Yellow is the New Green


Swedish no-mix toilets

Over a hundred years ago, Teddy Roosevelt noted that "civilized people ought to know how to dispose of the sewage in some other way than putting it into the drinking water." We still don't get it right, building huge networks of pipes that dump everthing together into one pipe, when both bodily waste products are considerably more useful if kept separate.

Rose George does an op-ed in the New York Times that expains why. Urine is full of phosphorus, which may soon be in short supply, so there is a market for it as fertilizer. So why not put urine-separating toilets in our homes?

The price of phosphorus fertilizers rose 50 percent in the past year in some parts of the world, as phosphate reserves, the largest of which are in Morocco and China, dwindle. (The gloomiest predictions suggest they'll be gone in 100 years.) Although half of sewage sludge in the United States is already turned into cheap fertilizer known as "biosolids," urine contains hardly any of the pathogens or heavy metals that critics of biosolids claim remain in mixed sewage, despite treatment.

In Sweden, where they are testing separating toilets on a large scale,

collected urine goes to municipal wastewater plants, but in much smaller volume so it's easier to deal with. Research by Jac Wilsenach, now a civil engineer in South Africa, found that removing even half of the nutrient-rich urine enables the bacteria in the aeration tanks to munch all the nitrogen and phosphate matter in solid waste in a single day rather than the usual 30. Urine diversion also makes for richer sludge and produces more methane, which can be turned into gas or electricity, Mr. Wilsenach said. In short, separating urine turns a guzzler of energy into a net producer.

The author notes that "there's the sitting problem: in most urine-diversion toilets, a man must empty his bladder sitting down." but as we have noted before, they make some very nice residential urinals now. Problem solved. New York Times

John Laumer reviewed the No-mix toilet earlier in TreeHugger, noting :

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.

Perhaps it is time to look at designing our cities with yet another pipe for urine collection, or to seriously look at no pipes at all.

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Waste Not, Want Not: The Future of Toilets

Tags: Cities | Waste