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• The potential of implementing management strategies in reducing waste-related greenhouse gas emissions was evaluated. • Three kinds of waste – food, sewage, and plastic were analysed was evaluated using life cycle assessment. • By diverting plastic waste away from incineration, the reduction in GHG emission is 61%. • By diverting food waste away from incineration, GHG emission amount is reduced to 54.69 % of the emission from BAU method. • The GHG emission of sewage sludge and food waste co-digestion reduces the current emission (incineration) by 64.3%. The potential of implementing waste recovery strategies on three kinds of waste – food, sewage, and plastic – in reducing waste-related greenhouse gas emissions in Singapore was evaluated using life cycle assessment. It was found that the proposed strategies are capable of reducing 1,087.80 kgCO 2 -eq per tonne of plastic waste, 53.00 kgCO 2 -eq per tonne of food waste, and 43.86 kgCO 2 -eq for the combination of one tonne of sewage waste and one tonne of food waste. When uncertainties of the three waste streams were considered in sensitivity analysis and projections of waste quantities to 2025 were performed up to a 95% confidence level, it was found that the proposed strategies could reduce about 37.13% of the GHG emissions from the business-as-usual disposal waste technology (that is, incineration). This corresponds to an average reduction of 0.53 million tonnes CO 2 -eq per year, which is equivalent to the annual GHG emissions from electricity consumptions of 256,322 households in Singapore. Graphical Abstract [Display omitted]. [ABSTRACT FROM AUTHOR]

• A Stirling engine based gasification CCHP system with food waste was introduced. • The optimal equivalence ratio was determined based on the cold gas efficiency. • Levelized total cost and primary energy saving ratio were used to optimize systems. • The monthly energetic, economic, and environmental analysis was conducted. • Sensitivity analyses of efficiencies, costs and CO 2 emission were carried out. Due to the tar contamination caused by the gasification process of biomass, the internal combustion engine (ICE) based gasification cogeneration systems require complicated gas cleaning devices to purify producer gas. In this paper, a Stirling engine based gasification combined cooling, heat and power (CCHP) system was introduced, which has the capability of mitigating tar condensation and contamination. The gasification CCHP system, including the gasification system, the Stirling engine system, and the absorption chiller system, can provide electricity, heat and cooling for a commercial building. The effects of the equivalence ratio on syngas composition and cold gas efficiency of the gasification process were analyzed herein. The optimal systems in Singapore and Shanghai can save respectively 75.9% and 70.5% levelized total cost compared to a conventional reference system. The Stirling engine based CCHP system had advantages over the ICE systems on overall consideration of the levelized total cost and the primary energy saving ratio. The monthly energetic, economic and environmental performance of the CCHP systems was evaluated under different modes and the above two systems' primary energy saving ratios, operation cost reduction ratios and CO 2 equivalent reduction ratios respectively reached 0.886, 0.462 and 0.701 in Singapore and 0.908, 0.535 and 0.710 in Shanghai in annual operation. The outcomes of this paper contribute to the design and deployment of such a CCHP system, and the developed models and analysis framework can be extended to different climate areas. [ABSTRACT FROM AUTHOR]

• Singapore's first 28-kW e high-flux solar simulator was designed and characterized. • Precise and flexible adjustment frameworks were employed. • The electricity-to-target transfer efficiency in a Ø60-mm target area is 29.6%. • A peak radiative flux of 7740 kW m−2 was measured. Singapore's first multi-source high-flux solar simulator (HFSS) that comprises an array of seven 4-kW e xenon short-arc lamps close-coupled with ellipsoidal reflectors is designed, constructed, and characterized. An indirect mapping system that consists of a water-cooled Lambertian target, a CMOS camera, and a heat-flux gauge is adopted herein to experimentally characterize the performance of the developed HFSS. A calibration constant of 192.8 ± 9.6 kW m−2 (GS µs−1)–1 is determined and used to transform the raw-flux maps with grayscale values to the absolute-flux maps. Utilizing a series of flexible and precise adjusters, the variability of ± 1 mm in the x- and y- directions of the peak flux points of the radiation modules is measured. A peak flux of 7740 kW m−2 is measured for the sum of all 7 radiation modules. Average radiative fluxes of 4191 kW m−2 and 2933 kW m−2 can be observed from circular target areas of Ø40 mm and Ø60 mm, respectively, associated with promising electricity-to-target transfer efficiencies of 18.8% and 29.6%. A Monte Carlo ray-tracing (MCRT) model is calibrated by the experimental data. Based on the minimum root-mean-standard deviation between the measured and simulated results of the radiative power on the target, the optimal parameters of the MCRT model include the arc radius of 3.4 mm and the reflector surface error of 1.1 mrad. [ABSTRACT FROM AUTHOR]

