Illustration redesigned by Devin Thorpe

Can your garbage produce energy

Two of the major environmental issues facing humanity right now: rising carbon dioxide levels and garbage. Some municipalities – and even some nations – believe that they’ve found the key to solving both of these problems at once. They’re using their garbage to generate electricity.

According to the Energy Recovery Council, there are 86 facilities in the U.S. that recover energy from garbage by incinerating it. Many more recover methane from landfills and refine it to use as fuel. If you look beyond American borders, the picture for incineration is brighter. The entire country of Sweden participates in energy recovery to such a great extent that the nation imports garbage to burn. If their national experiment continues to succeed, then waste-to-energy projects could see a resurgence in the U.S. after a late-20th-century failure.

There are two ways to extract energy from garbage: by burning the garbage itself and by refining and burning the methane that landfills generate. Both of these power sources derive from biological matter that ends up in the waste stream, from chicken bones to dirty napkins.

Burning trash

Burning trash can make power by generating steam that will then turn a turbine. The system first sorts the garbage to determine what can and can’t be burned safely and effectively. Then, a powerful, high-heat incinerator uses that flammable trash to boil water. Filtration systems make sure that the smoke from the garbage doesn’t end up in the air. Although it ends up buried, the sooty remains of the garbage takes up less space and doesn’t generate harmful methane.

Burning garbage isn’t a new practice, but using garbage for energy recovery is a 1970s innovation. Research indicates that burning garbage is preferable to landfilling it, and since flammable garbage often derives from renewable resources like plants, its carbon can enter the atmosphere with less impact. The principal behind incineration is the same as the use of biomass as fuel. The balance of the carbon emitted by burning a cotton tee-shirt is removed from the atmosphere by the cotton plant that uses it to produce more of the same resource. The CO2 balance is zero.

Historically, the problem with trash incineration has been smoke. Even biodegradable matter normally includes dyes, inks, and incidental plastics that make it into the air when they’re burned. This poses a health risk for nearby communities. Initial waste-to-energy facilities were located in disadvantaged communities, which bore the brunt of their effluent. In the 1980s, this led to an environmental backlash. Most incinerators were shuttered. Today, incinerator technology has improved considerably, largely as a result of the environmental movement that caused the decline of incinerators. Nevertheless, there have been no new waste-to-energy incinerators opened since 1995, possibly because extant facilities, including the Wheelabrator plant of Peekskill, New York, still release contaminants into the environment. The 86 active facilities in the U.S. produce about 2,720 megawatts of electricity per year.

Burning methane

Methane is a powerful greenhouse gas. Although it breaks down faster than carbon dioxide, it’s twenty-one times more powerful as a greenhouse gas. An energy recovery system can mitigate the damage methane does to the atmosphere, which could be why landfill methane recovery systems are becoming increasingly popular.

Landfills are already notorious for generating methane. In nature, food scraps would generally break down in the presence of oxygen, a process called aerobic decomposition. This produces little in the way of greenhouse gasses, which is why composting is such a climate-friendly way to get rid of consumables. However, the same organic matter in garbage is forced to break down in an increasingly anaerobic environment once it’s buried, whether under an impermeable layer of filler or under other garbage. When buried away from the air, the microbes that survive to consume the garbage are anaerobic. They generate methane – tons of it. In fact, landfills are the third-largest source of methane in the U.S. The EPA estimates that solid waste starts producing methane within a year of being put in a landfill.

When integrated into a landfill, energy recovery systems turn methane into fuel. This is a considerably more complex process than simple incineration. The methane must first be collected using taps installed in capped landfills. These are fairly common features on landfills anyway, since the methane must be vented from these buried dumps for safety purposes. Luckily, the methane rises to the top of the pile, making its extraction a simple endeavor.

This methane can’t be burned as-is. Carbon dioxide, hydrogen sulfide, and other waste gases also result from anaerobic decomposition. The methane capture system uses blowers or a vacuum to pull the mixture of gases into a tank, where it can either be flared or processed. Flaring is the practice of lighting methane on fire to reduce it to CO2 and water, which in and of itself can then produce power by generating steam. However, methane can also be further refined to natural gas standards if the municipality wants to use it in a more versatile way.

In contrast to basic incineration of garbage, methane recovery is enjoying a heyday. The Landfill Gas Energy Project, a project of the EPA, reports dozens of projects under construction and in the planning process.

Recovery from plastics

Any chemist will tell you that plastic is, at least partially, a petroleum product. That means that there may be chemical ways to return it to a useful state. It’s an attractive idea in a world beset by vast floating garbage patches. The American Chemistry Council eagerly advocates the idea of turning plastic back into fuel as part of municipal waste recovery. Its Plastic Packaging Facts website claims that “the United States recovered 27% of used plastics in 2013”. This organization also emphasizes that recovered plastics could create jobs and power cars.

But this course of action isn’t likely to improve the environmental crisis that faces us. Ultimately, it would move CO2 from plastics – where it is currently sequestered, however poorly –  to the air, where it would manifest as a far more urgent environmental threat.

The problem with recovering plastics from the waste stream is the one that we need to learn to ask ourselves about whenever confronted with a new energy technology: how will this impact the atmosphere? Ignoring this question and blindly pursuing the low-hanging fruit of easy energy has allowed our civilization to paint itself into an increasingly small corner. Now is the time to be skeptical about solutions that seem a bit too neat. Plastic recovery falls into this category.

Is energy recovery worth it?

Over half of the material that enters landfills is compostable. In an ideal world, composting would be the waste solution of choice; methane may burn cleaner than coal, but it is still a harmful carbon fuel. That said, as long as landfills are producing methane, municipalities will probably be interested in using this potential energy source – at least, for as long as it lasts – and burning methane is still a better option than allowing it to vent into the atmosphere. There’s also an economic angle to methane energy recovery that may factor in for some smaller towns and cities: space use. The CDC reports that landfills produce methane for about 20 years after being capped. Municipalities that run out of space for landfilling could face a sudden and painful removal of income when their convenient methane mines expire. A shift to municipal composting, such as the system San Francisco uses, could provide a better long-term income source for municipalities while forcing a phase-out of the waste practices that produce greenhouse gases in the first place. Ultimately, managing trash is a problem with no pat solution. But burning garbage, or at least burning the methane that results, maybe the best bet on the table until we can find a way to produce less. Even Swedish officials say that they hope that their country’s most famous fuel someday disappears.

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