Proactive Development of Optimal Solid Waste Management Strategies in Response to Future Waste, Energy, and Greenhouse Gas Policies

The future of sustainable solid waste management (SWM) will be shaped by changes to waste composition and the broader energy system including potential greenhouse gas (GHG) policies. For example, the electricity fuel mix has... [ view full abstract ]

The future of sustainable solid waste management (SWM) will be shaped by changes to waste composition and the broader energy system including potential greenhouse gas (GHG) policies. For example, the electricity fuel mix has been changing rapidly and this will affect the cost and emissions associated with electricity use as well as the life-cycle costs and benefits of energy recovery at SWM facilities. Collection of waste is typically the largest contributor to cost and fossil energy use in SWM systems. Many waste management companies have switched to hybrid and natural gas vehicles to reduce fuel costs, which could significantly affect the costs and environmental impacts associated with SWM activities, since the most commonly used diversion technologies typically require additional collection and transport of separated waste fractions. SWM diversion policies could provide additional incentives to recover energy from solid waste, and changing waste composition will impact beneficial energy generation from SWM activities (e.g., food waste and paper behave differently in anaerobic digestion [AD] and waste-to-energy [WTE] combustion). SWM planning models should consider how changes in the energy system and waste composition will affect future solid waste management.

It is critical to analyze the interrelated effects of energy and GHG policy with SWM policies to ensure that they work together to cost-effectively reduce environmental impacts. This study used the Solid Waste Optimization Life-cycle Framework (SWOLF) to explore how potential changes to the energy system and GHG policy affect SWM. SWOLF was combined with The Integrated MARKAL-EFOM System (TIMES) energy system modeling results to draw insights into how the energy system and GHG mitigation policies affect SWM by analyzing the SWM system of a hypothetical suburban U.S. city for 30 years into the future.

Two energy scenarios were developed: 1) A reference scenario based on the Annual Energy Outlook transportation and electricity cost and emissions projections (Reference) and 2) a scenario using an increasing renewable portfolio standard and CO₂ cap-and-trade limit (CO₂). These scenarios were combined with two SWM policy scenarios: 1) a base scenario (Base) and 2) a scenario with an increasing diversion target and decreasing GHG limit (Diversion/GHG). All scenarios minimized costs.

The optimal mass throughputs to the different SWM facilities for both Base cases are essentially the same because the changes in the energy system do not change the minimum cost processes. The energy system and GHG policy do affect the mass throughputs in the Diversion/GHG cases. The primary difference is that the CO₂-Diversion/GHG case uses WTE in the final two cases to meet the GHG and diversion targets. AD alone is unable to achieve the required GHG reductions because of the decrease in electricity GHG intensity. The results indicate that while reducing GHG emissions from the energy system will decrease nationwide GHG emissions, they will also affect the benefits associated with material and energy recovery from SWM activities, which will in turn affect optimal process choices. The specific changes in cost and GHG emissions are dependent on the relative changes to electricity and transportation cost and GHG intensity.