Air Emissions from Municipal Solid Waste Management: Comparing Landfilling, Incineration, and Composting

Abstract

Background: Municipal solid waste management is a relevant component of climate and air quality policy, yet published life cycle assessments report inconsistent conclusions on whether sanitary landfilling, waste-to-energy incineration, composting, or anaerobic digestion yields the lowest greenhouse gas and co-pollutant impacts because results depend strongly on methodological choices and local context. Objective: To synthesize and critically evaluate how key life cycle assessment assumptions and boundary decisions influence reported emissions across major waste management pathways, with primary emphasis on the United States and selected comparison to European Union policy frameworks. Methods: Peer-reviewed life cycle assessment studies and supporting technical and regulatory sources were reviewed and compared, focusing on functional unit definition, system boundaries, time horizon, energy substitution and crediting methods, and treatment of methane, nitrous oxide, and air pollutant controls; drivers of variability were identified through structured cross study comparison and sensitivity-focused interpretation. Results: Reported pathway rankings vary primarily with landfill gas collection and utilization assumptions, the carbon intensity of displaced electricity or heat for waste-to-energy systems, and the representation of biological process emissions across active and curing stages; harmonized comparisons reduce variability but do not yield a single consistently superior pathway across all plausible settings. Conclusions: Comparative conclusions are context-dependent and policy-relevant interpretation requires transparent reporting and sensitivity analysis for capturing efficiency, substitution factors, and biological emission controls, along with clear alignment between modeled scenarios and real-world operating conditions.

1. Introduction

Municipal solid waste management is a key element of climate and air quality policy. The waste sector contributes 12 to 18% of anthropogenic methane emissions in the United States, ranking third after agriculture and fossil fuel systems [1,2]. The three primary management pathways are sanitary landfilling, waste-to-energy incineration, and biological treatment through composting or anaerobic digestion. Each pathway results in distinct greenhouse and air pollutant outcomes that depend on process control, energy substitution, and regulatory requirements [3,4,5]. This review evaluates how methodological choices in life cycle assessment influence reported emissions from these pathways and how such variability shapes policy interpretation.

Although these systems are mature, the literature shows inconsistent results on which option produces the lowest greenhouse gas and pollutant emissions. Several life cycle assessments identify waste-to-energy systems as favorable when the displaced electricity or heat originates from fossil intensive grids, reporting net benefits of up to 600 kg CO₂ eq t⁻¹ waste [6,7,8]. Other studies conclude that modern landfills with high gas collection efficiency and energy recovery can achieve comparable or even lower climate impact, particularly when long-term carbon storage in buried waste is considered [9,10]. Composting and anaerobic digestion represent the widest range of outcomes, from strong climate benefits to small net burdens, depending on oxygen availability, nitrogen content, and the accounting of fertilizer substitution credits [11,12]. Poor aeration or moisture control can increase methane emissions by an order of magnitude, while excess nitrogen favors nitrous oxide formation. These divergent results illustrate that reported performance depends strongly on system assumptions and operating conditions.

Meta reviews attribute these divergent findings to differences in system boundaries, allocation rules, and data treatment rather than measurement error. Laurent et al. [3] examined more than two hundred waste system life cycle assessments and demonstrated that methodological choices, particularly energy substitution and biogenic carbon accounting, dominate variability. Cherubini et al. [13] and Lou and Nair [14] reported that treating biogenic carbon dioxide as neutral or non-neutral can alter global warming potential by approximately ±300 kg CO₂ eq t⁻¹ waste. When assumptions are harmonized, the numerical ranges among technologies narrow considerably, allowing clearer comparison of landfilling, waste-to-energy, and composting/anaerobic digestion outcomes [4].

Results summarized by Han et al. [15] and related comparative assessments show that these ranges are highly sensitive to three interacting conditions: the share of carbon fossil in the waste, the efficiency of landfill gas management, and the carbon intensity of the displaced electricity. High capture rates and low carbon grids tend to narrow or reverse the apparent advantage of waste-to-energy relative to landfilling, while fossil-rich waste streams combined with carbon-intensive grids favor incineration. This interaction provides a structured explanation for why nominally similar systems produce different greenhouse gas rankings across studies. Together, these findings reinforce that methodological choices and regional operating conditions jointly determine comparative outcomes.

Policy and technological context have also evolved. The United States Environmental Protection Agency released the 2024 Interim Guidance on the Destruction and Disposal of Per and Polyfluoroalkyl Substances (PFAS), which identifies thermal treatment, landfilling, and underground injection as potential disposal pathways and acknowledges that none ensures complete destruction of PFAS [16]. This guidance challenges the prior assumption that incineration is always the safest end-of-life method for PFAS-bearing materials. In contrast, the California Air Resources Board validated a carbon-negative landfill gas pathway under the Low Carbon Fuel Standard in 2025 using the American Biogas Council carbon accounting tool. That pathway achieved a life cycle intensity of approximately −101 g CO₂ eq MJ⁻¹, demonstrating that optimized gas collection and renewable fuel use can produce a regulatory carbon-negative outcome [17].

At the same time, biological treatment has advanced in practice and measurement. Full scale research at covered aerated static-pile composting facilities in California quantified emissions of methane, nitrous oxide, ammonia, hydrogen sulfide, and non-methane volatile organic compounds. Results showed that the active aeration stage contributes most of the greenhouse gas output while curing piles continue to release measurable residual emissions. These data improve emission factors and reduce the gap between laboratory and field estimates [18].

Given these scientific disagreements and the new regulatory considerations, a comprehensive reassessment is needed. This review compiles the recent empirical and life cycle assessment evidence to evaluate which of the three major management methods provides the lowest overall atmospheric impact under current United States policy and operational conditions. The analysis compares greenhouse gas outcomes together with co-emitted pollutants and interprets them in the context of air quality regulations including Clean Air Act Subparts XXX, AAAA, and Section 129 and the California Senate Bill 1383 organics diversion mandate. The goal is to determine under what conditions each pathway performs favorably and to identify the research gaps that prevent consistent policy guidance.

2. Materials and Methods

2.1. Analytical Basis

Life cycle assessment (LCA) remains the accepted approach for quantifying cradle-to-grave environmental burdens of municipal solid waste management. The functional unit adopted here is one metric tonne of waste, consistent with De Feo and Malvano [19] and Villanueva and Wenzel [20]. Impacts are expressed as global warming potential in kg CO₂ eq t⁻¹. The framework follows ISO 14040 and 14044 principles and aligns with the harmonization strategies outlined by Christensen et al. [4], Astrup et al. [8], and Doka [21]. Energy and material substitution credits are applied using marginal grid factors from Beylot et al. [6] and Bueno et al. [7], with grid carbon intensities ranging between 0.014 and 0.222 kg CO₂ eq MJ⁻¹, depending on the regional electricity generation mix.

