How Mumbai’s poor waste segregation contributes to methane emission spikes

Earlier this year, Mumbai’s Kanjurmarg landfill—a place that takes in most of the city’s waste—was found to be one of the largest emitters of the greenhouse gas (GHG) methane in the world, and one of only two landfills from India to make it to the top 25 list. As global warming accelerates, causing extreme and erratic weather across the world, the Paris Agreement's target of limiting the rise in global temperatures to 1.5-2°C by 2030 cannot be achieved at a reasonable cost without reducing methane emissions by 40-45 percent by that year, according to the United Nation Environment Programme's Global Methane Assessment 2021.

Methane is an odourless gas, but coupled with other landfill gases, it adds to local pollution, contributes to health issues and is also susceptible to fires. The residents of areas near the Kanjurmarg landfill have repeatedly complained of the unbearable stench from it and as part of an ongoing case in the Bombay High Court, two judges visited the landfill at night in April to personally inspect the odour. The High Court had pulled up both the municipal corporation as well as the company running the landfill, directing them to undertake a series of measures to control the stench.

Mumbai generates one of the highest volumes of waste in the country at around 6,300 tonnes per day of which around 72 percent is food waste. Methane emissions from Mumbai’s landfills have been a concern for years now and decomposing wet waste is one of its biggest causes. The international ranking points to the scale of the problem, which can be addressed through efficient waste management.

But chief engineer (solid waste management- projects) of Brihanmumbai Municipal Corporation (BMC) Avinash Kate cast doubt on the aforementioned rankings and said, “This particular report is based on a satellite study which may not be that accurate. We are commissioning our own study of methane emissions with the National Environmental Engineering Research Institute (NEERI) which will involve a drone survey, monitors and our own satellite data. Since the NEERI study will be across seasons, it will take a year at least,” said Kate.

(Source: GHG emission and carbon sequestration potential from MSW of Indian metro cities)

India 6th biggest emitter of methane

Methane, the second most abundant greenhouse gas after carbon dioxide (CO2), is 28 times more powerful than CO2 at warming the atmosphere, and is responsible for almost a quarter of global warming, as IndiaSpend explained in July 2022. Of India’s total GHG emissions, CO2 makes up for 80 percent followed by methane at 13 percent as of 2020.

Methane's impact is short-lived, as it remains in the atmosphere for just about a decade, compared to CO2, whose impact lasts for several decades. Methane, however, has far greater heat trapping capacity. In 20 years, methane can trap 80 times as much heat as CO2. Over a 100-year time frame, methane is 25 times as potent as CO2, according to the Global Methane Budget 2020. Fossil fuel production and consumption accounts for 35 percent of human-caused methane emissions, waste 20 percent and agriculture 40 percent, as per UNEP.

The International Energy Agency estimates that more than 85 million tonnes (Mt) of emissions tied to fossil fuels operations in 2025 came from the 10 biggest emitters of methane. China is the largest emitter, driven by coal operations, followed by the United States and Russia. India ranks sixth on this list.

Apart from their global warming potential, methane emissions lead to ground-level ozone (O3) pollution which causes approximately a million premature deaths every year globally, reduces crop productivity and harms ecosystems.

A model study estimated that methane contributes to approximately 35 percent of the present-day tropospheric ozone burden. Tropospheric ozone is a secondary air pollutant that is associated with adverse effects on human health, including asthma, reduced lung function, and chronic obstructive pulmonary disease, an August 2022 study in the journal Environmental Science and Policy noted. Another study estimated that in 2010, 1.0–1.2 million respiratory deaths in adults worldwide were attributable to O3 exposure. High CH4 emission scenarios could cause up to 91,000 additional global mortalities due to O3 exposure in 2050, whereas high CH4 mitigation scenarios could reduce O3 mortality by 40,000, the study said.

“Over the years of protest, despite judicial orders, the situation on the ground remains unchanged, with citizens continuing to suffer from foul odour, mosquito infestation, and significant health hazards affecting daily life,” a citizens group from Vikhroli called Shivsagar Yuvak Krida Mandal had said in a letter to chief minister Devendra Fadnavis earlier this year.

Mumbai’s methane impact equivalent to 1 million SUVs

In April, Telangana’s Secundarabad ranked fourth and Mumbai ranked 12th in the list of the world’s super-polluting methane emissions from the waste sector.

The report ranked 25 waste facilities in 18 countries responsible for the largest super-polluting methane rates detected from space in 2025, with a site in Argentina ranking number 1. Researchers from University of California Los Angeles’s STOP Methane Project analysed data showing nearly 3,000 plumes from more than 700 waste sites worldwide to identify the top 25 sites globally. A source emitting 5 tonnes of methane per hour (5,000 kg) would contribute about as much to global warming as one million SUVs, the researchers noted. The emissions rate for the site in Argentina was 7.6 tonnes per hour.

For Mumbai, which stood 12th, it was 4.9 tonnes per hour while for Secundarabad, which stood fourth, it was 5.9 tonnes per hour. The methane plume over Mumbai coincides with the location of the Kanjurmarg landfill. UCLA’s data also show a particular spike last winter in the Kanjurmarg landfill wherein methane emissions touched even 9.9 tonnes per hour in November 2025 and 6 tonnes per hour in December 2025. But the daily average stood at 4.9 tonnes per hour.

