Stop Flushing Down Fertility! The Case for Recycling Human “Waste”

By Sonja Muriel Plüss

A nutritious breakfast, the morning coffee, and soon follows the call to the toilet. If you are like me and live in a place with a sewage system, all it takes is a flush for the discharge to be gone from our worlds and we can move on with our morning rhythms. Little do we think about how much precious fertility is literally flushed down the drain during those rituals.

Nutrients that have been extracted through energy-intensive mining, transported across the globe, distributed on farms as fertilizers, taken up by plants, which are again transported for consumption by humans directly or indirectly through meat for instance - those nutrients are often forever lost for the food system once they are flushed down the toilet. This is not just a problem for food security, but also causes environmental damages, social injustices and a dependence on extractivism. To reduce those damages, the fertilizer/nutrient loop needs to be closed. I will be focusing on one part of the solution to closing the nutrient loop; the recycling of human waste.

What’s the problem? The Linear, Extractive and Destructive System of Phosphorus Flows

Phosphorus is one of the basic building blocks of life, as it is universally required for plants and animals to grow (Chen and Graedel 2016, 139). In a more closed agricultural system where compost, manure and plant matter are brought to the fields and transformed into nutrients by soil life, soil fertility can be upheld over generations. However, a large part of the world’s agricultural system relies on phosphorus that is extracted from phosphate rock through mining.

Phosphorus mining is concentrated in only a few areas of the world, mainly Morocco, China, Russia and the United States, and controlled by a handful of corporations (Heckenmüller, Narita, and Klepper 2014). There are a number of interlinked environmental and social problems linked to large-scale mining, similar to extractivist and industrialised agriculture.

First, there is the macroeconomic problem of the resource curse. An economy that is centred on the extraction and export of primary goods is dependent on and suffers instability from the volatile international prices of those goods. Furthermore, an extractivist economy specialised on export of primary goods needs to import the higher value manufactured goods, leading to a problem in the balance of payment (Acosta 2013). Even though large corporations are at the forefront of executing extractivist projects, they are often backed by governments believing in neo-extractivism as benefitting development (Svampa 2015).

Secondly, the resource curse and large-scale mining also has serious microeconomic manifestations, particularly elaborated on by Kirsch (2014). Local populations are dispossessed of their land, resources and other bases of livelihood and cultural assets, either directly through the land taken up by the mine or indirectly through the environmental damage mining creates also in surrounding ecosystems, mainly by discharging polluted water and toxic sludge/tailings (Kirsch 2014; Acosta 2013, 64, 68; Svampa 2015, 66). However, the indigenous and local populations cannot always be portrayed as victims alone, as they sometimes engage in the process of commodification of resources (Babidge 2016). Still, in terms of jobs, only few local people benefit from extractivist projects (Acosta 2013, 71).

Furthermore, the more a resource becomes scarce - which is the case of phosphate rock from which phosphorus is gained - the more energy, chemical and water intensive and thus damaging the mining process becomes. Indeed, we now talk of a peak phosphorus.  The reliance on phosphorus extraction through mining as a cheap agricultural input has transformed phosphorus, or soil fertility in general, from a renewable resource part of a circular system to a non-renewable resource in a linear system (Figure 1). Acosta describes this move from resources as renewable to non-renewable as the story of large-scale extraction (2013, 62).

Figure 1. “Major flows of phosphorus in the global agricultural phosphorus cycle. Broken green line indicates a major break in the cycle due to poor recovery and recycling of human waste; gray box indicates potential point to slow the flow of P through agricultural systems.” (Rose, Liu, and Wissuwa 2013)

So far I have talked about the problems of the linear, extractive system at the site of the extraction - mainly the phosphate mine. However, environmental problems also occur in relation to the agricultural sites where phosphorus is applied and the suboptimal handling of human waste containing phosphorus. Both cases lead to large amounts of phosphorus ending up in water bodies where they cause massive algae growth through a process called eutrophication. Eutrophication is a serious threat to aquatic ecosystems (Gilbert et al. 2005).

