Yellow Is the New Green - Sewage Treatment Wastes Energy

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IN the far reaches of Shaanxi Province in northern China, in an apple-producing village named Ganquanfang, I recently visited a house belonging to two cheery primary-school teachers, Zhang Min Shu and his wife, Wu Zhaoxian. Their house wasn’t exceptional — a spacious yard, several rooms — except for the bathroom. There, up a few steps on a tiled platform, sat a toilet unlike any I’d seen. Its pan was divided in two: solid waste went in the back, and the front compartment collected urine. The liquids and solids can, after a decent period of storage and composting, be applied to the fields as pathogen-free, expense-free fertilizer.

From being unsure of wanting a toilet near the house in the first place — which is why the bathroom is at the far end of their courtyard — the couple had become so delighted with it that they regretted not putting it next to the kitchen after all.

What does this have to do with you? Mr. Zhang and Ms. Wu’s weird toilet — known as a “urine diversion,” or NoMix (after a Swedish brand), toilet — may have things to teach us all.

In the industrialized world, most of us (except those who have septic tanks) rely on wastewater-treatment plants to remove our excrement from the drinking-water supply, in great volumes. (Toilets can use up to 30 percent of a household’s water supply.) This paradigm is rarely questioned, and I understand why: flush toilets, sewers and wastewater-treatment plants do a fine job of separating us from our potentially toxic waste, and eliminating cholera and other waterborne diseases. Without them, cities wouldn’t work.

But the paradigm is flawed. For a start, cleaning sewage guzzles energy. Sewage treatment in Britain uses a quarter of the energy generated by the country’s largest coal-fired power station.

Then there is the nutrient problem: Human excrement is rich in nitrogen, phosphorus and potassium, which is why it has been a good fertilizer for millenniums and until surprisingly recently. (A 19th-century “sewage farm” in Pasadena, Calif., was renowned for its tasty walnuts.) But when sewage is dumped in the seas in great quantity, these nutrients can unbalance and sometimes suffocate life, contributing to dead zones (405 worldwide and counting, according to a recent study). Sewage, according to the United Nations Environment Program, is the biggest marine pollutant there is. Wastewater-treatment plants work to extract the nutrients before discharging sewage into water courses, but they can’t remove them all.

And there’s also the urine problem. Urine, like any liquid, is a headache for wastewater managers, because most sewer systems take water from street drains along with the toilet, shower and kitchen kind. Population growth is already taxing sewers. (London’s great network was built in the late 19th century with 25 percent extra capacity, but a system designed for three million people must now serve more than twice as many.) When a rainstorm suddenly sends millions of gallons of water into an already overloaded system, the extra must be stored or — if storage is lacking — discharged, untreated, into the nearest river or harbor. Each week, New York City sends about 800 Olympic-size swimming pools’ worth of sewage-polluted water into nearby waters because there’s nowhere else for it to go.