Composting toilets treat human excrement using biological processes, turning it into organic compost material that can be used to fertilise the soil. They are small-scale, complete waste processing systems.
The eastern world has been using composting toilets for hundreds of years, but it is only in recent years that they have become more popular in the west.
Decomposing waste to turn it into something useful
All composting toilets decompose waste by creating the aerobic conditions for bacteria and other macro and micro-organisms to thrive. The objective is to destroy harmful pathogens, eliminate the risk to human health and environment, and transform the waste nutrients into fertile soil. They typically break down waste material to a small percentage of its original volume.
Most toilet composting systems are low-temperature (mouldering) toilets. The waste material must be left for long enough for pathogens to break down naturally.
Separating human waste
Compost that is too wet can become anaerobic and produce unpleasant smells. Because of this, our composting toilets separate urine from faeces. The collected urine (85% of the volume we produce) is therefore a bacteria-free liquid that can be used as a fertiliser or leached safely into the ground. (Beware toilets which separate out the liquid later on – this is a polluted hazardous waste and cannot be used until rendered safe).
The faeces and toilet paper are collected in a holding tank under the toilet seat with a composting medium using a screen to avoid any unpleasant sights and to keep out flies and other unwanted bugs. The tank either has a stirrer or rotation mechanism to distribute the material and allow even decomposition. When the tank is full it is removed and either stored until fully decomposed or added to a compost pile. No basement processing plant or mechanical removal is required.
Note that, by removing the urine at source the volume of solid matter produced is very small and, as moisture is extracted, becomes even smaller, normally leaving only 10% by volume of what comes out of us.