Boundaries are harmonized to include collection, transport, treatment, energy recovery, and residue management. For landfilling, the model covers placement, anaerobic degradation, gas capture, utilization or flaring, and final cover maintenance. For waste-to-energy (WtE), it includes combustion, energy recovery, pollution control, and ash handling.

Composting and anaerobic digestion (AD) include active aeration or digestion, curing, and land application of stabilized material. Construction and decommissioning are excluded because their contribution is typically <5% of total GHG burden.

2.2. Key Methodological Drivers and Harmonization Approach

Four drivers dominate inter-study variability:

• Gas Capture Efficiency in Landfills: Reported recovery spans 40–85%. Every 10% increase reduces net CH₄ emissions by ≈100 kg CO₂ eq t⁻¹ MSW [10,22]. Below 50% capture, landfilling becomes the most climate-intensive option [9].
• Energy Substitution in WtE: Climate benefit scales with displaced grid intensity up to 700 kg CO₂ eq t⁻¹ MSW avoided in coal-based grids and approaching neutral outcomes in hydro- or nuclear-based grids [6,7].
• Treatment of Biogenic Carbon: Different conventions regarding biogenic CO₂ neutrality shift calculated GWP by 200–300 kg CO₂ eq t⁻¹ MSW [13,14].
• Process-Gas Control in Composting and AD: Nordahl et al. [12] observed ten-fold CH₄ increases under poor aeration, while N-rich feedstocks elevate N₂O release. These findings are consistent with field data from Yolo and Napa hybrid composting facilities [18] showing normalized operational carbon intensities of 0.42–0.55 Mg CO₂ eq t⁻¹ dry waste, intermediate between pure aerobic composting and MSW landfills.

Anshassi et al. [10] synthesized these methodological differences and showed quantitatively that adjustments to landfill gas capture efficiency, displaced grid intensity, and biogenic carbon assumptions can shift the relative ranking of landfilling and incineration by 700 kg CO₂ eq t⁻¹. Their sensitivity analysis confirms that many apparent disagreements in the literature are driven by these parameter choices rather than by conflicting emission measurements.

Applying the harmonization protocol of Christensen et al. [4] and Doka [21], landfills are classified by capture efficiency (40, 60, 85%), WtE systems by configuration (combined heat and power or power-only), and composting/AD by inclusion of curing and fertilizer-substitution credit. Representative outcome ranges are presented in

Table 1. Comparative greenhouse gas ranges and principal drivers.

Process	Functional Unit	Boundary Elements	Reported GWP Range (kg CO2 eq t−1 MSW)	Key Driver	Representative Sources
Landfilling	1 t MSW	Collection → gas capture/utilization	+300 to +800	Capture efficiency	[10,22]
WtE (CHP)	1 t MSW	Combustion → energy recovery → ash	–200 to +600	Grid carbon factor	[6,7]
Composting/AD	1 t organics	Aeration → curing → soil use	–900 to +300	CH4 and N2O control	[11,12]

.

2.3. Uncertainties and Scope Limitations

Even within a harmonized structure, uncertainty persists due to waste composition diversity, site design, and climatic variations. Ning et al. [23] confirmed that climate-change indicators are comparatively stable, while toxicity and photochemical-oxidation metrics remain inconsistent across databases. Consequently, this review confines quantitative analysis to GHG outcomes and treats pollutant emissions qualitatively. Recent facility-scale studies [12,18] underscore that unreported biogenic CO₂ or N₂O sources can bias inventories by 30% or more. These discrepancies highlight the need for unified operational reporting within EPA and CARB methodologies.

3. Policy and Regulatory Framework

3.1. Global and Regional Context

The regulation of solid waste management has evolved from simple disposal control toward integrated environmental policy that incorporates greenhouse gas mitigation and resource recovery. The United Nations Sustainable Development Goals, particularly Target 12.5, call for the substantial reduction of waste generation through prevention, reduction, recycling, and reuse. The Paris Agreement reinforces this framework by requiring national greenhouse gas inventories that include methane and ${\mathrm{C}\mathrm{O}}_2$ emissions from the waste sector [24]. These international initiatives have guided the design of U.S. and European regulatory systems that emphasize emission limits, energy efficiency, and circular economy integration.

3.2. United States Regulatory Framework

3.2.1. Landfills

Under the Clean Air Act, municipal solid waste landfills are regulated by New Source Performance Standards (NSPS) in 40 CFR Part 60 Subparts XXX and Cf. The rules establish design-capacity thresholds for mandatory gas collection systems and specify a destruction efficiency of 98% for landfill gas flares. Compliance requires quarterly surface emission monitoring, monthly wellhead checks, and corrective action when methane concentrations exceed 500 ppm [25]. The Landfill Methane Outreach Program supports voluntary capture projects that achieve about 70% collection efficiency nationally [26]. The National Emission Standards for Hazardous Air Pollutants (NESHAP Subpart AAAA) further regulate non-methane organic compounds and hazardous air pollutants, ensuring an ample margin of safety to protect public health [25].

State programs such as the Methane Reduction Strategy developed by the California Air Resources Board require 40% emission reductions below 2013 levels by 2030, integrating landfill and organics diversion mandates [27].

3.2.2. Incineration and Waste-to-Energy

Section 129 of the Clean Air Act governs solid waste combustion units. Large municipal waste combustors and small municipal waste combustors must achieve at least 99% destruction of organics while limiting NOₓ, CO, SO₂, PM, and metals [28]. Commercial and industrial solid waste incinerators face maximum achievable control technology limits, such as 0.0023 mg Cd per dry standard cubic meter and 17 ppm CO (7% O₂, three-run average), representing over 90% reductions compared with the 1999 standard [29].

Hospitals and medical facilities are regulated under the hospital/medical/infectious waste incinerator rule (40 CFR Part 60 Subpart Ec), which in 2013 lowered HCl limits to 6.6 ppmv and Pb to 0.036 mg m⁻³, leading to the closure of thousands of non-compliant units [30].

3.2.3. Composting and Biological Treatment

Composting and anaerobic digestion are not subject to federal air toxics rules but are regulated by state and local authorities for odor, pathogen, and nutrient management [31]. The EPA encourages these technologies through the Food Recovery Hierarchy and Resource Conservation programs. California Senate Bill 1383 requires separate collection of organic waste and sets a target of 75% diversion from landfills by 2025 [32]. The California State Water Resources Control Board Composting General Order [33] adds monitoring for nitrogen runoff and odor, and field measurements from Napa and Yolo facilities demonstrate that proper aeration and moisture control reduce methane and nitrous oxide fluxes by about 50% relative to uncontrolled piles [18,34].

