What do you mean, composting toilet?

Composting toilets come in a variety of models:

They can be compact, completely above-ground single unit with a barrel that slowly turns and mixes the waste and a drawer at the bottom to remove dried waste,

 

 

Alternatively, the toilet could be mostly below ground with a long screw used to slowly churn waste through a ventilated chamber (#5 in the diagram below is a ventilation pipe) until dried waste falls into a collection bag (#4)

 

 

The toilets I will be working with likely do not involve churning bus rely on the work of gravity. A waste collects in a tall above-ground chamber and composts over time. Composted waste is removed from the bottom of this pile through a door.

 

Here is one of these toilets in Mzuzu, Malawi where I will be working:

 

While these look different, they all have the same general premise. The toilets compost human waste, much like you might compost your vegetable scraps for use in a garden. Through decomposition and removal of moisture.

You probably noticed the toilet does not involve flushing or water. The toilet is ventilated to allow flow of oxygen which not only helps release odors from fresh excrement, but provides oxygen to aerobic bacteria breaking down organic material and dries out the waste. This breakdown of organic matter results in an temperature increase, a key factor, along with moisture content and pH, in killing any pathogenic bacteria, viruses, or worms existing in the excrement.

To help dry the waste, and in some cases adjust the pH, a bulking agent is often added. A bulking agent is an additive such as ash, sawdust, or corn husks, often stored in a bucket nearby.

Storage time between fresh excrement and using composted waste in a garden, for example, will vary depending on how hot, acidic, and dry the waste gets during storage, what microbes are present, and if the end-product will be used to grow food.

Image sources:

Sun-Mar Compact https://www.sun-mar.com/prod_self_comp.html

EcoSan Waterless Toilet System http://www.ecosan.co.za/index.html

How Self-Contained Composting Toilets Work http://home.howstuffworks.com/green-living/compost...