Back into the cycle
Our vision is to make the earth better – and we mean that quite literally, because our “human output” contains valuable substances that we can bring back to the field as compost and fertilizer. This allows us to close the carbon and nutrient cycle (field – plate – toilet – field). This can replace synthetic fertilizers to a significant extent, improve soils and reduce the over-fertilization of our waters. But let’s start at the beginning: on the toilet.
We all go to the toilet every day and leave behind approximately 75 kg of solid waste and 550 litres of urine per year.
Quite a nice bunch.
There are two material streams in our toilets: the separately collected liquid urine and the solid mix that we collect under the toilet seat (made up of wood shavings, feces, urine and toilet paper).
Urine treatment
Urine contains exactly the same substances that are found in commercial plant fertilizers. Read more in this article about urine in permaculture by Beat Rölli. The three most important of these are nitrogen, phosphorus and potassium. Urine can therefore be used to make an excellent nutrient fertilizer. We’ll explain how you can do this at home in your own garden here.
If larger quantities are collected commercially, this requires the stabilization of nitrogen to prevent ammonia from evaporating and the removal of drug residues. There is a process for urine in Switzerland that has full fertilizer certification: the Vuna process. In the first step, microorganisms stabilize the urine. In the second step, a carbon filter removes 100% of the contaminants (this corresponds to a fourth purification stage in sewage treatment plants).
Unfortunately, such a system is not yet profitable for us. In the Zurich area, we supply Vuna at irregular intervals. We are also researching alternative processes at other locations. Do you want to help us produce more fertilizer? Demand strengthens supply: here you can order the urine fertilizer.
Recycling of solids
Our excrement consists largely of indigestible food components, mainly fiber, remnants of our intestinal flora and water. However, it only makes up about a tenth of our solid material flow. The rest is bedding, urine and toilet paper. There are various recycling processes: for example, feeding it into biogas plants, carbonization or composting. The latter has the greatest potential for closed cycles.
During composting, microorganisms break down the protein, sugar and fatty acid residues. You can read in detail how this works in this excerpt of the green waste recycling guide from the Swiss Compost Forum. This creates humus soil. Due to the density of the material, this is a particularly good carbon store. So good that 0.04% humus buildup per year could compensate for global emissions (see the 4-promille initiative). Humus with composted faeces is also particularly rich in nutrients and can be used as a basis for Terra Preta substrates.
Reusing the piles collected from a composting toilet in a private setting is easy to do. All you need is a little space and a lot of patience, because hygienising the pathogens in our shit takes either time or sufficient heat . Here we explain what you should pay attention to when composting in the garden.
On a large, commercial scale, classic hot composting is used. This also works for the contents of dry toilets. We were lucky that Verora and Bionika introduced us to their system of controlled microbial composting very early on. This enabled us to carry out our first scientific studies at Qualikomp in Emmen in 2019. The test was supported by the Swiss Climate Foundation and carried out by ETH Zurich and EAWAG. The results were positive.
The obstacle: regulation
In practice, we find ourselves in a dilemma because we can collect your human output and process it safely as described above, but there are no clear regulations about what can be done with the resulting products. The reason for this is that there is no explicit regulation for what we collect in the composting toilets as waste or raw material for fertilizer production – so there is no legal drawer into which the human output can be put.
This is because sewage sludge should not be used in agriculture for good reasons: it contains various wastewater and therefore a variety of pollutants, such as heavy metals. What we collect, however, is significantly different from sewage sludge.
However, there are several reasons why the contents of dry toilets should be processed into fertilizer: the plant nutrients they contain, the much lower pollution levels, as there is no contamination from other wastewater in the first place – and in addition, the existing contaminants are broken down during treatment before the products are used as fertilizer, as ensured in urine treatment and positive results from initial pilot tests for the composting process.
So what exactly do we do? We recycle as much and as high-quality as we can: composting before biogas or pellets before thermal recycling. We look for the best solution depending on the location.
To address this inadequate situation, we and many other actors in the VaLoo and NetSan networks are pushing for explicit and enabling regulation! This is the only way we can unlock the value and safety of products made from processed human waste!
You can find out more about our commitment and how we implement our ecological and social responsibility here.
