Pee-cyclingPosted: June 17, 2009
- 20 December 2006 by Graham Lawton
You recycle your household waste. You buy locally grown food, fit low-energy light bulbs and try not to use the car unnecessarily. Maybe you even irrigate the garden with your bath water. But you’ve still got an environmental monster in your house. Your toilet is wrecking the planet.
Before you point to the brick you’ve put in the cistern, it’s not about the water – well, not entirely. The big problem is pee. Your pee. Do you flush it away without a second thought? Tsk, tsk. Lose the green halo.
At first sight urine looks like an unlikely environmental menace. What harm could come from flushing away a fluid that is mostly water, plus a smidge of proteins and salts? Surprisingly, the answer is "a lot".
The problem with urine is that it is the main source of some of the chemical nutrients that have to be removed in sewage treatment plants if they are not to wreck ecosystems downstream. Despite making up only 1 per cent of the volume of waste water, urine contributes about 80 per cent of the nitrogen and 45 per cent of all the phosphate. Peeing into the pan immediately dilutes these chemicals with vast quantities of water, making the removal process unnecessarily inefficient.
To be fair, if you use conventional western plumbing there’s not an awful lot you can do about your personal pee-print right now. A lucky few, however, live or work in one of the buildings in continental Europe where you can find a future must-have eco-accessory: the urine separation toilet. These devices divert urine away from the main sewage stream, allowing the nutrients to be recycled rather than treated as waste. They could solve all the environmental problems associated with urine and even turn sewage plants into net producers of green, clean energy.
If you use conventional plumbing There’s not a lot you can do about your personal pee-print right now
So how do standard sewage systems deal with urine? Known in the business as "yellow water", urine enters the sewage system and mixes with solid waste ("black water"), "grey water" from household sinks and baths, and sometimes rainwater. It eventually arrives at a treatment plant, where it must be cleaned up enough to be discharged into a river.
The first step is to filter the sewage to remove large objects such as condoms, tampons and a random assortment of dead goldfish and false teeth. What remains flows into settlement tanks, to allow the feces to sink to the bottom. This solid sludge is separated off and stored in oxygen-free tanks, which are gently warmed for about two weeks. Bacteria break it down, generating methane gas that can be burned to produce electricity. The end product is an inert solid that is usually burned or dumped in landfill.
Meanwhile, the liquid portion of the sewage flows into oxygenated "aeration tanks". Here microbes guzzle the nutrient-rich organic material and multiply like crazy, converting nutrients into biomass. This eventually sinks to the bottom of settlement tanks as yet more sludge, while the liquid heads off for a final, energy-intensive "polishing", which strips out any leftover nitrogen and phosphate that the aeration stage couldn’t get rid of.
The whole process is very good at converting yellow, black and grey water into more or less clear water, but all that pumping, stirring, aeration and heating uses a lot of power – about 11.5 watts per head of population. That’s only a tiny portion of your personal daily energy consumption, but it mounts up. In the UK, population 65 million, it means waste water treatment consumes 65,000 gigajoules a day – about a quarter of the output of the country’s largest coal-fired power station. In a world where energy efficiency is ever more important, that’s not to be dismissed.
According to civil engineer and urine-separation expert Jac Wilsenach, it’s highly inefficient. Wilsenach spent six years at Delft University of Technology in the Netherlands working on the intricacies of sewage systems, and according to his calculations, today’s methods mean we are literally flushing energy down the pan.
In a paper published last March, Wilsenach calculated that if we were to separate out just half of our urine, the microbes in the aeration tanks could eat up almost all the nitrogen and phosphate (Journal of Environmental Engineering, vol 132, p 331). The energy-intensive polishing stage would become completely unnecessary.
There’s another, even bigger gain to be had from separating out the urine. Lower starting levels of nitrogen and phosphate mean that the microbes in the aeration tanks can do their job much more efficiently, taking just one day compared with about 30, thus reducing the energy demand of the aeration tanks. What’s more, the resulting sludge is richer in organic matter and generates more than three times as much methane. In fact, says Wilsenach, separating out 50 to 60 per cent of the urine could turn sewage works from net consumers to net producers of energy to the tune of about 2.5 watts per person.
So far so good. But how do you stop pee from getting into sewage in the first place? The answer is to install a special WC called a "urine-separation toilet" or often just a NoMix, after one of the leading brands.
On casual inspection a NoMix toilet looks pretty much like a normal one. But peer into the bowl and you’ll see that there are two waste pipes – a small front one and a larger rear one. The front one collects urine and diverts it into a storage tank (sometimes aided by a tiny trickle of water) to await its fate. The rear works like a standard flush toilet.
