We have developed a simple process to recover urine. Here’s how it is done

Every year on 19 November, the United Nations celebrates one of the greatest inventions of public health – the toilet. Those lucky enough to have access to one spend more than a year of their lives on it, but millions of people worldwide cannot use it, and many have never seen it.

Invented in 1775, the flush toilet has changed surprisingly little in the design. In reality, a toilet is nothing more than a seat (or a pan) connected to a pipe by a bend. If this pipe is further connected to a sewage system that transports excrement to a centralized treatment plant, wastewater can be safely transported to the area.

But worldwide, 80% of the wastewater produced receive no treatment, which causes damage to the environment and spreads diseases. Although wastewater contains nutrients when generated in households, the nutrients are diluted as they are flushed away. This makes it difficult to remove, even when it does reach treatment plants. Instead, they spread in the environment as pollution.

A reconsideration of sanitation should begin at the toilet itself. A way to excreta different management is to collect it separately. A toilet removed by urine do exactly what its name implies – it separates the urine from the feces. These toilets can be designed to look exactly like ordinary toilets hide a trap which diverts the urine.

We have developed a simple process which can encourage people to recycle urine. In our process, fresh collected urine is first made alkaline (high pH) to prevent the reaction that causes the typical pungent smell of ammonia and urine. Then, by evaporating water, urine is reduced in a dry powder which captures all its nutrients.

How to recycle urine safely

When urine is collected at home, the most nutrients in wastewater can be kept away from wastewater treatment plants.

The collected urine can also benefit the household. To take advantage of the nutrients that are transferred into urine, it can be recycled as fertilizer for agriculture. Previous research has shown that urine can be used effectively as an alternative to conventional fertilizers. In fact, human-produced urine contains enough nutrients to fertilize three-quarters of the food we eat.

By following a few simple steps, anyone can safely dry urine to produce a fertilizer. Here’s what you need:

Something to catch urine – a urinal, a toilet that removes urine or a clean bucket.

A small container – in the image below we use a plastic box from the shelf with dimensions 60 x 40 x 20 cm.

Alkaline material with a pH of at least 10, such as that produced from burning wood or limed lime produced by converting limestone. Choose something that can be applied in agriculture.

A fan that you will attach to the container and on to electricity or a battery.

Then you need to follow the next 10 steps.

Fill the container with the alkaline material. If you choose limed lime (about US $ 1 per kg), add about 3 kg each month for a household of four.

Connect your urine-separating toilet to the container with a short pipe with a diameter of 75 mm and a slope of at least 1%.

Attach an exhaust pipe to the container to transport moist air out of the bathroom.

Urinate as usual in the toilet or pour freshly collected urine immediately into the container.

Turn on the fan.

Repeat the process every day for the entire month.

At the end of the month you collect a dry powder that contains approx. 9% nitrogen, 1% phosphorus and 4% potassium. Save it for a few days at a temperature above 20 ° C. This will ensure that the product is safe to handle and apply at home level according to the World Health Organization Guidelines.

Apply it as fertilizer according to your plants’ needs.

To start the process again, replace the container with fresh alkaline material.

Spread the urine wisdom – if you see benefits, encourage others to try to dry their own urine.

Can it be done on a larger scale?

This is what we plan to do in South Africa next year. Together with several other stakeholders, we are leading an initiative aimed at repairing 1,000 urine-separating toilets using the urine-drying technology in the city of Durban, on the east coast of the country. We hope this will enable people to convert their own urine into a solid fertilizer that can be used to grow food.

A major motivation for the initiative comes from the current situation COVID-19 in South Africa, which has exposed many vulnerabilities. These include unemployment and food insecurity.

The recovery of urine collected from these toilets in small-scale horticulture can make a huge difference to local food security. In turn, it can also improve the local environment by promoting the greater use of toilets.

Durban has been at the forefront of the urine recycling movement worldwide – the city has almost 80,000 urine-separating toilets and more than 1,000 community ablution blocks with urinals. These toilets serve about 450,000 people. The drying of the urine collected from these toilets could be the next chapter in the city’s ongoing efforts to adopt new sanitation systems.

Prithvi Simha, PhD candidate in Environmental Engineering, Swedish University of Agricultural Sciences; Christopher Buckley, Professor and co-head of the Pollution Control Group, University of KwaZulu-Natal, en Jenna Senecal, Postdoctoral Researcher in Environmental Engineering, Swedish University of Agricultural Sciences


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