How to Recycle Phosphorus, the Most Least-Known Scarce Resource

How to Recycle Phosphorus, the Most Least-Known Scarce Resource

Picking up on “sustainable agriculture”, most people think of free range chicken. They imagine livestock on green pastures. Some better informed would probably imagine a few optimized chemical and physical cycles, drip irrigation, compost based fertilizer, and limited pesticides. Haber-Bosch, the couple of celebrated innovators that revolutionized nitrogen supply, may be a name that quite a few are familiar with. However, although every one of us consumes farmed products every single day, it goes beyond average knowledge that our crops need various nutrients to grow and only a relatively few people have any good idea about where these nutrients are sourced. Even less so, whether the fundamental ingredients of life are renewable or not.

Apart from space, light, and water, plants require three more major elements to grow, nutritional elements. Of all nutrients, the most vital ones are nitrogen, potassium and phosphorus. Despite the one fact they all have in common – without them, not one plant could grow – their supply situation is pretty diverse. Nitrogen, principal element of proteins, makes up 78% of the air in our atmosphere. Either the complicated way, with the help of the Haber-Bosch process and a fair bit of energy, or simply using plants from the legume family (in conjunction with certain bacteria), you can capture this nitrogen straight from the air and make it available for other plants. Potassium and phosphorus, however, are minerals. Traces of these minerals can be found everywhere life is (or was), but the necessities of large-scale agriculture require extraction from vast ground deposits through mining activities. In contrast to nitrogen gas, potassium and phosphorus minerals are relatively finite resources. However, potassium is available in abundant reserves, whereas the extraction of phosphorus could peak in a few decades. The chances that we’ve already reached peak oil, or better peak cheap oil, are high, and peak phosphorus is just a question of time. While other vulnerable resources required for farming, especially water, receive a good deal of media attention, awareness of the diminishing sources of phosphorus remains locked in the academic ivory tower.

The recently finished “European Sustainable Phosphorus Conference” aimed to change this. Its website hints at possible ways of turning the current practice, easily dubbed a phosphorus one-way street, into a phosphorus cycle:

Europe already has the knowledge and the technology to recycle phosphorus from wastewater, manure and bio waste.

There we go, three renewable phosphorus sources. How come nobody thought of this before? Although the excess nutrients that cause environmental damage could be captured and turned into something useful, namely fertilizer, none of these secondary sources are widely used as of May 2013. Instead, as mentioned above, phosphorus is mined in the form of phosphate rock. The biggest share of phosphate rock is located in a handful of countries: China, Russia, USA and Morocco. Industrial, not biological, plants in these countries usually refine the rock into phosphoric acid. Phosphoric acid, when mixed with anhydrous ammonia for fertilizer use, has considerable destructive potential. Still, big agricultural producers like the European Union import incredible quantities of mineral fertilizers. Most farmers and agricultural institutions have gotten used to this practice and are far from adopting a resource-efficient attitude. On its website, Stockholm Environmental Institute‘s Arno Rosmarin outlines how inefficient current phosphorus use is:

Q: How much phosphorus is now wasted?
A: About 40% of the original [phosphorus] content of sedimentary rock is lost through the processing to concentrate, to phosphoric acid and fertilizer. An additional 40% is lost in the application of fertilizer. Erosion from soil is a significant loss, especially in areas with precipitation and runoff. So globally, only about 20% of the original P ends up on people’s plates (…)

The renowned sustainability expert calls for the reuse of phosphorus from all possible sources. Any flow containing leftovers of plants and living beings can serve as a nutrient source, namely manure, organic solid waste, wastewater and sewage sludge. Excreted, yes, but still extraordinarily nutrient-rich. Rosmarin continued with “manure from animal holding facilities needs to be made available to the farmers growing feed”. Taking the above mentioned waste streams and extracting phosphorus from them, he says, “is relatively well researched.” However, it is “not scaled up”, as in becoming more affordable when widely used, and being widely used when it becomes more affordable. He also mentions a new technology under development. “Extracting Struvite (NPMg) from wastewater and urine is a new option that is being developed in both the EU, North America and even in some developing countries.” We’ll see what that brings.

