Improving urban ecosystem holistic sustainability of municipal solid waste-to-energy strategy using extended exergy...

Waste-to-energy technologies play a crucial role in integrated waste management strategies to reduce waste mass and volume, disinfect the waste, and recover energy; different technologies have advantages and disadvantages in treating municipal solid waste under urban conditions. This paper applies the extended exergy accounting method to develop an analytical framework to identify the optimal waste-to-energy strategy from an urban ecosystem holistic sustainability perspective. In the analytical framework, urban ecosystem costs and revenues are formulated as a multi-criteria cost-benefit quantitative model. The urban ecosystem cost is divided into five categories, and the urban ecosystem revenues consist of direct and indirect parts. The direct part is the chemical exergy of the waste-to-energy plants produced product, and the indirect part includes equivalent exergy content of power generation substitution, human health risk elimination, disamenity impact removal and environmental degradation avoidance. Proposing an indicator system to evaluate the waste-to-energy strategy impact on the sustainability of the urban ecosystems and social, economic and environmental sub-ecosystem. Detailed analysis of food waste treatment scenarios of a food center in Singapore was done as a case study to illustrate this analytical framework. Base scenario is current practice that food waste disposal in incineration plant. Anaerobic digestion and gasification are proposed as potential technological solutions for on-site food waste treatment in scenario I and II respectively. In different scenarios, the urban ecosystem costs are estimated to be 71,536.01, 61,854.87 and 74,190.34MJ/year respectively, and the urban ecosystem revenues are estimated to be 135,312.66, 405,442.53 and 298,426.81MJ/year respectively. We show that the scenario where food waste is treated by anaerobic digestion outperforms both the base scenario and scenario II in terms of urban ecosystem costs and revenues, technical energy conversion efficiency, contribution to urban ecosystem holistic sustainability, and natural, social, and economic subsystems improvement, making it the optimal municipal solid waste-to-energy strategy choice.