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Feeding the Future

The Future Of Composting: Turning Food Waste Into Fuel And Plastic

Through the process of biorefining, Hong Kong’s Starbucks are experimenting with doing something other than throwing out their old coffee grounds. They’re turning them into biofuels.

It sounds like magic: presto change-o, cheesecake becomes park benches, or low-fat raspberry coffee cake turns into laundry detergent. But the reality is closer than it may appear. It’s not so much magic as it is science, but food waste may soon become valuable products.

According to researcher at the American Chemical Society annual meeting and expo in Philadelphia, the process would take food waste and turn it into something useful. Lin and her colleagues at the Hong Kong City College had previously worked on reuse strategies for food from the school’s cafeteria. Now, they are teaming up with Starbucks Hong Kong and a nonprofit organization called The Climate Group to set their sights on a larger target: the 1.3 billion pounds of food dumped into landfills or otherwise wasted each year.

The process hinges on what’s called a biorefinery. Similar to the way that oil refineries convert petroleum into fuels and ingredients for hundreds of consumer products, biorefineries convert corn, sugar cane, and other plant-based material into a range of ingredients for bio-based fuels and other products.

A food biorefinery involves an upstream processing step, which uses a mixture of fungus to break down food waste into simple sugars. The blend then goes into a fermenter, a vat where bacteria convert the sugars into succinic acid. Succinic acid is one of the top molecules in green chemistry, and could be used to make everything from laundry detergents to plastics to pharmaceutical agents and surfactants. The acid is a colorless, crystalline compound already used in lacquers, dyes, and perfumes.

Figuring out what to do with our food waste is a pressing problem. In Hong Kong alone, Starbucks produces nearly 5,000 tons of used grounds and unconsumed waste bakery items every year. Currently, this waste is incinerated, composted, or disposed of in landfills. Lin’s process would convert these piles of foul-smelling waste into useful products, avoiding incineration and reducing the resulting pollutants. Three of Hong Kong’s landfills are going to reach capacity by 2018, making the problem even more pressing for the small country.

Lin says that there are waste companies interested in making pilot studies into biorefining on a city-level, and an announcement about one could come as soon as next month. "If the [pilot] strategy works, the effect for building the infrastructure to make the acid would be very quick," she said. Each kilo of stale pastry yields 0.45 kilograms of succinic acid, while cheesecake offers 0.44 kilograms, she says.

As for the coffee grounds, a Hong Kong-based recycling organization has been using the grounds to fertilize organically grown mushrooms that are then sold to the city’s Sheraton Hotel. Delicious.