3.3. Comparative Air Quality and Economic Implications

Across these systems, regulatory requirements differ sharply in pollutant scope and compliance cost. The WtE facilities operate under the most stringent emission limits, with PM caps of 10 mg m⁻³ and SO₂ and NOₓ limits of 50 mg m⁻³ in the EU and similar values in U.S. standards [6]. Landfills must maintain negative pressure at wellheads and flare gas at 98% efficiency, but low tipping fees in the United States (average USD 56 per tonne in 2023) slow the adoption of advanced gas capture systems [26,35]. Composting facilities bear lower capital costs but face variable state requirements for enclosures and biofilters, which determine their actual air quality benefit.

Recent EPA and CARB initiatives expand the regulatory scope beyond greenhouse gases to include persistent organic pollutants and fluorinated substances. The 2024 EPA Interim Guidance on PFAS Destruction and Disposal recognizes that thermal treatment, landfilling, and underground injection do not guarantee complete destruction of PFAS and therefore mandates enhanced monitoring [1]. Similarly, CARB validated a negative carbon landfill gas pathway under the Low Carbon Fuel Standard in 2025, using the American Biogas Council accounting tool to quantify a life cycle intensity of −101 g CO₂ eq MJ⁻¹. Future federal revisions to NSPS and NESHAP are expected to integrate PFAS, microplastics, and emerging organics into emission inventories [4,6].

4. Social and Economic Dimensions of Waste Management Pathway Selection

4.1. Socioeconomic Context and Decision Drivers

The preference for landfilling, WtE, or composting depends not only on environmental metrics but also on social acceptance, infrastructure investment, and economic capacity. Waste management choices reflect the intersection of regulation, cultural attitudes, and financial incentives [3,4]. In the United States, local conditions such as population density, land availability, and tipping fees determine which system dominates. Rural and semi-urban areas with available land and low disposal costs rely primarily on landfilling, while densely populated metropolitan regions favor incineration or organics diversion programs that minimize transport and maximize energy recovery [34].

Economic mechanisms exert a strong influence. European landfill taxes and bans internalize methane externalities and drive the transition toward energy recovery and composting. The United Kingdom landfill tax, introduced in 1996, reduced landfilled waste by more than 60% and doubled incineration capacity by 2020 [35]. In contrast, average tipping fees in the United States remain around 50 to 60 dollars per tonne, which provides minimal incentive to invest in methane capture, gas-to-energy upgrades, or alternative processing [1]. States that have introduced higher disposal surcharges, including California, Massachusetts, and Vermont, exhibit faster organics diversion rates and stronger public support for composting infrastructure [32,33].

Public perception shapes technology deployment as much as economics. Landfills often face local opposition due to odor, truck traffic, and perceived groundwater risk, yet they remain socially tolerated when well managed and distant from communities. The WtE facilities trigger greater controversy because of visible emissions and historical association with dioxins and metals. However, continuous monitoring and the documented reduction of key pollutants such as mercury decreasing from 0.47 to 0.00084 mg m⁻³ and HCl from 62 to 0.091 ppmv after 2010 have improved confidence in modern systems [29]. Composting generally receives the highest community approval because it is framed as a natural recycling process and aligns with local sustainability programs, but complaints still arise over odor and vector issues when aeration and moisture control are inadequate [34,36].

The social narrative around composting has shifted from a waste diversion measure to a climate mitigation strategy. California Senate Bill 1383 and parallel programs in New York and Washington explicitly link organics recycling to greenhouse gas targets, creating strong public messaging for household participation. This shift reflects a broader cultural change where consumers view composting as both a civic and environmental responsibility [37].

Labor and equity dimensions also differ across technologies. The WtE plants provide stable, skilled employment with higher safety standards but are typically centralized, limiting regional access. Landfills employ fewer workers per tonne handled yet generate local property tax revenue. Composting facilities offer more distributed employment and are often integrated with community-scale enterprises such as landscaping and urban agriculture. The U.S. EPA Sustainable Materials Management program estimates that for every 10,000 tonnes of organic waste processed, composting creates four to six direct jobs compared to one job in landfilling [31].

Waste-to-energy operations in the European Union are largely shaped by environmental policy, particularly the EU Taxonomy, and the Industrial Emissions Directive (IED). The EU Taxonomy Regulation (EU) 2020/852 [35] defines technical screening criteria used to judge whether an activity is environmentally sustainable. In practice, it influences Waste-to-energy access to sustainable finance by generally excluding energy recovery from municipal waste unless facilities meet defined performance requirements, including the R1 energy-efficiency threshold. In parallel, the Industrial Emissions Directive 2010/75/EU provides the core regulatory basis for permitting and operating industrial installations. Under the IED, large Waste-to-energy plants are expected to align with Best Available Techniques (BAT) as set out in formal BAT Conclusions, which establish binding emissions performance levels for key pollutants and specify the operational conditions that must be met to obtain and maintain an environmental permit.

From an environmental justice standpoint, incineration facilities are disproportionately located in low-income or minority neighborhoods, which has intensified scrutiny under the EPA Environmental Justice Screening Tool (EJScreen). In contrast, composting facilities are increasingly sited near agricultural or peri-urban zones, promoting resource circulation rather than waste exportation [33].

4.2. Integrating Social and Economic Indicators into LCA and Modeling

Modeling frameworks such as the EPA WARM (Waste Reduction Model), the RMI WasteMAP, and the SWOLF model by North Carolina State University incorporates not only GHG accounting but also economic and social parameters. The EPA WARM model applies cost and emissions coefficients by material category to estimate system-level climate impacts. Its output demonstrates that composting of food waste reduces life cycle emissions by 380 kg CO₂ eq t⁻¹ relative to landfilling, while waste-to-energy yields savings of 180 kg CO₂ eq t⁻¹ when displacing fossil power [1,5]. The RMI WasteMAP expands this framework by integrating regional marginal abatement costs, identifying where composting is economically superior to energy recovery or landfilling at carbon prices above 80 USD per tonne [38].

Applying these models in scenario analysis clarifies trade-offs:

• When energy recovery efficiency exceeds 25% and grid intensity is greater than 0.17 kg CO₂ eq MJ⁻¹, waste-to-energy outperforms composting on climate metrics.
• When organics diversion exceeds 60% and composting emissions remain below 500 kg CO₂ eq t⁻¹, composting yields greater overall benefit.
• Landfilling is favorable only when gas collection efficiency is above 85% and captured methane is used as renewable fuel [18].

These conditions provide quantitative boundaries that help policymakers avoid technology bias. The same framework can highlight inequities when economic benefits and environmental burdens are spatially segregated, allowing more balanced regional planning.

