Let’s talk about phosphorus depletion

14Nov
Let’s talk about phosphorus depletion
Phosphate mine in Togo. Wikimedia commons/Alexandra Pugachevsky

Guest post by Joe Bartram

Not really clickbait, is it?  I could have called this article MANY things.  “The war on crap” was a favourite.  Or, “Why Morocco will be the next Saudi Arabia”, for a somewhat tedious economic spin.  “The effect of human activities on global nutrient cycles and implications for human society and the environment” was out for obvious reasons.

Still here? Congratulations! In that case I’ll assume you’re here for the long-haul, and I’ll get started. Thanks to Climate Change, pretty much everyone these days is aware of the global carbon cycle, and how human influences are upsetting the flow of global carbon, to disastrous effect. It is less common knowledge that anthropogenic influences have also disrupted many other global ecosystem processes, of which none falls under the radar or is more problematic than the phosphorus cycle.

The phosphorous cycle. Image courtesy of wwtlearn.org.

The phosphorus cycle. Image courtesy of wwtlearn.org.

Phosphorus – the only biogeochemical cycle without a significant gaseous phase, and hardly any soluble phase.  As such, it cycles through the environment much more slowly than nitrogen or carbon – so slowly indeed, that on a global level its movement is driven by tectonic processes.

Well, I hear you cry, this is all very interesting, but why do we care?  Apart from being component of the nucleotides essential to life, Phosphorus forms the basis of NPK (Nitrogen-Phosphorus-Potassium) fertilizers which drive modern high-intensity agriculture, and incidentally feed the world.  And it’s running out.

Historical sources of phosphorus for use as fertilizers, including manure, human excreta, guano and phosphate rock (1800–2000), Cordell et al., 2009, Global Environmental Change, 19,  292 - 305

Historical sources of phosphorus for use as fertilizers, including manure, human excreta, guano and phosphate rock (1800–2000), Cordell et al., 2009, Global Environmental Change, 19, 292 – 305

Today, the only economically viable sources of phosphate are phosphate rocks, which are limited and depletable.  Just how much Phosphorus remains is a contentious question, but conservative estimates put depletion of exploitable reserves within 200 years (Cordell et al., 2009).  Adding an extra stroke of black to this already bleak picture is the fact that most of the globe’s reserves of phosphate rocks are controlled by a handful of nations.  Indeed, Morocco alone controls an estimated 77% of global reserves (Cooper et al., 2011).  Under these conditions, it is quite easy to imagine that this humble mineral may become as valuable and fought-over a commodity in the next century as oil is today.

This considered, it is a dark irony that while exploitable phosphorous is becoming increasingly scarce, it is becoming hyper-abundant in the biosphere, with disastrous consequences.  Human activities have tripled the natural flow of the nutrient through the biosphere (Smil 2000), leading to large-scale eutrophication and environmental collapse in many freshwater ecosystems.

Most anthropogenic phosphorous makes its way into the biosphere through agricultural runoff and waste, but these sources can (and indeed are) be tackled through existing improvements to agriculture management practices.  A far more insidious anthropogenic flux of phosphorous into the environment is, frankly, crap.  Recycled animal and human excreta has been used as fertiliser for millennia, and in this way phosphorous cycled continuously with minimal losses.  Indeed, manure is still a major source of phosphorous.  However, the innovation of modern plumbing opened this loop, discharging vast quantities of phosphorous into the environment, with well-documented consequences.  The solution to environmental pollution and phosphate shortage is of course to close the loop on the cycle. But how to go about this?

Even with modern methods of reclamation, human sewage is a major source of phosphorous entering aquatic environments, and the various treatment processes dedicated to phosphate removal are inefficient, requiring dedicated reactors.  While novel approaches such as struvite precipitation continue apace, these fail since they attempt damage mitigation downstream of the problem (Adnan et al, 2003).

Solving the phosphate cycling problem requires a much more fundamental and yet simple paradigm change in our approach to sewage management.  The waterless toilet.

The difficulty of processing human waste to reclaim the useful nutrients scales fairly astronomically with how diluted it is.  Consequently, while toilet plumbing might be hygienic and easy for the end user, it is necessarily costly and inefficient to process.  The alternative is dry toilets, especially those that separate urine and faecal matter.  Various designs for these already exist, and have been implemented in many places around the world.

Using modern methods, dry toilets can be as hygienic and water friendly as plumbing, and greatly ease the problem of phosphorous reclamation.  Since urine is essentially sterile, if collected this way it requires an absolute minimum of processing to make safe for agricultural use, while undiluted faecal matter is much more readily sanitized for the same purpose.  Thus, by a single simple innovation, a major source of environmental pollution and a major agricultural limitation could potentially be circumvented.  This approach also has a host of side benefits, principally greatly relieving our dependence on water for sanitation, and hopefully postponing our eventual water crisis.

As always, our emerging phosphorus shortage is a complex issue that will require a complimentary approach.  Here I’ve discussed just one of them, chosen for the simple delight that so simple and unexpected a change in our approach might have such a great potential benefit.

Recommended reading

Adnan A., D.S. Mavinic, F.A. Koch 2003, Pilot-scale study of Phosphorus recovery through struvite crystallization: examining the process feasibility, Journal of Environmental Engineering and Science, 2(5): 315-324

Cooper J., R. Lombardi, D. Boardman, C. Carliell-Marquet 2011, The future distribution and production of global phosphate rock reserves, Resources, Conservation and Recycling, 57: 78-86

Cordell D., J.-O. Drangerta & S. White 2009, The story of phosphorus: Global food security and food for thought, Global Environmental Change, 19(2): 292-305

Smil V. 2000, Phosphorus in the Environment: Natural Flows and Human Interferences, Annual Review of Energy and the Environment, 25: 53-88

Joe Bartram is a research student in the 2014 cohort.