Emission Accounting and Mitigation Strategies for Landfill Gas: Quantifying Methane and Carbon Dioxide in Sustainable Waste Management Systems

Priyanka Dwivedi; Devendra Singh Rathore; Chitra Bhatangar
and Vaibhav Purohit

doi:10.5772/intechopen.1015239

Abstract

The sustainable approach to waste management has been a critical frontier in climate mitigation action. Comprehensive accounting tools are used for the mitigation of green house gases (GHGs) emissions in the landfill context. A number of analytical models for GHGs are considered, specifically for the estimation of methane (CH₄) and carbon dioxide (CO₂). The theoretical models range from the Default method to the Landfill Gas Emissions Model (LandGEM) standard industrial method, the Modified Triangular Method (MTM), and the First Order Decay Method (FOD), which is a complex kinetic approach. A robust integrated approach, known as Measurement, Reporting, and Verification (MRV), is needed for the validation of climate data and reduction of GHG. The MRV is bolstered by comparative analysis among more advanced high-precision satellite technologies and conventional theoretical estimation models. The study explores remote sensing techniques for GHGs accounting, such as TROPOMI data, hyper spectral and thermal sensors, for the accurate detection and measurement CH₄ emissions. Conversely, conventional methods based on waste composition data, decay rates, waste age, and other relevant factors ascertain the model’s predictability and reliability. Although inherent uncertainties in these parameters are overcome by using the Monte Carlo model, enhances reliability. Life cycle assessments (LCA) provide a mitigation framework. LCA is also used to identify hot spots in the value of the waste-to-energy system. The chapter’s findings advocate the integration of stringent regulatory standards with technologically advanced approaches. This research offers an extensive roadmap to reduce the footprints of landfills in a circular economy.

Keywords

life cycle accounting (LCA)
hyper spectral sensors (HSS)
environmental footprint
Modified Triangular Method (MTM)
Monte Carlo Model (MCM)

Author Information

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Priyanka Dwivedi *
- Department of Environmental Sciences, MLS University, Udaipur, India
Devendra Singh Rathore
- Department of Environmental Sciences, MLS University, Udaipur, India
Chitra Bhatangar
- Department of Environmental Sciences, MLS University, Udaipur, India
Vaibhav Purohit
- Department of Environmental Sciences, MLS University, Udaipur, India

*Address all correspondence to: priyanka.advent@gmail.com

1. Introduction: Emission accounting and mitigation strategies for landfill gas

The landfills serve as the final dumping pathway for municipal solid waste (MSW) worldwide, and this practice is common in both urban and suburban settings. Driven by rapid urbanization, the proliferation of packaging materials, and increasing consumerism, MSW has risen unprecedentedly. This surge eventually necessitates the continuous operation of landfills and their frequent expansion to accommodate the growing volume of waste. The anaerobic decomposition of the organic fraction of MSW at landfills causes the formation of “Landfill Gas” (LFG). The formation of LFG due to the anaerobic fermentation of MSW evolves across different phases at the landfill surface: initial aerobic breakdown, acidogenesis, acetogenesis, methanogenesis, and the maturation phase. The primary constituents of the LFG mixture are carbon dioxide (CO₂) in the range of 40–50% and methane (CH₄) in the range of 50–60%, along with trace amounts of nonmethanogenic organic compounds (NMOCs), hydrogen sulfide (H₂S), and other gases. This composition demands meticulous emission accounting grounded in a framework designed by the Intergovernmental Panel on Climate Change (IPCC) [1, 2] which standardizes quantification alongside regulatory compliance, carbon project development, green house gas (GHG) protocols, and corporate sustainability reporting. Scoping delineates system boundaries, while critical modeling parameters like waste degradability, moisture, and cover integrity form the foundation for GHG inventories.

Measurement, Reporting, and Verification (MRV) leverages a versatile toolkit, blending onsite surface sweeps and gas wells with models such as Landfill Gas Emissions Model (LandGEM) or IPCC first-order decay (FOD). Drone technology emerges as transformative, deploying hyper spectral sensors and thermal imaging for real-time fugitive emission mapping across vast sites, often integrated with mobile platforms and continuous ground-based networks tuned to satellite data like TROPOMI for methane plume detection. These enable model-based verification through planning tools that simulate scenarios, with uncertainty quantification via sensitivity analyses and Monte Carlo methods ensuring defensible baselines.

The techno-economic portfolio, facilitating biological oxidation via biocovers and bio-filters to oxidize CH₄ gas, containment, flaring, and LFG utilization for energy context, is being formed under mitigation planning. Performance guide selection matrices calculate CO₂e reductions as the differential between baseline and project emissions, while cost-effectiveness analyses weigh capital/operational expenses against abatement value.

Life Cycle Assessment (LCA) provides a holistic evaluation, tracing impacts from waste generation through disposal and mitigation – quantifying embedded energy, leachate, and odor alongside GHG savings. Detailed LCA stages reveal, for instance, that LFG-to-energy systems yield net negatives in global warming potential (GWP) when crediting displaced fossil fuels, though trade-offs emerge in eutrophication from digestate.

Policies framed under the Paris Agreement and net-zero pledges of climatic initiatives incentivize MRV-compliant projects via carbon markets with AI-driven predictive modeling, future trends amplifying drone swarming and satellite constellations for global monitoring. In synthesis, emission accounting transcends documentation, actively shaping mitigation investments and policy, positioning integrated LFG management as essential for sustainable waste systems amid escalating urbanization.

