When it comes to recycling, pee and poo oughtn't mix. We think of them as the same thing—human waste—but in fact they are not mixed within the body and shouldn't be mixed afterwards, though we often do so out of convenience and the design of modern toilets.
The reason they shouldn't mix is because urine is rich in nitrogen and phosphorous while feces are carbonaceous. Separated, these can be valuable resources, but combined they become a useless sludge that needs to undergo laborious and energy-intensive processing before anything can be reclaimed. And we are literally flushing resources down the toilet. As an article in the farmer's information website A Growing Culture points out, it would be better if we could easily extract nitrogen and phosphorous from separated urine rather than taking it out of the Earth:
Modern agriculture gets the nitrogen it needs from ammonia-producing plants that utilize fossil fuels such as natural gas, LPG or petroleum naphtha as a source of hydrogen. This energy-intensive process dumps carbon dioxide into the atmosphere, it consumes a finite hydrocarbon resource, and it is not sustainable.
Modern agriculture gets the phosphorous it needs from phosphorous-bearing rocks. But these reserves are rapidly dwindling and increasingly contaminated with pollutants such as cadmium. In as little as 25 years apatite reserves may no longer be economically exploitable and massive world-wide starvation is predicted to follow.
If we are serious about achieving sustainability in this regard, our first, and perhaps most important duty, lies in not mixing urine with feces.
Enter the NoMix toilet, developed in Sweden in the 1990s.
The NoMix's bowl is designed in such a way that the urine is collected in the front, the feces in the back, and both are whisked away through separate plumbing, with the latter being disposed of in the conventional manner and the former recycled. While that raises new infrastructural challenges, the concept was interesting enough for EAWAG, a Swiss aquatic research institute, to intensively explore the NoMix's feasibility in research trials. Running from 2000 to 2006, that project was called Novaquatis, and during their seven years of testing, Eawag shrewdly realized that "An innovation for private bathrooms can only be widely implemented if it is accepted by the public":
For this reason, all Swiss NoMix pilot projects were accompanied by sociological studies. 1750 people were surveyed - and their attitudes towards urine source separation are highly favourable. Despite a number of deficiencies, the NoMix toilet is well accepted, especially in public buildings.
Things looked even better by 2010, when CNET reported that "Of the 2,700 people surveyed in Switzerland, Germany, Austria, Luxembourg, the Netherlands, Sweden, and Denmark, 80 percent say they support the idea behind the technology, and between 75 and 85 percent report that the design, hygiene, smell, and seat comfort of the NoMix toilets equal that of conventional ones."
In 2012, researchers from Singapore's Nanyang Technological University apparently cloned or licensed the NoMix, adding a vacuum function for the urine collection. Here's a video giving you an idea of how either system is meant to work (except for the vacuum discrepancy):
With development taking place in both Europe and Asia, and apparently positive results, the NoMix seemed like a home run.
Yesterday, however, the BBC reported that NoMix's manufacturer has quietly stopped making them, "deciding the revolutionary technology is commercially too much of a risk."
The BBC got ahold of Tove Larsen, a key member of the original Novaquatis project, for an explanation. "Although 80-85% of the people thought that [the NoMix] was really a good idea, the more they had to live with the toilets themselves, the more critical they were towards this technology, which is not really mature." Larsen is probably referring to some facts they uncovered in their research: The urine-carrying pipes are susceptible to scale, or the buildup of mineral deposits; that means the pipes have to be regularly flushed with acid. Furthermore, the toilets must be cleaned daily using no chemicals, but a cloth rag and a 10% citric acid solution.
Then there are the problems with actual use. A lot of women are hesitant to actually sit on a public toilet, preferring to squat and hover over it; this changes the angle of the stream, which can then miss the target. And even properly seated, they are apparently required to sit at a particular angle to generate the required aim, and "some users find it difficult to adopt the required sitting position."
As for men, one model of the NoMix requires them to sit in order to pee, while another model only requires accurate aim; most guys can probably handle the latter but are unwilling to do the former. And "Children in particular," says the research, "have problems targeting the right compartment, which increases the need for cleaning."
Alas, these inconveniences—or failures of design?—were enough to send the promising technology down the drain.