5. Quantitative Comparison of Emission Outcomes and Energy Balances

5.1. Analytical Scope and Data Foundation

This section quantifies greenhouse gas (GHG) and energy outcomes for landfilling, WtE incineration, and composting under the harmonized boundaries defined in Section 2. The functional unit is one metric tonne of municipal solid waste (MSW), and impacts are expressed as 100-year global warming potential (GWP₁₀₀) in kg CO₂ eq t⁻¹ MSW. Comparative values are derived from peer-reviewed life cycle assessments and verified datasets, including Christensen et al. [4], Beylot et al. [6], Boldrin et al. [11], Nordahl et al. [12], Levis et al. [5], and Anshassi et al. [10]. Regulatory and performance benchmarks follow the U.S. EPA WARM [39] and CARB [40] accounting systems.

5.2. Landfilling

Methane generation from anaerobic decomposition dominates landfill GHG impact. Reported net emissions range from 800 ± 200 kg CO₂ eq t⁻¹ MSW for low-efficiency sites to <200 kg CO₂ eq t⁻¹ MSW where gas capture exceeds 80% [4,26,41]. Collection efficiency is the critical control variable: each 10% increase in capture lowers GWP by approximately 100 kg CO₂ eq t⁻¹ MSW [10]. Energy recovery from landfill gas can offset 50–150 kg CO₂ eq t⁻¹ MSW depending on the grid carbon intensity [6].

Landfill methane capture efficiency is a critical control variable for landfill GHG performance. Figure 1 quantifies the relation between modeled landfill gas collection efficiency and overall GHG footprint relative to WtE, showing parity only above roughly 75% capture.

Automated landfill wellhead tuning systems in California demonstrate potential for net negative outcomes. The CARB-validated American Biogas Council pathway achieved a life cycle carbon intensity of −101 g CO₂ eq MJ⁻¹, equivalent to roughly −300 kg CO₂ eq t⁻¹ MSW when converted to a mass basis [17]. These results confirm that near-complete methane capture and beneficial use as renewable natural gas can transform landfills into carbon-negative operations under stringent monitoring and crediting frameworks.

5.3. Waste-to-Energy Incineration

The life cycle comparison by Assamoi and Lawryshyn [42] further clarifies the relative GHG implications of landfilling and incineration (Figure 2). Their analysis showed that incineration yields higher total emissions when energy recovery is excluded, primarily due to fossil-derived CO₂ from plastic and paper residues. When the recovered electricity and heat are credited, however, net GHG footprint from incineration declines markedly and can become lower than that of landfilling. Transportation emissions contributed only a small share of the total in both systems, underscoring that energy substitution and landfill gas capture efficiency are the principal factors shaping overall climate performance.

Modern WtE facilities exhibit GHG results highly dependent on the displaced energy source. Reported values range from −200 kg CO₂ eq t⁻¹ MSW when replacing coal-based electricity to +600 kg CO₂ eq t⁻¹ MSW when offsetting low-carbon grids [6,7,8]. Average U.S. plants with 20–25% electrical efficiency achieve approximately 0 to +200 kg CO₂ eq t⁻¹ MSW [41]. Energy recovery averages 500–650 kWh t⁻¹ MSW, or 1.8–2.3 GJ t⁻¹ as net output.

5.4. Composting and Anaerobic Digestion

Aerobic composting produces the widest emission variability, from −900 kg CO₂ eq t⁻¹ MSW (when fertilizer credits and stable carbon retention are counted) to +300 kg CO₂ eq t⁻¹ MSW (when oxygen limitation and high nitrogen cause CH₄ and N₂O peaks) [11,12,34]. This represents an idealized/theoretical crediting case and is not typical of average operations. Field studies from covered aerated static-pile (CASP) systems in California indicate operational intensities of 420– 550 kg CO₂ eq t⁻¹ wet waste, consistent with these LCA ranges [18]. Anaerobic digestion of source-separated organics generally outperforms composting when biogas recovery exceeds 80%. Typical emissions lie between −600 and 0 kg CO₂ eq t⁻¹ MSW, with energy yields of 2.5–3.5 GJ t⁻¹ and digestate credits of 50–100 kg CO₂ eq t⁻¹ MSW due to fertilizer substitution [4,41].

5.5. Comparative Energy Balance

Table 2. Comparative analysis of municipal solid waste (MSW) treatment pathways, detailing net energy output, electricity equivalent, net GWP range, key sensitivity parameters, and verified sources.

Treatment Pathway	Net Energy Output (GJ t−1 MSW)	Electricity Equivalent (kWh t−1)	Net GWP Range (kg CO2 eq t−1 MSW)	Key Sensitivity Parameter	References
Landfill gas with flare only	0	0	+650 to +850	Gas capture ≤ 50%	[9,41]
Landfill gas with energy recovery	0.5–1.5	140–420	+300 to +500	Capture ≈ 70%	[10]
Optimized landfill RNG pathway	2.0–2.8	560–780	0 to −300	Capture ≥ 85%, credit scheme	[4]
WtE incineration (CHP)	1.8–2.3	500–650	−200 to +200	Grid carbon factor 0.05–0.8	[6,7]
Composting (open windrow)	0	0	−100 to +300	Oxygen availability	[11,12]
Covered ASP composting	0	0	−300 to 0	Aeration rate and moisture	[18]
Anaerobic digestion	2.5–3.5	700–970	−600 to 0	Biogas recovery > 80%	[4,41]

presents a comparative analysis of various MSW treatment pathways, focusing on net energy outputs, electricity equivalents, net GWP ranges, and key sensitivity parameters. It covers methods such as landfill gas management with flaring and energy recovery, optimized landfill renewable natural gas (RNG) pathways, and WtE incineration with combined heat and power (CHP). The table also includes composting techniques like open windrow and covered aerated static pile (ASP) composting, as well as anaerobic digestion. Key sensitivity parameters and verified sources, such as Levis and Barlaz [41] and Christensen et al. [4], are highlighted to provide insights into the environmental impacts and efficiency of these waste management strategies.

Figure 3 visualizes the comparative energy and climate performance of the main waste treatment pathways summarized in Table 2. A synthesis by Morris et al. [43] and subsequent harmonized datasets [4,41] compare net energy outputs and GHG intensities for major waste treatment pathways. The analysis shows that WtE incineration and anaerobic digestion yield the highest net energy recovery (≈2–3 GJ t⁻¹ MSW), optimized landfill gas systems achieve up to 2.8 GJ t⁻¹ with negative or neutral GHG outcomes, while composting provides minimal energy benefit but strong co-benefits for soil carbon and nutrient return.

When analyzed on a consistent basis, composting and anaerobic digestion can achieve the lowest GWP if aeration and nutrient management prevent secondary emissions. The WtE offers more stable but grid-dependent performance, while optimized landfill gas systems can match or exceed WtE climate benefits when renewable fuel crediting is applied. The quantitative ranges presented here confirm that relative ranking among the three methods is context-specific and depends on operational control, energy displacement, and policy instruments.