2. Accounting of landfill emissions, LFG characterization, and its generation across different phases

As stated earlier, landfill organic waste fraction decomposition happens in four major phases [3]. Each phase consists of a distinct gas profile. Phase I, which prevails under an oxygen-laden environment (aerobic), supports the initial breakdown of the organic waste fraction that mostly yields CO₂ with minimal CH₄ gas [4]. In Phase II of LFG emission, also known as anaerobic acidogenesis, high concentrations of CO₂ gas (up to 60%) are produced along with low CH₄ (<5%), volatile fatty acids (VFA), traces of volatile organic compounds (VOCs), and hydrogen sulfide (H₂S). The most significant phase, Phase III, is named methanogenesis, during which the generation of CO₂ ranges between 40–60%, and CH₄ extends from 45 to 60%, exhibiting peak generation. Additionally, traces of other compounds such as NMOCs range from 0.5 to 1.5%, ammonia and H₂S vary from 0–100 ppm, and these deviations constitute about 1–2% [1, 5]. The steady-state Phase IV stabilizes CH₄ at 45–60% and CO₂ levels over a long yearly duration. These trace constituents impact the energy use and odor of the landfill site [6]. The six months after the deposition of the MSW, gas production commences, and the gas persists for a period of 20 years before steadily declining in concentration. Emissions are not constant over the lifetime of the landfill and change substantially, fluctuating in accordance with the undergoing biochemical phases. Therefore, delving deep into the temporal dynamics of LFG production necessitates its accounting, as it is the foundational pillar [7]. The critical accounting regime depends on the phases of generation of specific gases, particularly the steady generation of methane (CH₄) from the beginning of the aerobic phase to the fermentation phase of increased CH₄ production, continuing until stabilization occurs. This indicates that it follows a variable yet predictable pattern. A concrete CH₄-focused accounting framework is employed by taking into account standard models for assessing CH₄ emissions from landfills, such as the FOD method [2]. The accuracy of these methodologies hinges on the approach ofMRV to track crucial inputs, such as MSW composition and climatic fluctuations across the lifecycle of the landfill, resulting in accurate estimation of total emissions [8].

2.1 Foundation and accounting of GHGs

The mitigation of GHGsrelies on an accounting and theoretically robust framework that enables their comparison, quantification, and mitigation. The science of the Earth system is the key basis that establishes the global warming associated with the anthropogenic sources of GHG emissions [9]. A methodological accounting framework is required for persistent GHGs like CO₂, CH₄ and NO₂ which influence radiative forcing and accumulate in the atmosphere [10] (IPCC, 2021). The carbon-based accounting theory is tuned to principles from financial accounting applied to the environmental niche. Its objective is to measure gaseous emissions consistently across sectors, organizations, cities, and nations [11]. The most widely used system or framework is the Greenhouse Gas Protocol (GGP), which differentiates gaseous emissions into Scope 1, relating to the accounting of direct emissions; Scope 2, which accounts for indirect emissions from energy sources; and Scope 3, consisting of emissions from the value chain system. The GGP is classified into three approaches based on scopes, which represent the theoretical principle in which gaseous emissions are considered under the canopy system of interrelated economic activities rather than individual sources.

The climate policy framework, in which the GHG accounting system is embedded, also relies on criteria of attribution and allocation rules [9, 12, 13]. Out of these two rules, attribution pertains to responsible sources of emissions, whereas allocation relates to emissions from products, processes, or areas. The two principal rules are significant in international negotiations based on factors of comparability and fairness [12]. Moreover, there is a standardized metric to assess the GWP of GHGs. Over a specific time horizon, considering a 100-year period, each gas is evaluated in terms of its CO₂-equivalents [2, 14].

The ambiguity in GHG management systems, due to gaps in data, assumptions by models, and measurement errors, enhances the need for robust, conservative measurement methods and a fair reporting system. Credible mitigation solutions are based on the accounting principles of theoretical consistency, transparency, accuracy, completeness, and comparability [15].

2.2 Overview of MRV and models

2.2.1 Models and MRV framework

The models and MRV frameworks translate emission sources into measurable data as shown in Figure 1. These are the most widely used operational accounting systems. For instance, the integrated assessment models (IAM) consider energy, land use, climate dynamics, and economic growth in order to measure GHG mitigation pathways. These models correspond to scenarios also considered by shared socio economic pathways (SSP) and the IPCC [15, 16].

Figure 1.
MRV framework for landfill gas emission accounting. Source: author’s generated from an AI tool.

The actions and mitigation measures framed under the MRV system ensure its trust worthiness and measurability. Measurement pertains to the direct monitoring of GHGs for the gathering of data via remote sensing interface, monitoring, and emission factor (EF). On the other hand, the disclosures of collected datasets are made under a standardized reporting system, which accounts for project-based documentation, corporate sustainability reports (CSR), and national GHG inventories. The independent assurance is devised under the verification of the reported data to determine whether it has been correctly measured or not and whether it complies with the theoretical methodologies.

Nationally determined contribution (NDC) of the Paris Agreement, under which the MRV system is institutionalized at the country level [8]. These countries could regularly monitor the progress made toward curbing GHG emissions. The GHG level reduction strategy and the targets are set by using appropriate, comparable, and transparent techniques. The two devised systems are MRV and CDM. To develop more insights about the MRV system, which is crucial for the carbon credit market (CCM), it deals with the credits earned through the reduction in emissions so they can be traded. As a result, MRV contributes to reducing the risk related to double accounting of GHGs and increases environmental stewardship.

Currently, digital technological advancement also supports the MRV system. For instance, monitoring of GHGs through the use of satellites and analysis of data through automated systems improve spatial coverage; registries enabled by block chain and reduced transactional costs have all resulted in improved transparency [17]. One of the salient features of the MRV model is its incapability of maintaining a balance between accuracy and feasibility, specifically when considering developing countries where there is limited infrastructure for GHGs data.

2.2.2 GHG mitigation techniques

The practical application of climatic theory involves mitigation strategies aimed at reducing and eradicating undesirable GHGs. These technologies are classified under industrial processes, agriculture, carbon removal, energy demand, and energy supply. In the energy sector, the replacement of conventional energy systems, such as the combustion of fossil fuels, is displaced by renewable energy techniques like solar power, wind turbines, and hydropower. The robust smart grid and energy storage have improved the flexibility of the system, resulting in the integration or enabling of a variety of power-generating renewables. Despite this, energy demand is being met efficiently through the use of energy-efficient technologies, which help lower emissions as well as energy usage without compromising services.

To follow the climatic theories, mitigation enabled the switching of fuels, optimization of processes, and carbon capture and storage (CCS) in the industrial sector. Other than industrial GHGs mitigation efforts, the CCS technique is deployed to all point sources in order to capture and store CO₂. The captured CO₂ is ultimately stored in geological formations. The decarbonization process within hard-to-abate domains like steel and cement industries is, although theoretical, pragmatic as well through the CCS technique. This emerging trend for the capture, storage, and utilization of CO₂ aims to transform it into fuel and other materials.

