Methane emissions from MSW landfills represent a lost opportunity to capture, recover and use a significant energy resource
Representative photo: iStock Greenhouse gases (GHG) emitted from the waste sector include carbon dioxide, methane and nitrous oxide, among others.
While methane accounts for only about 14 per cent of the GHG emissions from the waste sector, its atmospheric concentration has more than doubled over the last two centuries, primarily due to anthropogenic activities.
Methane’s global warming potential (GWP) — the ability of the gas to trap heat in the atmosphere — is 25 times more than carbon dioxide (CO2) and has been second only to CO2 in terms of causing climate change during the industrial era.
Recently, the Intergovernmental Panel on Climate Change identified methane’s GWP between 28-36, considering its impact for a 100-year timeframe.
Methane is considered a short-lived climate pollutant, meaning it has a relatively short lifespan — of approximately 12 years — in the atmosphere.
In addition, methane potentially contributes to the formation of ground-level ozone or tropospheric ozone (O3), a hazardous air pollutant and greenhouse gas. Exposure to ozone causes one million premature deaths every year globally.
Wastewater treatment and discharge (both industrial and domestic) contribute the highest to methane emissions from the waste sector.
Methane is produced during the decomposition of organic matter in wastewater. This can occur in both wastewater treatment plants and after wastewater is discharged into the environment. The amount of methane produced depends on several factors, including the type of wastewater, the treatment process and the environmental conditions.
Another source is solid waste disposal on land. Methane is produced during the decomposition of organic matter in solid waste. This can occur in landfills, open dumps and other waste disposal sites. The amount of methane produced depends on several factors, including the type of waste, the disposal method and the environmental conditions.
India’s methane emissions in 2016 (excluding land use, land-use change and forestry) were 409 million tonnes of CO2 equivalent, according to India’s Third Biennial Update Report.
Of this, 73.96 per cent was from the agriculture sector, 14.46 per cent from the waste sector, 10.62 per cent from the energy sector and 0.96 per cent from the industrial processes and product use sector.
A pie chart showing sector-wise data on methane emissions. Source: India’s third BUR, MoEFCC, 2021
Open dumpsites and landfills indeed represent significant sources of anthropogenic methane gas emissions. In India, a substantial portion of the waste generated is biodegradable.
Even when landfills are scientifically capped, mixed municipal solid waste (MSW) continues to emit methane for an extended period. When mixed MSW is deposited at a landfill site, a series of biochemical reactions occur, leading to the generation of methane gas, as well as other GHG and toxic gases.
Besides, methane emissions from MSW landfills represent a lost opportunity to capture, recover and use a significant energy resource. For example, the organic waste in MSW can be converted into compost or biogas.
Landfill gas (LFG) emissions from an open dumpsite. Source: Methane emissions from open dumpsites in India: Estimation and mitigation strategies, Richa Singh, Centre for Science and Environment, New Delhi.
As reported by many biogas plant owners, typically, 1 tonne per day (TPD) of segregated biodegradable waste generated in Indian cities has the potential to produce 80 to 100 cubic metres of biogas.
This biogas primarily consists of methane (50-75 per cent), carbon dioxide (25-50 per cent) and smaller amounts of nitrogen (2-8 per cent). Some levels of hydrogen sulphide, ammonia, hydrogen, and various volatile organic compounds are also present. This translates to approximately 42 kg of methane or 1176 kg of CO2 equivalent (considering that 1 TPD of biodegradable waste generates 60 cubic meters of methane, and the density of methane gas is 0.7 kg/m³).
This implies that the disposal of biodegradable waste in landfills or dumpsites is extremely harmful from a climate change perspective and represents a wasted opportunity. In landfills, methane is produced in an uncontrolled manner and is released into the environment as a climate pollutant.
However, if this waste is subjected to a bio-methanation process in centralised and decentralised facilities with gas collection systems, it can be used for various beneficial applications, such as converting biogas into bio-CNG, generating electricity or producing other types of fuel.
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