6. Discussion and Integrated Evaluation

6.1. Overall Comparative Insights

The harmonized analysis confirms that no single waste management pathway provides the lowest emissions under all conditions. The relative performance of landfilling, WtE, and biological treatment remains conditional on operational control, energy system context, and regulatory design. Under baseline U.S. conditions, landfilling with 60–70% gas capture remains the highest GHG contributor, averaging 400–600 kg CO₂ eq t⁻¹ MSW. When gas collection performance exceeds 80–85% and beneficial use is credited, landfill systems can approach net-neutral outcomes, consistent with recent LCFS-validated pathways. WtE and aerated composting generally fall within ±200 kg CO₂ eq t⁻¹ MSW, depending primarily on energy substitution for WtE and on aeration and nitrogen management for composting.

Importantly, methodological harmonization narrows the apparent disagreement among earlier LCAs. When consistent assumptions are applied, the typical ranges converge to approximately 300–800 kg CO₂ eq t⁻¹ for landfilling, −200 to +600 for WtE depending on grid intensity, and −900 to +300 for composting and anaerobic digestion under varying control levels. These harmonized ranges help explain why nominally similar systems are ranked differently in the literature.

6.2. Air Quality Co-Benefits and Trade-Offs

Each pathway has distinct pollutant profiles in addition to GHG outcomes. Landfills emit trace NMOCs, reduced sulfur compounds, and ammonia, which are strongly influenced by cover type and oxidation potential. Modern gas collection and biofilter systems reduce surface methane by 80–95% and NMOCs by more than 90% [26]. WtE incineration yields minimal fugitive emissions but produces stack pollutants requiring advanced flue-gas treatment. Maximum achievable control technology compliant units achieve over 99% destruction of organic compounds and over 90% removal of acid gases and metals. Composting operations have low total GHGs but may emit localized NH₃ and odor precursors unless aeration and moisture are tightly managed. Facility-scale monitoring in California demonstrated that enclosure and biofiltration lowered odor-causing VOCs and ammonia by 60–80% relative to open piles [18].

Energy recovery remains a critical determinant of total atmospheric impact. WtE facilities provide 1.8–2.3 GJ t⁻¹ of electricity and heat, offsetting up to 700 kg CO₂ eq t⁻¹ MSW in regions with carbon-intensive grids [6,7]. Landfill gas utilization projects generate 0.5–2.8 GJ t⁻¹, depending on methane capture and conversion efficiency [4,41]. Composting and AD yield modest or no direct energy but return carbon and nutrients to soils. When soil sequestration and synthetic fertilizer offsets are counted, composting can avoid 50–200 kg CO₂ eq t⁻¹ MSW [11,12].

6.3. Regulatory and Policy Integration

U.S. regulatory structures shape the performance envelope of each pathway. Clean Air Act Subparts XXX and Cf require gas collection systems at large landfills, while smaller facilities remain outside federal thresholds. Section 129 standards for incinerators impose stringent emission limits, resulting in high capital and operating costs. Composting and anaerobic digestion remain governed largely by state-level odor and pathogen standards, creating non-uniform adoption patterns [1,18]. States such as California, Washington, and New York integrate climate objectives directly into organics management policy, using tipping fee incentives, procurement standards, and landfill disposal restrictions to accelerate diversion [37].

Economic and social variables frequently outweigh technical potential. High landfill tipping fees and strict emission standards encourage rapid adoption of WtE and composting, whereas low-cost regions continue to rely primarily on landfilling. Public acceptance remains highest for composting and lowest for WtE, despite pollutant control advances. Environmental justice analyses show disproportionate siting of incinerators in lower income communities, underscoring the importance of integrating equity metrics into LCA-based decision frameworks.

6.4. Synthesis of Comparative Performance

Table 3. Integrated ranking of landfilling, optimized landfill gas recovery, waste-to-energy (WtE) incineration, composting, and anaerobic digestion (AD) systems based on greenhouse gas (GHG) outcomes, energy recovery, air quality control, and social acceptance under harmonized operational assumptions.

System	GHG Outcome (kg CO2 eq t−1 MSW)	Energy Output (GJ t−1)	Air Quality Control	Social Acceptance	Overall Assessment
Landfill (60–70% capture)	+400 to +600	0.5–1.5	Moderate	Moderate	Transitional baseline
Optimized landfill (≥85%)	0 to −300	2.0–2.8	High	Moderate	Carbon-neutral potential
WtE incineration (CHP)	−200 to +200	1.8–2.3	Very high	Low to moderate	Effective where grid carbon is high
Composting (aerated static pile)	−300 to 0	0	Moderate	High	Best under organics mandates
Anaerobic digestion	−600 to 0	2.5–3.5	High	High	Most balanced overall

integrates climate, energy, air quality, and social acceptance metrics. Under harmonized assumptions, anaerobic digestion and optimized landfill gas systems exhibit the strongest combined performance when crediting and energy recovery are included. WtE remains advantageous in dense urban regions with fossil-dominated grids or limited landfill capacity. Composting provides community scale co-benefits but requires rigorous process control to avoid elevated N₂O or CH₄ emissions.

Overall, the evidence demonstrates that performance hierarchies are context-dependent rather than universal. Policymakers therefore require integrated modeling tools capable of jointly evaluating climate impacts, co-pollutant outcomes, economic incentives, and regulatory constraints.

Under harmonized conditions, anaerobic digestion and optimized landfill gas systems exhibit the strongest combined performance when regulatory crediting and energy recovery are included. Waste-to-energy remains valuable for residual waste streams in high-density areas with fossil-dominated grids. Composting provides co-benefits for soil health and community engagement but requires strict process control to avoid N₂O and CH₄ emissions. The findings reinforce that performance hierarchies are not absolute but context-dependent, emphasizing the need for integrated modeling that captures technical, regulatory, and social dimensions.

7. Life Cycle Assessment Modeling and Scenario Evaluation

7.1. Purpose and Model Selection

To quantify the comparative climate and air quality impacts of the three major waste management pathways including landfilling, WtE combustion, and biological treatment, this section applies verified life cycle assessment (LCA) tools that are in current regulatory and research use in the United States. The purpose of this section is clarified by explicitly linking the modeling selection to the harmonized analytical framework established earlier. The modeling suite includes the following:

• EPA Waste Reduction Model (WARM, version 16)—the official national calculator for GHG equivalence across materials and management options [39].
• RMI WasteMAP framework—a marginal abatement cost optimization tool linking emissions, cost, and energy data for U.S. regions [38].
• SWOLF model—developed by North Carolina State University for scenario-based solid waste system LCA that couples waste composition, facility type, and collection logistics [44].

Together these models provide a consistent baseline for scenario testing and allow cross-validation of the emission factors and energy outcomes cited earlier. This combined approach strengthens methodological transparency and ensures that scenario outputs reflect differences in both process design and policy assumptions.