The mitigation of GHGs is also applied to land use, relating to nature-based solutions comprised of carbon soil sequestration and afforestation, whereas in the agricultural sector, the adoption of climate-smart agricultural practices, such as improved management of fertilizers, is emphasized. These mitigation strategies cobenefit resilience and biodiversity; however, they are troubled with monitoring and permanency.

2.3 LCA, effectiveness, and economics of mitigation techniques

To evaluate the effectiveness of mitigation technologies and to avoid burden shifting across their full life cycle, the LCA is conducted by various organizations and sectors. LCA is a systematic approach that starts with the extraction of resources and continues until the end-of-life disposal in order to quantify the environmental implications [18]. Therefore, LCA theory places a strong emphasis on impact categories, system boundaries, functional units, and making it possible to compare technologies consistently.

The other crucial component of the mitigation technique is the economic theory, which enables the assessment of the effectiveness of the mitigation. There are two assessment units under economic theory: one is cost-benefit analysis, based on the comparison of mitigation costs with the avoidance of climatic disruption, while on the other hand, cost-effectiveness analysis identifies the best suitable option that incurs the lowest cost for emission reduction. The social cost of carbon is internalized by market-based tools, namely emissions trading programs and carbon taxes, which balance private incentives with social welfare [19].

To comprehend the economics and critical scale for learning the economic concepts that explain the gradual drop seen in costs, as observed in the field of renewable energy [20]. Rebound effects emphasize the need for complementing policies, since efficacy increases may partially offset emission reductions through higher consumption.

2.4 Climatic policy, future trends, and its synthesis

The mitigation framework, models, economics, and accounting for GHGs are collectively addressed under climate policy. The 10th anniversary of the Paris Agreement treaty, that is, COP 2025, advocated the bottom–up approach in which national policies should align with the global temperature reduction goal of 1.5 degrees from the preindustrial era [21]. National policies attribute to regulatory standards, market mechanisms, and fiscal incentives.

The upcoming trend signals toward net zero goals, mainly focusing on carbon removal as well as GHG emissions. The mitigation pathways are being improved with advancements in climate finance, digitization of the MRV system, and negative emission techniques [22]. Despite these advancements, focus is also given to some dimensions that may influence the mitigation pathways either directly or indirectly; these include the socioeconomic aspects of decarbonization, financial equity, and its transitioning principles.

The mitigation pathways synthesis advocates the theoretical coherence of various frameworks, as demonstrated earlier: MRV systems, climate-resilient policies, scalable methodologies, robust accounting models, and other environmentally friendly policies. Integration of all these frameworks has resulted in the enhancement of efficiency, ambitions, and credibility while addressing complex challenges across the world in the twenty-first century.

3. The foundation: Principles and frameworks for LFG emission accounting

As stated earlier, the climatic mitigation schemes, where the waste sector is one of the addressed sectors, include regulations, finance, and estimation for LFG accounting as the analytical foundation [18]. The LFG primarily consists of methane (CH₄) and carbon dioxide (CO₂), and their distribution across the landfill is uneven over decades, relying mainly on climatic conditions and waste composition; therefore, it is partially sensed through direct field measurements [23]. The uncertainties in scientific accounting need to be balanced with the LFG accounting system through proper policy implementation, market credibility, corporate transparency, and effective policy execution [8].

3.1 Accounting framework driven purposely

The LFG principle is based on the foundation of the integral purpose-driven methodological choices. Different attributes are prioritized for varied contexts of accounting; these are consistency, enforceability, completeness, and conservatism. The emission evaluation of LFG for one landfill differs substantially. These varied attributes depend on objectives like regulatory compliance, carbon credit, disclosure of corporate sustainability, and national reporting [11].

3.1.1 IPCC framework

The IPCC methodologies are adopted and relied upon by the United Nations Framework Convention on Climate Change (UNFCCC) in order to strengthen the GHG inventorization [15]. The IPCC guidelines render a graded arrangement that creates a balance among the methodologies' edification and availability of data.

There are three-tier methodologies given under IPCC to evaluate the GHGs. These are: Tier 1 consists of the composition of waste, oxidation factor (OF), decay rates, methane generation potential, and default parameters that are uniform and applicable worldwide. The default parameters create uncertainties and less sensitivity when dealing with the country-specific circumstances. Therefore, the formulation of Tier 2 came in order to address and inventory the country-specific GHGs data, resulting in improved precision and conserving consistent time series measurements. Tier 3 structures the advanced level, model dynamics, data-level facility deployment, and also facilitates site-specific, either temporal or spatial differences noticed during the capture of GHGs in direct measurement [24].

FOD equation of IPCC, computed for the purpose of generating the inventories, is represented below:

CH4=∑Wi×DOCi×DOCf×F×16/12×e∧−kt−i

where W_i represents waste disposed in year i

F refers to the fraction of methane (CH₄) in LFG

k represents the constant of decay rate.

DOC refers to degradable organic carbon

DOCf represents the fraction of DOC that can be decomposed.

The accounting of GHGs and generating inventory focused on its consistency and completeness, instead of developing accuracy at the facility level, often deviated from the precise project or regulatory-based evaluations [1, 2].

3.1.2 Accounting of regulatory compliances

Accounting system regulations are established to fortify legal compliance and environmental standards. For instance, new source performance standards (NSPS) of the United States Environmental Protection Agency (USEPA) for municipal landfill sites (MSW landfill sites) and corresponding regulatory policies in other jurisdictions [5]. Clarity, auditability, and conservatism are the significant pillars of these methods.

The regulatory model framework typically follows conservatism in methane generation potential, decay rate constant, and procedures prescribed for calculations to evaluate whether the LFG exceeds the threshold limit, necessitating capture, collection, and storage for control [3, 6]. Despite this, overestimation of GHG emissions sometimes occurs while using these models, resulting in environmental protection assurance and minimized evasion of regulations. The higher estimation of emissions is often observed when using these models compared to the corporate inventories reported at the national level.

