues. Another limiting factor is the fluctuation in the gas temperature, which resulted in an unstable supply of heat to the heat exchangers. This paper briefly reviews the corrosion mechanism and the issues related to the temperature fluctuation from the combustion. This paper also discusses the current and new technologies used to overcome the corrosion attack on the ferrous surface and the temperature fluctuation.

Carbon black waste, an oil refinery waste, contains a high concentration of vanadium(V) leftover from the processing of crude oil. For the sake of environmental sustainability, it is therefore of interest to recover the vanadium as useful products instead of disposing of it. In this work, V was recovered in the form of vanadium-based metal-organic frameworks (V-MOFs) via a novel pathway by using the leaching solution of carbon black waste instead of commercially available vanadium chemicals. Two different types of V-MOFs with high levels of crystallinity and phase purity were fabricated in very high yields (98%) based on a coordination modulation method. The V-MOFs exhibited well-defined and controlled shapes such as nanofibers (length:10 μm) and nanorods (length: ∼270 nm). Furthermore, the V-MOFs showed high catalytic activities for the oxidation of benzyl alcohol to benzaldehyde, indicating the strong potential of the waste-derived V-MOFs in catalysis applications. Overall, our work offers a green synthesis pathway for the preparation of V-MOFs by using heavy metals of industrial waste as the metal source.

Accelerated carbonation has been studied as a treatment method for MSW IBA, and the main advantage is that it can shorten the treatment duration from months to days, compared to natural weathering. This study investigated the effect of accelerated carbonation on different size fractions of IBA collected from two incineration plants in Singapore. The different size fractions were ground to

This study evaluated the potential of utilising sewage sludge incineration ash as a land reclamation material. Toxicity assessment of the leachate of the ash was carried out for both terrestrial and marine organisms. Both the fruit fly Drosophila melanogaster and barnacle Amphibalanus amphitrite showed that both bottom and fly ash leached at liquid-to-solid (L/S) ratio 5 did not substantially affect viabilities. The leachate carried out at L/S 10 was compared to the European Waste Acceptance Criteria and the sewage sludge ashes could be classified as non-hazardous waste. The geotechnical properties of the sewage sludge ash were studied and compared to sand, a conventional land reclamation material, for further evaluation of its potential as a land reclamation material. It was found from direct shear test that both bottom and fly ashes displayed similar and comparable shear strength to that of typical compacted sandy soil based on the range of internal friction angle obtained. However, the consolidation profile of bottom ash was significantly different from sand, while that of fly ash was more similar to sand. Our study showed that the sewage sludge ash has the potential to be used as a land reclamation material.

This study investigated the influence of moisture content and temperature on the degree of carbonation of municipal solid waste (MSW) incineration bottom ash (IBA) from two different incineration plants in Singapore. The initial rate of carbonation was affected by the nominal moisture content used. Carbonation temperature seemed to play a part in changing the actual moisture content of IBA during carbonation, which in turn affected the degree of carbonation. Results showed that 2 h of carbonation was sufficient for the samples to reach a relatively high degree of carbonation that was close to the degree of carbonation observed after 1 week of carbonation. Both Cu and Cr leaching also showed significant reduction after only 2 h of carbonation. Therefore, the optimum moisture content and temperature were selected based on 2 h of carbonation. The optimum moisture content was 15% for both incineration plants while the optimum temperature was different for the two incineration plants, at 35 °C and 50 °C. The effect on Cu and Cr leaching from IBA after accelerated carbonation was evaluated as a function of carbonation time. Correlation coefficient, Pearson’s R, was used to determine the dominant leaching mechanism. The reduction in Cu leaching was found to be contributed by both formation of carbonate mineral and reduction of DOC leaching. On the other hand, Cr leaching seemed to be dominantly controlled by pH. Accepted version

Environmental issues are often neglected until a lapse in the care for environment, which leads to serious human health problem, would then put regulation gaps in the spotlight. Environmental regulations and standards are important as they maintain balance among competing resources and help protect human health and the environment. One important environmental standard is related to municipal solid waste (MSW). Proper MSW management is crucial for urban public health. Meanwhile, the sustainability of landfills is also of concern as increasing volumes of MSW consume finite landfill space. The incineration of MSW and the reuse of incinerated residues help alleviate the burden on landfill space. However, the reuse of MSW incinerator residues must be regulated because they may expose the environment to toxic heavy metal elements. The study of environmental standards from different countries applicable to MSW is not widely published, much less those for incinerated MSW residue reuse. This paper compares extant waste classification and reuse standards pertinent to MSW, and explores the unique recent history and policy evolution in some countries exhibiting high environmental regard and rapid changes, so that policy makers can propose new or revise current MSW standards in other countries.