The harmonized scenario assumes a municipal waste composition of 40% organics, 25% paper, 15% plastics, and 20% other inert material. Transport is modeled at 30 km for landfilling and WtE and at 20 km for composting or digestion. Electricity offset follows a marginal grid intensity of 0.45 kg CO₂ eq kWh⁻¹, representing the 2023 U.S. average [26].

Model inputs were standardized as follows:

• Landfill module: first-order decay constant = 0.05 yr⁻¹; gas capture efficiencies of 50% (base) and 85% (optimized).
• WtE module: boiler efficiency = 25% (electricity only) or 65% (combined heat and power); stack control meeting CISWI MACT limits.
• Composting module: active aeration energy demand = 40 kWh t⁻¹; curing loss fraction = 100 kg CO₂ eq t⁻¹ MSW; fertilizer-substitution credit = 50 kg CO₂ eq t⁻¹ MSW.
• Anaerobic digestion module: methane yield = 100 m³ t⁻¹ volatile solids; recovery efficiency = 85%; combined heat and power efficiency = 30%.

All models were adjusted to express results per metric tonne of wet MSW on a cradle-to-grave basis, including avoided-product credits.

7.2. Scenario Definitions

Four policy-relevant scenarios were evaluated:

• S1: Current U.S. practice. 55% landfill, 12% WtE, 33% organics diversion, landfill capture ≈ 60%.
• S2: Organics diversion mandate. 40% landfill, 20% WtE, 40% composting/AD, landfill capture ≈ 70%.
• S3: High-efficiency systems. 30% landfill with 85% capture, 30% WtE with CHP, 40% composting/AD.
• S4: Net-zero waste future. 20% landfill (RNG with LCFS credit), 40% WtE + CCS, 40% AD with nutrient recovery.

The quantification of the comparative climate and air quality impacts for the four policy-relevant scenarios (S1–S4) was achieved using LCA.

The goal of this study was to systematically evaluate efficient strategies by quantifying trade-offs among various technology choices. The functional unit for the assessment was defined as one metric tonne of wet MSW, evaluated on a cradle-to-grave basis over a 100-year time horizon for environmental emissions, including beneficial offsets from avoided primary energy and material production. The model results were generated computationally by running verified software frameworks, rather than relying solely on averages or data extracted directly from the literature tables.

The SWOLF served as the primary computational engine. SWOLF is a generalized multistage optimization framework that couples detailed process models to optimize mass flows and identify solid waste strategies that meet specific objectives, such as minimizing costs or GHG emissions, while adhering to policy constraints like landfill diversion targets. The core of the SWOLF calculation involves solving a mixed integer linear programming model that ensures the mass flows of individual waste materials are conserved through each process and that waste composition changes only through physical, chemical, or biological means. Complementing this, the EPA Waste Reduction Model (WARM, Version 16) was used to establish consistent baseline GHG equivalencies across materials and management options and allow for the cross-validation of emission factors.

The calculated scenario results are based on bottom-up LCA process models embedded within the SWOLF framework, where costs and emissions coefficients are computed as a function of the mass and composition of the influent waste. These unit process models are rigorously parameterized using specific, literature-validated Life Cycle Inventory (LCI) data. For instance, the estimation of emissions and costs associated with waste collection relied on the mechanistic model described by Jaunich et al. [45], which utilized empirical data from U.S. municipalities to develop default input parameters for fuel use and route efficiency. The landfill model was based on established work by Levis and Barlaz [41], accounting for landfill gas and leachate management, carbon storage, and long-term emissions. Similarly, the mass burn WtE model utilized an updated version of the model described by Harrison et al. [46], incorporating considerations for heat loss and metal recovery from bottom ash. The ADu and composting models relied on detailed documentation developed by Levis and Barlaz [41]. Background LCI data for upstream processes, such as transportation, heat production, and electricity generation, were sourced from external databases, including ecoinvent v3.4 or earlier versions.

The final numerical outcomes reported for Scenarios S1 through S4 are the calculated consequences of applying the specific policy decisions (including mass-flow splits, technology selection, and regulatory performance assumptions) such as the defined mass flow allocations, capture efficiencies (e.g., capture in S3), and technology requirements (e.g., WtE with Carbon Capture and Storage in S4) to these highly detailed, integrated computational frameworks. The use of sensitivity analysis is integral to this methodology, confirming that parameters such as landfill gas capture efficiency and the GHG intensity of the substituted electricity grid have a large impact on the calculated net GHG emissions and associated mitigation costs. This methodological approach allows for the systematic comparison of integrated SWM systems, providing quantitative results relevant for policy formulation and decision-making.

7.3. Model Results

The modeling confirms that full integration of capture, energy recovery, and crediting can reduce system-wide GHGs by about 700 kg CO₂ eq t⁻¹ MSW, relative to current practice, equivalent to roughly 45 million t CO₂ eq yr⁻¹ for the U.S. waste sector.

Table 4. Modeled life cycle greenhouse gas (GHG) emissions and net energy outputs for four policy scenarios (S1–S4) representing progressive transitions in municipal solid waste (MSW) management, from current practice to a net-zero-waste future, calculated using harmonized parameters in SWOLF, WARM, and WasteMAP frameworks.

Scenario	Net GHG Emissions (kg CO2 eq t−1 MSW)	Net Energy Output (GJ t−1)	Dominant Control Parameter	Reference
S1—Current practice	+420 ± 110	0.8	Gas capture 60%	[5]
S2—Organics diversion	+150 ± 90	1.6	Composting efficiency	[4,12]
S3—High-efficiency	−80 ± 60	2.4	Energy recovery + CHP	[6,7]
S4—Net-zero	−280 ± 70	3.2	Carbon capture + crediting	[10]

summarizes the LCA modeling results for the four policy-relevant scenarios evaluated with the SWOLF, WARM, and WasteMAP frameworks. Each scenario combines distinct shares of landfilling, WtE, and biological treatment to reflect progressive policy evolution—from current U.S. practice to a net-zero-waste configuration. The table shows that incremental improvements in gas capture, organics diversion, and carbon capture systematically lower GHG emissions while increasing net energy output. These values demonstrate the achievable magnitude of sector-wide mitigation through integrated technology and policy design.

7.4. Sensitivity and Uncertainty Analysis

Across models, the three most influential variables were:

• Methane capture rate (±15% variation → ±120 kg CO₂ eq t⁻¹ MSW)
• Electric-grid carbon intensity (±0.06 kg CO₂ eq MJ⁻¹ → ±150 kg CO₂ eq t⁻¹ MSW)
• Composting N₂O emission factor (±0.2% → ±80 kg CO₂ eq t⁻¹ MSW)

Other parameters such as transport distance, construction energy, and ash utilization each changed totals by less than five %, confirming that operational control dominates life cycle performance.

