Waste Not, Want Not: A Phosphorus Tale
As usual, Ben Franklin had it largely right with his sage advice: “Waste not, want not.” Take phosphorus, for instance. It’s a ubiquitous and much-needed mineral. Along with carbon, hydrogen, oxygen and nitrogen, it’s one of the fundamental building blocks of life. Phosphorus atoms are essential to every molecule of DNA, RNA and ATP — all fundamental cellular components of every living organism on the planet. Carbon, hydrogen and oxygen are ubiquitous and readily available in a form that most plants and animals can use, so they tend to not be limiting components. Nitrogen is also abundant, though its gaseous form is not readily available to most plants and animals; that’s another story for another day. Phosphorus, though, is in a category unto itself.
Unlike C, H, O and N, phosphorus is generally found in the soil in relatively dilute quantities. From there, plants absorb it, convert it into the life-supporting molecules mentioned above, and grow. You know the story: Plant grows, animal eats plant, another animal eats that animal, and so on. With each sequential phase the phosphorus is taken up by the next consumer and either absorbed into its own cellular components or excreted as, well … let’s just say it’s excreted. This is a long way of saying that excreta (especially urine and guano) have a lot of phosphorus.
Where it starts to get a little tricky is that in order for plants to grow bigger and bear more fruit or grains, which is what farmers generally want, more phosphorus is needed. Manure can be used to boost growth, but these days the most common way for commercial growers to boost yield is to use fertilizers made from rock phosphate, a concentrated form of phosphorus that is mined from one of a few specific places on the planet. In the U.S., most of that phosphorus comes from one mine in Florida. There are differing perspectives on how long the global phosphorus mines will last, but it’s definitely not forever. What this means is that we need to start developing alternative supplies of phosphorus fertilizer, and stretch our existing supply if we want to continue to grow as much food as we currently do.
Meanwhile, it turns out that while phosphorus in the soil helps plants grow, when that phosphorus gets into lakes and rivers it helps algae grow, and pretty much no one likes that. One of the major sources of phosphorus pollution (notice I wrote one, not the only) is effluent from sewage treatment and large-scale farming operations. Generally this is a source of friction between water advocates and waterfront property owners, and sewage treatment agencies. For a variety of historical reasons, most sewage effluent still has considerable amounts of phosphorus. The same is true for large-scale livestock operations, which, from a waste perspective, are basically small cities that produce a lot of manure. So, one naturally thinks, how do we realign this situation so that the phosphorus that is currently being dumped into our rivers and lakes can instead be used by farmers to grow the food we need while extending the life of our nation’s phosphate mines?
There are multiple answers to this question, but one that is creating quite the buzz these days is a process that can harvest a form of phosphorus known as “struvite.” A blog I wrote on innovation last fall included a paragraph on Ostara, one of the companies that is leading this revolution, that is relevant here:
- This is a win-win opportunity because it not only results in cleaner water, but it also eliminates struvite from building up inside of pipes, a costly maintenance problem. Ostara goes beyond the basic technology with its interesting business model. Rather than leaving the utility to have to sell the resulting fertilizer, Ostara purchases it from the utility, and then does the branding, marketing and re-selling itself, allowing it to develop economies of scale that would be impossible for an individual utility. Its signature operation is in Portland, Ore., but the big news this year at WEFTEC was the announcement that Ostara has signed an agreement with Chicago’s MWRD, which will make Chicago the world’s largest nutrient recovery operation. Interestingly, Chicago has no legal obligation to lower its phosphorus limits. From what David St. Pierre, its general manager, told me, he’s taking this step because he and his board want to be out front on this.
The magic of their process, or so I’ve been told, has to do with pH manipulation. At low pH, the phosphorus stays in solution and does not build up in the pipes. But as soon as the pH starts to rise (which naturally happens in sewage pipes), struvite begins to precipitate out. Ostara has developed a process that captures and harvests the struvite rather than allow it to build up in the pipes where it causes problems. One can think of this like the scale build-up some people experience in their toilets. The scale is essentially struvite. Adding a small amount of vinegar, which is acidic, fairly quickly loosens up the struvite so that it can be quickly scrubbed off of the ceramic toilet bowl.
We can and need to do a better job of getting phosphorus and other nutrients out of our wastewater and out of our waterways. With opportunities like struvite recovery, I like to think this will happen because it’s good for everyone: good for people, good for utilities, good for farmers and good for business. To learn more about what leaders in this field are thinking, I hope you’ll take a look at The Johnson Foundation at Wingspread’s recently released convening report, “The Road Toward Smarter Nutrient Management in Municipal Water Treatment.” I’d love to know what you think.