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Why (not) recover phosphorus from wastewater?

highlights• Phosphorus is an essential element to life,

and it is widely used to boost agricultural production through its inclusion in fertilizers.

• Phosphorus is a finite resource, and its few geographically concentrated mineral reserves are declining, affecting the price of fertilizer and food security on a global scale; with particularly severe consequences in poorer countries.

• The release of phosphorus in the environment due to untreated / partially treated wastewater or agricultural runoff poses serious environmental challenges.

• Phosphorus recovery from wastewater is technologically feasible and helps to slow down phosphorus depletion through phosphorus recycling.

• The implementation of phosphorus recovery from wastewater can support the achievement of at least six goals of the 2030 Agenda on Sustainable Development.

Water insights

2017/1

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The conclusions of the World Water Development Report (WWDR) 2017: “Wastewater: The Untapped Resource” are multifold. In addition to stressing our responsibility in reducing pollution at the source, removing contaminants from wastewater flows and reusing reclaimed water, the report also emphasizes the opportunities that improved wastewater treatment presents through the recovery of useful by-products. There are many substances that offer this potential, namely: salts, nutrients such as phosphorus, nitrogen or potassium, and a selection of various inorganic compounds. Although each of these has its own implications for the environment when concentrations become too high, the issues around phosphorus are unique and as such merit and more in-depth discussion.

What is phosphorus? First and foremost, phosphorus is an element and thus, like other elements, it is unique on the periodic table and in nature. More importantly, it is also a macronutrient which makes it essential for the development of all living beings by forming a key, structural component of DNA and RNA (Childers et al., 2011). Therefore, phosphorus plays an essential role in cell replication, a process that allows us to grow and our bodies to sustain themselves. Humans and animals extract most of their required phosphorus through metabolism, whereas crops withdraw it from the soil: while phosphorus-related malnutrition in humans is uncommon, soil phosphorus deficiency is a much more prevalent issue (MacDonald et al., 2011). With a higher soil phosphorus content, significantly greater crop yields can be achieved, and so any phosphorus deficiency contributes directly to the global crop yield gap (Pradhan et al., 2015). This recognition and the addressing of this issue in the 1960’s contributed its part to the enthusiasm and effects of the green revolution (Elser and Bennett, 2011). The revolution, in turn, contributed greatly to the fight against poverty and world hunger by instigating the transition from our old agricultural practices to a much more efficient and intensified form.

Agricultural phosphorus application may have come with improvements to global food security, but also poses a threat to the environment (Ulrich et al., 2016). One form of improper phosphorus management expresses itself as the over application of phosphorus fertilizers. Through seepage and runoff processes, as well as untreated wastewater discharge, phosphorus excesses often come into contact with surface water. Because phosphorus is also a limiting nutrient, the smallest quantities in open surface water can spark the growth of disproportionately large algal blooms which have a detrimental effect on water based ecosystems in causing eutrophication and thus the essential suffocation of the aquatic life (EPA, 2010). The existence of many de-oxygenated dead zones in the ocean are attributed to high nutrient loadings which affect an estimated 245,000 km2 of marine ecosystems (Corcoran et al., 2010). Fortunately, many countries set strict phosphorus limits on wastewater effluent. However, in all but the most highly developed countries, the vast majority of wastewater is released directly to the environment without adequate treatment (WWAP, 2017) with all the environmental and societal implications thereof.

Phosphorus pollution isn’t all that good for the environment, but why else should we recover phosphorus from our wastewater? Currently, most phosphorus is sourced from open-cast, ‘rock phosphate’ mines. Rock phosphate formations develop over geological time scales as dissolved phosphorus in the ocean gradually precipitates under specific physical and chemical conditions. The rate at which we exploit these formations is far out of proportion to the rate at which they form, essentially making phosphorus an non-renewable resource. Largely due to uncertainty on the amount of remaining phosphorus reserves (Edixhoven et al., 2013), there exists a wide range of different estimates on how long our current reserves will last. Some scientist predict a complete exhaustion within the next 50-100 years (Steen 1998, Smil 2000, Van Vuuren et al., 2010), while others predict the reserves lasting us another good 300-400 years (van Kauwenbergh, 2010). Despite these current studies showing significant discrepancies amongst each other, all of them conclude with the same striking message that our current consumption is unsustainable and that we will sooner or later have depleted the natural stock. This leads many