3.1.3 Accounting for carbon in project development

The GHG emissions accounting for the landfills to quantify the reduction in emissions with respect to the baseline scenarios uses carbon-reducing technologies as acknowledged under Verra, a voluntary standard, and the Clean Development Mechanism (CDM). This LFG emissions accounting underpins the reduction in terms of monetarily credited financial value [8, 21].

The baseline scenarios are the estimated, typically presumed gas values or show no gas capture, whereas the destruction efficiency (DE), residual fugitive emissions, and volume of monitored gas volumes are covered in project-based emissions [25]. To maintain integrity by safeguarding the environment, there is a requirement for third-party mandatory verification, parameters of conservative selection, and uncertain discounts. Due to these factors, the LFG accounting framework produces lower carbon reduction credits compared to its theoretical potential for mitigation [26].

3.1.4 GHG protocols and corporate sustainability

The organization owns or operates the landfill sites that have recorded methane (CH₄) emissions under the GHG protocol of Scope 1 emissions. The objective is primarily based on transparent, accurate disclosures of emissions to the stakeholders, regulators, and investors. Scrutinized corporate reports, due to growing climatic declarations – one of them being the Task Force for Climate-Related Disclosures (TCFD) – align with robust methodologies [27].

The corporate reporting marked great emphasis, unlike inventory accounting, which is based on facility-level precision and subsequent improvement. The organizations dealing with the reporting might refine inputs for models by using supplemented emission estimates through direct measurement techniques with site-specific data of waste in order to increase credibility for corporate reporting [17].

3.1.5 Scoping and system boundaries

Scoping is classified into three categories: Scope 1 relates to the landfill surface fugitive emission of methane (CH₄), onsite devices like flares and engines used for combustion, and the collection system. Unattended gas is quite challenging to quantify [23]. Scope-2 deals with indirect emissions, such as the management system for leachate and gas extraction systems like blowers, which consume electricity purchased from external sources, as well as monitoring equipment. Whereas Scope 3 refers to the fuel or power generated from the gas, often called avoided emissions. For instance, the gas is used to generate upgraded compressed natural gas and electricity with the aim of displacing nonreplenishable fossil fuels [2].

Scoping is the deciding factor for the outcomes of accounting for LFG; therefore, assert boundaries needed to avoid comparisons among the emission reduction techniques, relevant source omission, and dual counting [12].

3.2 Modeling parameters critical role

Accounting for LFG is highly sensitive and depends on a few key parameters that directly impact mitigation strategies, financial planning, and the prevalence of overall uncertainty. The decay constant (K) refers to the rate at which the organic waste fraction decomposes to produce methane (CH₄) at landfills. The “K” depends on operational practices, the composition of waste, the presence of moisture, and climate [2, 18]. Underestimation of “K” could lead to uncontrollable emissions from landfills and extend the mitigation measures, while exaggeration of the “K” value could result in premature investment in oversize gas collection facilities [5].

Per unit mass of waste from which methane is generated is known as methane generation potential (Lo), and it is derived from the composition data of waste. The discrepancy arises in Lo directly pronounced in areas where detailed studies are lacking in the characterization of waste [15].

Methane oxidized by the methanotrophs in the cover soil of a landfill site is represented as the methane OF. In contrast to the guidelines of the IPCC, which have provided default OF values, it varies widely due to dependence on moisture, temperature, soil properties, and design cover [6].

All these factors, like OF, Lo, and K values, demonstrated that accounting for LFG is a complex exercise in uncertainty management fundamentally. Fair and accurate documentation is required by adopting polished versions for measurements of LFG, parameter selection, and sensitivity tests to ensure that the outcomes of accounting meet the objectives of climate policies and effectively support mitigation targets [2].

4. Toolkit for quantification: From onsite measurements to model-based verification

Accurate quantification of methane (CH₄) corroborates mitigation strategies and credible claims for climate and regulatory compliance more effectively [18]. Earlier LFG estimations relied on conventional theoretical models for futuristic planning and reporting in the form of inventory, but as time progresses, advancements in analytics and sensing have gathered attention. These advancements have led to an increased interest toward verified onsite real-time measurement of LFG. This transition in measurement approaches has benefitted accuracy and performance evaluation of the techniques employed, through which mitigation strategies can be planned accordingly [28]. Additionally, it has emphasized the requirement to integrate measurements and models, and address uncertainty issues while managing landfills under the system of LFG accounting [2].

4.1 Planning tool: A model based evaluation

4.1.1 FOD model of IPCC

To estimate the methane generation from waste disposal sites, the IPCC has introduced a model named the FOD model [18]. This model presumes that the DOC in solid waste decays exponentially as time passes, from months to years, which is directly proportional to the release of methane (CH₄).

CH4t=∑x=1tWx.DOC.DOCf.F1612ke−kt−x

where,

Wx = waste mass dumped in year x

DOC = degradable organic carbon

DOCf = decomposable fraction of DOC

F = fraction of CH₄ in LFG

K = rate constant in which decay occurs

It is assumed by this model that there is homogeneity in the composition of organic waste, steady environmental conditions such as moisture, temperature, and oxygen levels, and constant kinetic decay rates [24]. However, when it is applied for long-term planning and inventory creation, these default assumed parameters introduce discrepancies or uncertainties at the site level.

4.1.1.1 Sailent Features of this model

Temporal uncertainty: significant deviation in methane generation occurred due to factors such as moisture variability, uncertain waste placement, and engineered and operational practices adopted as a control strategy [6].

Compositional uncertainty: DOC content and rate of decay differ substantially with climatic factors, waste type (paper, greens, and food), and compaction [29]. The model relied on default parameters, which lacked the specific conditions present at a particular site. This resulted in an overestimation of methane, which is not compatible with field-based measurements.

4.1.2 Ex-ante analysis using the FOD model

Although there are limitations in evaluating methane generation from this model, it also played a crucial role as a performer where direct field measurements are impractical and not available for some reason. Ex – ante predictions are required for the exhibition and planning of gas collection systems and energy generation [30, 31]. The three common applications of FOD:

Well field extension planning: the density and time needed for horizontal or vertical gas extraction wells as progression in waste placement. This model provides information.

Sizing gas collection and control system (GCCS): FOD estimates the peak generation rates of gas, which are used to design the capacity of blowers, flares, piping of headers, and other energy recovery systems.