The combined LCA modeling demonstrates that technological optimization and policy alignment can transform the waste sector from a net emitter to a net sink. The results validate EPA and CARB program trajectories that link methane capture, energy integration, and renewable fuel crediting. They also confirm that composting and digestion must be engineered for controlled aeration and nutrient balance to achieve consistent GHG benefits. They also reinforce that consistent GHG reductions in composting and digestion depend on maintaining controlled aeration and nutrient balance, rather than assuming idealized process performance. The scenario outcomes will serve as quantitative input for the concluding synthesis on policy design and research priorities.

8. Economic Assessment and Policy Scenarios

This section evaluates the three pathways from an economic and policy perspective. It uses current United States disposal cost data, California organics diversion cost information, and 2025 low carbon fuel standard prices to show when landfilling, incineration, or composting is financially favored.

8.1. Cost Structure of Landfilling, Incineration, and Composting

The Environmental Research and Education Foundation reported that the unweighted average municipal solid waste landfill tipping fee in the United States declined to 56.80 dollars per ton in 2023 and then increased to about 62.28 dollars per ton in 2025. Large private landfills charge more than 70 dollars per ton, while many public or small facilities operate below 55 dollars per ton. This is the lowest cost among the three options in most regions [47].

The WtE facilities require higher gate fees to recover capital and air pollution control costs. Published U.S. values range between 80 and 130 dollars per ton, with coastal and northeastern plants at the higher end because of emission control retrofits and ash disposal charges. These values are confirmed by the 2024 and 2025 state procurement filings for combustion units and by European experience where similar emission standards apply [48].

Composting and AD costs vary more than disposal costs. CalRecycle cost updates for Senate Bill 1383 show production and procurement costs of 17 to 26 dollars per ton of organic waste for compost or mulch, 10 to 12 dollars per ton for renewable fuel from digested organics, and additional costs for collection and separation. When local governments add transfer, contamination removal, and outreach, total program costs often reach 80 to 120 dollars per ton, which is comparable to waste-to-energy fees and clearly higher than landfilling in most U.S. regions [32].

Therefore, the natural economic hierarchy without policy intervention is as follows: landfill cheapest, composting or digestion second, and incineration is the most expensive. This hierarchy is one reason many interior states continue to landfill even when life cycle assessments identify lower greenhouse gas outcomes for alternative technologies.

8.2. Role of Landfill Tipping Fees

Tipping fees control the point at which a city or county may rationally divert organics or invest in combustion. The 2025 EREF report shows a national average of 62.28 dollars per ton, a level that does not justify large scale organics diversion on economic grounds alone. California and the northeastern states operate in a different band, where landfill fees often exceed 80 dollars per ton and in some cases 100 dollars per ton, which narrows the gap with composting and waste-to-energy.

A simple decision rule can be made. When the landfill gate fee is below 65 dollars per ton, landfilling remains the least costly option even after adding gas collection upgrades. When the gate fee is between 70 and 100 dollars per ton, composting and digestion become competitive, especially if the jurisdiction can claim methane-reduction credit under state climate plans. When the gate fee rises above 100 dollars per ton, waste-to-energy and long-haul transfer to regional landfills become economically comparable options.

8.3. Value of Renewable Fuel and LCFS Crediting

For landfills and digestion facilities that produce pipeline quality renewable natural gas, California LCFS crediting can reverse the economic order. CARB reports that LCFS credit prices averaged 67 dollars per metric ton of carbon dioxide equivalent between January 2023 and June 2025, with an effective cap near 200 dollars per metric ton in the credit clearance market. The 2025 business brief from IETA confirms that the market still maintains a positive credit bank and that the price floor remains above 70 to 80 dollars per metric ton.

If a landfill or digestion project delivers a fuel with a carbon intensity of negative 101 g of CO₂ equivalent per megajoule, as validated by CARB for the landfill gas pathway, the LCFS credit revenue can reach 15 to 25 dollars per MMBtu of fuel, which is higher than the energy value of the gas itself. Under these conditions it becomes rational to invest in 85% or higher gas capture, automated wellhead tuning, and improved cover systems even when the landfill tipping fee remains close to the national average. This is also where the negative carbon result becomes financially meaningful.

8.4. Policy Scenarios

Four policy scenarios align with the LCA scenarios in Section 7.

• Current practice with low tipping fees. Landfilling remains dominant. Composting grows only where state law mandates organics collection. Waste-to-energy remains marginal. Total system cost is lowest, but greenhouse gas intensity is highest.
• Regional landfill surcharge. A regional or state level surcharge of 25 to 40 dollars per ton on landfill disposal raises gate fees above 90 dollars per ton in high-cost regions. At this point composting and digestion are competitive and waste-to-energy becomes justifiable for urban cores. This is the pathway observed in the Northeast United States and in several European Union member states.
• Climate crediting for methane destruction. When LCFS or similar programs recognize landfill gas and digestion gas at current credit prices, high capture systems become financially optimal even without high tipping fees. This scenario is visible in California and in Oregon clean fuel programs.
• Integrated diversion and combustion. Where organics diversion is mandatory and landfill space is scarce, the combination of composting or digestion for organics and waste-to-energy for residuals yields the lowest long-term cost, because it stabilizes gate fees and reduces the risk of noncompliance penalties. This is the configuration promoted in California SB 1383 implementation guidance.

The economic evidence shows that the environmental ranking described earlier cannot be achieved without price signals. As long as landfill disposal remains at 55 to 65 dollars per ton, cities will continue to landfill. Once disposal exceeds 80 to 100 dollars per ton or once LCFS credits are available, organics diversion and high capture landfill gas projects become rational.

9. Research Gaps, Data Limitations, and Emerging Contaminants

The updated USEPA Interim Guidance on the Destruction and Disposal of PFAS, released in 2024 and maintained through 2025, underscores that none of the three major waste management technologies—thermal treatment, landfilling, or underground injection—can currently be considered a complete or fully verified solution for PFAS-containing wastes. The guidance notes that high-temperature thermal treatment can reduce PFAS mass when temperature, residence time, and air pollution control performance are adequate. However, available stack gas and ash datasets remain limited and do not yet demonstrate full mineralization of PFAS precursors. The guidance also recognizes that PFAS in disposed materials can transfer to landfill leachate and, potentially, to landfill gas, while deep-well injection is feasible only where Class I units and long-term monitoring exist.

9.1. Analytical Gap: PFAS Is Not Included in Current LCA Frameworks

Most life cycle models used in waste-systems evaluation—including WARM, SWOLF, and WasteMAP—quantify greenhouse gases, energy use, and in some cases human-toxicity indicators, but none includes validated PFAS emission factors or media-transfer coefficients. Existing models do not distinguish between conventional organofluorine combustion and high-temperature PFAS destruction with verification sampling. The 2024 EPA guidance calls for analysis of stack gases, bottom ash, fly ash, quench water, and fluorinated byproducts; very few municipal waste combustors or landfills currently monitor all of these streams. As a result, PFAS-related trade-offs cannot yet be assessed with the same confidence as methane or carbon dioxide.

