Organic waste diversion legislation enacted in 10 states aims to reduce landfill methane emissions. The success of such legislation should be measured by methane emissions reduction, not just organics diversion from disposal. This will help ensure we prioritize both waste reduction and environmental protection. In October 2023, the US Environmental Protection Agency (EPA) released its estimates of potential emissions reduction from food waste diversion on a national scale in a report titled “Quantifying Methane Emissions from Landfilled Food Waste.”[1] The challenge facing landfill owners and operators today is the noted limitations of direct measurement technologies for surface-level methane concentrations, which are years away from providing accurate annual methane emissions estimates.
Landfills now use EPA’s standardized regulatory landfill gas models (LandGEM or equivalent) to report methane emissions. These tools are easy to run, but their simplicity limits them to producing emissions estimates that are approximate at best. Landfill gas models struggle to accurately estimate methane generation, making them prone to error when defining emissions from organics diverted from disposal.
Alex Stege, SCS’s National Expert on Landfill Gas Modeling, will present at the 2024 Global Waste Management Symposium. His presentation will cover the challenges and uncertainties that landfill gas models face while quantifying methane recovery, emissions, and emissions reduction. Alex is presenting for the 6th consecutive time at this conference, sharing insights from decades of experience in developing and applying landfill gas models and other waste sector GHG emissions models, including the Solid Waste Emissions Estimation Tool (SWEET), to estimate landfill methane utilization potential, methane emissions reduction, and the impacts of organics diversion.
Alex’s presentation will summarize state-level legislation targeting organic waste before zeroing in on Washington’s HB 1799. HB 1799 sets a statewide goal to reduce organic waste disposal by 75 percent from 2015 levels by 2030, which would require a decrease from about 3 million tons in 2023 to 700,000 tons by 2030. Estimates of methane emissions reduction from diverting this waste from Washington’s landfills are prepared by running SCS and Inter-governmental Panel on Climate Change (IPCC) landfill gas models to project methane generation, from which assumed rates of methane collection and oxidation are applied to calculate net emissions. Projected reductions in annual methane emissions increase from about 7,500 metric tons (Mg) in 2030 to 17,000 Mg in 2040 and 21,000 Mg in 2050. Cumulative methane emissions reduction will exceed 157,000 Mg by 2040 and 350,000 Mg by 2050.
Achieving these levels of emissions reductions will depend on efforts by the state’s municipalities to develop or access an organics collection and processing infrastructure, which will be difficult in remote regions. Estimating impacts at the scale of municipalities and landfills requires developing a schedule for reducing organic waste disposal, which is achievable, reflects site-specific historical disposal rates, and accounts for prior progress towards the diversion goal. SCS is assisting municipalities in Washington and other states to meet the requirements of organics diversion legislation. This experience informs our calculations of organics diversion’s effects on methane emissions and our forecasts of methane fuel supply for renewable natural gas projects.
Using the Solid Waste Emissions Estimation Tool (SWEET), in 2020, International Solid Waste Association’s (ISWA) Task Force on Closing Dumpsites completed a study of waste sector short-lived climate pollutants (SLCPs) and other greenhouse gas (GHG) emissions in Tyre Caza, Lebanon. SWEET model runs used data on municipal solid waste (MSW) generation, collection, disposal, and diversion under existing and potential alternative management scenarios proposed in an Integrated Waste Management Plan (IWMP) for Tyre Caza. Waste sector emissions reductions exceeding 45% of baseline levels are achievable by 2030 if all dumpsites are closed and remediated, waste burning is stopped, and a new sanitary landfill is developed with 60% methane collection and combustion. Additional emissions reduction accrues from implementing the IWMP and upgrading existing waste treatment facilities to increase waste diversion rates from current levels (22%, including informal sector recycling) to 40%. Estimates of all of Lebanon’s waste sector emissions using SWEET were developed for this mini-review article using published data on the amounts of MSW collected, disposed, and diverted, with adjustments to account for indirect GHG reductions from composting and anaerobic digestion (AD). A 50% reduction in emissions from baseline levels can be achieved by 2034 if, by 2025 diversion of collected wastes to recycling, composting, and AD facilities are increased from 14% to 28%, and all residual MSW is disposed of in sanitary landfills with 65% methane recovery.