Prediction of potential energy generation from gas: estimated methane generation by this model is used for feasibility analysis of LFG conversion to energy, determining how much methane can be recovered over the lifetime of the project [28].

The contexts of under design risk reduction conservative probabilities are deliberately employed. In contrast, the limited overview of actual system functioning and fugitive discharge of LFG has been provided by the model.

4.2 Verification and improvement tool for direct measurement

4.2.1 Top–down versus bottom–up approaches

There are two approaches followed for accounting or quantifying LFG. The top–down concept relates to the emission measurements by analyzing the concentration of methane in the atmosphere and inferring fluxes by considering the meteorological data. Whereas, the bottom–up approach refers to the summing up of individual components while calculating the emissions. For instance, tracer correlation technique, satellite and aircraft-based remote sensing, and airborne mass balance method are part of the top–down approach [32, 33]. The bottom–up approach includes flux chamber technique, equipment-level EF, and methane concentration and flow well head data [34].

The top–down approach methods evaluated the emissions collectively, including operational upsets, surface leaks, system losses, etc., keeping them valuable in terms of verifying the total release of methane. Yet, their limitation lies in providing diagnostic insight for certain sources, along with their sensitivity to changeable atmospheric conditions and plume threshold detectability [2].

While the bottom–up approach furnishes high spatial resolution and attribution of sources, this approach also tends to underestimate emissions and involves labor-intensive efforts when coverage for measurements is episodic or incomplete [32, 33]. Therefore, the best practice adopts a hybrid system where bottom–up inventories are used in conjunction with the accuracy and confidence exhibited by the bottom–up approach.

4.2.2 The paradigm emergence of the MRV framework

The estimation of the methane realm evolved in the form of a MRV framework. Transparency, independent verification, and repeatability, in correspondence with regulatory initiatives, corporate net-zero commitments, and the carbon market, are the main focus of this system [25].

4.2.3 Modern methane MRV systems consist of advanced sensing modalities

4.2.3.1 Advanced sensing technologies

The advancement in sensing techniques propagates widely, available under the toolkit of MRV, specifically in the landscape of methane quantification and mitigation at the landfill site as shown in Figure 2. The continuous ground-based sensors, mobile platforms, and drones, along with satellite analytics, represent the individual temporal and spatial attributes considered for the estimation of methane emissions. Collectively, they form a planned multiscale monitoring system and also serve as the foundation of advanced technologies.

Figure 2.
Advanced modern modalities for GHG mitigation at the landfill site. Source: author’s generated from an AI tool.

4.2.3.2 Mobile platforms for monitoring and drone technology

The coverage of large, unreachable, and complex sites is assessed through target-based surveys using these technologies. The methane analyzers of high sensitivity, mounted on this equipment, can effectively scan or measure the gas collection infrastructure, landfill surfaces for methane systematically, perimeters of the site, and identify hotspots of methane emissions such as cap deformities, well head leaks, and exposed piping. The modulation of sensors and satellites using this framework helps identify areas of concern and alerts operators to conduct thorough investigations. This system also assists in verifying mitigation strategies adopted during investigations. Ground-based emission estimates are typically episodic and highly sensitive to meteorological conditions [33]. The high precision in spatial resolution of this equipment makes it reliable for detecting leaks, defects, and operational disruptions through proper diagnosis.

4.2.3.3 Continuous ground-based satellite-tuned sensor network

These satellite-tuned sensors furnish complementary potential for high-frequency, time-resolved data of methane. The static ground-based sensors are placed at different locations in and around the facility, which monotonously record the concentration of methane at minute intervals. The capture of intermittent and transient methane emission episodes is crucial, corresponding to system failures, waste placement practices, and fluctuations in barometric pressure. The disproportionately high or low emissions arise as a result of these issues and can be corrected by periodic surveys [33]. Continuous streams of data encourage system under performance detection, temporal emission dynamics understanding, and trend analysis. In contrast, their effectiveness depends on appropriate air dispersion models and the placement density of the sensors, which should be relatable to the emission rates and the observed concentration of methane.

4.2.3.4 Methane analysis based on satellite

It is an independent and scalable section of monitoring that enables emission surveys across large geographic areas. For instance, GHGsat and other high-resolution spatial satellites offer scalable detection of methane plumes in the form of absorption of the infrared spectrum reflected in sunlight. They provide an overview of large point source emissions from individual units. Satellite-based observations play a substantial role in planning mitigation, independent verification, and regulatory supervision due to their ability to reveal persistent point and anomalous sources of emissions, unlike reported observations by operators. There are certain limitations to satellite-drawn data, such as sensitivity to surface reflectivity and cloud cover. However, due to the frequent mobility of satellites, efforts to revisit areas establish them as accountable and effective screening tools within the framework of MRV.

The integration of three modalities, regulated by satellite, forms a tiered monitoring structure that consists of broad-scale continuous detection, performance tracking, and diagnosis at the individual facility or unit level. This three-layered support system, consisting of emission estimation and episodic accounting, advances toward real-time assessment that drives the management of methane, facilitates speedier mitigation, and increases credibility in the reporting of its emissions.

4.3 Management and quantification of uncertainties

The remediation of uncertainty is the critical element when assessing the quantity of methane, as it corresponds to its credibility. Real-time emission measurements and models contain inherent errors, which occur due to varied parameters, representative samples, precision of instruments, and presumable analytical conditions.

The best treatment for uncertainty involves the following practices:

To report the point estimates in conjunction with the confidence intervals or ranges of error.
The distinction between random error and systematic bias.
Assessing the propagation of error across the stream of emission calculation, specifically at the time of evaluating the financial and climate claims proportional to the reduction of methane.

The uncertainty influences the performance assessment of mitigation effects in some ways:

Determination of regulatory compliance
Carbon credits eligibility and validity
Destruction and avoidance efficiency claims

Therefore, a disclosure of uncertainty increases credibility and strengthens authenticity, aligning with the quantification of true limits in reported outcomes [2].

