Recent events in Ukraine have alerted gardeners to the fact that much of the agricultural fertilizer we have used is sourced from the breadbasket of Europe, as Ukraine is often called.
Most fertilizers provide nitrogen and phosphorus with some potassium, which are manufactured by steam, chemical, or compaction granulation, to enable nitrogen to be released into the soil for plant use.
However, with a serious shortage of these available globally, the search for nutrients we could use instead may be very close to you.
Read on to hear about research into recycling human urine into fertilizer is happening worldwide and ways to help use it in your own garden.
What nutrients does urine contain?
Urine is mainly water (80-90%), excreted with approximately 11 parts nitrogen (N) to 1-2 parts phosphorus (P) and 2.5-4 parts of potassium (K). These are the elements you may recognise from the details listed on commercialized NPK fertilisers.
The various elements in urine do depend on what an individual person has eaten and drunk but on average, these are the proportions in human urine. Scientists lament that most of these nutrients are flushed back into wastewater treatment plants and not re-utilized in our agricultural fields.
Urine is completely sterile when fresh; I remember an experienced first aider telling me that in an emergency, urine could even be used to clean a cut! Although I am not recommending this, I am going to remind you of the history of urine collection, why humanity considered this useful in the past and what it can be used for nowadays.
First, let’s look at the benefits and any drawbacks of urine collection.
What are the benefits of collecting urine?
- It is free fertiliser! It also helps you to feel better about recycling waste and this gives you a lot of brownie points with regard to environmental waste.
- You save water by not flushing urine away. Urine goes straight into your composting toilet (more below), gets covered with green waste, and then reused as fertiliser after some time.
- You gain valuable fertiliser for hungry plants such as squashes, cucumbers, tomatoes, aubergines, and beans.
- There is little consumer resistance. Studies have shown that the public is not averse to using urine fertiliser on food plants as it helps to regenerate waste and make valuable fertiliser. 3,800 people in 16 different countries took part in surveys and the results suggest that 80% of respondents were in agreement with recycling urine for this purpose and would buy products grown in this way. In fact, Switzerland made history by becoming the very first country to license a urine-based fertiliser for use on food plants, called Aurin.
Are there any downsides?
- It is tricky to separate urine with a conventional flush system although you can buy appliances to do this which you can place on the toilet seat or buy a complete system. See more in The Urine Trap below.
- You need to age liquid urine to make it worthwhile and this process will eliminate pathogens almost completely after 9-12 months. Because it comes into contact with air, urea may react which may cause a loss of some of the nitrogen but you will still have considerable amounts of potassium and phosphorous. Not to mention that you’re actively recycling waste!
- You may need to construct separate buildings or ways to collect urine to store, which can be DIY versions but you can also purchase these direct from many UK companies. There are detailed instructions below for how to make a DIY composting toilet.
- Chemical residues. Some research shows that contraceptive hormones show in urine as do other chemicals, so if you are taking any medication think carefully if you want to use your urine. To be honest, if you are healthy and fit probably the urine you produce is as well so this is merely to keep you aware that your urine is the remains of what you eat, drink and consume.
How can urine be safely converted into usable fertiliser?
- A really garden-friendly method is to create a specialised toilet for urine conversion. In Cardiff, I visited Riverside community garden, located inside Pontcanna permanent allotments, a beautiful green lung right in the middle of the city to view their homemade compositing toilet and to get some ideas.
One surprise for me about this toilet was its pleasant appearance with wooden walls which allow light to permeate while you twinkle. To my surprise, it smelled delightful, probably due to the hay and green matter provided in a box to cover after you have done your business, and the smell is often the reason why most people decide not to have one.
Lewis Mottram (my brother-in-law) explained how the toilet building was constructed from willow and cherry laurel posts and then thatch was made with reeds from the Levels, an area nearby.
There is a normal toilet seat with a drop where urine flows into a bed of wood chips, sawdust, and other dry waste material sourced from local landscape gardeners, tree surgeons, and the council’s parks department.
“We allow it to soak into this material and add a fresh layer after each use. Gradually, this rots down into a nutrient-rich compost that can be dug directly into their growing areas.”
See some tips on how to make your own DIY structure below.
