We were 8 people at the workshop, most had experienced composting toilets as a user, some had experience with composting excreta.
We talked about the different modules of the Dixie toilet and discussed various use scenarios for the converted toilet. One is a potential cooperation with a local social NGO where homeless people sometimes queue on the pavement in front of the building. They had a Dixie but removed it because of the smell, now people use the bushes. The situation means: flat surface, no room for tanks in the ground; people don't all read German, it needs to be intuitive to use correctly; mainly men, mainly urine; there's danger of vandalism, needs to be fire-resistant and not easy to topple over.
We discussed materials for the walls:
- Wood looks and feels nice, the three companies in Germany that provide composting portacabins (EcoToi, Goldeimer, Nowato) build with wood. It's also easier to use for construction, depending on the varnish fully recyclable, after some time becomes less easy to clean if there is no-one there to do it as soon as it gets wet (sprinkled or puked on)
- Metal is fire-resistant, only looks good if coated which makes it less recyclable, harder to work with, very heavy which is only good if the cabin is intended to stay in place, easy to clean but not all metals are urine-resistant
- Dixie uses fire-resistant plastic, there are many cabins of this type already out there, mainly one type of plastic so it's fully re (down)cyclable but fire retardands are highly toxic, looks shabby but is very easy to clean with a power hose (the tank has an outlet for the cleaning water at the bottom that can be connected to the sewers)
Seat/ tank/ separation
We discussed possible seat designs
- For men it's better to provide a urinal, much cleaner to use and it separates at source (that's the thing on the left)
- A separation seat like this one is not that expensive but it clogs up easily and get dirty because people don't know ho to aim right, experience shows that it's not suitable for public toilets unless someone is there to do cleaning all the time
- the easiest model to achieve separation is a bucket under the seat with a sieve or some small holes to allow liquids to drip to the tank underneath. In a Dixie there is very little room for such a bucket as the tank is a flat rectangle of ca. 40 -50cm deep. A bucket that fits into that space would leave the colleted faeces very close to the bottom of the next person using it: even when covered people wouldn't like it
- a possible solution is to open the tank at the bottom and build the Dixie on a pedestal to make room. Problem her is: it makes it less attractive to simpy try it out as you cannot go back to chemical if you find it doesn't work for that location. The price for such an experiment is rather high and it would then be easier to just build a toilet that is designed for this purpose right away. Dixie is designed to be used with the liquid that can be pumped out through the hole where the seat is.
A composting toilet doesn't stink if the feaces and urine are kept separate, the urine is kept anaerobic and the faeces are kept dry and aerated
- urine can be colleted in a container with a valve. We discussed different types of valves: Ping-Pong ball, commercial valve models (with holes as an inlet), disc valve (like the simple artificial heart valve models), rubber valve made of a condom/ ballon or any other flexible narrow tube that can be pulled over the end of a funnel, inserting a long tube into the container all the way to the bottom so the surface area in the tube is very small and the surface area in the container is not connected to outside air.
- Maike thought of using oil to cover the surface of the urine to prevent it from getting in contact with oxygen. She tested a EM-Solution: they don't 'eat' the oil, it still needs to be tested with actual urine to see if it works, downside: makes cleaning the container much more difficult. It may not be necessary if we have a good valve.
- faeces can be covered with (resin and dust reduced) sawdust, activated charcoal or simply a soil and leave mix. There needs to be enough material to cover (see experience at the Berlin OSCEdays 2016) and using a shovel is not intuitive: some people pour water into the toilet to 'flush', others loose cover material all over the place, especially the toilet seat which incombination with misaiming will cause it to stick there and make a mess.
Maike suggested installing a 'flush' system with a closed box at the top containing the cover material, a turning piece at the outlet of the box that will automaticaly measure the right amount and is turned by pulling a chain, so the box and chain look like a traditional water toilet. The material then falls through a pipe that leads directly into the bucket at an angle that will cover the faeces
- Stefan has experience with aeration, they use a tube with holes that leads air into the colleted faeces from the side (holes in it facing sideways and down for easy cleaning). That is not so feasible when you want to remove the bucket upwards through the hole, it would need to be inserted from the top. Stefan says there's no problem with cleaning in their version of the toilet.
Ayumi from the Dycle project has experience with making Terra Preta from Diapers (very similar material)
- toilet paper needs to be compostable
- charcoal works well but you need space to store the colleted material
- if you store on private land German law is not such a problem
Stefan has experience with leaves: works very well too, no smell
We will advise the NGO that it may be much easier to simply put up a urinal and maybe provide a separate toilet for women (and urgent cases). We will also point them towards Nowato to discuss further options as they have more variations on offer
We will not continue to hack an actual Dixie because it is not well suitable for the necessary changes. Separation is rather difficult to achieve and the toilet tank needs to be cut open to provide access for a removable collection container. We currently have no funds to run such an experiment.