Phosphorus recycling from human excreta in French agroecosystems and potential for food self-sufficiency

Abstract

Phosphorus (P) is an essential constituent of life but large P losses from agroecosystems and sanitation systems are a major source of eutrophication in water bodies.These losses are doubly detrimental as P in human excretions can be used for crop fertilization.Through a unique dataset of 20,000 French WasteWater Treatment Plants (WWTPs) operational measurements over two decades and a P mass balance, we assess the fate of human excretions and their agricultural potential.Despite 75% of French WWTPs sludge being spread on crops, only 50% of the excreted P makes it back to agroecosystems. This is among the highest rate in Western countries where assessments have been made.Meanwhile, another 35% of the excreted P ends up in surface waters or the environment through WWTP discharge, individual autonomous systems diffuse losses, and sewers leaks.The remaining 15% is incinerated or sent to landfills.Moreover, while WWTP removal efficiency increased in the 2000s, reaching an 80% national average, it has been followed by a decade of stagnation in every French basin.The final removal efficiency for each basin, from 65% to 85%, closely matches whether the area was defined as P-sensitive in the European directive.Our results suggest that recycling all P in excretions could help supply 7 to 34% of French food supply without changing the current food system.Reshaping agricultural systems (shifting to more plant-based diets, decreasing P losses and food waste) would enable to go even further on the road to food sufficiency.