You don’t even have to do anything special to make this separation happen – apart from one thing. "The toilet is constructed in a way that if a man or woman sits on the toilet most of the urine is collected," says Bjartur Swart of engineering firm Grontmij in Drachten, the Netherlands, which is conducting urine separation trials across the country. Yep, that’s right. In the urine-separating future, men will sit down to pee.
Although small-scale urine separation has been practised for centuries (pee has been used in industries ranging from textile dyeing to blacksmithing, for example), it is something of a minority pursuit today. Modern experiments started in Sweden in 1994 with the founding of two "ecovillages" – Understenshöjden in Stockholm and Björsbyn in the far north – whose houses and apartments were fitted with urine-separation toilets. There, the urine is stored for collection by local farmers who use it as a fertiliser.
Other villages have followed suit and Sweden is now the urine-separation centre of the western world, with around 3000 NoMix toilets in use. Denmark has also set up urine-separation projects including one at the Svanholm Gods farming collective near Skibby, the largest producer of organic vegetables in the country (bear that in mind if you ever buy organic vegetables from Denmark).
The urine from all these projects ends up being sprayed directly onto fields, which works fine as long as only a few people are contributing. It doesn’t take much, though, for supply to start outstripping demand. "Recycling urine directly is not feasible in cities, but that is where the focus should be because that’s where the biggest amount of waste comes from," says Wilsenach, now at South Africa’s national research institute CSIR in Stellenbosch.
So what to do with the urine? The answer is, recycle it indirectly – in other words, extract the nutrients and turn them into fertiliser. In the Netherlands, Grontmij trucks the stored urine to a special treatment plant where the phosphate is precipitated out as a mineral called struvite (ammonium magnesium phosphate). This is a useful fertiliser and can help reduce demand for mined phosphate, which can only be a good thing: phosphate rocks are often contaminated with heavy metals, and mining and refining them generates waste and uses lots of energy. Some estimates suggest the world’s phosphate mines will be exhausted in 100 years. Yet at the moment we literally pour tons and tons of perfectly good phosphate down the drain.
The other nutrients in urine can also be turned into fertiliser. Novaquatis, a branch of the Swiss Federal Institute of Aquatic Science and Technology (EAWAG) on the outskirts of Zürich, is experimenting with extracting nitrogen and potassium in forms that can be sprayed directly onto crops. Once the urine is treated it is clean enough to go directly into a river.
Crucially, these methods of extracting nutrients directly from urine consume much less energy than dealing with its vastly diluted form in general waste water. There’s an extra energy cost from trucking the urine in, but Wilsenach says it’s minuscule compared with the savings.
If all these benefits weren’t enough, using a NoMix toilet saves water too. According to research done by EAWAG, it reduces your use of flush water by 80 per cent, cutting the average household’s overall water use by about 25 per cent. Bear in mind that the water that fills up the toilet cistern is clean enough to drink: "We use good quality drinking water to flush away urine," says Wilsenach.
So where next for urine separation? Grontmij and Novaquatis have set up pilot projects across the Netherlands and Switzerland, and a handful of places are now doing it for real, including the public library in Liestal, Switzerland. Swiss citizens can even buy their very own NoMix toilets and storage tanks if they want, even though the sewage system is not yet ready and the urine ends up flowing into the waste water stream as normal. Urine separation is also taking root in Austria and Germany.
In surveys, people say they would be happy to use NoMix toilets and buy vegetables fertilized with processed urine. There is even a way round what could seem the biggest obstacle to widespread acceptance. "If a man doesn’t like sitting, he can urinate just in a normal way and use the [front] hole as a target," says Swart.
One day we may look back at our habit of flushing pee away with drinking water as staggeringly wasteful. "Water and waste are two of the greatest challenges the world faces at the moment," says Jacob Tompkins, director of Water-wise, a London-based water efficiency campaigning group. "Anything that looks at our low-efficiency way of dealing with the waste stream is extremely important."
Of course it would take time and money to convert existing sewage systems. But even if urine separation isn’t coming to your area any time soon, that’s not an excuse for inaction. Keeping urine out of the waste stream any way you can pays dividends. So what are you waiting for? Next time you need to take a leak, give the bathroom a miss and head straight for the flower beds. Then you can replace your green halo.
They can be very simple;
Or more esthetically pleasing;
The one above is at the top of the article is a beautiful Japanese sawdust toilet.
Here is a link to Joseph Jenkins wonderful book- The Humanure Handbook.
Here are exact instructions. Building a sawdust toilet
I paid 18.00 at Lowe’s for a wooden toilet seat. I got the buckets free from a local sub-shop. It feels SO good to not be flushing an average of 40 GALLONS a day of water. My water bill has dropped considerably, my compost is baking away and the plants love the fertilizer. Between Bokashi composting, growing my own veggies and recycling all yard clipping and leaves, I am getting more and more “off the grid”. It is deeply satisfying.