How Waste Incineration Works

How Waste Incineration Works

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Humans create a whole lot of waste, however if you toss something away, how a lot are you aware about the place it goes or the way it’s dealt with? This article is the fourth in a five-part series that explores what occurs to the tons of supplies we discard.

In the U.S., there are two major strategies of rubbish disposal — landfilling and incineration. Here is how incineration works in America.

Landfilling is by far the extra frequent of the 2, however incineration is the one which generates essentially the most heated (sorry) dialogue. Incineration’s popularity as a polluting, unsustainable methodology of disposal will not be completely honest. Under the fitting circumstances, incineration will be your best option for a group, however it isn’t with out environmental impacts.

According to the most recent EPA data, within the United States, 23.6% of municipal strong waste (MSW) is recycled. Another 8.5% was composted and 6.1% was meals waste managed through other pathways. The remaining 61.8% was disposed of as rubbish, both in a landfill or incinerator. There are 72 incinerators operating in the U.S. They deal with solely 11.8% of the nation’s rubbish, with the remainder going to landfills.

Like landfilling, incineration has modified quite a bit over time. Proponents of the know-how don’t even name it incineration anymore, however extra on that later. Branding apart, the environmental impacts can differ extensively relying on the age of the system. The earliest incinerators have been simply massive, inefficient furnaces. They diminished the quantity of waste, however massive portions of ash and incompletely burned waste nonetheless ended up on the dump.

The 1970 Clean Air Act (CAA) banned the uncontrolled burning of MSW and positioned restrictions on particulate emissions. Existing incinerators have been required to put in new know-how or stop operations. However, lots of them failed to take action. The CAA was up to date in 1977 and once more in 1990 primarily to set new deadlines for bettering emissions from incinerators.

Facilities constructed after the CAA, particularly after the 1990 replace, do meet a lot increased air high quality requirements. However, the majority of incinerators in operation right this moment — 55 of them — have been constructed earlier than 1990.


The waste administration trade normally calls incineration “waste-to-energy,” or WTE, to emphasise the vitality restoration course of that makes trendy incinerators each a waste disposal and electrical energy producing utility.

In most incinerators and all newly constructed ones, the warmth launched from burning waste is used to provide electrical energy. This electrical energy may help to offset the price of constructing and sustaining the ability (which is normally considerably extra expensive than landfilling). On the EPA’s waste management hierarchy, vitality restoration is much less environment friendly than recycling and ranks above disposal. Recycling, of plastic no less than, saves extra vitality than combustion generates. But recycling plastic has develop into its personal challenge, and plenty of communities have been pressured to deal with plastic as nonrecyclable.

Plastics are petroleum merchandise and so have excessive vitality content material. That makes them precious gasoline for incinerators. But burning plastics (and different waste supplies) generates carbon dioxide, a greenhouse fuel that’s arguably as harmful because the toxins that the Clean Air Act regulates. In 2016, greater than half of the 12 million tons of carbon dioxide launched by incinerators within the U.S. got here from plastics.

Incinerators constructed after 1990 are undeniably cleaner and safer than earlier generations of the know-how, however many individuals really feel that emitting even hint quantities of poisonous substances like dioxins, acids, and heavy metals is neither protected nor acceptable.

waste-to-energy plant
Wheelabrator Technologies’ Waste-to-Energy plant in Massachusetts, in service 1975. Photo: Fletcher6, CC BY 3.0

The Waste Incineration Process

Every incinerator is exclusive, however the commonest approach is known as “mass burn.” The general process adopted in a mass burn incinerator consists of 5 steps.

  1. Waste preparation: Oversized objects are eliminated and sure recyclables like metals are recovered. The remaining waste is commonly shredded earlier than it enters the incinerator.
  2. Combustion: Waste is burned in an oxygenated single combustion chamber. Materials are burned at extremely high temperatures of 1,800-2,200 levels Fahrenheit. At these temperatures, waste ought to be utterly combusted, leaving nothing however gases and ash.
  3. Energy restoration: The gases launched throughout combustion are cooled with water, producing steam by means of warmth restoration. The steam is used to energy electrical turbines.
  4. Environmental management: The cooled fuel is handled by scrubbers, precipitators, and filters to take away pollution. The solids that kind throughout remedy, known as residuals, are disposed of in a landfill.
  5. Environmental launch: The handled fuel is launched into the environment. There ought to be no seen smoke from the smokestack as a result of the remaining gases ought to be free from particulates.

Because incineration makes use of such excessive temperatures, it might probably destroy many pathogens and a few poisonous supplies. For this cause, incineration is the popular methodology of disposal for biomedical and another particular wastes, even in communities the place MSW is landfilled.

Environmental Concerns

As many are fast to level out, incineration nonetheless has drawbacks. Not all byproducts of combustion are as helpful as electrical energy. Fly ash can be recycled as an ingredient in concrete however can be a hazardous material that comprises heavy metals and different pollution.

Incineration can by no means utterly change landfilling. Waste have to be presorted earlier than burning — with outsized and sure hazardous objects going to the landfill. But waste additionally stays after burning. From 15-25% (by weight) of the MSW burned stays as backside ash that goes to the landfill.

Many folks concern that incineration conflicts with efforts to cut back waste. While there’s a monetary incentive to generate as a lot vitality as potential, international locations with the highest recycling rates additionally are typically those that depend on waste-to-energy over landfilling. Even so, incinerators depend on a relentless stream of waste to function effectively. Countries like Sweden which might be good at recycling and depend upon waste-to-energy for a major quantity of vitality have needed to resort to importing rubbish to maintain their incinerators operating.

Whether landfilling or incineration for WTE  makes extra sense for a group relies on the assets and eco-vulnerabilities of the placement. Communities that lack appropriate area for a landfill or a low-carbon technique of transporting waste to a landfill, or communities the place WTE is cleaner than their present vitality combine, may be finest served by incineration.

Ultimately, generating less garbage is the one strategy to eradicate the environmental impacts of rubbish.

Read half 5 of this five-part sequence, How Curbside Recycling Works. Originally printed on November 5, 2019, this text was up to date in February 2022.