Turning Trash Into Joules

Landfills aren't sustainable, and even if they were, nobody wants to live near one. Here's how some engineers are turning trash into treasure.

You Can Throw It, but You Can’t Throw It Away

Here on Planet Earth, the only way to really “throw something away” is to launch it at a velocity of seven miles per second (25,000 mph, or 11.2 km/s) – about 33 times the speed of sound. With today’s rocket technology, it costs $10,000 to launch one pound (2.2 kg) of payload into space. This is why we have landfills – but landfills are not sustainable, and even if they were, nobody wants to live near one. That’s why some innovative individuals are looking for ways to transform us into a no-waste society.

Energy Is Valuable – That’s Why It’s Measured in Joules

Some people look at a garbage can and see nothing but trash. Engineers, on the other hand, see it as a treasure chest filled with Joules, so let’s take a look at some of the ways in which waste is being converted into energy.

Dubai (or Not Dubai): The World’s Largest Waste-to-Energy Plant

Two waste-to-energy (W2E) facilities currently under construction are vying to be the world’s largest W2E plant: one in Dubai (UAE) and one in Shenzhen (China). Both are scheduled to open in 2020.

Dubai’s 185-megawatt W2E plant will process up to 1.8 million tons of garbage every year, creating enough electricity to power 120,000 homes – a little less than a typical coal-fired power plant. The heat from the incinerated trash boils water to turn a steam turbine that generates electricity. The flue gases are treated with lime and filtered to remove carbon and other pollutants. Any metals present in the garbage will be recovered from the ash and recycled.

Image courtesy of the Dubai Media Office

Image courtesy of the Dubai Media Office

Near Hong Kong, the city of Shenzhen is building a 165 MW W2E facility that will keep 1.8 million tons of trash out of its rapidly bulging landfills. Like the Dubai plant, Shenzhen burns trash at over 800 degrees Celsius, using the heat to drive a turbine. As a state-of-the-art W2E plant, it includes pollution-control technology to clean the exhaust.

Image courtesy of Schmidt Hammer Lassen Architects

Image courtesy of Schmidt Hammer Lassen Architects

Shenzhen’s circular W2E plant will include an education center and public tours. Two-thirds of its 66,000 square meter roof will be covered in solar panels, allowing the cylinder to generate an additional 6.6 MW of clean electricity.

Olive This Idea

Thanks to my Mediterranean heritage, I’m a big fan of olive oil, but I wasn’t aware that the extraction process produced so much waste. To obtain the tasty product, olives are crushed and pressed, with water added to help the extraction process. The resulting liquid is sent to a centrifuge, where the oil and water are separated. Instinctively, I would think that the water could be used on crops as a form of fertilizer, but tests have shown that it does more harm than good.

Chemists at the Mulhouse Institute of Materials Science devised a method to turn the waste into biofuel, clean water, and fertilizer. Even better, they used another waste product – sawdust – in the process. The mix of sawdust and wastewater is dried, and the water vapor is condensed into clean, distilled water. The remaining solids are fed into a pyrolyzer (because you can’t say “oven” in a scientific paper), where the intense heat produces biofuel and solid fertilizer.

In Nature, There Is No Waste

Nature is the ultimate recycler, as anyone with a compost bin will tell you. Animals breathe oxygen and emit CO2 as a waste product. Plants consume CO2 and produce oxygen. Bacteria eat fecal matter and turn it into soil, which then grows food that animals turn into energy … and fecal matter. Reduce, reuse, and recycle are three methods to decrease the amount of material entering a landfill. Waste-to-energy closes the loop entirely, and that’s what long-term sustainability is about.


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