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Figure 1: World Phosphate Rock Reserves 2010

Morocco and Western Sahara

2%1%1%2%3%6%85%

China

United States

Jordan

Brazil

Russia

Others

individuals to draw parallels between phosphorus and another group of non-renewable resources, namely of fossil fuels (Edixhoven et al., 2013, Smit et al., 2009, Cordell et al., 2011). The biggest difference between the two is the distinct availability of greener alternatives for energy, whereas there exist no known substitute that can replace phosphorus.

But, it gets worse? Indeed, phosphate rock is not only limiting in absolute amounts, it is also geographically concentrated to only a select, few regions (Cordell and White, 2013). Van Kauwenberg, a lead scientist at the International Fertilizer Development Center, estimated in 2010 that just four countries control 94% of the world’s remaining reserves – namely: Morocco, Western Sahara, China and the United States (Figure 1).

The global reserve distribution is not representative of the origin of actual phosphorus production. The United States Geological Survey reported that in 2015, 76% of global phosphorus was supplied by the following countries: China 45%, Morocco and Western Sahara 13%, United States 12%, and Russia 5% (USGS, 2016). Africa is the worlds’ largest exporter of mineral phosphorous but, ironically, also the continent with the largest food shortages (Childers et al., 2011). Farmers here often have insufficient purchasing power to access fertilizer markets or are geographically too isolated (Cordell et al., 2011, Kochian, 2012). One immediate consequence of gradual phosphate rock depletion will be a further reduction in accessibility by small-holder farmers that comprise the area’s already coping with food shortages. Europe, on the other hand, has among the largest phosphorus surpluses in its soil due to over-fertilization in the past (Sattari et al., 2012). Having no significant mines of its own, however, it is entirely dependent on phosphorus imports which makes it politically susceptible (De Ridder et al., 2012). A geographical concentration would not be so bad if phosphorus was not so essential to agriculture and thus a nations’ food security, nor if it was not rapidly depleting. Given this fact, it is far from unthinkable that this geographic concentration can lead to more geopolitical tensions in the future (Childers et al., 2011).In summary, the human impact on the natural phosphorus cycle is unsustainable and poses significant threat to future food security. The dwindling of rock phosphate reserves will reduce future phosphorus production, while phosphorus demand continues to rise as populations grow and living standards improve (Mew, 2016). Despite these trends, much phosphorus is being wasted through wastewater streams which results in the pollution of water resources and their dilution in the ocean where it is inevitably lost.

What can we do? Unfortunately, there is no single solution to solving phosphorus pollution and insecurity (Cordell and White, 2013). Tackling the looming phosphorus scarcity requires a multifaceted approach consisting of at least a reduction in over-fertilization, recycling crop residues and food wastes and increasing the efficiency of crop and livestock phosphorus utilization (Childers

Source: Van Kauwenberg, 2010

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et al., 2011); a reassessment of how we use and treat wastewater is also an important contribution, but appears to have greater implications for phosphorus pollution than for the global phosphorus reserves. Nevertheless, by far the biggest phosphorus-laden wastewater flows come from urban areas and the livestock sectors. Despite this, with the exception of a few local cases, there currently exist no financially attractive phosphorus recovery technology that can compete with phosphate ore based fertilizers (Schoumans et al., 2015). The added value of increasing phosphorus security and reducing environmental pollution, together with the rapid technological innovations in sanitary engineering and the expected price hikes of non-sustainable phosphorus ore, will all contribute to the implementation of phosphorus recovery technologies in wastewater treatment plants in the future. On top of that, policy and regulations that address the Agenda 2030 for Sustainable Development (UN General Assembly A/RES/70/1) will provide even more incentives to recover phosphorus from wastewater as it benefits no less than six of the Sustainable Development Goals:

Peace and JusticeBy improving the phosphorus security of nations through a reduction in their dependency on others.

