Food waste reduction and recycling: a solution to the World’s phosphorus crisis
Common arguments for why cities should reduce and recycle food waste are to lower greenhouse gas emissions, increase levels of service to households, reduce the need for landfills and/or incinerators, and to close the loop. But there is one more very compelling reason to address food waste: to solve the World’s phosphorus crisis. And cities, as aggregators of phosphorus, are at the centre of the solution.
Phosphorus – The Challenge
Phosphorus is an essential nutrient for life. Without phosphorus, food production is not possible. Thus, just like water, it is a key element of life. At the current rate of consumption, many countries will face a crisis as their phosphorus reserves are depleted.
The use of phosphorus started as mineral fertiliser in agriculture. Now it is also used in a wide variety of products like pharmaceuticals, flame retardants and chemicals1. Over the last 50 years the use of phosphorus has increased from 4 till 24 Mton per year2.
Historical sources of phosphorus fertilizers (1800-2010).
Image sourced from Cordell, 2014
Demand vs supply
The demand for phosphorus is increasing due to this wider application, a rising global population and global trend towards more meat and dairy-based diets, which are significantly more phosphorus intensived3. It is expected the demand for phosphorus will increase by 50-100% by 20504.
On the supply side, there are four issues making phosphorus scarce:
- Reserves of phosphorus are limited. Depending on which scientists you ask, the world’s phosphate rock reserves will last for another 352 to 4005 years1. Limited supply can result in price shocks which already happened in 2008 when prices increased with 800%.
- It becomes harder to mine good quality. The concentration of phosphorus in mined rock is decreasing and the concentration of unwanted clay particles and heavy metals like cadmium are increasing.
- There are no substitutes. Where oil can be substituted with other sources of energy, phosphorus has no substitute for food production3.
- Reserves are unevenly distributed. It is estimated that the world resources of phosphate rock are in total 300 billion tons. 85 to 90% of world’s remaining reserves are controlled by only five countries which are Morocco, China, Algeria, Syria and Jordan. China, the U.S. and South Africa keep their mined phosphorus for their own use whereas Morocco and Jordan are the largest exporters6. Morocco controls up to 85 percent of the remaining phosphate rock reserves. However, many of Morocco’s mines are located in Western Sahara, which Morocco has occupied against international law5. Importing countries are thus vulnerable to price fluctuations and supply disruptions in producing countries3.
Countries like India, Europe and Australia need to prioritize securing a supply of phosphorus to sustain their food production. The EU is addressing the issue on the look for alternative solutions6.
Mineral phosphorite or rock phosphate is mined to produce wet-process phosphoric acid, or to produce elemental phosphorus.
Challenge on local level
On a local level, phosphorus is not always an issue because of a lack of it. Sometimes there is too much of it. Four-fifths of the phosphorus is lost or wasted in the supply chain. Cities around the world face problems with an excess of phosphorus in their rivers, lakes and oceans where it can cause toxic algal blooms. Examples are the Ganges river in India, the Baltic Sea, China, the Great Lakes of North America and Australia’s Great Barrier Reef. Algal blooms can kill fish and other aquatic life, pollute our drinking water and damage our tourism and fishing industries3.
Algae polluted water in brackish water
More than 384 million urbanites (46 percent of all people living in the 100 largest cities) get their drinking water from watersheds with high nutrient pollution. As watersheds are exploited for agricultural purposes, and as agriculture intensifies, the use of fertilizers increases and more fertilizers end up in the water. The task of raw water quality maintenance seems harder for the developing world than for the developed. Cities that are likely to have the biggest increase in nutrient loading from agriculture are located in Brazil, Argentina, and parts of sub-Saharan Africa7.
Cities grouped by phosphorus yield
Photograph sourced from The Nature Conservancy, 2016
The current linear model of mining, using and wasting should become more circular: a model in which phosphorus is used again and again and again. This would enhance the self-sufficiency of a country through a more sustainable use of phosphorus. Cities have a crucial role in this value chain: almost all nutrients enter cities in the form of food that people buy and consume.
Cities can partially prevent unnecessary consumption of food, and hence unnecessary demand for phosphorus. The average diet today results in the use of around 3.2 kilograms phosphate per year. This is 50 times greater than the 1.2 grams per person per day recommended daily intake3. The best way to limit phosphorus in our diet is to limit intake of fast food, convenience food, processed food and beverages8. A public awareness campaign for healthy food and/or food waste reduction thus also helps to reduce the use of phosphorus. According to the waste hierarchy, prevention is prefered to recycling. As an example, read about San Fransisco where information and education is one of the five success factors.
