Food waste can be repurposed to supply drinking water and power while reducing the release of greenhouse gases into the atmosphere.
Food waste can be converted into carbon-rich materials which can trap solar energy to desalinate seawater and generate electricity. Swee Ching Tan and colleagues at the National University of Singapore describe this innovation in the journal Nano Energy.
“Repurposing food waste in this way would offer sustainable drinking water and power supplies while also mitigating land and air pollution and reducing the release of greenhouse gases,” says Tan.
He explains that roughly 1.3 million tons of food waste is generated globally each year, amounting to around one-third of all food produced for human consumption. At present, much of the carbon in that waste is eventually released into the atmosphere as carbon dioxide, when the waste is burned in power plants, or as the even more powerful greenhouse gas methane if left to rot.
“Our process can cut the emission of carbon-containing gases by half,” says Tan, while at the same time creating a very useful carbonaceous product.
The simple procedure is achieved by a ‘carbonising’ process that converts the food waste into a largely carbon-containing residue by heating it in a furnace. Many, but not all, of the other atom types in the food – largely hydrogen, oxygen, nitrogen, phosphorus and sulphur – are given off as various gases.
The carbonaceous products do, however, retain various chemical ‘functional groups’ – small groups of atoms that bestow specific chemical and physical properties on the materials. They also have a variety of interesting porous structures, perhaps making them suitable for a variety of applications in addition to those demonstrated in this article.
When immersed in salty water and exposed to solar energy, the obtained products exhibited effective desalination properties, retaining the salts of the solution while pure water evaporated off to be cooled and condensed back into liquid. This could form the basis of a sustainable and efficient method for converting seawater to drinking water.
The researchers have moved towards real practical application of this process by incorporating the material within a small prototype system that can float in the sea and collect the purified water in storage bottles. The prototype is sufficiently sturdy to perform well in the wave-disturbed water likely to be encountered in real near-shore applications.
The researchers also demonstrated a small-scale steam generation system that could make use of the heat difference between the sea surface and light facing side to generate electricity.
“This is the first time that food waste has been recycled for desalination and simultaneous electricity generation,” says Tan. He points out that, in principle, this offers a combined solution for two major global challenges – supplying drinking water while providing renewable electrical energy – at the same time as reducing greenhouse gas emissions.
To illustrate the magnitude of the potential benefits, Tan points out that one day's potato wastage in the UK, if recycled for solar desalination, would release approximately 400 tons less carbon dioxide than incineration of the food waste, while meeting the daily drinking water requirement of 250,000 people.
Article details:
Tan, S. C. et al.: “Food-derived carbonaceous materials for solar desalination and thermo-electric power generation,” Nano Energy (2019)