In the last few years, we’ve gotten used to separating out the garbage, splitting re-usable material from what’s really trash. But there’s one big area of the waste chain where we still dispose of everything together: the bathroom.
That’s unfortunate, for two reasons.
First, urine contains lots of phosphorous, nitrogen, and potassium—key ingredients for fertilizers. And feces produces methane, which can be burned to make electricity. Retrieving these goods becomes more difficult, and more energy-intensive, when the two sources are combined.
Second, flush-it-all systems use a lot of water. It’s estimated we use 4,000 gallons of fresh water per person, per year, to send down 13 gallons of feces, and 130 gallons of urine. That, in turn, is mixed with greywater from showers, sinks, and laundries, increasing the volume sewage plants have to cope with.
Advocates of 21st-century sanitation say we should separate yellow and brown at the source, maintaining the purity of the chemical- and energy-rich matter, while freeing up scarce water supplies for more important things.
And that’s the idea behind the new No-Mix Vacuum Toilet developed by researchers at Nanyang Technological University, in Singapore. Using a suction system more normally seen in an aircraft, the toilet separates feces from urine, while using only a fraction of the normal water volume. The research team says flushing liquids requires only 0.05 gallons, while solids need 0.26 gallons. Conventional toilets require 1.06-1.6 gallons per flush, meaning the No-Mix Vacuum could save thousands of gallons a year, if installed in a public place.
"Having the human waste separated at source and processed on-site would lower costs needed in recovering resources, as treating mixed waste is energy intensive and not cost-effective," says Wang Jing-Yuan, director of the university’s Residues and Resource Reclamation Center. "With our innovative toilet system, we can use simpler and cheaper methods of harvesting the useful chemicals and even produce fuel and energy from waste."
Wang hopes to commercialize the design within three years—but we’ll have to wait and see if it catches on. Europe has installed several thousand NoMix toilets, including some with vacuums. But, while surveys show the public is in favor of such designs, the reality is that they tend to be more expensive than normal toilets, and require new plumbing and hardware. Plus, people have to become used to using a toilet with a front and back compartment—a psychological and practical adjustment for many.
Unless the cost of fertilizer and electricity rise still higher, it may be some time before we all start using NoMixes. But there could be plenty of early adopters. The researchers see a strong market in new-build housing, in communities not linked to the mainstream sewage system, or in high-frequency locations, like hotels and public bathrooms.