Next to prevention, cities should become an urban mine. Cities could support the harvest of phosphorus from recycling of manure, waste water, animal by-products (e.g. bones), and food and other green waste (via composting or via ashes)6. One important source is wastewater. Examples of harvesting nutrients are available: In Amsterdam, the local water company Waternet, recovers about 900 ton/year struvite from wastewater9.
Another form of harvesting is food waste recycling. Food waste is the solid waste fraction containing the most phosphorus per kilogram, it can easily be recovered and is a substitution possibility of nutrients to chemicals. In a case study in Sweden, three forms of recycling food waste were compared: recovery from residual waste (incineration), recovery from source separated organic waste (compost), and recovery from source separated food waste (anaerobic digester). The highest yield is to recover phosphorus from the digestate of digested food waste10. Recovery from municipal solid waste incineration is less favourable due to the trace metal content in the residu. This reduces potential application to agricultural land11.
Food waste as renewable source of phosphorus
Cities could become a hub of recovery within the phosphorus chain. They should become an urban mine and make the chain of phosphorus circular. This will limit dependency on uneven distributed sources and decrease excessive nutrient polluted areas within their territory. This can be achieved through implementing legislation, policies and programs aimed at recycling food waste to recover phosphorus, or better yet, reducing the demand for phosphorous by food waste prevention programs.
- Faradji, C. and de Boer, M. (2016). How the great phosphorus shortage could leave us all hungry. [online] The Conversation. Available at: https://theconversation.com/how-the-great-phosphorus-shortage-could-leave-us-all-hungry-54432. Accessed 2 Aug. 2017.
- Cordell, D., Drangert, J. and White, S. (2009). The story of phosphorus: Global food security and food for thought. Global Environmental Change, 19(2), pp.292-305.
- Cordell, D. (2014). The Story of Phosphorus: 7 reasons why we need to rethink the management of phosphorus resources in the global food system | Phosphorus Futures. [online] Phosphorusfutures.net. Available at: http://phosphorusfutures.net/the-phosphorus-challenge/the-story-of-phosphorus-8-reasons-why-we-need-to-rethink-the-management-of-phosphorus-resources-in-the-global-food-system/. Accessed 2 Aug. 2017.
- Cordell, D. (2010). The Story of Phosphorus – Sustainability implications of global phosphorus scarcity for food security. [online] Available at: http://liu.diva-portal.org/smash/get/diva2:291760/FULLTEXT01.pdf. Accessed 2 Aug. 2017.
- Cho, R. (2013). Phosphorus: Essential to Life—Are We Running Out?. [online] Blogs.ei.columbia.edu. Available at: http://blogs.ei.columbia.edu/2013/04/01/phosphorus-essential-to-life-are-we-running-out/. Accessed 2 Aug. 2017.
- European Union. (2014). Phosphorus – introduction paper. [online] Available at: http://ec.europa.eu/transparency/regexpert/index.cfm?do=groupDetail.groupDetailDoc&id=13639&no=26. Accessed 2 Aug. 2017.
- The Nature Conservancy. (2016). Urban Water Blueprint. [online] Available at: http://www.iwa-network.org/wp-content/uploads/2016/06/Urban-Water-Blueprint-Report.pdf. Accessed 2 Aug. 2017.
- Majorowicz, R. (2017). Low-phosphorus diet: Best for kidney disease?. [online] Mayo Clinic. Available at: http://www.mayoclinic.org/food-and-nutrition/expert-answers/faq-20058408. Accessed 2 Aug. 2017.
- Waternet. (2015). WWTP Amsterdam-West: The recovery of phosphorus. [online] Available at: http://p-rex.eu/uploads/media/13_Waternet_Lelijveld.pdf. Accessed 2 Aug. 2017.
- Lu, X. (2014). Feasibility Study: Phosphorus Recovery from Household Solid Organic Waste. [online] Royal Institute of Technology. Available at: http://www.diva-portal.se/smash/get/diva2:762012/FULLTEXT01.pdf. Accessed 2 Aug. 2017.
- Kalmykova, Y. and Karlfeldt Fedje, K. (2013). Phosphorus recovery from municipal solid waste incineration fly ash. Waste Management, 33(6), pp.1403-1410.