MSW stands for municipal solid waste, the everyday trash and garbage generated by households, businesses, schools, and institutions. In environmental science, MSW is a central topic because of its massive scale, its contribution to greenhouse gas emissions, and the challenge of managing billions of tons of discarded material each year. The United States alone generated 292.4 million tons of MSW in 2018, which works out to about 4.9 pounds per person per day.
What Counts as Municipal Solid Waste
MSW includes durable goods like tires and furniture, nondurable goods like newspapers and disposable cups, containers and packaging such as milk cartons and plastic wrap, plus yard waste and food scraps. Food waste is the single largest component, making up 24% of all U.S. municipal solid waste by weight. Packaging, containers, and durable goods together account for about 48%.
What MSW does not include is important too. Industrial waste, construction debris, sewage sludge, and agricultural waste all fall into separate categories. Household hazardous waste, items like solvents, pesticides, oil-based paints, old batteries, and expired medications, technically gets generated alongside regular trash but is supposed to be separated and managed under stricter rules. In both the U.S. and EU, once hazardous items are sorted out of household waste, they must be handled as hazardous waste. In practice, many people throw these items in the regular garbage anyway. A Canadian survey found that 22% of households with expired medication simply put it in the trash, and 42% did the same with dead batteries.
Where All That Waste Ends Up
Half of all MSW generated in the U.S. goes to landfills. That’s a significant improvement from 1960, when 94% was landfilled, but it still represents more than 146 million tons buried each year. About 32% is recycled or composted (69 million tons recycled, 25 million tons composted), and roughly 12% is burned in facilities that capture energy from the process.
Environmental scientists pay close attention to the waste management hierarchy, a ranking system the EPA uses to prioritize strategies from most to least preferred. At the top is source reduction and reuse: generating less waste in the first place. Next comes recycling and composting. Third is energy recovery through controlled combustion. Landfilling sits at the bottom as the least desirable option.
Why Landfills Are an Environmental Problem
Landfills are the third largest source of human-caused methane emissions in the United States, responsible for 14.3% of the country’s methane output in 2021. To put that in perspective, U.S. landfill emissions equal the greenhouse gas output of nearly 23.1 million gasoline-powered cars driven for a year. Methane is a potent greenhouse gas, trapping far more heat in the atmosphere than carbon dioxide over a 20-year period, which makes landfill emissions a significant driver of climate change.
Landfills also pose risks to soil and groundwater. As rain filters through buried waste, it picks up dissolved chemicals and forms a toxic liquid called leachate. This liquid can carry heavy metals like manganese and barium, high levels of dissolved solids, ammonia, nitrates, and organic acids into surrounding soil and water. In countries where landfills lack proper linings or monitoring, including parts of India, Nigeria, Brazil, and Argentina, nearby water sources have been found contaminated with concentrations of these pollutants high enough to make the water unsafe to drink. The severity of contamination depends on a landfill’s age, size, and whether it’s still actively receiving waste.
The Food Waste Problem
Because food waste is the largest single material in the waste stream, diverting it from landfills is one of the most impactful things waste managers can do. When food decomposes in a landfill without oxygen, it generates methane. When that same food is composted in an oxygen-rich environment, it breaks down into a nutrient-rich soil amendment instead, with far lower greenhouse gas emissions.
Despite this, only about 3% of food waste in the U.S. is diverted from the waste stream each year. Of that small fraction, composting is the most common alternative to landfilling. Backyard composting works for yard waste and small amounts of food scraps, but large-scale diversion requires industrial composting facilities, which remain limited in many regions. The EPA considers any method of putting food waste to beneficial use preferable to burying or burning it.
Waste-to-Energy as a Middle Ground
Waste-to-energy plants burn MSW in controlled combustion chambers, using the heat to produce steam that drives turbines and generates electricity. About 35 million tons of U.S. waste goes through this process each year. Older incinerators were notorious polluters, running with few or no gas cleaning systems. Modern facilities operate under much stricter standards and use sophisticated filtration and monitoring equipment to control emissions, making them a viable option for waste that can’t be recycled or composted.
A Growing Global Challenge
MSW is not just an American issue. According to the World Bank, the world generated roughly 2 billion tonnes of solid waste in 2016 and is projected to produce 2.59 billion tonnes annually by 2030 and 3.40 billion tonnes by 2050. The fastest growth is happening in Sub-Saharan Africa, where waste generation is expected to nearly triple by 2050 (from 174 million to 466 million tonnes per year). South Asia and the Middle East and North Africa are each projected to roughly double their output over the same period.
East Asia and the Pacific already produce the most waste by region at 468 million tonnes per year, projected to reach 714 million tonnes by 2050. North America’s waste is expected to grow more modestly, from 289 million to 396 million tonnes. These projections make MSW management one of the defining environmental challenges of the coming decades, particularly for rapidly urbanizing regions that lack the infrastructure to handle the volume.