What is waste-to-energy?

Incinerating municipal solid waste (MSW) to generate electricity is the most common implementation of waste-to-energy. Globally, about 13% of municipal waste is used as feedstock in a waste-to-energy facility.¹ MSW includes solid waste such as food waste, product packaging, clothes, furniture and lawn clippings from residential, commercial and institutional sources.

Waste-to-energy can be one of many solutions for the world’s growing waste problem as it can reduce the volume of waste sent to landfills. It can also produce lower greenhouse gas (GHG) emissions than other waste management methods.

WtE is an alternative to fossil fuel-based energy production, but it's not a renewable energy source because it's not a natural or infinite resource such as the wind or the sun. WtE is also not a totally clean energy source, as waste incineration and WtE transportation processes produce carbon emissions and other airborne particulates.

Most large WtE facilities generate energy from waste by using a controlled incineration method. The process typically follows these steps:

1. Waste is transported to the WtE plant, where any recyclable material is removed.
2. A crane blends the waste and transfers it to the combustion chamber.
3. The waste is burned at a high temperature—between 850°C (1,562°F) and 1,450°C (2,642°F).²
4. The resulting heat converts water (usually in vertical pipes within the chamber) into steam.
5. The steam’s pressure turns the blades on a generator, and it produces electricity.

Different types of waste have different calorific values, or energy contents, when burned. Waste with high calorific values, such as plastics, produce more heat and will generate the most energy. Organic waste, such as soil, has a low calorific value.

Incineration, the direct combustion of waste at a high temperature, is the most common WtE technology and the most commercially viable. However, there are other energy recovery methods that use waste, such as:

Besides composting, anaerobic digestion is a controlled, oxygen-absent process that encourages the decomposition of organic solid wastes by using microorganisms. While it can occur naturally, AD is also used in residential or industrial settings to produce a fuel called biogas. Biogas, which mainly consists of methane and carbon dioxide, is considered a renewable energy source.

As a thermochemical treatment, pyrolysis exposes organic waste to high temperatures without oxygen present. This process initiates decomposition and disintegration of the material. The byproducts are commonly carbon-rich char (biochar) and combustible gases. Some of these gases can then be condensed into a combustible liquid called bio-oil or bio-crude.

The decomposition of organic material in landfills creates a natural byproduct called landfill gas. LFG consists of methane, carbon dioxide and a small percentage of non-methane compounds. It can be collected, treated and used as fuel for industrial uses, vehicles and more. LFG recovery is one method for reducing landfill methane emissions.

Gasification is also a thermochemical treatment, which converts organic waste (biomass) into a combustible gas by using high temperatures and a controlled amount of oxygen, steam or both. The result is a combustible natural gas called syngas or producer gas used to make ammonia and methyl alcohol (methanol). It can also replace gasoline as a biofuel alternative.

Waste-to-energy plants that incinerate MSW produce two types of ash: fly ash and bottom ash.

Fly ash—or air pollution control residue (APC)—consists of the hazardous and fine particulates removed from a WtE plant’s flue gas, the fumes produced from incineration. Fly ash generally undergoes treatment to reduce its negative environmental impacts, largely in the form of air and water pollution of nearby ecosystems. While there are efforts to recycle and reuse fly ash, it’s commonly sent to hazardous waste landfills.

Bottom ash—or incinerator bottom ash (IBA)—is all ash left over that is not fly ash. It consists mainly of silica, calcium, iron oxide and aluminum oxide. Large magnets can remove some of these materials for recycling and repurposing. For example, construction companies might use bottom ash to make concrete or bulk fill. The rest is sent to landfills.

The ash output generated by WtE plants is significantly smaller than the waste that goes into them. It ranges from 15–25% by weight and 5–15% by volume of the waste precombustion.³

Waste-to-energy has many benefits when compared to traditional waste management systems:

Waste-to-energy systems receive scrutiny from environmental activists as they don't discourage waste production or encourage circularity. WtE often toes the line between circularity and linear resource use. While metals can be extracted and recycled or reused, it’s better for the environment and more energy efficient to outright recycle materials, especially plastic and paper, which cannot be extracted post-incineration.

WtE also requires large-scale waste disposal and solid waste management systems to function on a commercial scale. Such requirements largely put this solution out of reach for the roughly 2.7 billion people globally who are still without waste collection.¹

Waste-to-energy plants are common in densely populated areas with limited land, such as Japan and European countries such as Denmark, Sweden, Germany and France. In Western Europe, WtE is the leading method of MSW management, treating about 40 million tonnes. Waste-to-energy will further expand in this region due to the 2023 agreement by the EU and the UK to include waste-to-energy in emissions trading schemes.¹ WtE has experienced slower growth in the US, where ample land and lower costs have made landfilling a more attractive option.

In the Middle East, Dubai is home to the world’s largest waste-to-energy facility. Operated by the Warsan Waste Management Company, the power plant will use 1.9 million metric tons of trash each year, around 45% of Dubai’s total waste. The project will generate 200 megawatts of electricity each day, enough to power 135,000 homes.⁵