People do strange things for attention. Children throw tantrums, celebrities shave their heads and UNICEF builds a machine to take the sweat from your clothes and turn it into drinking water. UNICEF, at least, is trying to raise awareness of the lack of clean water for children with its unusual machine. Unveiled during the Gothia Cup, and built by Swedish engineer Andreas Hammar, the aptly named Sweat Machine works by using membrane distillation to separate water from other components of sweat.
Unlike other membrane-based processes of water purification, such as reverse osmosis, membrane distillation is a thermally-driven process that employs a hydrophobic, microporous membrane. The water (or sweat) to be processed is heated, while the water on the permeate side of the membrane is kept cool. The temperature difference across the membrane creates a corresponding difference in pressure which pulls water, in the form of vapor, over to the permeate side of the membrane. Water’s naturally high surface tension keeps the liquid phase of the water out of the membrane’s pores.
Membrane distillation is good choice for compact desalination and water purification units because the process doesn’t require the energy and equipment to create the extreme pressures needed for reverse osmosis. Heating the feed water can be done with the waste heat of a power plant or factory or with renewable energy sources like solar power. While membrane distillation has been used at the laboratory scale since the 1960s, its potential to provide easy access to drinking water for remote or rural areas is only now being recognized.
During the Gothia Cup, UNICEF encouraged everyone to hand in their sweaty clothes and take in a glass of their recycled fluid. The Sweat Machine managed to wring out about 10 mL of water out every sweaty shirt.
You can read UNICEF’s original press release and learn more about their clean water campaign here.