It is quite literally one of the few elements that hold us together. Without it, almost every oxygen-respiring organism would slump into an organic soup (Ruttenberg, 2013) More importantly, it supplies energy to most aerobic organisms’ cells, allowing lifeless organic compounds to move, grow and well, be alive (Ruttenberg, 2013)!
The effects of phosphorus fertiliser use on crops. Source: Franklin D. Roosevelt Presidential Library and Museum (53227(1828)
In agriculture, phosphorus is a vital ingredient in fertilisers that prevent topsoil degradation after harvests have removed soil nutrients (Cordell, Drangert, & White, 2009). This phosphorus is mined from rocks (aptly named apatite) that have substantial concentrations of phosphorus (Daneshgar, Callegari, Capodaglio, & Vaccari, 2018), supplied by tectonic uplift of buried oceanic sediments as seen below (Ruttenberg, 2013).
The global phosphorus cycle. Upward arrows indicate phosphorus replenishment. Source: Ruttenberg et al. (2013)
Our society effectively relies on a resource that takes tens of thousands of years to replenish to feed an ever-growing population (Cordell et al., 2009; Ruttenberg, 2013)! Unsurprisingly, we exploit this finite resource like there’s no tomorrow (Daneshgar et al., 2018). We pump more phosphorus than the ground can hold, causing the excess to leach into our rivers and oceans; stimulating toxic algae blooms that kill fish and create anoxic dead zones when the nutrients have been exhausted (MIT, 2016).
The depletion of phosphorus reserves is a hotly debated topic (Daneshgar et al., 2018). Daneshgar et al. (2018) gave a tentative estimate of a few centuries, while Cordell et al. (2009) painted a grim few decades remaining of unequal phosphorus distribution between the rich and poor. As an environmentalist, the concept of relying on a finite resource gives me the same anxiety as a looming deadline; it’s an itch that I cannot tolerate.
Anthropogenic phosphorus budget, landfill and sewage losses are fairly significant. Source: Cordell et al. (2009)
Ultimately, the ideal outcome is closing the anthropogenic phosphorus loop and preserving natural phosphorus flows. The recovery of phosphorus from wastewater treatment, while not a large proportion of anthropogenic phosphorus loss, is still a significant point-source emitter that we can feasibly amend (Cordell et al., 2009; Daneshgar et al., 2018). Furthermore, the inherent global distribution of wastewater treatment plants (WWTP) could equalise the current oligopoly of phosphorus source countries (Daneshgar et al., 2018). At least, it’s better than twiddling our thumbs.
Source: PUB
In conventional WWTPs, most of the phosphorus in wastewater is removed in sludge to meet effluent discharge standards and lost when the sludge is incinerated and landfilled (Cornel & Schaum, 2009).
Phosphorus-recovering WWTPs typically utilise magnesium and calcium salts to crystallise phosphate fertilisers from wastewater, wet sludge or incinerated sludge ash after pre-treatment to remove other pollutants like heavy metals (Cornel & Schaum, 2009). Other novel approaches such as the use of algae sequestration have been tested, but trade away phosphorus recovery performance for the production of ready-made livestock feed and organic fertiliser (Shilton, Powell, & Guieysse, 2012).
In the pursuit of recovering and reusing a finite resource, we should not lose sight of other environmental objectives too. After all, it would be pointless if phosphorus recovery uses more energy than phosphorus extraction from apatite (Daneshgar et al., 2018) since we would be exchanging different forms of environmental degradation.
Just imagine if our upcoming Integrated Waste Management Facility had a zero-energy phosphorus recovery system; we could be one step closer to sustainable food self-sufficiency!
References:
Cordell, D., Drangert, J. O., & White, S. (2009). The story of phosphorus: Global food security and food for thought. Global Environmental Change. https://doi.org/10.1016/j.gloenvcha.2008.10.009
Cornel, P., & Schaum, C. (2009). Phosphorus recovery from wastewater: Needs, technologies and costs. Water Science and Technology. https://doi.org/10.2166/wst.2009.045
Daneshgar, S., Callegari, A., Capodaglio, A. G., & Vaccari, D. (2018). The potential phosphorus crisis: Resource conservation and possible escape technologies: A review. Resources. https://doi.org/10.3390/resources7020037
Massachusetts Institute of Technology(MIT) (2016). Eliminating depletion and environmental damage with efficient phosphorus use and reuse. Mission 2016. Retrieved from https://web.mit.edu/12.000/www/m2016/finalwebsite/solutions/phosphorus.html
Ruttenberg, K. C. (2013). The Global Phosphorus Cycle. In Treatise on Geochemistry: Second Edition. https://doi.org/10.1016/B978-0-08-095975-7.00813-5
Shilton, A. N., Powell, N., & Guieysse, B. (2012). Plant based phosphorus recovery from wastewater via algae and macrophytes. Current Opinion in Biotechnology. https://doi.org/10.1016/j.copbio.2012.07.002