Conclusion: SWEET allows solid waste planners to compare emissions resulting from implementing different programs and to quantify the effectiveness of available waste management options in reducing emissions of GHGs and air pollutants. Full article access is on Sage Journals.
About SWEET: SWEET was developed by the U.S. Environmental Protection Agency (EPA) under the auspices of the Global Methane Initiative and in support of the CCAC. Abt Associates and SCS Engineers supported the development of SWEET. SWEET provides estimates for the full suite of GHG and air pollutant emissions in the waste sector, including methane, black carbon, CO2, nitrogen oxides, sulfur oxides, particulates, and organic carbon (CCAC, 2018). Emissions estimates are provided for the following sources: (1) waste collection and transportation, (2) open burning of waste, (3) landfills and open dumps, (4) organic waste management facilities (composting and anaerobic digesters), (5) waste-to-energy facilities and (6) waste handling equipment. Note that emissions from fuel and waste combustion are the only CO2 emissions included in SWEET’s calculations, which exclude biogenic CO2 emissions from waste disposal sites. Published reports by the US EPA (e.g., EPA, 1998, 2015), Intergovernmental Panel on Climate Change (e.g., IPCC, 2006), and other sources (e.g., SCS Engineers, 2007, 2009; United Nations Framework Convention on Climate Change (UNFCCC), 2004) were used to develop calculation methods and emissions factors for the waste sector emissions sources. CO2e conversions use a 100-year Global Warming Potential (GWP). The black carbon GWP is 900 (Bond et al., 2013).
The International Solid Waste Association – ISWA, published a comprehensive report completed by SCS Engineers for ISWA under the Climate and Clean Air – CCAC, on reducing Short-Lived Climate Pollutants. A CCAC Solid Waste Emissions Estimation Tool – called SWEET, was used to investigate waste sector emissions of short-lived climate pollutants -termed SLCPs, and other greenhouse gases – GHGs.
Data was collected where multiple waste management scenarios in Tyre Caza, Lebanon. Publications on waste management in Lebanon, including an Integrated Waste Management Plan and Updated Master Plan for the closure and rehabilitation of uncontrolled dumpsites throughout Lebanon, provided data that were used in this study along with updated information provided by Lebanon’s Office of the Minister of State for Administrative Reform.
Different management options for reducing emissions of SLCPs over the short- and medium-term. Comparing emissions reductions achieved by implementing a range of programs over a meaningful time horizon provide greater clarity of vision to see which strategies produce the most climate benefits and are worth a high level of effort and the commitment of resources to achieve.
SWEET is designed to be used by solid waste planning professionals worldwide. It allows some degree of flexibility in selecting key inputs, which gives it greater control and ability to reflect local conditions but adds a level of complexity that may be difficult for some users to navigate. While offering users control of some model assumptions, SWEET includes many calculations and assumptions that are necessarily fixed and can produce unintended results given the model’s limitations. In addition, the assignment of input data that appropriately reflects actual and expected conditions can be challenging, especially when there is a large amount of information to be considered.
The reports on solid waste management in Lebanon and Tyre Caza following the waste management crisis provided multiple sources of data that required evaluation and processing before being used in SWEET.
Click here to read, share, and download the report, ESTIMATION OF WASTE SECTOR GREENHOUSE GAS EMISSIONS IN TYRE CAZA, LEBANON, USING THE SOLID WASTE EMISSIONS ESTIMATION TOOL (SWEET)
ISWA and CCAC will be sponsoring a training workshop on the use of SWEET in the future. For advice and guidance using SWEET contact Alex Stege, SCS Engineers Senior Project Advisor, and Expert on Landfill Gas Modeling.
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