Composting Toilets for Islands
About Composting Toilets
On many remote islands septic tanks or municipal sewage treatment is not available. As a result many island owners purchase composting toilets to manage human waste. A composting toilet is “a system that converts human waste into fertilizer or soil through the natural breakdown of organic matter into its essential minerals.” The process of converting human waste into safe and useable compost material can take anywhere between 3 months to a few years to complete depending on factors such as climate and temperature.
How they Work
There are two types of composting toilets available to island owners. The first type are those that are
self-contained or complete the process “in-situ”. The second type is a system that transfers waste from a low-flush or vacuum flush toilet to a remote composting unit below the toilet.
Some composting toilets use electricity to complete the composting process. Other models do not require electricity and simply require the owner rotate a drum within the composting toilet to aid in the aerobic breakdown of the waste. Small systems typically can not complete the composting on site rather they prepare the human waste for transfer to a secondary site such as a compost pile
Maintenance
Composting toilets, much like septic systems eventually need some material manually removed. However, a full size, automated composting toilet does not need to have solids removed for 
several decades. This is impressive compared to septic systems that may have to be pumped yearly or smaller composting toilets which may have to be cleaned several times a year.
Considerations
It is important to remember that human waste can be hazardous, thus it is unsafe to come into contact with improperly or incompletely composted human waste. Therefore, human waste should not be used as fertilizer without ensuring that it is composted thoroughly.
It is recommended that in cooler climates such as the Northern US, UK and Canada that the waste is allowed to compost for at least one year. Cooler climates slow down the aerobic processes thus time to break down than in tropical climates. It is also recommended that “humanure” should not be used as a fertilizer on crops that are directly handled and eaten such as vegetables and salad leaves, but instead applied as a mulch around bushes or fruit trees.
How much do they cost?
The cost of composting toilets varies greatly but they tend to be between 25-75% cheaper than septic systems which can cost between $15,000 and 20,000. Prices are on average around $2000 for a composting toilet with prices varying depending on the type of model purchased.
Sources:
http://en.wikipedia.org/wiki/Composting_toilet
http://compostingtoilet.org/