- Urine needs to be stored if it’s in liquid form. A storage container is useful and this will need to be allowed to age for 9-12 months, to remove pathogens. After this, use it diluted with water and apply it to the soil (not the leaves of plants). Urine is very rich and will cause root burn if applied directly, so make sure you dilute it at least 1:2 but I prefer 1 part urine to 9 parts water. This is excellent for hungry plants like tomatoes, cucumbers, squashes, pumpkins, beans, and so on. Make sure you direct this water at the roots, not the leaves or fruit.
- Directly on your compost heap. Urine is a well-known compost activator and if you have somebody in your household who is willing to do their business directly on the heap under the shadow of nightfall or leaf cover, then fantastic. Another alternative is to use a bucket and then pour this onto a compost heap once a week. If you have several heaps or bins, then use it on each one every week or so and this will add nutrients and also cut down on that smell of stale urine, which is the odour of public lavatories.
- Urine can be dried. Many techniques are being investigated worldwide because transporting urine is difficult, and costly and its main ingredient is water so it is heavy. If urine can be dried, then all the nutrients can be released easily and used in its dried form. There are many exciting projects worldwide working on this, see more details below.
- Urine was used for tanning leather in many countries. It was generally used to remove the hair was leather before tanning and colours were added. The Romans are known to have collected urine and even taxed it, which is similar to what happens in North Korea to this day where each citizen has a daily quota to supply, although this is used mainly for agriculture.
Historic collection of urine.
Since time immemorial, humans have re-utilised our waste products which are excreted in many different ways. Peeing on a quiet patch in the woods on a winter walk was as frequent in the past as it is now. More surprising uses of urine are its use as a stain remover (before washing clothes) before the invention of soap and it was also used in the tanning industry to remove hair.
In rural areas, it could be stored in large containers to remove pathogens and then applied to fields. However, in cities with dense populations, the amount of waste makes this process more difficult. Bedpans had to go somewhere and both urine and solid waste were still collected by people in cities up to Victorian times, with the solids and sludge later being used in agriculture.
In urban settlements, some dedicated collectors arrived at doors early in the morning or late at night to collect material. Nowadays, we rely on our sewage and sanitation systems to dispose of this valuable waste.
The World Health Organisation (WHO) has been working to devise methods to recycle waste urine and many studies have concentrated on trying to dry urine rather than separate it in conventional sewage systems.
The sheer volume of urine (containing about 90-95% water) makes drying an easier option than transportation. Extraction of nutrients by drying is now being studied in Africa, and other sites, which has the added benefit of available grey water can be used for other purposes in sites where rainfall is scarce.
In the 21st century, urine (and sewage) is collected in specialised toilets which separate waste easily in both Korea and Japan but the emphasis is on clean collection methods, and it is made very easy. Germany has many types of toilet and separates urine from faecal material for further processing.
Private landowners have always been permitted to build pits to fill with composting waste providing it does not interfere with local water supplies and the waste is covered and not a public nuisance. Many allotments, rural public museums, stately homes, and campsites often provide communal composting toilets, and the sludge is collected at the end of the summer for use in local agriculture.
Festivals also offer this service and it adds to the environmentally friendly nature of the marketing and advertising connected with the event.
Now let’s look at how research worldwide is finding new ways of converting urine (and sewage).
What commercial products result from urine collection?
- Building bricks in Cape Town, South Africa.
Construction bricks using sand, urine, and urease-producing bacteria have been placed in moulds where they react chemically to fit the shape of the mould, in this case, bricks that can be used in construction. These bricks require no firing either, which is a great energy saver.
- Lunar building materials. The European Space Agency is studying the use of human urine as a resource for habitat building on the Moon.
- Electricity production. Studies are experimenting with new ways of producing electricity by placing urine into microbial fuel cells.
- Direct urea fuel cells (DUFC). In South Korea, scientists are in search of a way to both purify wastewater and generate clean energy. These fuel cells utilise urine and the Korea Maritime and Ocean University has shown that they can provide energy generators for houses and towns. Not only are they recycling urine, they are turning it into energy in rural areas where power can often be an issue while also producing clean water. Win win!
- Drying urine into solids. In Sweden, self-contained toilets that dry urine, mixed with other nutrients and then convert it into solid urea are being trialed in the head office of the Swedish public water and wastewater utility VA SYD in Malmö.
- Recovering phosphorus from hydrolysed urine is happening at Stanford University in California, where William Tarpeh is experimenting with selective re-absorption of nutrients using beads. His research is focusing on producing more environmentally friendly beads than have been previously used, thereby producing less damage and more nutrients.
