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Toilet technology makes fertiliser

Urine can be turned into commercially available fertiliser.  Image credit: Shutterstock/ Peter Gudella
Urine can be turned into commercially available fertiliser. Image credit: Shutterstock/ Peter Gudella

Office blocks and universities could turn pee into commercially available phosphorus and nitrogen fertilisers, thanks to a bioelectrical reactor in development by researchers across the EU.

Fresh urine contains approximately nine grammes of nitrogen and one gramme of phosphorus per litre, and the average person produces between one and one-and-a-half litres a day which currently goes to waste. Researchers believe human urine could provide 18 % of the phosphorous and 25 % of the nitrogen currently used for soil fertilisation in the EU.

With a growing human population and almost no phosphorus reserves in Europe, we rely on imports.

Dr Philipp Kuntke, Wetsus

By extracting these compounds rather than flushing them down the sewer, we could reduce energy-intensive ammonia production and cut our reliance on imported phosphorous ore.

‘We require phosphorus to ensure the production of crops and, with a growing human population and almost no phosphorus reserves in Europe, we rely on imports,’ said Dr Philipp Kuntke, from Dutch water research firm Wetsus, who was involved in the project, known as ValuefromUrine.

It’s possible thanks to urine-separation toilets and urinals, which stop it being diluted by other wastewater streams.

It means the EU-funded project, which finishes next year, has been able to develop a three-step process that uses a bioelectrical reactor, called a microbial electrolysis cell, powered by organic compounds such as sugars and fatty acid which are already in the urine.

Bacteria are grown on an electrode and are used to make electricity. Image courtesy of ValuefromUrine/ Mariana Rodríguez Arredondo

The end-products are struvite and ammonia sulphate, which are commercially available phosphorus and nitrogen fertilisers.

By the time the project ends in August 2016, the researchers hope to have designed a device that fits into a 20-foot container and can turn one cubic metre of urine into about 1 kilogramme of phosphorus and 10 kilogrammes of ammonium every day.

Diverting urine from wastewater could also reduce the cost of water treatment, as it accounts for approximately 80 % of the nitrogen that enters treatment plants. ‘If you look at the cost of wastewater treatment plants, the majority of the costs go into processes that remove nitrogen,’ Dr Kuntke said

Down the pan

It’s not the only way to make Europe’s toilets less wasteful. Toilet flushing accounts for a quarter of European domestic water use, plus there is the infrastructure required for sewage systems and the energy used by water treatment plants.

One obvious way to deal with these issues is dry toilets – they don't use any water and the waste drops into a pit, so no sewage system or treatment is required.

A Europe-wide group of researchers has developed a new type of water-free toilet that could be used at high-frequency locations such as motorway service stations, as well as a kit toilet for remote locations and a mobile unit that can be deployed during major events.

To do this they made a bug-killing plastic and coating which smoothed the pipework to lower the risk of stinky blockages and keep bacteria and parasites in check, as well as an odour-killing biofilter.

Their work was part of the EU-funded DRYCLOSET project, and the plan is now to produce and sell the toilets commercially.

DRYCLOSET is building dry toilets that use worms to compost human waste. Image courtesy of DRYCLOSET

They also improved the compostability of waste by developing a way to skim off the solids and send them to a worm bed, a process known as vermicomposting, increasing the safety of compost compared with bacteria.

‘In most traditional dry toilets there is no separation between urine and solids so the composting process is done by microbiological activity,’ explained Isabelle Czekajewski, a research and development engineer at Sanisphère, the French company coordinating the project.

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