Using a toilet can pay for your coffee or buy you bananas at a university in South Korea, where human waste is being used to help power a building. Cho Jae-weon, an urban and environmental engineering professor at the Ulsan National Institute of Science and Technology (UNIST), has designed an eco-friendly toilet connected to a laboratory that uses excrement to produce biogas and manure. The BeeVi toilet — a portmanteau of the words bee and vision — uses a vacuum pump to send faeces into an underground tank, reducing water use. There, microorganisms break down the waste to methane, which becomes a source of energy for the building, powering a gas stove, hot-water boiler and solid oxide fuel cell. “If we think out of the box, feces has precious value to make energy and manure. I have put this value into ecological circulation,” Cho said. An average person defecates about 500g a day, which can be converted to 50 liters of methane gas, the environmental engineer said. This gas can generate 0.5kWh of electricity or be used to drive a car for about 1.2km (0.75 miles). Cho has devised a virtual currency called Ggool, which means honey in Korean.