Waste to Energy: Creating a Circular Economy
By Robin Pan
Waste is a rapidly growing problem today. Americans generate 268 millions of tons of waste per year, most of which ends up in landfills. However this isn’t a green or permanent solution - if we look at Massachusetts for example, there’s currently 6 landfills left in the state, all of which are set to be full by 2030. What then?
Oftentimes we view waste as something useless to get rid of, but what if we were to change the narrative? Instead of something to hide and store, we need to look at waste as a resource. This allows us to achieve a circular economy, in which materials are repurposed in a closed loop, reducing waste and decoupling economic growth with resource consumption. One aspect of this is turning waste into energy.
The most common form of waste-to-energy is in the form of incineration of municipal solid waste, aka common household trash. About 85% of waste can be burned to generate energy and this incineration can reduce the volume of waste by 87% by turning it to ash. The remaining ash is then disposed of. However, despite the strict air quality standard for emissions (emissions are required to be 99.999% water vapor), fumes from incineration may have negative effects on the health of nearby residents, posing an environmental justice concern. However, the alternative of landfills still risks leachate contamination of water sources and other health risks. A majority of residents in a 2017 survey reported that they would prefer to live by an incinerator than a landfill. Still, it’s clear that incineration isn’t a perfect solution. It may instead be beneficial to pair incineration with other forms of waste-to-energy solutions.
Anaerobic digestion may be a solution to supplement incineration. Food waste is incredibly inefficient to incinerate, since its high water content means it takes more fuel and thus more energy to burn compared to other forms of waste. Food waste has incredible potential since it’s rich in nutrients and organic matter and anaerobic digesters can maximize this potential by turning food, yard and other organic waste into energy and fertilizer. Anaerobic digestors utilize bacteria to convert organic matter into biogas (methane, CO2) and digestate liquid. This biogas can be utilized in a similar way as natural gas for heating, electricity, or powering cooling systems. It can also be purified to generate renewable natural gas which can be used in vehicles. The digestate is a rich source of nutrients that can be utilized as fertilizer. It also reduces greenhouse gas emissions from disrupting the soil, and reduces volume of waste and cost of waste treatment. However, this can be expensive to implement and can take 5-6 years before return on investment. New technology is making anaerobic digesters more efficient however. Cornell researchers were able to increase efficiency and speed from several days to a few hours using hydrothermal liquefaction technology and Michigan State University currently uses anaerobic digestion to process 24,000 tons of food waste a year, generating 380kW of electricity per hour. It can also be paired with a hydroponic vegetable garden so that the garden is powered by excess heat from digestion and digestate liquid fertilizes the soil.
Other technologies also exist to convert waste to energy, although on a smaller scale. Stockholm has the world’s first large-scale biochar plant. Citizens contribute garden or park waste which gets sequestered into a biochar, a substance similar to charcoal, that can be put back into the soil to facilitate plant growth and act as a carbon sink. Biochar production also releases pyrolysis gas as a byproduct which is also used to generate electricity. This plant has saved the equivalent of 700 cars worth of emissions per year and heats 80 apartments per year. Inspired by Stockholm’s success, Minneapolis is now also in the process of increasing biochar usage.
Although waste to energy has the potential to remove 6.27 to 5.24 gigatons of carbon dioxide, it’s not a perfect solution and risks health problems for nearby residents, who are often lower income or BIPOC. Rather, it should be viewed as a necessary tool to be used alongside other solutions in the toolbox to help us move to a zero-waste, net-zero, cleaner, greener future.