Taking the P out of pee

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ENGINEERS at the University of Surrey are investigating how phosphorous can be filtered from human urine in a bid to avoid shortages of a critical element for food production and to protect the environment.

The notion that society will run out of phosphorous is hotly contested. What is certain is that phosphorous is crucial element in fertilisers required to grow our food and it is produced from phosphate rocks concentrated in just a handful of countries, with Morocco holding a whopping 70% of deposits. While we may not run of reserves any time soon, there are concerns that geopolitical conflict and cost increases could disrupt supply chains and affect food security.

Maano Tshimange, researcher at Surrey’s school of chemistry and chemical Engineering, is investigating how demand for virgin supplies of phosphorous can be reduced by using a membrane to filter it from urine.

“Getting phosphorus from urine could be a simple, cheap alternative. And let’s face it, there’s so much of it available that we'll never be caught short. Human urine alone could provide as much as 11% of the world’s phosphorus needs,” Tshimange said.

The project will involve collecting 15 litres of urine from volunteers at toilets across the university’s Guildford campus. The investigation will then focus on filtering out the phosphorous using a forward osmosis process, which has the advantage of requiring less energy and produces relatively low membrane fouling. The study will run until summer 2025 and will investigate the efficiency of their membrane including how best to prevent its pores from being clogged.

Environmental concerns and wasted phosphorous

A 2022 study on global phosphorous use found that our use is highly wasteful and unsustainable. It estimated that 34% of all fertiliser – around 5m t/y – simply runs off unused from agricultural land into rivers and lakes causing harmful algal blooms, killing wildlife, and costly cleanup operations.

Meanwhile, 80% of all wastewaters are discharged without treatment to remove phosphorous. In 2019, there were more than 100 full-scale plants across the world recovering phosphorous from wastewater but with very few countries requiring that phosphorous be removed from wastes, the study authors called for the wider implementation of stringent regulations.

Other innovative approaches

In the UK, there are legally binding targets to cut phosphorous pollution from wastewater plants by 80% by 2038 compared to 2020.

Earlier this month, UK water firm United Utilities announced it would lead a project investigating alternative approaches for recovering phosphorous from waste treatment works. The ALT-P project is looking at alternatives to the metal-based coagulants used at rural facilities in a bid to reduce costs and chemical inputs. It has been examining electrocoagulation and natural coagulation at its Woolton wastewater treatment works. Meanwhile, its partners Southern Water and the University of Portsmouth are investigating the use of reactive media.

Lisa Mansell, chief engineer for innovation and carbon at United Utilities, said: “Through the ALT-P project, we aim to determine what can be achieved using alternative approaches and the climate benefits these could deliver for the water sector. The project is really opening up new opportunities and we are now understanding, in more detail, what is required from us as water companies to incorporate these processes.”