So... Why Don't We Just Burn All Our Trash?

Incineration as a way to deal with waste is used around the world today, both formally and informally. In the United States, we landfill about 5 times more waste than we combust (2018 figures, EPA website). This varies between states, depending on land availability and usage requirements. Incinerators are still widely used in places where they don't have as much viable landfill space available, such as the state of Florida with its generally swampy land profile.

In short, we don't burn all our trash because 1) it creates air pollution, 2) municipal solid waste (MSW) is not a great fuel for energy generation, and 3) incinerators produce ash that still ultimately goes to a landfill.

Incinerators used to be much more popular in the U.S., but the Clean Air Act Amendments of 1999 (source) provided more oversight and requirements for hazardous waste incineration practices to protect public health. This has reduced incinerators' prevalence and changed the way we address waste, and has substantially reduced hazardous waste fumes from entering the air of U.S. communities. (If you live in U.S. Region 7, you can thank my mother-in-law, Lisa, for the cleaner air you're breathing due to her 30+ years as a public servant!)

Aside from solely hazardous fumes, there are also carbon emissions to consider. Given the recycling rates for plastics today, we can tell that a lot of the carbon-rich plastics we use end up in our MSW streams instead of our recycling waste streams. If the plastics are being burned and melted, the carbon in them is being aerosolized and put into the atmosphere, contributing to climate change.

Pollution is obviously a negative, but proponents of incinerators often advocate for their use due to the energy produced from the practice. However, MSW isn't a great choice for a fuel source to be burned is primarily due to the water content present in the mixed waste profile. There's a lot of moisture-rich food waste and yard clippings our municipal waste streams. Until more widespread composting services are accessible to communities in the U.S., this is unlikely to change. Yard waste programs have become more widespread over the past few years, which is a great step in the right direction. Currently, we tend to lump most waste products into one homogenous category, instead treating each waste stream as a unique challenge to re-incorporate into a more circular economy.

According to the U.S. EPA, "A typical waste to energy plant generates about 550 kilowatt hours (kWh) of energy per ton of waste." One ton is equivalent to 2000 pounds in the U.S. vernacular, so one pound of waste produces approximately 0.275 kWh of energy. Below is a chart I created comparing municipal solid waste as a fuel source to other materials commonly burned for fuel, using data from the EIA (source). Coal is known to be one of the least efficient fossil fuels, and it takes about three times as much garbage by weight to produce an equivalent amount of energy.

The last big thing no one talks about: incinerator ash still goes to the landfill. By weight, incinerator ash makes up 15-25% of the original content put into the incinerator (source). This ash goes to the landfill, and increases the risk of groundwater contamination due to its new form. A great paper from the state of Oregon's website (link) likens the relative risks between the original material and the remaining ash in the landfill to coffee beans versus ground coffee- pouring water over the whole beans will not extract coffee, pouring water over the grounds will. The ash is a greater hazard than the waste because it will impact the leachate (precipitation filtered through the landfill and pumped out at the bottom) from the landfill more substantially.

Informal waste incineration happens all around the world and has many adverse human health effects, but that could be an entire blog post in itself. Landfills are obviously not without their issues, but they are certainly a piece of the puzzle that will always exist to some degree, even as we move towards a circular economy.

Me, unsuccessfully climbing a tree at Pine Bend Sanitary Landfill (MN)\

This blog post was inspired by a text I got from my friend Eve, who is a rockstar chemist and fellow woman in STEM. Thanks for reading, I hope it was helpful!