4.4 Evidence based estimation

Scalable transitioning of methane quantification advances from models to the verification of evidence. Models suggest planning, whereas outcomes validate on the basis of estimation. The development in the MRV frameworks relates to the integration of multilayered measurement techniques, ex-ante modeling systems, and meticulous assessment of uncertainty, which indicates that the best approach is incorporated in landfill management. These two tools collectively enhance accuracy in accounting but also enable the mitigation policies evolving in the context of climate and regulatory regimes.

5. Mitigation strategy portfolio: A techno-economic analysis guided by accounting

Waste management relies on the effectiveness of methane mitigation measures. Not only does its existence depend on the deployment of mitigation technologies, but it also demands a portfolio of aligned strategies synchronized with an accounting framework, system stability, and emission pathways [2].

5.1 Emission pathways connected to the strategic classification

The emission life cycle is greatly influenced by methane mitigation planning, which determines when and where intervention in the emission life cycle can be undertaken [33, 35]. The life cycle of emitted gas includes the occurrences before and after gas generation, as well as the duration of its migration. Each phase presents a distinct challenge while accounting for the emissions, which substantially impacts the reporting framework and the perceived measures taken for effective mitigation [36].

5.1.1 Preventive measures for avoiding methane emissions

At the source level, prevention of methane emission involves diverting the organic fraction of the waste that undergoes anaerobic digestion environments. Other than anaerobic fermentation, commonly adopted methods are organic waste recycling and composting. These methods, in terms of a physical point of view, offer great potential to mitigate methane emissions from landfill sites.

From the emission accounting perspective, under which preventive measures are being taken, it is, however, inferred as controversial. While estimating the quantity of methane that would have been generated had organic waste been dumped at the landfill site – which is calculated by a counterfactual baseline – for this reason, reported emission reduction strategies are often demonstrated as “avoided emissions,” Decay rate, model assumptions, waste composition, and climatic conditions become unclear as a result of avoided emissions. The slight variation in baseline properties drastically influences the comparability and verification, resulting in fluctuations in the reporting of benefits [3].

Moreover, the disparities that appeared in actual emissions compared to the avoided emissions are often temporary. These diversions appear promptly, while methane generation through modeling interfaces extends over decades, in coordination with the reporting of inventory on a yearly basis. Questions arise due to discounting and permanence (GHG Protocol, 2015). As a consequence of this, the treatment methodologies might be subdued or tend to be considered inconsistent in terms of voluntary and regulatory accounting systems, even though they have a strong environmental rationale [36].

5.1.2 Biological oxidation and containment for targeting fugitive emissions

The fugitive methane emissions from the landfills, which escape from the active gas collection framework, are the key indicators of containment and biological oxidation. Engineered soil cover, biocover, and geo-membranes, complemented with methanotrophs, curb the surface emissions of methane by contributing to the oxidation process, converting methane to carbon dioxide [37].

The principal challenge in the realm of accounting for methane is the OF evaluation. OF is the fraction of methane biologically transformed prior to its release into the atmosphere. The rate of oxidation relies on certain atmospheric factors; these are temperature, moisture, thickness of cover soil or other material, seasonal fluctuations, and composition of substrate. Therefore, OF is site-specific [38]. Even though pilot studies often show higher oxidation potential, it is still difficult to convert these findings into long-term, defensible site-wide values.

The reliance on default OFs used mostly by accounting systems does not reflect real field performance. Most accounting frameworks primarily rely on default OFs that may not reflect actual field performance and results, leading to either optimistic exaggeration or conservative underestimation [33, 35]. The tracer gas estimation technique and surface flux determination have been gaining increasing attention and confidence, yet they remain economically nonfeasible and lack scalability [36]. The position occupied by verification and containment is intermediary in the mitigation portfolios since it serves as technically viable, though with limited scope in the accounting framework.

5.1.3 Managing the generation of gas through active collection and control

The active gas collection framework comprises piping and a gas well network, blowers, a robust energy recovery unit, and flares to capture the large volume of methane within the premises of waste disposal facilities. These systems are the pillars of the mitigation system worldwide for landfill methane. These systems generally support the accounting framework due to the direct estimation of emissions from the operational values [39].

To determine the gas collection efficiency (CE) serves as a critical challenge in the accounting framework. CE is defined as the capturing of the volume of methane by the system. The CE is not directly measured; therefore, it is inferred through surface emission estimations and modeling portfolios, such as the inverse approach in modeling [23]. It is assumed that the calculated value of CE is significantly influenced by operational practices, system failure, well spacing, and the permeability of waste.

Whereas the destructive efficiency or potential of flares and while DE for engines and flares is generally represented as well-characterized and high, discrepancies in CE markedly impact the total emission estimations. Consequently, reported performances of the mitigation measures might diverge substantially from theoretical observations, particularly at sites where the prominence of heterogeneous waste coincides with minimal system maintenance [36].

5.2 Accounting outputs is the major aspect of technological selection

The emission trajectories and rates of gas production determined through the modeling of gas generation rates played a key role in financial planning and the selection of technologies. The gas modeling framework is not confined to inventorization and reporting, but it also facilitates justifiable capital expenditures and forecasting potential revenue generation [33, 35].

The forecasted gas production depends on its timing and magnitude, which collectively influence whether the landfill operator should invest in a gas-to-energy (Gte) configuration or flare assembly installations. The landfill owners and stakeholders choose the flaring option when gas flow is low or declining due to minimal operational complexity and the lower capital investment required. Whereas high flow rates of gas, with their continuation over an extended period of time, enable GtE projects such as the generation of electricity; transforming gas to natural gas promotes the offset of higher upfront investment balances with revenue generation [3].

The gas generation models enclosed within the accounting framework are crucially assumed. This is due to reasons such as the waste acceptance rate, decay rate constant, and climate rectifications, which can position the project to potentially meet the criteria for financial feasibility. In techno-economic assessment, it is the central driver, rated substantially higher than merely performing a reporting exercise within the accounting system. Overestimation of gas production could lead to underperforming strategies for power generation and stranded assets, while conservative predictions might delay profitability [36]. Thus, the accounting of LFG is not merely a reporting exercise but a techno-economic decision-driven subject aimed at achieving meaningful outcomes.

5.3 Mitigation system performance matrix

The system-level outcomes and component efficiencies distinction is required for evaluating the performance of mitigation. There are three important matrices which are specifically considered: DE, overall recovery rate, and CE of gas [39].

