‘Liquid gold’: Australian scientists look to recycle human urine to fertilise city parks

Could human urine be liquid gold for horticulturists?

A new trial is examining if "number one" could be a cheap and sustainable source of fertiliser for plants and lawns in Australia's city parks.

The study, by Griffith University, aims to find out if "urine diversion toilets" being trialled in Brisbane and Sydney, might stop valuable excretions of potassium, phosphorus and nitrogen from disappearing down the S-bend.

"It's the perfect liquid gold and currently we just flush it down the toilet," associate professor Cara Beal, of Griffith University's Cities Research Institute, said.

Beal said the four-year project would investigate different toilet designs and incorporate new technology developed by a University of Melbourne chemical engineer.

Human urine is sterile, but can also contain undesirables such as pathogens, hormones and antibiotics that need to be processed.

"But the good stuff is the nitrogen, phosphorus and potassium that plants love. The technology is important, but that's not the barrier to closing that nutrient loop and reusing our most precious resource we generate," Beal said.

"We have the technology. The issue is looking at the regulatory approvals and getting our health and planning departments to understanding this."

The trial is part of an initiative known as Nutrients in a Circular Economy being led by the University of Technology Sydney and including other universities, such as Griffith, and commercial and government partners.

The trial will look at any health risks from using human urine, as well as investigating how it stacks up economically as a source of fertiliser.

Potential sites in parks in Brisbane and Sydney had been identified, but there were still consultations and regulatory approvals to be negotiated, Beal said. Toilets could be installed by the end of this year.

Beal said generating nitrogen was energy intensive and phosphorus was a finite resource that was mined.

She said: "As a society, if we are to get to net zero carbon emissions we are going to have to move away from synthetic fertilisers."

Tackling the community's instinctive "yuck factor" would also be part of social studies to be carried out under the trial.

The trial will use technology being developed by Dr Stefano Freguia, a chemical engineer at the University of Melbourne who has designed a self-powering system using electrical charges and membranes to separate the valuable elements from urine.

"It's one of several technologies that have been developed over the last 10 years. We have used human waste since the beginning of time, but recently we have become justifiably picky," he said, saying modern life had added contaminants such as pharmaceutical products and pathogens to our human waste stream.

"Our lifestyles have changed. This technology we're developing needs to address this," he said.

He said the liquid fertiliser produced by the technology - which can be as small as a 20cm cube depending on the volume needed - has a smell of ammonia "which isn't so hard on our noses" as human urine.

Prof Stuart Khan, an expert on wastewater management at the University of New South Wales who is not involved in the project, said in the future phosphorus was likely to become scarce and societies would be forced to find new sources.

"There's a lot of interest in urine separation, particularly in parts of Europe and Scandinavia," he said.

"Phosphorus isn't renewable but we use it as a fertiliser and grow all our vegetables with it and then ultimately we flush that down the toilet.

"We have no way to recover it from the ocean and there's no new phosphorus that's being deposited.

"There are public health risks that need to be managed, but there are good reasons to think this can be done very well.

"Once people understand the importance of sustainable use of limited resources, I think that will outweigh any kind of yuck factor."

Would the picnicking public agree?