Saving the World – with a Stink!

The latest from Nature (vol 602, p 202) on how to save the world: collect urine. This is, of course, a well-established technology – the ancient Romans did it. They collected it from special urinals through the city and did all sorts of things with it. One of the more interesting, according to Catullus, was to use it as a tooth whitener! The urine was also collected and taken to a fullonica (a laundry) and after dilution, was poured over dirty clothes. A worker would stand in a tub and stomp on the clothes – conceptually similar to a modern washing machine. It was similarly used to clean wool and remove the fats, etc, to prepare it for dyeing. It can be used to make leather soft, and when mordant dyeing, it can also make the dyes brighter. And, of course, if you feel so inclined, you could advance to medieval times and make saltpetre, which is essential for gunpowder. But urine uses come and they go, so how now do they save the world?

The lead, apparently, comes from Sweden, and in particular the island of Gotland. They are going to put some public flush-free urinals around the island and hope to collect about 70,000 litres of it. They are then going to dry this into chunks apparently with the texture of concrete, which they powder and compress into pellets for fertilizer. Currently, a local farmer uses the product from a pilot plant to grow barley which goes to a local brewery and thus forms a complete cycle. That is real recycling.

The problem here, of course, is it is necessary to separate the urine from the rest of the sewage. Either you need separate toilets, or you have an interesting design issue. There are, apparently, a number of similar projects in a number of different countries. Currently, it has been estimated that humans produce enough urine to replace about ¼ of our nitrogen and phosphate fertilizers. It also contains potassium and many  micronutrients. Also, by not flushing, we save a lot of water. As for problems, the first we face is we have to redesign our toilets and then design a way for how we treat it. The treatment will have to be dispersed, thus a building might have its own urine system. Currently, we have one sewage system that takes everything, but we cannot afford a further such system, especially since for a dispersed system sooner or later some people will put anything down the second system. As for “saving the world”, one estimate is that communities that do this could lower their overall greenhouse emissions by up to 47%, their energy consumption by up to 41%, fresh water usage by 50%, and nutrient  pollution from waste-water by up to 64%. The greenhouse emission savings go a very long way to saving the planet alone, provided everyone did it, because if properly managed, not only do you reduce methane production, but also the much more difficult nitrous oxide, which is more long-lived than carbon dioxide. Then, if you deal with this properly you could get more imaginative: bags to collect urine from cows! Fix the dairying greenhouse problem in one go.

Sounds good, so what’s the problem? Toilet design, to start with. What people come up with tends to be unwieldly, awkward to use, and outright smelly, especially if urine gets mixed with the faeces. A clever redesign of a toilet might overcome that, but now you have to collect the separate urine, with no additional water added. It will drain, but leave a smell. Either you collect in a tank that then has to be taken somewhere, or you re-pipe the building. Then what? In an urban setting, it is not practical to install a separate sewer system, and since it is about 95% water, transporting is very expensive for what you get. One trick is to hydrolyse the urine (because much of the nitrogen is present as urea) then add something like magnesium sulphate (maybe supplemented with some phosphate) and you get a precipitate of magnesium ammonium phosphate (struvite), which is an excellent slow-release fertilizer. The problem now is the phosphate in the urine is not balanced with the nitrogen (which is why supplanting it is desirable), you have lost the potassium, and does the average household want to do this every weekend? As you can see, saving the world is more difficult than it looks like at first sight.