DE is represented as the fraction of total collected methane that is being consumed or destroyed by the energy transformation facility and flaring system. This is the least uncertain parameter, which is usually more than 98% and considerably stable.

CE refers to the capturing efficiency of methane by the cover material and well fields. The designing and operational activities influence the CE. It is a significant source of uncertainty [23].

Total gas recovery rate is associated with the product of two efficiencies: destruction and CE. It is a meaningful measure of real-world mitigation initiatives. The recovery rate of gas often demonstrates the discrepancies that exist between actual outcomes and theoretical results. In contrast, the model-informed condition, where the recovery rate surpasses the range of 80–90%, typically shows lower values during field monitoring events due to the occurrence of leakage, spatial variability, and downtime of the gas [36].

For improving credibility in accounting and the adoption of realistic planning in mitigation, it necessitates the identification of discrepancies. Theoretically estimated potential of methane generation can undermine the sureness of methane reduction reporting; therefore, certainty or overreliance is generally avoided while considering investments. The key parameters which needed to be considered as shown in Figure 3 while performing mitigation based on matrix. Thrive in methane mitigation strategies, the integrated robust pathways of containment, control planning, portfolio systems, and preventative conventional accounting approaches prioritize enhancing transparency.

Figure 3.
Landfill gas emission mitigation performance matrix. Source: author using an AI tool.

5.4 Integrated mitigation strategies and its implications

The diverse mitigation portfolios required for customization in the context of policy-driven and site conditions in techno-economic assessment are demonstrated in the accounting system. The measurement problem, with incremental benefits provided by the containment and oxidation of methane, shows that an active gas collection system offers quantifiable reductions, albeit with limitations in CE, and, lastly, preventive strategies provide substantial long-term advantages despite dealing with challenges in accounting [2]. The reliable accounting approach is a measure of precise emission reduction techniques that reflect credible investment opportunities and atmospheric outcomes.

6. Mitigation effective evaluation: Integrating accounting into performance assessment

The robust methane mitigation effectiveness evaluation necessitates a wise accounting framework that renders climatic outcomes via operational practices. The emission reduction estimations, financial viability, and comparison among the alternative pathways of mitigation have been adopted by the landfill owners and the decision-makers. It is the integration of LFG accounting into performance-based analysis.

6.1 Calculating CO₂ equivalent reductions: Baseline and project emissions

The calculation of carbon dioxide (CO₂) equivalent is the basis for performance analysis for emission reduction as one of the mitigation pathway strategies. The quantity of methane that would have been generated without the occurrence of any mitigation plan is the commencement phase where a baseline scenario needs to be established. The use of baseline emissions, typically by the FOD model, is employed to estimate methane generation over time based on the composition and quantity of waste, atmospheric conditions, and existing management approaches, as given in [39]. The estimated modeled values are used to assume the collection efficiencies and oxidation in soil cover. The modeled assumptions are also made for voluntary and regulatory accounting frameworks [36].

To assess the actual performance of emission reduction outcomes, the project emissions are accounted for. The emissions of the project include evaluated quantities of LFG collected, utilized for energy generation, and flared. This is demonstrated in three ways: the volume of produced LFG and its conversion to CO₂ equivalent (CO₂e), which is specifically evaluated for each gas in the LFG mixture as a GWP. Moreover, residual methane that is directly released into the atmosphere, also known as fugitive methane emissions, cannot be ignored while calculating the project emissions. The estimation of fugitive emissions is done using flux chamber methodology, default emission, and OFs [40]. The quantification of methane is measured in CO₂e. The default CE and available onsite emission records are typically used for estimating the fugitive emissions. The ancillary data of equipment and biogenic CO₂ that has been released from combustion activity is also used in energy generation projects as an additional form of emissions from the landfills. Therefore, to evaluate the net emissions, the subtraction of total emissions of the projects from the baseline emissions is performed. The result of this difference shows the amount of methane destroyed or avoided during mitigation operations. The CO₂e expression is used for net emission reduction and is applied to various components, such as supporting carbon market participation, internal reporting or tracking of sustainability, and regulatory recording. Additionally, it is also used to enable differentiation across various projects in terms of their CO₂e.

6.2 LCA as the holistic sustainability lens

The wider environmental effects of various mitigation planning and pathways are absent or not reflected accurately in fugitive emission accounting, which represents the on-site climatic benefits. Therefore, to address this issue, the LCA methodology is being used to widen the analytical boundary beyond the landfill site in order to evaluate the total climatic implications due to mitigation actions taken across their complete life cycle. Studies have shown that mitigation actions in conjunction with engineered bio-covers, energy utilization, and gas CE significantly lower the climatic implications throughout the life cycle of landfills in comparison to the uncontrolled disposal of waste at landfill sites. LCA provides a realistic performance evaluation of CE and methane oxidation [37]. This LCA is a viable option for comparing power generation alternatives such as electricity, natural gas upgrading, flaring, and the diversion of landfill waste for anaerobic fermentation and composting [41]. For instance, when LCA is applied to the assessment of electricity generation objectives, it not only accounts for landfill methane destruction but also estimates the avoided emissions from displaced fossil fuel-based electricity generation. In contrast, when guiding decisions for investment and policy frameworks, the LCA outcomes must be used with caution, as they are susceptible to methodological considerations that involve system boundaries, displacement assumptions, and allocation schemes, as noted by the Climate and Clean Air Coalition [7, 42].

These avoided emissions substantially increase the net advantage from a climatic perspective, specifically in the sector that deals with carbon-intensive power grids. Conversely, emissions from the installation, manufacturing, and functioning of energy conversion systems should be included in the LCA, as it exhibits a burden-shifting effect.

The economically viable flaring technology furnishes some benefits when applied for LCA. This process exhibits substantial methane depletion with no generation of avoided emissions through fossil fuel consumption. As a result, it provides less climatic performance in comparison to recoverable energy processes. The indirect emissions generated from the waste diversion techniques, although they minimize methane emissions, at the same time introduce emissions in the form of material processing, nitrous oxide emitted from the composting process, and transportation. Therefore, waste diversion methods further complicate the comparability among their own operations.