A novel biomass gasification-based combined cooling, heat and power (CCHP) system, which is composed of a gas-fueled internal combustion engine, variable-effect LiBr-H 2 O absorption cooling, and dehumidification air-conditioning with desiccant coated heat exchangers, was introduced. The temperature and humidity independent strategy was applied in the gasification-based CCHP system to enhance cooling production, in which the variable-effect absorption chiller and desiccant dehumidification air-conditioning were driven by the exhaust heat and jacket heat of the gas engine based on energy cascade, respectively. The operation strategy of the system followed the electric load. Validated by experimental data, a zero-dimensional code of the gasifier with Gibbs free energy minimization, an artificial neural network model of the variable-effect absorption chiller, and a 1-D dynamic model of the dehumidification air-conditioning, were built with reasonable deviations. The results of energetic, economic, and environmental (3E) analyses for the proposed gasification-based CCHP systems that were applied in two different buildings indicate that woody chips are the most favorable feedstock under the climate of Singapore. The total performance is more sensitive to the feedstock cost than to the natural gas cost. This work enables to contribute valuable data to the practical application of the biomass gasification-based CCHP system in Singapore's building sector. • The variable-effect absorption cooling and desiccant dehumidification were studied. • 3E benefits from redwood, woody chips, and sewage sludge schemes were investigated. • Total performance is more sensitive to feedstock cost than to natural gas cost. • Compared to redwood and sludge, woody chips is the most favorable in Singapore. [ABSTRACT FROM AUTHOR]

The auto-regressive distributed lag (ARDL) bound testing approach was used to study the relationships between the monthly household electricity consumption and outdoor PM 2.5 concentration with the consideration of ambient temperature and the number of rainy days for Singapore and Shanghai. It is shown that there are significant long-run relationships between the household electricity consumption and the regressors for both Singapore and Shanghai. For Singapore, a 20% increase in the PM 2.5 concentration of a single month is in the long-run significantly related to a 0.8% increase in the household electricity consumption. This corresponds to an electricity overconsumption of 5.0 GWh, a total of 0.7–1.0 million USD in electricity cost, and 2.1 kilotons of CO 2 emission associated with electricity generation. For Shanghai, a 20% decrease in the PM 2.5 concentration of a single month is in the long-run significantly related to a 2.2% decrease in the household electricity consumption. This corresponds to a 35.0 GWh decrease in the overall household electricity consumption, 1.6–5.1 million USD decrease in electricity cost, and 17.5 kilotons of CO 2 emission. The results suggest that the cost of electricity consumption should be included in the economic cost analysis of PM 2.5 pollution in the future. A 1 °C increase in the monthly temperature is in the long-run significantly related to a 13.6% increase in the monthly electricity consumption for Singapore, while a 30 degree days increase in heating & cooling days ( HCDD ) is in the long-run significantly related to a 24.9% increase in the monthly electricity consumption for Shanghai. A 5-day increase in the number of rainy days per month is in the long-run significantly related to a 3.0% and 5.8% increase in the monthly electricity consumption for Singapore and Shanghai, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • A municipal solid waste to energy/resources system was proposed. • The performances of the gasification and dehumidification system were analyzed. • The performance decline of the desiccant coated heat exchanger was evaluated. • Mechanical tests of char-mortar mixtures were conducted. Energy consumption and waste management are two significant challenges for human societies. To realize zero waste management, a pilot-scale demonstration of the conversion of municipal solid waste to energy/resource, which is comprised of a gasification system and a dehumidification air-conditioning to produce heat, cooling, and construction-used char, is investigated and analyzed. The waste heat (60 °C hot water) from a gasification system is applied to drive a dehumidification system for cooling, while the char from the gasification is added to the construction material. The effect of cycle time and air flow rate on the performance of the dehumidification system is also analyzed. The waste to energy efficiency of 57.2%, the maximum average moisture removal of 11.6 g/kg DA , and thermal coefficient of performance of 0.76 are obtained under the climate conditions of 34 °C, 67.5% relative humidity in Singapore. Through comparison between the brand new and used desiccant coated heat exchanger, it is noted that there is a 29.37% decrease of average moisture removal corresponding with a 17.1% loss of thermal coefficient of performance. A 14.6% compressive strength increment after seven days of curing age and 10.3% of compressive strength increment after 28 days are investigated by studying the mechanical behavior of a mortar containing char. [ABSTRACT FROM AUTHOR]

Despite the potential of poultry manure as a sustainable waste stream, poultry manure is unsatisfactorily utilized due to the lack of public confidence in both food safety and environmental concerns. In this paper, the energy, environmental and microbial risk assessments of an industrial-scale chicken manure gasification plant in Singapore are demonstrated to overcome the barriers of poultry manure utilization and standardize the management practice. The gasification products and performances are analyzed and optimized based on a numerical chemical reaction kinetics model. The life-cycle assessment results show that the gasification-based treatment has less greenhouse gas emissions than direct land application and anaerobic digestion approaches. Finally, the quantitative microbial risk assessment shows that all the potential pathogenic hazards in chicken manure can be removed through the gasification process, which proves the safety of chicken manure biochar for further agricultural applications and shows the potential infection risk of direct land application. [Display omitted] • An industrial-level chicken manure gasification plant in Singapore is demonstrated. • Gasification is benchmarked with direct land application and anaerobic digestion. • Energy, environmental and microbial risk were studied for chicken manure solutions. • Chicken manure gasification reduced GHG emissions and risks to public health. [ABSTRACT FROM AUTHOR]