Ending hungerWastewater recovery will improve the access to phosphorus fertilizers, further closing the yield gap.

Clean water and sanitationBy alleviating wastewater treatment costs through the remarketing of recovered phosphorus and the reduction in maintenance costs related to struvite-scaling.

Sustainable cities and communitiesBy creating a circular economy where waste water materials are recovered and recycled.

Responsible consumption and productionWhere we reduce our dependency on open cast phosphate mines, and diversify our sources to more sustainable alternatives.

Healthy life below waterBy further reducing the phosphorus load in treated waste water thus reducing phosphorus pollution of the environment.

Phosphorus issues are gaining increased attention globally, and the technology and the knowledge are already available to facilitate the large scale implementation of phosphorus recovery. However, we need to overcome the remaining hurdle of the lacking economic feasibility. Until then, cases where phosphorus recovery for agricultural reuse has already been implemented will serve as prime examples from which government can learn how to regulate phosphorus recovery in such a way that maximum benefits are achieved for both the environment and the urban community, as well as the livestock and agricultural sectors.

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KEY POLICY MESSAGES

• There is no single solution to achieving phosphorus security, therefore, recovery has to complement phosphorus consumption reduction plans, fertilizer application guidelines and other measures that promote a more efficient use.

• Implementing phosphorus recovery technologies offers the opportunity to better protect the environment and reduce operational costs of wastewater treatment plants.

• Phosphorus recovery from wastewater for food production is recommended as it offers opportunities to link SDG 2 (food and agriculture), SDG 6 (water and sanitation) and SDG 12 (sustainable consumption and production), therefore fostering a circular economy across the sanitation and agricultural sectors.

• The adoption of strategic plans to improve national phosphorus security will reduce dependency on few nations as well as improve national food security.

• Carrots-sticks measures that improve the competitive position of recovered phosphorus are needed to stimulate the widespread adoption of phosphorus recovery.

REFERENCESChilders, D. L., Corman, J., Edwards, M., and Elser, J. J. 2011. Sustainability Challenges of Phosphorus and

Food: Solutions from Closing the Human Phosphorus Cycle. BioScience, 61(2), 117–124. doi.org/10.1525/bio.2011.61.2.6

Corcoran, E., Nellemann, C., Baker, E., Bos, R., Osborn, D., and Savelli, H. 2010. Sick Water? The Central Role of Wastewater Management in Sustainable Development. United Nations Environment Programme. doi.org/10.1007/s10230-011-0140-x

Cordell, D., Rosemarin, A., Schröder, J. J., and Smit, A. L. 2011. Chemosphere Towards global phosphorus security : A systems framework for phosphorus recovery and reuse options. Chemosphere, 84(6), 747–758. doi.org/10.1016/j.chemosphere.2011.02.032

Cordell, D., and White, S. 2013. Sustainable phosphorus measures: strategies and technologies for achieving phosphorus security. Agronomy, 3(1), 86–116. doi.org/10.3390/agronomy3010086

De Ridder, M., Jong, S. de, Polchar, J., and Lingemann, and S. 2012. Risks and Opportunities in the Global Phosphate Rock Market. The Hague: The Hague Centre for Strategic Studies (HCSS). Retrieved from www.hcss.nl/news/risks-and-opportunities-in-the-global-phosphate-rock-marketrobust-strategies-in-times-of-uncertainty/610/

Edixhoven, J. D., Gupta, J., and Savenije, H. H. G. 2013. Recent revisions of phosphate rock reserves and resources: A critique. Earth System Dynamics, 5(2), 491–507. doi.org/10.5194/esd-5-491-2014

WWAP Water Insights 2017/1

Prepared by Dirk-Jan Kok (TU Delft), with contributions of Angela Renata Cordeiro Ortigara (WWAP) and Pay Drechsel (IWMI)

Suggested citation: WWAP (United Nations World Water Assessment Programme). 2017.

