Urine is a resource

Chris Simoens
08 July 2019
Human urine can be a source of fertilisers that also provides a solution to an urgent environmental problem occurring in South Africa as well as on Belgian pop festivals.

Sanitation in Africa often leaves much to be desired. If people have a toilet, it is mostly  limited to a pit in the ground. The urine and faeces end up in a simple excavated pit, the so-called 'pit latrine', where they seep into the soil and ground water as the pit walls are not waterproof.

And that causes pollution! For example, urine contains nitrogen (N), phosphorus (P) and potassium (P). These are actually fertilisers that can make surface and ground water excessively rich in nutrients. This leads to excessive growth of algae, causing water organisms to suffocate. The quality of local drinking water sources is also considerably reduced.

In short, poor sanitary facilities are not only detrimental to people's health, they also create a serious environmental problem.

 

School in South Africa

“In 2013, I learned that South Africans were looking for a solution to the urine problem, particularly at the University of South Africa (UNISA) and the University of Johannesburg (UJ),” says Sebastiaan Derese of Ghent University. He immediately dedicated his doctorate to it, under the guidance of Prof. Arne Verliefde. “Strangely enough, at the same time, agriculture suffers from a lack of the fertilisers N, P and K. The animals, which are too few, enjoy greater freedom than in our country, which prevents farmers from recovering the small amount of manure produced.”

The experiment took place in a school in Lochiel, a small town on the border with Eswatini. Derese: “That school was very demanding. As it is often the case in South Africa, they used a number of common latrines in a row, connected to a well. Whenever the well was full, they built new toilets a little further on.”

The aim was to set up a system to purify the urine before discharging it, which would avoid the installation of new toilets after a few years.

 

Urine contains nitrogen (N), phosphorus (P) and potassium (P). These are actually fertilisers that can make surface and ground water excessively rich in nutrients.

Separate sump trays

First of all, it is necessary to separate the urine from the faeces. But the school in Lochiel already used separate sump trays for this  purpose. Derese: “Such sump trays are already fairly well known. For example, the company Sanergy in Kenya has been using them successfully for some time now, to produce organic manure, among other things. According to them, it's easy to encourage people to use such a system.” The urine is collected undiluted, rinsing water is not needed, which directly saves water.

The research did not take into account the faeces. “Especially the urine is very rich in nutrients, the faeces contain a lot of carbon (C). Together with urine this forms a good fertiliser, but faeces also contain a lot of germs which are absent in the urine. Faeces are especially useful to produce biogas by fermentation.”

 

Urine without  N, P or K

The next step was to isolate N, P and K from the collected urine. “Technically that's quite simple”, says Derese. “Bacteria spontaneously end up in the urine that convert the N-containing urea into ammonia, 99-99.5% of which can be easily removed with a selective membrane, a kind of filter.”

“Precipitation by adding calcium or magnesium salts allows the extraction of the remains of P and K. The dissolved P and K clump together into a kind of crystals that you can separate from the urine.”

At the end of this process, urine, free of N, P and K, no longer causes algae blooms. It still does contain the remnants of medicines. Derese: “In South Africa we don't intend to remove these for the time being. The same applies to wastewater treatment in Belgium (see box).”

It is easy to make good drinking water from urine. However, that process requires a lot of energy. It is better to make drinking water from groundwater or surface water.

“Yet it is easy to make good drinking water from urine. All you need is a special membrane (for “reverse osmosis”) and a filter with activated carbon. With both filters, you can remove the last trace of pollution from the urine. However, that process requires a lot of energy. It is better to make drinking water from groundwater or surface water, that is less expensive.” The urine without N, P and K could be purified even more with, for example, a reed bed, which doesn't cost much. This will require further research.

 

Gentse Feesten and Dranouter

Derese - and his team of various Master students - have experimented the system not only in South Africa, but also in Belgium. Especially during summer festivals. The first time was during the Gentse Feesten in 2016. Then every year at the Dranouter festival, as part of the WAVE project (Water Vision on Events). “The situation at festivals is very similar to that of rural Africa”, says Derese. “The urine is often discharged directly into a nearby ditch or the organisers pay for the external processing. The festival organisers are also requesting a solution to this problem.”

 

A stand with devices to purify urine at the Dranouterfestival.
© UGent

At festivals, urine collected in mobile urinals passes through a purification system that extracts N, P and K. Part of the purified urine is then converted into drinking water. Derese: “So far, this has been limited. Of the 5,000 litres of processed urine, we only produced 80 litres of drinking water. We offered them in 10 ml shot glasses. It was more of a publicity stunt, partly to convince people that you can make real drinking water out of urine.”

The research has progressed so far that urine purification is technically and practically feasible. It is possible to make an automatically rotating treatment device that is about the size of a large wardrobe. There may be some work to be done on the extraction of P and K - it could probably be cheaper - but the principle works very well.

A purification unit the size of a large wardrobe.
© UGent

Profitable model

“At the moment, we are trying to find out whether the system is also financially feasible”, says Derese. For example, the researchers are thinking about working with local operators. A local operator could install a number of toilets with a purification device. He could then earn money by (1) asking for money from the users of the toilets and (2) selling the N,P and K to the farmers.

“However, we do not know yet which scale is required to make a profit. Do you need 1000 or 500 users? And what are the prices the farmers normally have to pay for their N, P and K? From 1000 l of urine you get 5 to 8 kg of pure N and 0.5 to 1 kg of P and K. We also don't know yet how long a device will last. Does it take 10 years or more before it is worn out?”

In short, the challenge now is to develop a potentially cost-effective approach. Because that is the only way to make it really sustainable, as it can run without subsidies.

The urine purification has three advantages: (1) The sanitary situation becomes much healthier, (2) you produce usable fertilisers and (3) you save water and increase the water quality of streams, rivers and ground water.

Off-the-grid

“So we are quite close to our final goal: an off-the-grid toilet”, concludes Derese. “A system that allows you to process urine into fertilizers and reasonably purified water, regardless of the sewage system. That has three advantages: (1) The sanitary situation becomes much healthier, (2) you produce usable fertilisers and (3) you save water and increase the water quality of streams, rivers and ground water.”

Derese sees concrete applications in Belgium mainly at pop festivals and possibly also in public buildings and newly built neighborhoods. In existing houses it is much more difficult because you have to install separate water pipes for the urine.

How does Belgium treat its wastewater?

 

What you flush in a toilet, bath or sink ends up in the sewers. The wastewater is transported to a treatment plant, where it comes into contact with bacteria that feed on N, P and K. Nitrogen gas is released and disappears into the air. P is precipitated with aluminium or iron salts as a kind of hard, insoluble stone. As from this ‘stone’ no P can be extracted, it is no longer usable as a fertiliser.

 

The remaining sludge - with the bacteria - is then dried and incinerated. The remaining purified water is discharged into rivers and streams. However, it does contain residues of medicines that end up in the environment. It goes without saying that these are removed during the production of drinking water. Drinking water in Belgium is guaranteed to be 100% pure!

 

So the process of purifying waste water can clearly be further improved. For example, by recovering N and P and developing useful applications for the sludge.

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