What Figure 1 does not depict explicitly is the spatial component, the global geopolitical particularities of the phosphorus flow. Phosphorus flows are linked to trade of not only phosphate as a raw material or fertilizer, but also through the global large-scale trade of food products (Nesme, Metson, and Bennett 2018). Most flows originate in the Americas and end up in Western Europe and Asia. China, for instance, is a net importer of phosphorus - phosphorus that will not return to its original rock or soil anymore, depriving the origin countries of that resource.

The linearity of the phosphorus flow is also connected to the development of sewage systems which dispose, rather than reuse human waste. The “Sanitation Revolution”, closely linked to the Industrial Revolution, was intended to improve the sanitary conditions in European and North American cities. Returning the “night soil” to the land for fertility was no longer possible as cities and their distance to farms grew (Ashley, Cordell, and Mavinic 2011, 740). This means the loss of precious resources, even for those countries that are net importers of phosphorus.

The story of phosphorus flows is a story of losses, but also the story of extraction, dispossession, and environmental destruction, largely for the gain of large corporations. It exemplifies how extractivist economic setups are underpinned by and uphold linear infrastructures, such as large-scale, export oriented food systems or end-of-pipe sewage systems.

What can we do about it? Turning Urine to Gold and Shit to Humus

We need to move to a post-extractivist economy (Acosta, Svampa) and refocus on circularity, also for phosphorus. One strategy to undermine the extractive, industrial phosphorus system and improve circularity is the recycling of human waste.

The UN Water report in 2017 focuses on the shift of seeing wastewater as waste to regarding it as an “untapped resource” (WWDR 2017). Where there are sewage systems in place, wastewater treatment plants can be built in ways that they are able to extract nutrients and also retain some biomass. However, nutrient recovery from wastewater is limited because the nutrients are highly diluted. Human waste is mixed with large amounts of water from households and even rain. Separating the different “wastes” - urine, black water (faeces) and grey water (the rest) at the source would increase the potential for resource retention immensely. Separating urine is particularly valuable as around half of the phosphorus in wastewaters stems from urine (Besson et al. 2021).

Oftentimes, ‘western-style’ sewage treatment ‘solutions’ are what is aspired there in developing countries where they are not yet in place. However, not only do they contribute to phosphorus and other resource losses, but the ‘water carriage central end-of-pipe treatment’ belongs to the most expensive and energy intensive part of urban infrastructure (Abeysuriya, Mitchell, and Willetts 2006). It is crucial to re-examine this aspiration in the planning of new infrastructures for human waste management.

A solution that is more efficient for resource extraction from human wastes than even an adapted wastewater plant is the compost toilet (Figure 2). In compost toilets, the separation of urine and faeces is simple, and each remains concentrated. The faeces are composted and turn into precious humus. The urine can be used as a fertilizer directly, or also treated to regain its phosphorus in more pure form. The inhabitants of Pianta Monda, a Swiss mountain ecovillage I have visited, have been brainstorming about how to transform the urine they collect into a powder and sell it as fertilizer - not just because of the excitement to offer an unorthodox product, but also because of a serious concern for circularity. Not just in faraway ecovillages, but also in urban compartment buildings, compost toilets can be an economically and environmentally viable alternative (Anand and Apul 2011), and their widespread adoption would allow for the scaling up of ideas such as the one that emerged in Pianta Monda. Some pioneer projects guide the way, such as an office building in Seattle (Walton 2013), or an eco-neighbourhood in Bielefeld, Germany (sdg21 2021).

Figure 2. A compost toilet in which the liquid and solid waste is separated and reused as fertilizer and component of nutrient-rich humus respectively. Photo from the author.

There are a multitude of arguments for the phosphorus recovery from human waste in particular and increased phosphorus circularity in general. Phosphorus circularity reduces the dependence on environmentally and socially harmful mining activities. It can also contribute to strengthening local economies instead of multinational mining companies. Phosphorus extraction from human waste furthermore lowers water pollution. Lastly, as phosphate rock is increasingly scarce, retaining the phosphorus that is in circulation is also crucial for sustained food security.

