Life Cycle Comparison of Two Options for MSW Management in Puerto Rico: Thermal Treatment vs. Modern Landfilling

Abstract

The management of municipal solid wastes (MSW) in Puerto Rico is becoming increasingly challenging. In recent years, several of the older landfills have closed due to lack of compliance with federal landfill requirements. Puerto Rico is an island community and there is limited space for construction of new landfills. Furthermore, Puerto Rico residents generate more waste per capita than people living on the continental US. Thermal treatment, or waste to energy (WTE) technologies are therefore a promising option for MSW management. It is critical to consider environmental impacts when making decisions related to MSW management. In this paper we quantify and compare the environmental implications of thermal treatment of MSW with modern landfilling for Puerto Rico from a life cycle perspective. The Caguas municipality is currently considering developing a thermal treatment plant. We compare this to an expansion of a landfill site in the Humacao municipality, which currently receives waste from Caguas. The scope of our analysis includes a broad suite of activities associated with management of MSW. We include: (i) the transportation of MSW; (ii) the impacts of managing waste (e.g., landfill gas emissions and potential aqueous run-off with landfills; air emissions of metals, dioxins and greenhouse gases) and (iii) the implications of energy and materials offsets from the waste management process (e.g., conversion of landfill gas to electricity, electricity produced in thermal treatment, and materials recovered from thermal treatment ash). We developed life cycle inventory models for different waste management processes, incorporating information from a wide range of sources — including peer reviewed life cycle inventory databases, the body of literature on environmental impact of waste management, and site-specific factors for Puerto Rico (e.g. waste composition, rainfall patterns, electricity mix). We managed uncertainty in data and models by constructing different scenarios for both technologies based on realistic ranges of emission factors. The results show that thermal treatment of the unrecyclable part of the waste stream is the preferred option for waste management when compared to modern landfilling. Furthermore, Eco-indicator 99 method is used to investigate the human health, ecosystem quality and resource use impact categories.