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Description

Life cycle assessment (LCA) can be a valuable tool to evaluate the trade-offs associated with different products and processes. It has been increasingly used to evaluate the environmental impact of solid waste management systems; however, the availability of high-quality studies applicable to the USA are limited. In addition to providing a basic overview of LCA, this report provides information on the greenhouse gas (GHG) emissions and fossil energy use associated with curbside municipal solid waste (MSW) management scenarios including landfilling, recycling, and yard and food waste composting. 

Under 4 different collection scenarios, a combination of landfill with gas to energy combined with recycling contributed to the greatest reduction in GHG emissions and energy demand assuming a closed-loop (e.g., bottle to bottle) recycling system. However, the end use of the recyclables are very important and sustainability benefits can be highly variable and even erased under some non-closed loop end use scenarios. For recyclables with marginal or highly variable emissions or energy savings, transport distance to the secondary process can become an important consideration. Emissions and energy savings were found to be different depending on the recyclable being evaluated (e.g. paper, plastic), which suggests that focusing on specific materials that offer the greatest emission reduction when recycled may leader to great overall savings. 

The comparison of these management scenarios is particularly important considering national, state, and local programs commonly use landfill diversion as a metric of sustainable materials management (SMM). A key observation from this study suggests that increased landfill diversion is not directly correlated with lower GHG emissions. Similarly, curbside recycling may not provide emissions or energy savings in all situations. GHG and energy benefits highly depend on the type of material being recovered and the assumption that materials are being reused in a closed-loop remanufacturing process. 

GHG impacts associated with waste management activities are influenced by a variety of stakeholders. In scenarios with landfill diversion options (i.e., recycling and composting) the majority (66-70%) of GHG emissions can be attributed to product manufactures and consumer behavior. Of the activities the waste industry can control, landfilling has the largest impact on GHG emissions, and efforts to improve gas capture rates provide the highest GHG benefits. Collection activities are the second largest contributor and the results of this study confirm that companies can continue to reduce emissions by transitioning waste collection vehicle (WCV) fleets to lower-carbon alternatives. 

The study results suggest that while composting offers benefits, other endpoints (e.g. backyard composting, anaerobic digestion (AD), bioreactor landfilling) may offer greater reduction in GHG emissions. Organics diversion activities can have other positive local/regional environmental impacts which should be considered in conjunction with any potential reduction in GHG emissions or energy demand. Overall, landfilling, recycling, and composting are important components of the waste management system, but maximizing recovery and closed-loop remanufacturing of materials through recycling has the greatest potential for reducing GHG emissions and energy demand associated with curbside material recovery. 

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