So when we read that current technology is already capable of reusing phosphorus, one question arises: why are these methods not scaled up? The answer lies in a few questions all natural resource management issues have in common. How can something that mother nature provides be priced? Even if we know the sustainable practice we ought to use, who do you set in the control center’s chair? Is that institution equipped with sufficient funds and legitimacy? How do you face uncertainty, how do you tackle complexity? A publication put together by Stockholm Environment Institute mentions hard constraints for phosphorus. Page 6 of “Governance Innovations for Improved Phosphorus Management and Reuse ‐ Voices from the Baltic Sea Region” (PDF available here), says:

[A]s with all complex issues, the uncertainties remain high. What is the exact lifetime of low-cost phosphorus rock globally, and how urgently should we respond? How do we manage phosphorus application in the absence of adequate soil maps or even basic monitoring data in some countries? How can we price phosphorus transfers through manure when the phosphorus content varies? While some countries have sludge regulations with compulsory requirements for recycling a fraction of the sludge to arable land, uncertainties regarding bio‐security make it difficult to scale‐up and to generate acceptance among consumers and farmers.


Well, in the long run, at the largest scales, these are tough challenges. The above-mentioned document explores what expectations the policies tackling the problem have to meet, and how policies could be effected in a contemporary, bottom-up approach. That’s where the “Governance” in the document’s title came from. The good news is, however, that on a micro level, is has never been easier than today to establish a nutrients balance, preferably a sustainable one. Farm by farm, municipality by municipality – you as a decision maker can capture and recycle the phosphorus flows that occur within your dominion. All you have to do is get in touch with your favorite research institution or sustainability consultant. Then ask your chosen source of wisdom about programs you can access that deal with materials flow modeling and the recycling of nutrient flows.

One such institution is the “von Thünen-Institut” in Germany. Its researchers, Maximilian Schüler and Hans-Marten Paulsen, modeled an organic dairy farm in northern Germany with the life cycle assessment software umberto. The dynamic model of the farm originally aimed to calculate and compare the overall environmental performance of different dairy breeds. However, the beauty of material flow modeling is that once the model is set up, you can use it in many ways, the most important being the optimization of farm practices. Both in terms of lower emissions and higher yields. Before trying (and ‘erroring’), the simulation can prevent you from getting nasty surprises and set the right parameters straight away. What’s most relevant in the sense of this article, however, is the possibility of evaluating the nutrient balance. The power point presentation for Schüler’s and Paulsen’s dairy farm simulation is available for download in 2011’s umberto user workshop documentation (free after registration). The following preview, part of that presentation, shows that a simple agricultural practice such as harvesting grass may incorporate quite a few processes and material flows. However, when modeled adequately, they give you a good overview of what’s happening between blade of grass and gulp of milk. The model section displayed here has three direct inputs – diesel, vegetable oil (Rapsöl), and pasture land – and a couple of indirect ones – nutrients (Nährstoffbilanz) and seeds (Saatgut). Four mechanical steps separate the crop from the animal feed – mowing (Mahd), turning (Wenden), swathing (Schwaden), and collecting (Gras abfahren). For outputs, you have the grass on the one hand and on-site emissions on the other. You also need land to store the grass (Landfläche). Here’s what their material flow model of grass harvest looks like. Have fun while setting up yours!




Further Reading

  • Stockholm Environment Institute (2012): Governance Innovations for Improved Phosphorus Management and Reuse ‐ Voices from the Baltic Sea Region, Synthesis from ‘Pre‐consultation’ for EU Green Paper on Sustainable Phosphorus. Baltic Compass. PDF download
  • Q&A: Arno Rosemarin on the first European Sustainable Phosphorus Conference (Anna Löfdahl), 6/5/2013,
  • J.J. Schröder, D. Cordell, A.L. Smit & A. Rosemarin (2010): Sustainable Use of Phosphorus. Wageningen University and Research Centre, Stockholm Environment Institute, PDF download
  • Annual Fertilizer Imports/Exports for the US: USDA Economic Research Service
  • FAO (2012): Current world fertilizer trends and outlook to 2016. PDF download

Article image by Dennis Jarvis (CC BY SA 2.0), Showing Tunisia‘s Biggest Phosphate Mine in Metlaoui.



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