Exploit urinals for cheap fertiliser, says Indian inventor

Toilet opening
Copyright: Flickr/waterdotorg

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  • Urine contains phosphorus, nitrogen and potassium — all vital for plant growth
  • The waterless urinal design uses no chemicals or consumables
  • India has thousands, saving water, but few are being used to collect urine

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Recycling urine collected at public toilets is a cheap and simple way to produce fertiliser, according to the developer of a waterless urinal.

Human urine contains three nutrients — phosphorus, nitrogen and potassium — that are essential for plant growth, says Vijayaraghavan Chariar, a researcher at the Indian Institute of Technology Delhi.

Each person produces four to five kilograms of these nutrients in their urine annually, says Chariar, with this valuable material lost through what he calls modern “flush and forget” sanitation systems that often end up polluting waterways.

“Urine is a resource,” he says. “If it can be separated in restrooms whenever possible — definitely in public institutions and other public places — then we can easily recycle it. But it takes more energy and effort to recover these nutrients once the urine is mixed up with other matter in sewage systems.”

“Urine streams are the easiest way to recover biowaste. Reusing urine should be mandatory immediately”

Jan-Olof Drangert, Linköping University

Waterless urinals already exist, but current designs often require the frequent replacement of odour-preventing cartridges, making maintenance a prohibitive cost, despite potential savings through lower water use, according to Chariar.

“What we have come up with are urinals for the developing world,” he says. “These are products that use no chemicals. Nothing would need to be replaced for three years, if not longer.”

Since the urinals were put on sale in May 2013 through Ekam Eco Solutions, the company Chariar founded to market his innovation, about 4,000 units have been installed in India.

His prefabricated Waterless Public Urinal Kiosks store urine in tanks and use a patented cartridge to stop the smelly gases escaping. This eliminates the need for fresh water to flush away the urine, he explains. According to the company’s website, the cartridge uses a ball valve to trap the gasses, whereas other models use membranes or liquid sealants that gradually degrade and need replacing.

For “high-volume” urinals in public places, each urinal can save 155,000 litres of fresh water a year, he adds.

But there has been little interest in using the design’s potential to harvest urine, he says, with nearly all of the urine being disposed of through traditional sewage systems.

Chariar puts this partly down to politicians thinking that the cost of transporting urine would be prohibitive. Yet he notes that simply adding magnesium chloride to urine and adjusting its acidity will lead to a phosphate mineral called struvite forming. This can be filtered out from the bulk liquid and it would be much lighter, easier and cheaper to transport to rural areas, he says.

Jan-Olof Drangert, an ecological sanitation researcher at Linköping University, Sweden, says that the often-cited idea that the expense of transporting the liquid urine would limit its take up is also incorrect as this cost could be comparable with that of moving chemical fertilisers.

Because of that, he thinks the key roadblock is political will, not the need for cheaper transportation.

“The view that transport costs will be a deciding factor in using this resource is too pessimistic,” he says. “The deciding factor is rather the perception of urine. [Policymakers] have simply decided that this is not a recoverable product.”

But given the potential gains for agriculture, Drangert sees little reason to delay using human urine on a large scale, particularly in developing countries where crop yields have been curtailed because of limited access to commercial fertilisers.

“Urine streams are the easiest way to recover biowaste. They’re directly available for plants and you have essentially no health problems associated with it,” he says. “Reusing urine should be mandatory immediately [in these countries].”