Why (not) to recover phosphors from wastewater? Water Insights 2017/1. Paris, UNESCO.

Photo credits: Phosphorus harvested from the treatment process for municipal sewage ©Albert Normandin/Vancuver Sun

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Elser, J., and Bennett, E. 2011. Phosphorus cycle: A broken biogeochemical cycle. Nature, 478(7367), 29–31. doi.org/10.1038/478029a

EPA. 2010. Nutrient control design manual. EPA/600/R-10/100. United States Environmental Protection Agency, Washington D.C., EEUU.

Kochian, L. V. 2012. Plant nutrition: Rooting for more phosphorus. Nature, 488(7412), 466–467. doi.org/10.1038/488466a

MacDonald, G. K., Bennett, E. M., Potter, P. a, and Ramankutty, N. 2011. Agronomic phosphorus imbalances across the world’s croplands. Proceedings of the National Academy of Sciences of the United States of America, 108(7), 3086–3091. doi.org/10.1073/pnas.1010808108

Mew, M. C. 2016. Phosphate rock costs, prices and resources interaction. The Science of the Total Environment, 542(Pt B), 1008–12. doi.org/10.1016/j.scitotenv.2015.08.045

Pradhan, P., Fischer, G., van Velthuizen, H., Reusser, D. E., and Kropp, J. P. 2015. Closing Yield Gaps: How Sustainable Can We Be? Plos One, 10(6), e0129487. doi.org/10.1371/journal.pone.0129487

Sattari, S. Z., Bouwman, A. F., Giller, K. E., and van Ittersum, M. K. 2012. Residual soil phosphorus as the missing piece in the global phosphorus crisis puzzle. Proceedings of the National Academy of Sciences of the United States of America, 109(16), 6348–53. doi.org/10.1073/pnas.1113675109

Schoumans, O. F., Bouraoui, F., Kabbe, C., Oenema, O., and van Dijk, K. C. 2015. Phosphorus management in Europe in a changing world. Ambio, 44(2), 180–192. doi.org/10.1007/s13280-014-0613-9

Smil, V. 2000. Phosphorus in the environment: Natural flows and human interferences. Annual Review of Energy and the Environment, 25, 53–88. doi.org/10.1146/annurev.energy.25.1.53

Smit, A. L., Bindraban, J. ., Schröder, J. J., Conijn, J. G., and van der Meer, H. G. 2009. Phosphorus in agriculture: global resources, trends and developments (Vol. 282). Wageningen.

Steen, I. 1998. Management of a non-renewable resource. Phosphorus and Potassium, (217), 25–31. Retrieved from cat.inist.fr/?aModele=afficheN&cpsidt=2380873

Ulrich, A. E., Malley, D. F., and Watts, P. D. 2016. Lake Winnipeg Basin: Advocacy, challenges and progress for sustainable phosphorus and eutrophication control. The Science of the Total Environment, 542(Pt B), 1030–9. doi.org/10.1016/j.scitotenv.2015.09.106

UN General Assembly A/RES/70/1 2015. Transforming our world: the 2030 Agenda for Sustainable Development.

USGS (United States Geological Survey). 2016. Mineral Commodities Summaries Phosphate Rock, (703), 120–121.

Van Vuuren, D. P., Bouwman, A. F., and Beusen, A. H. W. 2010. Phosphorus demand for the 1970–2100 period: A scenario analysis of resource depletion. Global Environmental Change, 20(3), 428–439. doi.org/10.1016/j.gloenvcha.2010.04.004

Van Kauwenbergh, S. 2010. World phosphate reserves and resources. Fertilizer Outlook and Technology Conference, International Fertilizer Development Center. Muscle Shoals, Alabama.

WWAP (United Nations World Water Assessment Programme). 2017. The United Nations World Water Development Report 2017: Wastewater: The Untapped Resource. Paris.

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