Don't flush that fertilizer!

Normal ecosystems use and reuse critical nutrients like phosphorus. But humans aren't normal


Andrew Leonard
June 6, 2009 2:06AM (UTC)

Longtime readers of How the World Works know that before the financial crisis distracted me from my previous fixations with the role of monitor lizards in 17th century Indian history and titanium dioxide deposits in Northern Florida, I also kept a close eye on fertilizer.

Without sufficient supplies of fertilizer we can't feed the nine billion people expected to live on this planet by 2050. And when one bows down to worship the three members of the holy trinity of fertilizer -- nitrogen, potassium, and phosphorus -- it's important to realize that, in the case of phosphorus, there is good reason to believe that the world just doesn't have enough of the stuff.

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The current issue of Scientific American has the best article I have yet read on the state of all things phosphorific, by David A. Vaccari. I heartily recommend it.

Two passages stood out for me.

Land ecosystems use and reuse phosphorus in local cycles an average of 46 times. The mineral then, through weathering and runoff, makes its way into the ocean, where marine organisms may recycle it some 800 times before it passes into sediments. Over tens of millions of years tectonic uplift may return it to dry land.

Harvesting breaks up the cycle because it removes phosphorus from the land. In prescientific agriculture, when human and animal waste served as fertilizers, nutrients went back into the soil at roughly the rate they had been withdrawn. But our modern society separates food production and consumption, which limits our ability to return nutrients to the land. Instead we use them once and then flush them away.

That's right, instead of reusing phosphorous 46 times, we chow down some snack food produced from an unholy concoction of corn and soy and then flush it straight out. That's gotta stop. Because, I don't know about you, but I'm an impatient guy, and I just can't see myself waiting for tectonic uplift to replenish supplies.

Half the phosphorus we excrete is in our urine, from which it would be relatively easy to recover. And separating solid and liquid human waste -- which can be done in treatment plants or at the source, using specialized toilets -- would have an added advantage. Urine is also rich in nitrogen, so recycling it could offset some of the nitrogen that is currently extracted from the atmosphere, at great cost in energy.

So forget about low-flow toilets designed to minimize water usage. If you really want to be eco-conscious get yourself a specialized waste-separating, phosphorous-and-nitrogen collecting toilet. It'll be the ultimate environmentalist status symbol -- even better than a Prius!


Andrew Leonard

Andrew Leonard is a staff writer at Salon. On Twitter, @koxinga21.

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