Can sewage help secure world food supply?

Image: Ivan Bandura, Unsplash

The phosphorus present in sewage could help provide a solution to global food insecurity if it was removed during the wastewater treatment process and recycled, say scientists.

The chemical is vital for life on Earth, and is extracted from phosphate rock for use in crop fertilisers, livestock feed and food additives. However, a major new report led by the UK Centre for Ecology & Hydrology (UKCEH) and the University of Edinburgh warns that global mismanagement of this finite nutrient is causing twin crises, brought into sharp focus with fertiliser prices skyrocketing in recent months.

Global food security is under threat as many farmers struggle to afford sufficient phosphorus fertiliser for their crops. Meanwhile, overuse of fertilisers and sewage pollution mean millions of tonnes of phosphorus is unnecessarily pumped into lakes and rivers each year, damaging biodiversity and affecting water quality.

The Our Phosphorus Future report is the most comprehensive global analysis of the challenges and possible solutions to the phosphorus crisis to date. It calls on governments across the world to adopt a 50-50-50 goal: a 50% reduction in global pollution of phosphorus and a 50% increase in recycling of the nutrient by the year 2050.

"More efficient use of phosphorus in agriculture and increased recycling, for example from wastewater, can increase resilience in the food system while reducing pollution of lakes and rivers."

Professor Bryan Spears, UKCEH

Written by a team of 40 international experts from 17 countries, it is supported by the United Nations Environment Programme (UNEP).

A key recommendations in Our Phosphorus Future is improving wastewater treatment to remove phosphorus from sewage, so it can be reused and does not enter lakes and rivers. The report says many waste streams and residues represent a significant untapped phosphorus resource. There are more than 30 different technologies available to recover phosphorus from waste streams and new ones emerging all the time.

The report makes other recommendations, including:

  • Integrating livestock and crop production so phosphorus in animal manure is applied to crops, reducing the demand for chemical fertilisers
  • Moving towards more sustainable diets, which would reduce the amount of phosphorus needed to grow animal feed
  • Reducing global food waste, meaning less demand for crops and animal products, and therefore phosphorus

Just four countries control around 70% per cent of the annual global production of phosphate rock from which phosphorus is extracted - China, Morocco, US and Russia - leaving the market exposed to massive fluctuations in costs and supply due to political disputes, trade wars and escalating fuel prices. Since 2020, for example, the prices of both phosphate rock and fertiliser have increased by around 400%, and continue to rise.

This instability exacerbates the impacts of other global factors influencing fertiliser costs, such as the effect of the war in Ukraine on the price of natural gas.

Professor Bryan Spears of UKCEH, one of the report’s lead authors, says: “Many countries are highly dependent on imported phosphorus fertiliser for food production, leaving them exposed to fertiliser price fluctuations.

"More efficient use of phosphorus in agriculture and increased recycling, for example from wastewater, can increase resilience in the food system while reducing pollution of lakes and rivers that are biodiversity hotspots and important for drinking water supply.”

Phosphorus pollution accelerates the growth of algal blooms. Image: Mihály Köles, Unsplash

Phosphorus pollution in lakes, rivers, and coasts accelerates the growth of algal blooms which produce toxins that are harmful to animals and humans who come into contact with or consume contaminated water. The cost of responding to water-based phosphorus pollution in the UK alone is estimated at £170 million per year.

The experts hope their report will raise awareness of the need for sustainable phosphorus management informing collaborations between scientists, governments, farmers and industries.

For the full Our Phosphorus Future report and videos summarising each chapter, see