In India, the waste sector contributes to around 2.5 percent of our total emissions.

In 2014, when the share of GHG emission from 23 metro cities was projected through 23 models, results showed that Mumbai had the highest emission of CO2 and methane even back then, while Visakhapatnam had the least.

“The reason for strikingly high emission of GHGs from Mumbai is attributed to high CH4 generation rate which also depends on average annual rainfall i.e. 2,334.60 mm/year,” a 2014 paper published in Urban Climate, by researchers from the Indian Institute of Technology, Roorkee, had noted.

The study had estimated that the total global warming potential of GHG emitted through dumping of municipal solid waste from these 23 cities had 88 percent contribution from methane.

Another study published in August 2022 in Science Advances had found that more than a quarter of methane emissions (26 percent) in Mumbai originated in landfills. For national capital Delhi, landfills accounted for 6 percent of methane emissions.

Why waste management keeps failing

Mumbai generates around 6,300 tonnes solid waste every day, of which 5,900 metric tonnes is directed to the Kanjurmarg facility. At this facility, about 5,000 tonnes is processed in a bio-reactor while the rest is treated with compost (windrow composting). Mumbai has around 47 dry waste segregation centres.

The residents of Kanjurmarg, Vikhroli, Bhandup and other neighbouring areas of the landfill have repeatedly complained of the odour coming from the site, mosquitoes, and health hazards affecting hundreds of thousands of people. Meanwhile, a Vikhroli resident had moved the Bombay High Court. The High Court had already cautioned the state government and BMC that it may order closure of the Kanjurmarg facility if urgent and effective steps are not taken to address pollution and hazardous emissions at the site.

“Biodegradable waste should not be dumped in landfills because the biodegradation process contributes significantly to methane and other GHG emissions. The average concentration of methane in a dumpsite ranges between 3 to 15 per cent by volume, which is much higher than the ambient concentration of methane (0.00017 per cent by volume),” a 2023 report by Delhi-based think-tank Centre for Science and Environment had noted.

The civic engineer Kate said that BMC’s engineers are monitoring the stench in the area every night between midnight and 6 a.m.

“The odour might be caused by Hydrogen Sulphide, ammonia and mercaptans which cause the most stench but don’t cause any health hazards. These are within limits, all reports are shared with the pollution control board and the operator has to follow all the conditions laid down in the environment clearance given to the project,” he said.

Activist Rishi Agarwal who has been working on Mumbai’s waste crisis for more than 30 years is not convinced.

“The law clearly states municipal bodies will not collect mixed waste but segregation is neither being done nor is being enforced,” said Agarwal. “About 80 percent of a ward's waste should be managed within the ward boundaries. BMC should allocate one to five acres of land in every ward free of cost to waste management entrepreneurs who can do construction debris recycling, biomethanation, composting, plastic waste collection or a material recovery facility. The lack of space is a challenge in Mumbai which can be tackled this way.”

He believes that the civic body needs to look at newer ways of processing waste.

“We have suggested that wet waste from the city’s western suburbs, especially from the hotels near the airport, need not travel to a dumping ground in the eastern suburbs at all. BMC should collect it and set up a methanation plant at the erstwhile Gorai dumping ground site. The compressed biogas thus produced could power public buses,” said Agarwal who warned that material recovery facilities (MRFs) can become overwhelmed by the sheer volume of waste arriving every day and the same might be happening at the Kanjur landfill as well.

Kate said the BMC is planning to move the MRF within Kanjurmarg landfill’s premises further away from the residential area to control the odour.

T.S. Bisht, deputy programme manager at CSE, said that Delhi is no different when it comes to failing to segregate waste at home as it depends heavily on public awareness and participation.

“In practice, waste often ends up being collected together in the same trucks,” said Bisht. “Authorities have tried different approaches, such as using separate collection systems for different types of waste, but these efforts have not always been successful. Another issue is the limited number of Material Recovery Facilities (MRFs). In a city like Mumbai, the volume of waste generated is simply too large, around 5,000 to 7,000 metric tonnes per day. Managing and segregating such a massive quantity of waste through MRFs alone is extremely difficult. That is why sorting your own waste at home before handing it over to civic bodies is absolutely necessary.”

The civic engineer Kate listed a number of measures the civic body is planning to improve waste management and tackle the methane emissions from Kanjurmarg landfill.

“The landfill already has measures to capture methane through captive power technology. The excess gas is also flared when needed. We will increase the green belt around it,” he said.

When asked why Mumbai’s wet waste is reaching the landfills, why segregation and composting is not happening at source and why BMC has also not deployed separate trucks, Kate said, “It is a two-way street. We are getting mixed waste from societies. Even biomedical and sanitary waste has to be segregated. Source segregation has to be done, Mumbaikars don’t have a way out. We will plan awareness drives once again,” said Kate.

BMC recently also announced fines for individuals, housing societies and establishments that fail to undertake four-way segregation in a fresh drive to improve waste management in the city. The four categories as mandated in the Solid Waste Management Rules 2026, apart from dry and wet waste, include sanitary waste and special care waste such as tubelights, medicines etc.

(Prem Babar, intern with IndiaSpend, contributed to this report)

This report is republished with permission from IndiaSpend, a data-driven, public-interest journalism non-profit. It has been lightly edited for style and clarity.