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Shang et al. Carbon Footprints 2025, 4, 24 https://dx.doi.org/10.20517/cf.2025.28 Page 5 of 18

where Q is the maximum expected landfill gas production (m /a); i is the year; n = (current year) - (year of
3
M
initial waste reception); j represents every 0.1 year, with a time step of 0.1 years; k is the methane generation
rate, taken as 0.3/a, which falls within the range of 0.1 to 0.5 according to Chinese landfill design standards;
L is the ultimate methane generation potential (m /t), taken as 80.352 after 2006 according to Chinese
3
0
landfill design standards; M is the amount of waste buried in the i-th year (t); t is the age of the j-th portion
ij
i
of waste landfilled in year i; is the methane concentration.
Because methane from solid waste in the inventory is assumed to be fully released within a year, the formula
can be simplified according to GCPI guidelines, as shown in Equation (2):

where is methane emissions (10,000 tons/year); MSW is the total amount of urban solid waste
T
generated (10,000 tons/year); MSW is the landfill treatment rate of urban solid waste; L is the methane
0
F
generation potential of managed landfill sites (10,000 tons of methane per 10,000 tons of waste); R is
methane recovery (10,000 tons/year); OX is the oxidation factor, taken as 0.1 for qualified waste treatment
plants. When R is considered in the formula, methane emissions are obtained; when R is excluded, the total
methane produced is calculated.

Urban sewage
Domestic sewage is primarily derived from residential sources. Methane emissions are calculated following
the GCPI methodology, as shown in Equation (3):

where is the total methane emissions from domestic sewage treatment in the inventory year (10,000
tons of methane/year); TOW is the total organic matter in domestic sewage (kg BOD/year), estimated from
COD content converted from total sewage discharge; EF is the emission factor (kg methane/kg BOD); R is
methane recovery rate (kg methane/year). The emission factor (EF) is calculated as the maximum methane
generation capacity (B ) multiplied by the methane correction factor (MCF). According to GCPI, each
0
kilogram of BOD in domestic sewage can produce 0.6 kg of methane, while the reference value for MCF is
0.165.

Agricultural cropping
In the agricultural cropping sector, methane emissions mainly originate from straw residue, which can be
either “returned to the field” or “removed from the field”. According to a 2021 Chinese government report,
the off-field utilization rate of straw in China was 33.4%, with five primary applications: feed, fertilizer, base
material, fuel, and raw material. Of these, fuel accounted for only 8.9% of off-field use. Off-field straw is
typically processed in large-scale anaerobic fermentation reactors. Methane generation efficiency varies with
straw type and treatment technologies, such as biochar application, hydrothermal carbon enhancement,
calcium peroxide combined with zero-valent iron, pretreatment with fermentation aids, and co-digestion