- TOOPI Organics, France was founded in 2019 near Bordeaux and it has patented a urine-based bio-stimulants which enrich human urine with microorganisms useful for agriculture and simultaneously aims to recycle approximately 750,000 litres of urine annually in the process. This type of project offers any rural area a double benefit of reusable water and recycled nutrients. Field trials in farms close to Paris showed favourable results when compared with conventional synthetic fertilisers.
- The Urine Trap. This Austrian design presented a toilet that could separate urine in 2017 in Austria and was the brainchild of EOOS. Its unique design was financed by the Bill and Melinda Gates Foundation, and is now being tested and adapted for use in the University of KwaZulu in Natal,in Africa.
Although there are some dangers to a build-up of sewage in arid deserts (or emergency disaster areas) where cholera can emerge in sites where good hygiene and a lack of running water is also a problem, this should not be a problem in a UK backyard. So how can you safely use this valuable resource in your own garden?
Urine Fertilizer FAQs
So how can I use urine in my garden?
Straight on the compost heap! Fresh urine is very concentrated and experts recommend aging it to lose any transferable pathogens. Used as a compost activator, this will actively get those autumn leaf piles collected in autumn working.
Leaves add bulk but they may be slow to decompose if they are very dry so adding urine will add liquid in addition to valuable nutrients. An old trick learned in allotments is that fresh urine is a fantastic compost activator so if you have anybody willing to do this, both the nutrients and the activation will speed up the process.
However, do not use urine daily because it will saturate the pile with nitrogen and what you want is to add some to the heap or leaf pile once a week, and to a different part of the garden but too much is not beneficial overall.
You can construct a special toilet for urine only and encourage the household to use that. A toilet like a camping loo works well. You can also build a special building like the one pictured. For gardening purposes, this could also be covered with climbing sweet peas, clematis, or beans which will be nourished by the supplies of urine
You will need:
Enough space to be able to construct a small room, with a container or with a deep pit in the earth. Surrounding this, you can build a structure from natural materials using old branches, tree prunings, straw, or reeds. To finish, you will need a toilet seat with a lid and a plank to place this.
- First you need to use a large container to hold the waste. The one pictured has been cut to size with a cover fitted to the plank o the top. You can also dig a hole directly into the earth approximately 3-4 feet square and use this as the base of the composting area into which the urine flows. Place the excavated earth around the hole and then stakes can be placed into the ground at the perimeter to make the interior room of the toilet.
- Next, cut a hole the size of a toilet seat in a plank of wood and secure this in place over the composting hole. You can use an old wooden or plastic chest, old bricks, old furniture, or construct something from wood. This needs to be sturdy to hold the weight of the people who will sit on it – test it out on some willing members of the family before it is fixed in place!
- When secured, place your toilet seat on top of the plank and then allow a gap below for the urine to fall into. It is best to purchase a seat with a lid that can be closed down to keep the flies off the compost below.
- Fill this excavated part with a layer of wood chip or sawdust, allowing the urine to seep through that layer to disguise the smell. Make sure you can access this area from the back by making a removable board or even a door, once the urine has composted nicely so that you can remove the finished compost easily.
- After the removal of compost, you can replace the door and start again by adding new sawdust or straw to start again.
If you don’t think your DIY skills are up to this, you can just buy a camping toilet and empty it onto a pile of dry sawdust, leaves, and paper waste to compost over several months.
- Using urine fresh, you will need to dilute it as it is very strong so use one part of urine, topped up with 9 parts of water. This can be grey water (saved from washing up, bath water, etc) or saved rainwater. However, aged urine tends to smell because it produces ammonia, that very evident stink from public toilets! To avoid this, either store the urine in a sealed container or use it in a composting toilet that flushes through old sawdust or woodchips and allow the compost to age for 6-12 months.
- Turn urine into solids by adding an alkaline ingredient to your toilet or container. There are many products on the market and looking at all the research I have done, these will soon be available to purchase. The many websites below will point you in the right direction, if you are interested.
By now, you will be aware of exactly what you are flushing down that toilet of yours and considering if you have space to use it in your garden. Let me see pics of any DIY composting toilets if you make one and do let us know if you hear about any other uses for urine!
- Scientists Perfect Renewable Power from Urine While Cleaning Wastewater in South Korea (goodnewsnetwork.org)