How the Wheelie Bin Composting System works
Here at Free Range Designs we’ve been scratching our heads for a while over how to design and make a compost toilet that fits in with our modern day lives, is attractive, simple to use and easy to maintain.
We were looking for a design of composting toilet that would not be site-specific and could be sent out to customers anywhere, and that would also not require professional installation, therefore making it much more affordable. Well, after quite a few cups of tea and some scribbling we came can up with a design that uses the ubiquitous wheelie bin in order to save and store human manure (humanure) for composting.
This system uses two or more standard 240 litre household rubbish wheelie bins: one “live” bin for collecting the humanure and the others for resting while the contents break down to form rich compost.
The wheelie bin sits inside the composting chamber beneath the toilet seat, collecting the precious humanure. When it is full, you simply remove the side panel of the toilet structure, reach in and wheel out the bin with the lid shut. You then replace with a fresh bin and leave the old one to sit for a while - we recommend sticking a sign on the bin J Once a bin has been stored for about a year, all the pathogens have been destroyed and the compost inside is safe to handle and ready to use on your garden or allotment.
(Human pathogens don’t like conditions outside the human body, so almost all will be dead after a few hours. Only one type of roundworm egg can survive a year-long decomposition period, but even though it is a tiny risk, we recommend using the compost on fruit trees and bushes, rather than the vegetable garden.)
Keeping urine separate is usually the key to a successful composting toilet. Our toilets all come with a wee separator, which is used to divert the urine into a separate container or soak away. This keeps the solid waste odour free and optimises the composting process. For the process to work aerobically, moisture levels need to be controlled: too dry, and the mass decomposes slowly or not at all; too wet and anaerobic organisms thrive, creating undesirable smells.
We developed the urine separator ourselves when we weren’t able to find a suitable product anywhere else. It is designed to fit standard piping and attachments and is made from recycled plastic. It slides in under the toilet seat platform and is easily removed for cleaning.
As urine is high in nitrogen, potassium and phosphorus, it can be used as a fertiliser (on nonfood plants) when mixed about 1:10 in water.
A soak is a source of carbon, like sawdust, straw, hay, shredded paper or earth. Addition of the right amount of soak is important for good decomposition because bacteria like to eat a balanced diet of carbon and nitrogen. Human waste contains a lot of nitrogen so a good amount of carboniferous material is needed to avoid the bacteria giving off excess nitrogen in the form of ammonia, which is what is smelly.
As well as absorbing liquid, the soak also allows oxygen into the pile, so it can decompose aerobically, to produce nitrates, phosphates and sulphates – all very useful. Without a soak, the pile will decompose anaerobically and produce methane, ammonia and hydrogen sulphide – all smelly and not very useful.
So you just need to keep a bucket of soak next to the loo and drop a handful into the toilet after each use.
Tips to Improve your Compost
Add a handful of worms at the bottom of your empty wheelie bin and again periodically as the bin fills up. Worms are nature’s best decomposers and they will help accelerate the composting process.