Changing Toilets is not Enough

Nutrient recovery from human waste is only one part of the solution, not least because merely around 22% of the extracted phosphorus is actually consumed as human food (Chen and Graedel 2016, 139). Increased phosphorus circularity requires fundamental changes in the whole food system (Nesme, Metson and Bennett 2018). It requires agricultural systems that are regenerative instead of highly input dependent, a localisation of food systems so that closing resource cycles is facilitated, or also lower meat consumption as the large-scale production of meat is particularly phosphorus intensive. Our “wastes” should become our basis of life. The thought might seem gross to some, but we actually need the morning toilet routines to be two-directionally linked to the breakfasts we eat.


Abeysuriya, Kumudini, Cynthia Mitchell, and Juliet Willetts. ‘Kuhn on Sanitation: Dignity, Health and Wealth for the Children of the Revolution’, 5–18, 2006.

Acosta, Alberto. ‘Extractivism and Neoextractivism: Two Sides of the Same Curse.’ Beyond Development: Alternative Visions from Latin America 1 (2013): 61–68.

Anand, C., and D. S. Apul. ‘Economic and Environmental Analysis of Standard, High Efficiency, Rainwater Flushed, and Composting Toilets’. Journal of Environmental Management 92, no. 3 (1 March 2011): 419–28.

Ashley, K., D. Cordell, and D. Mavinic. ‘A Brief History of Phosphorus: From the Philosopher’s Stone to Nutrient Recovery and Reuse’. Chemosphere, The Phosphorus Cycle, 84, no. 6 (1 August 2011): 737–46.

Babidge, Sally. ‘Contested Value and an Ethics of Resources: Water, Mining and Indigenous People in the Atacama Desert, Chile’. The Australian Journal of Anthropology 27, no. 1 (2016): 84–103.

Besson, Mathilde, Sylvaine Berger, Ligia Tiruta-barna, Etienne Paul, and Mathieu Spérandio. ‘Environmental Assessment of Urine, Black and Grey Water Separation for Resource Recovery in a New District Compared to Centralized Wastewater Resources Recovery Plant’. Journal of Cleaner Production 301 (10 June 2021): 126868.

Chen, Minpeng, and T. E. Graedel. ‘A Half-Century of Global Phosphorus Flows, Stocks, Production, Consumption, Recycling, and Environmental Impacts’. Global Environmental Change 36 (1 January 2016): 139–52.

Glibert, Patricia, Sybil Seitzinger, Cynthia Heil, JoAnn Burkholder, Matthew Parrow, Louis Codispoti, and Vince Kelly. ‘The Role of Eutrophication in the Global Proliferation of Harmful Algal Blooms’. Oceanography 18, no. 2 (1 June 2005): 198–209.

Heckenmüller, Markus, Daiju Narita, and Gernot Klepper. ‘Global Availability of Phosphorus and Its Implications for Global Food Supply: An Economic Overview’. Working Paper. Kiel Working Paper, 2014.

Kirsch, Stuart. ‘Chapter 1. Colliding Ecologies’. In Chapter 1. Colliding Ecologies, 15–52. University of California Press, 2014.

Nesme, Thomas, Geneviève S. Metson, and Elena M. Bennett. ‘Global Phosphorus Flows through Agricultural Trade’. Global Environmental Change 50 (1 May 2018): 133–41.

Rose, Terry, Lei Liu, and Matthias Wissuwa. ‘Improving Phosphorus Efficiency in Cereal Crops: Is Breeding for Reduced Grain Phosphorus Concentration Part of the Solution?’ Frontiers in Plant Science 4 (5 November 2013): 444.

sdg21. ‘Ökosiedlung Bielefeld-Waldquelle | sdg21’, 20 August 2021.

Svampa, Maristella. ‘Commodities Consensus: Neoextractivism and Enclosure of the Commons in Latin America’. South Atlantic Quarterly 114, no. 1 (1 January 2015): 65–82.

Walton, Brett. ‘This Seattle Office Building Has Composting Toilets...’ Circle of Blue (blog), 27 June 2013.

WWDR. ‘Wastewater, The Untapped Resource’, 2017.

Author: Filipe Calvao