Project developers and policy framers can find mitigation solutions that improve climatic actions completely while minimizing unforeseen environmental trade-offs with the application of LCA, rather than adopting optimization in site-specific processes.

6.3 Cost-effectiveness analysis: Linking emissions with economics

The analysis of cost-effectiveness is expressed in terms of economic feasibility (dollars per ton of CO₂e abated) of emission minimization. It also offers direct differentiation among the mitigation options for landfill methane. As stated earlier, flaring is the most cost-effective option based on its operational and capital cost incurrence. However, it has cons in terms of no revenue generation unless it is part of a regulatory compliance system. The requirement of higher upfront capital investment for the conversion of LFG to electricity is yet remarkably achieved in the realm of fuel credits, incentives, and cost-effective sales of power. Renewable natural gas (RNG) refinement initiatives significantly improve cost-effectiveness as they are capital-intensive [33, 35]. Though RNG is effective in revenue generation and emission reduction, its inclusion in carbon markets and renewable fuel programs, such as the Climate and Clean Air Coalition [42], enhances its impact. In addition to lowering emissions, RNG can also minimize abatement costs, achieve net negative expenses, and generate profits.

7. Policy, markets, and the future of integrated gas management

The LFG economic feasibility, design, and operation are increasingly shaped and usually assessed in terms of market mechanisms and public policy. Carbon markets and regulations are the major forces behind the shift to an integrated gas measurement-driven management system rather than merely being restricted to a compliance system.

7.1 Regulations as drivers

The main driver of technological up gradation in LFG control is now limited by environmental factors. The strict regulations in accounting and reporting frameworks have led to a decrease in the tolerance for uncertainty present in emissions estimated through default and modeled methodologies, especially for those with minimum values of emissions used to determine controlled methane. Landfill operators are obligated to implement better gas collection infrastructure, resilient cover systems, and more advanced monitoring technology. This is being done as regulators shift toward measurable performance and away from broad assumptions. Reported emissions and related liabilities have frequently gained attention. These regulations effectively penalize underperforming systems while rewarding establishments that can demonstrate high capture efficiency [30, 39]. The accounting system now directly impacts engineering options and capital investment plans rather than being merely a passive reporting tool [2].

7.2 Carbon markets as enablers

The mitigation of methane can be transformed into valuable assets that are compliant with the carbon market, sold voluntarily, and serve as a complementary process. Standardized and fair accounting solutions for measuring the emission reduction potential are provided by carbon reduction or offset methodologies [25]. These carbon offsets are produced by registries like the American Carbon Registry and the Climate Action Reserve, 2021 [43]. Approaches like project financing with minimum risk for investors are made possible by defining baselines, uncertainty deductions, system limits, and monitoring criteria, as outlined by the Climate Action Reserve [43]. Many landfill owners and operators utilize carbon credits to finance improvements such as automated control systems, increased well field density, and continuous monitoring technology, which would otherwise not be profitable [28]. The gap between regulatory pressure and beneficial financial outcomes is effectively minimized by carbon markets. They also promote the adoption of the most advanced technologies.

8. Conclusion and synthesis toward precise accounting and effective mitigation

8.1 Key insight

The method used to successfully execute mitigation schemes in the waste domain is affirmed by the accuracy of the data on which decisions are being inferred. Incorrect data or fallacies in emission accounting are likely to alter the mitigation outcomes. The accuracy of the data used to make decisions for climate mitigation is crucial for the waste sector’s potential. If mitigation options are chosen based on an erroneous or flawed emission accounting system, they cannot be optimized or altered as methane release and collection vary significantly. However, they are associated with clear and focused operations. The complex accounting framework provides minimal practical advantages. Consequently, rather than being purely technologically driven or policy endeavors, efficient mitigation and accurate measurement must be seen as mutually reinforcing cornerstones of sustainable waste management.

8.2 The role of accurate accounting

The empirical basis for understanding the actual climate impact of waste disposal is provided by robust LFG accounting. High-emitting sites can be obscured, the legitimacy of climate agreements can be undermined, and mitigation resources can be misallocated due to discrepancies in emissions estimates. Policymakers and landfill operators can prioritize transparency, assess performance over time, implement initiatives, and guarantee accountability with improved accounting. Even well-established mitigation initiatives run the risk of being ineffective or misguided in the absence of reliable data.

8.3 The necessity of action-oriented mitigation

Accounting systems that are not connected to observable mitigation results are unable to produce significant climate advantages. Investments in gas capture, utilization, or reduction technologies that quantifiably lower emissions should be guided by measurement technologies. Performance-driven mitigation acknowledges that results are ultimately more significant for the climate than recommended practices. These options ensure that emission reductions are genuine, verifiable, and long-lasting, while promoting innovation.

8.4 Policy and investment recommendations

This synthesis leads to three linked recommendations. Firstly, to lower uncertainty in LFG estimates, consistent investment in measurement infrastructure is crucial. This includes developing operators’ and regulators’ capabilities, standardizing procedures, and enhancing monitoring systems. Secondly, rather than using prescribed measures, policies should reward performance-based results. These programs align economic incentives with climate goals by rewarding MRV for reductions in emissions. Thirdly, waste management regulations should be comprehensive, requiring cutting-edge gas management systems for residual waste that cannot be avoided, while simultaneously focusing on upstream waste diversion techniques, recycling, and reduction processes [44–47].

8.5 Toward integrated waste and climate policy

Even in challenging circular economy scenarios, landfills are still a part of the system, as acknowledged by holistic waste policies. Although refuse streams will produce LFG for many years to come, upstream diversion of waste minimizes volume and degradability. Therefore, ensuring a top-notch gas collection and treatment system is an essential addition to waste reduction initiatives rather than their replacement. Integrated waste management policies can reduce waste production, optimize resource recovery, and regulate inevitable emissions all at the same time.

8.6 Final statement

Robust LFG accounting and mitigation systems are crucial for climate action within a sustainable waste management portfolio; it is not merely a technical exercise. When combined, they help close the gap between the larger goals of a low-carbon future, circular economy, and refuse disposal methods. The trash industry can contribute credibly and quantifiably to global climate goals by combining comprehensive policy design and precise measurement with efficient, performance-driven mitigation operations.

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