by Nicholas Rodricks, ARPA-E Summer Scholar

Trash has a way of going unnoticed. Whether an apple core, a bag of chips, or an old microwave, we give little thought to throwing away everyday items. In reality, our trash’s journey is only just beginning when we throw it in the garbage. The quantity of our garbage is staggering, and with concerns around pollution and storage, the U.S. still struggles to answer the question “where should it all go?”

U.S recycling rates are still relatively low, so it is important that we create ways to derive value while also reducing our waste stream. ARPA-E is exploring ways to use technology to maximize our waste stream’s energy value. Two of ARPA-E’s recent Special Topics Informing New Program Areas work towards innovation in this space. The Waste into X (WIX) special topic focuses on how to repurpose ash from waste-to-energy plants into useful products. The Mining Incinerated Disposal Ash Streams (MIDAS) special topic focuses on how to extract critical materials from waste-to-energy (WTE) plants.

Landfills remain the primary way to dispose of municipal solid waste (MSW) in the U.S. According to the Environmental Protection Agency (EPA) at least 139 million tons[1] (52% of the total waste stream) of MSW is sent to landfills. Other studies show greater numbers[2] [3] meaning even more waste is potentially being left in landfills where it has close to zero value.

Recycling and composting accounts for another 35% of waste according to the EPA, a rate that is plummeting as foreign markets continue to refuse U.S. recyclables.[1] The final 13% of our waste stream is incinerated. This portion of the waste stream is where ARPA-E sees the potential for great progress and innovation.

WTE is a process by which the heat from incinerated waste is used to produce electricity. Today, combined with landfilling, just 75 WTE facilities are responsible for the MSW produced by the entire U.S population of 328 million.[5] [3] A once-robust part of the domestic waste disposal landscape, 30 WTE facilities have closed over the past 20 years,[4] [2] while only one new facility was built during that time. Those facility closures have a great deal to do with the legacy of WTE but are not necessarily a reflection of where the technology stands today.

In the past, landfills have been more cost efficient than WTE facilities. Landfills are inexpensive to build, easy to maintain, and can be located out of the public eye, but are far behind WTE in capturing energy from waste. Landfills are the third largest source of methane emissions, after fossil fuels and agriculture, and they provide no mechanism for recycling or repurposing any of the materials disposed at the facility. In short, landfilling inhibits any opportunity to extract value from the waste stream.

Potential advancements in WTE technology, such as those presented in ARPA-E’s WIX and MIDAS special topics, provide the opportunity for incineration to become a more economical and beneficial part of the waste and energy landscape. The resources available in our trash are almost entirely untapped, meaning that tons of critical materials lie wasted in landfills. Value estimates of discarded minerals like gold, copper and iron, often in the form of e-waste, are upwards of $50 billion annually. ARPA-E is interested not only in extracting valuable materials from waste ash but also in recycling that ash into other materials. By using the incineration process to extract critical materials, WTE could become an essential component in repurposing our trash.

To become more popular, WTE’s environmental impacts must be addressed. Improvements in filtration technology have already significantly reduced the environmental impacts of WTE. With the addition of emissions regulations, including MACT (Maximum Achievable Control Technologies), a standard level of control introduced in the early 2000’s, emissions from WTE facilities have seen a precipitous drop. Between 1990 and 2005 emissions of lead, cadmium, and mercury dropped 90% or more, as did particulate matter, while sulfur dioxide and nitrogen oxide dropped 88% and 24% respectively. Changes in regulations pushed WTE facilities to improve filtration technology, installing better bag houses, fabric filters and in the case of newer facilities, selective catalytic reduction.[6]

WTE facilities currently rely on landfills to dispose of waste ash, the byproduct of burning trash. Ash can be toxic and requires safe disposal, and as a result has to be sent to the landfill. ARPA-E is interested in advancing technology to use and recycle this byproduct rather than throw it away. Reclaiming e-waste from municipal solid waste or repurposing ash into building materials would help close a recycling loop for the 4.5 pounds of trash the average American disposes of each day.[1] WTE provides an opportunity to convert that waste into electricity, but also to create a valuable product.

Repurposing ash will produce an additional revenue stream for WTE facilities, making them more economically competitive while also eliminating their reliance on landfills for ash dumping. Coupled with improvements in recycling and reductions in waste production by citizens, WTE can be a clean, sustainable way to derive additional value from the waste stream and reduce overall waste.

Improvements in pollution controls, incineration efficiency, and use of byproducts like ash make WTE an exciting space to advance technology. Legacy facilities that are pushing the limits of their lifespan have given the industry a negative reputation when, in fact, WTE has improved significantly over the last several decades.

When implemented effectively, WTE is a sustainable, long-term solution to landfills with significant potential. In order for the U.S. to lead in this space, innovations in WTE technology are needed to update aging facilities and compete with the low cost of landfilling.

Efforts to reduce waste and improve recycling are essential, but at present, do not operate at the scale needed to conquer our growing waste problem. Advanced WTE technology can help bridge the gap by reducing U.S. greenhouse gas emissions and derive value by repurposing waste streams. ARPA-E looks forward to supporting the next wave of technical innovation to reduce and better reuse our waste.

Nick Rodricks was an ARPA-E Summer Scholar. Read more about him at the DOE Scholars Program.

1. United States Environmental Protection Agency, 2017. Facts and Figures about Materials, Waste and Recycling. Accessed March 2019. https://www.epa.gov/facts-and-figures-about-materials-waste-and-recycling/national-overview-facts-and-figures-materials.
2. Themelis N. J., & Shin D., “Survey of MSW Generation and Disposition in the US. MSW Management.” [262 million tons in 2012] (2015).[https://www.mswmanagement.com/collection/article/13019760/survey-of-msw-generation-and-disposition-in-the-us].
3. Powell J. T., Townsend T. G., & Zimmerman J. B., “Estimates of solid waste disposal rates and reduction targets for landfill gas emissions”. Nature Climate Change, 6 (2), p. 162 (2016).
4. Ana Isabel Baptista, Adrienne Perovich. 2019. U.S. Municipal Solid Waste Incinerators. New York: Tishman Environment and Design Center.
5. Ted Michaels, Karunya Krishnan, 2018.2018 Directory of Waste to Energy Facilities, Energy Recovery Council.
6. United States Environmental Protection Agency, 2005. National Emissions Inventory, Air Emissions from MSW Combustion Facilities, Accessed March 2019. (https://archive.epa.gov/epawaste/nonhaz/municipal/web/html/airem.html)