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Page 4 of 18 Shang et al. Carbon Footprints 2025, 4, 24 https://dx.doi.org/10.20517/cf.2025.28

various sources into a unified system. This study addresses that gap by investigating methane generation
patterns, key drivers, and mitigation potential across waste sources under China's strengthened methane
control policies. The findings aim to provide actionable insights for policymakers and recommendations for
enhancing waste methane management.

METHODS
Methodological framework
Waste refers to discarded environmental pollutants generated by human activities such as production,
construction, and daily life, which are no longer considered usable at a given time and place. According to
the IPCC National Greenhouse Gas Emission Inventory, waste can be classified by greenhouse gas emission
sources into municipal solid waste (MSW), sludge, industrial waste, and other categories. This study
develops a methane emissions accounting framework for waste, structured around five socioeconomic
sectors: urban sewage, urban living, agricultural activities, industrial activities, and other activities
[Figure 1]. These categories capture the primary activities responsible for waste generation in both urban
and rural contexts. The framework is designed to “open the black box” of methane generation from waste,
enabling an analysis of the sources, transformations, and pathways of element flows within each sector.

Methane emissions from waste primarily originate from the decomposition of organic matter through
anaerobic processes. The anaerobic conditions in landfills are the dominant source of methane, as organic
residues from diverse disposal processes across activity sources enter landfills and decompose. At the
subsector level, urban domestic sewage, municipal waste, livestock and poultry manure, crop residues, and
organic industrial waste can all generate methane. Industrial waste, however, is generally recycled or
properly treated, as enterprises are directly responsible for its management. As a result, methane generation
and disposal in the industrial sector occur over relatively short intervals in an efficient and centralized
manner. Because industrial waste is rapidly processed after generation, it is not the main focus of this study.
In contrast, commercial/institutional waste, park waste, and medical waste typically contribute to methane
emissions once deposited in landfills. Accordingly, this study focuses on methane emissions from four sub-
sectors: municipal solid waste, urban sewage, agricultural cropping, and livestock and poultry farming.

Data sources
The provincial methane inventory for waste in China was constructed in accordance with the Handbook of
Methods and Coefficients for Pollution Emission Calculation in Emission Source Statistical Surveys, the
Technical Guidelines for Compilation of Integrated Emission Inventory of Air Pollutants and Greenhouse
Gases (Trial), and the Guidelines for Compilation of Provincial Greenhouse Gas Inventory (GCPI) . The
[33]
[34]
accounting data used in this study were mainly retrieved from the China Rural Statistical Yearbook ,
China Urban Construction Yearbook, and China Urban and Rural Construction Yearbook , covering the
[35]
period 2018-2022. Data on the grass-feed ratio and straw utilization rate were drawn from official statistics,
policy documents, and research reports issued by the State Council and the Ministry of Agriculture and
Rural Affairs of China.

Methane emissions accounting methods for each sector
Municipal solid waste
Urban solid waste, after recycling and landfilling, undergoes processes of adjustment, transition, and
acidification, during which methanogenic bacteria generate methane. Part of this methane is subsequently
treated through leachate management systems. The LandGEM model, proposed by the U.S. Environmental
Protection Agency, is used to estimate landfill gas production , as shown in Equation (1):
[36]