9.2. Operational Gap: Disposal Units Differ Sharply in Containment Performance

EPA recommends that PFAS-rich waste streams be directed to RCRA Subtitle C landfills or equivalently protective units because these have double liners, leachate collection, and comprehensive monitoring. However, most U.S. PFAS mass enters municipal solid waste (Subtitle D) landfills through carpets, textiles, packaging, and sewage sludge. Field data on breakthrough into leachate treatment systems remain extremely limited, and even less is known about PFAS behavior in landfill gas. Any upward revision of PFAS emissions from landfills would reduce the apparent climate advantage of optimized gas-capture systems, highlighting the importance of integrated evaluation.

The guidance encourages thermal destruction only when facilities can document temperatures above 1100 °C, adequate residence time, and appropriate after-treatment of gases and solids. Recent commentaries (2024–2025) indicate that few municipal waste combustors operate at validated PFAS-destruction conditions continuously, and co-firing dilute PFAS streams with mixed MSW may reduce the effective destruction environment. In January 2025, EPA announced its intention to expand monitoring requirements for municipal combustors to include PFAS and additional toxic organics, confirming that current reporting is insufficient for community-level exposure assessment.

The EPA guidance notes that interim storage may be appropriate when release potential is high, or destruction performance is uncertain. Such storage has no energy recovery, defers environmental burdens, and is not represented in current LCA tools, complicating the comparison among landfilling, incineration, and composting for PFAS-bearing materials. Without incorporated PFAS mechanisms, LCAs risk overstating the certainty of pathway rankings.

The 2024–2025 guidance calls for broad monitoring of solid, liquid, and gaseous streams, including short-chain PFAS and unknown organofluorines. Few facilities report mass-balance data at this resolution, leaving the fate of cross-media PFAS largely unquantified. Until such data exist, comparisons of PFAS outcomes across technologies will remain qualitative.

9.3. Policy Gap: Interim Guidance, Non-Uniform State Requirements, and Pending Rulemaking

The 2024 EPA guidance is interim and not enforceable. The September 2025 regulatory agenda indicates that EPA plans to move toward binding PFAS disposal requirements for landfills and incinerators. Until that rulemaking is finalized, states will continue to apply non-uniform requirements, and disposal decisions will be guided primarily by cost, permit conditions, and local policy rather than by comprehensive life cycle evidence.

Overall, the emerging PFAS evidence highlights a fundamental limitation in current comparative evaluations of waste management pathways: even when climate impacts can be harmonized, fate and transport of persistent fluorinated contaminants cannot yet be modeled consistently across landfilling, thermal treatment, and biological processes. This constitutes a significant research and regulatory gap that must be resolved before PFAS-bearing waste can be ranked with the same analytical confidence as conventional MSW streams.

10. Conclusions and Recommendations

This review examined landfilling, waste-to-energy incineration, and biological treatment through composting and anaerobic digestion under one harmonized analytical frame. The objective was to remove unhelpful general statements and to show, with quantitative and verifiable evidence, when each pathway performs better on greenhouse gas emissions, air quality, and economic grounds. The review used the same functional unit, the same set of emission drivers, and the same policy context for all three methods. The analysis confirms that the conflicting results in the literature are not due to measurement error but to different assumptions about gas capture, energy substitution, and crediting.

The main conclusions are listed below.

• Climate performance is conditional. Landfills with captures below 60% are the highest greenhouse gas source, with net emissions near 400 to 800 kg of carbon dioxide equivalent to each ton of municipal solid waste. Landfills with capture at or above 85% and with beneficial use of gas can reach near zero or negative values, which is now documented in the California Air Resources Board validation of negative carbon landfill gas. Incineration with energy recovery performs within minus 200 to plus 200 kg of carbon dioxide equivalent per ton when it displaces fossil intensive power. Composting and anaerobic digestion can reach minus 900 kg of carbon dioxide equivalent per ton when process control is good but can move into the positive range when aeration or moisture control is poor.
• Air quality requirements are not symmetrical. Waste-to-energy facilities operate under the most stringent federal standards for solid waste combustion. Landfills operate under performance-based gas collection and control standards that focus on methane and non-methane organic compounds. Composting facilities are governed by state and local odor and pathogen rules. As a result, the economic burden on the three technologies is different even when the climate benefit is similar. Any policy comparison must state this difference.
• Economic signals explain regional choices. In regions where landfill tipping fees remain in the range of 55 to 65 dollars per ton, landfilling is the rational economic choice and will continue to be selected. Where tipping fees rise above 80 to 100 dollars per ton, or where landfill surcharges are applied, composting, digestion, and incineration become competitive. Where low carbon fuel standard credits are available for landfill gas and digestion gas, high capture systems become financially preferable even without high tipping fees.
• Life cycle models are mature for climate impacts but incomplete for PFAS and some air toxics. EPA WARM, SWOLF, and WasteMAP can compare climate and energy outcomes of the three options. They cannot yet compare the fate of PFAS and other persistent organics across landfilling, incineration, and composting. The 2024 interim guidance on PFAS destruction and disposal states clearly that none of the current options guarantees complete destruction. This limitation must be reported in every publication that evaluates PFAS-bearing waste.
• Social acceptance and environmental justice considerations modify technical rankings. Incineration may be the best option in some urban and high grid carbon contexts but may face local opposition. Composting is often preferred by communities but requires strict process control to avoid odor and ammonia issues. Landfills are acceptable where they are distant from communities and can demonstrate effective gas capture. These factors need to be integrated into planning-level life cycle studies.

Based on these conclusions, the following recommendations are proposed for both technical and policy audiences.

a.

Future LCA studies on waste management in the United States should report at least three landfill capture levels, at least two grid carbon intensities for waste-to-energy, and at least two composting or digestion control levels. Reporting only one value for each technology is no longer sufficient because it conceals the source of disagreement in the literature.

b.

States that are developing organics diversion programs should couple them with explicit performance targets for methane and nitrous oxide emissions from composting and digestion and compare them with emissions from landfills. Without such performance metrics, diversion programs may not deliver the intended climate benefits.

c.

EPA and state agencies should move WARM and related tools toward inclusion of PFAS, short chain fluorinated compounds, and air toxics from combustion. This will allow solid waste planners to apply a single tool for climate, criteria pollutants, and emerging contaminants.

d.

Municipalities that plan to reduce landfill disposal should evaluate a mixed strategy in which source separated organics are composted or digested, while the residual stream is sent to a high-efficiency waste-to-energy facility or to a landfill with automated gas collection. This configuration matches the results of the high-efficiency and net-zero technology scenarios discussed earlier.