• A clapboard-type internally circulating fluidized-bed solar reactor was introduced. • The gas flow rate had a significant effect on the particle circulating rate. • Solar-to-thermal conversion efficiencies of SiC, alumina, and sand were reported. • The bed mass had an apparent effect on the solar-to-thermal conversion efficiency. • SiC presented the highest solar-to-thermal conversion efficiency of 10.7 ± 0.4%. Fluidized-bed based solar reactors for the gasification of biomass have been widely recognized as a promising approach to produce high-quality syngas due to the merits, e.g. continuous operation and superior heat and mass transport. In this work, a novel high-temperature solar reactor with a clapboard-type internally circulating configuration that can efficiently mitigate the overheating of the bed wall affected by non-uniform solar radiation, is designed, constructed, and experimentally investigated under Singapore's first 28 kW e high-flux solar simulator. To investigate the flow dynamics in the high-temperature solar reactor, a transient 3D computational fluid dynamics multi-phase model is developed accordingly and validated by the experimental data. The simulated results can well clarify the flow and thermal behaviours in experiments. The effects of the gas flow rate and bed mass on the thermal performances of different Group-B particle materials are studied through experiments and simulation. The results indicate that increasing the bed mass in the solar reactor is capable of mitigating the overheating of the absorber surface caused by hot spots. The gas flow rate is dependent on the particle thermo-physical properties and shape as well as the clapboard geometric parameters. The highest solar-to-thermal conversion efficiency (defined as the ratio of the accumulated sensible heat of the particles to the solar power input) of 10.7 ± 0.4% is achieved by SiC due to its superior thermal conductivity. [ABSTRACT FROM AUTHOR]

Organic waste, the predominant component of global solid waste, has never been higher, resulting in increased landfilling, incineration, and open dumping that releases greenhouse gases and toxins that contribute to global warming and environmental pollution. The need to create and adopt sustainable closed-loop systems for waste reduction and valorization is critical. Using organic waste as a feedstock, gasification and pyrolysis systems can produce biooil, syngas, and thermal energy, while reducing waste mass by as much as 85-95% through conversion into biochar, a valuable byproduct with myriad uses from soil conditioning to bioremediation and carbon sequestration. Here, we present a novel case study detailing the circular economy of gasification biochar in Singapore's Gardens by the Bay. Biochar produced from horticultural waste within the Gardens was tested as a partial peat moss substitute in growing lettuce, pak choi, and pansy, and found to be a viable substitute for peat moss. At low percentages of 20-30% gasification biochar, fresh weight yields for lettuce and pak choi were comparable to or exceeded those of plants grown in pure peat moss. The biochar was also analyzed as a potential additive to concrete, with a 2% biochar mortar compound found to be of suitable strength for non-structural functions, such as sidewalks, ditches, and other civil applications. These results demonstrate the global potential of circular economies based on local biochar creation and on-site use through the valorization of horticultural waste via gasification, generating clean, renewable heat or electricity, and producing a carbon-neutral to -negative byproduct in the form of biochar. They also indicate the potential of scaled-up pyrolysis or gasification systems for a circular economy in waste management., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Biochar, produced as a by-product of pyrolysis/gasification of waste biomass, shows great potential to reduce the environment impact, address the climate change issue, and establish a circular economy model. Despite the promising outlook, the research on the benefits of biochar remains highly debated. This has been attributed to the heterogeneity of biochar itself, with its inherent physical, chemical and biological properties highly influenced by production variables such as feedstock types and treating conditions. Hence, to enable meaningful comparison of results, establishment of an agreed international standard to govern the production of biochar for specific uses is necessary. In this study, we analyzed four key uses of biochar: 1) in agriculture and horticulture, 2) as construction material, 3) as activated carbon, and 4) in anaerobic digestion. Then the guidelines for the properties of biochar, especially for the concentrations of toxic heavy metals, for its environmental friendly application were proposed in the context of Singapore. The international status of the biochar industry code of practice, feedback from Singapore local industry and government agencies, as well as future perspectives for the biochar industry were explained., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The compositions of food wastes and their co-gasification producer gas were compared with the existing data of sewage sludge. Results showed that food wastes are more favorable than sewage sludge for co-gasification based on residue generation and energy output. Two decentralized gasification-based schemes were proposed to dispose of the sewage sludge and food wastes in Singapore. Monte Carlo simulation-based cost-benefit analysis was conducted to compare the proposed schemes with the existing incineration-based scheme. It was found that the gasification-based schemes are financially superior to the incineration-based scheme based on the data of net present value (NPV), benefit-cost ratio (BCR), and internal rate of return (IRR). Sensitivity analysis was conducted to suggest effective measures to improve the economics of the schemes., (Copyright © 2016 Elsevier Ltd. All rights reserved.)