Composting toilets

Millions of people do not have access to safe water. Many regions suffer from extreme drought. The next world war could be fought to control fresh water sources.
→ Doesn’t it seem like a waste to flush litres of drinking water down the toilet every day?

Composting toilets rely on natural decomposition to break down your waste. Little or no water is needed and the end result is compost which can be used in your garden. BowenArrow Products manufactures urine-diverting toilets, which means you have direct access to an excellent fertiliser, rich in phosphorous and sterile (from healthy individuals).

Separating urine also improves the composting process and reduces the quantity of waste stored. Typically, the decomposition process eliminates 90% of the original volume (in other words, it breaks down to a surprisingly small amount of compost).

Safety

Compost is safe to use in your garden provided it has been allowed to break down the waste sufficiently. Generally, this means the composting chamber needs to be above 60°C for a period of time (various sources advise from several hours to a week at that temperature). 60°C may seem quite hot, however the naturally-occurring microbes responsible for composting produce heat.

For complete pathogen removal, the World Health Organisation recommends composting for a month at high temperature, followed by a period of several months to two years of secondary composting/maturation (pasteurisation) after the compost is removed from the toilet. This period is shortened in warmer climates and if the compost heap is turned occasionally. These measures are only necessary if the compost is to be used in growing leafy vegetables and root plants.

Bulking

Urine-diverted toilet systems have a lower water content in the compost, although it can still be advantageous to add bulking organic matter, to prevent the compost from becoming too compacted. Popular additives include:

  • wood shavings and tree bark
  • ash
  • pieces of paper (including toilet paper)
  • straw clippings
  • leaves

Some species of worms (e.g. red wrigglers and tiger worms) can also be included in the composting process, as can food waste. Depending on your system, these may be more suitable for addition during a secondary composting phase.

Odour

With urine diverted away from the composting chamber, the largest source of odour is eliminated. However, almost all systems are ventilated, usually using a small electric fan to pull air through the system and outside. BowenArrow Products sell fan units suitable for drop chutes, and the Ultimate SC model includes an fan integrated into the pedestal.

Cleaning

Organic disinfectants such as vinegar or diluted citric acid can be sprayed onto the bowl and any residue wiped away with toilet paper. It is not disastrous if water enters the chamber, but too much water will inhibit the composting process (ideally between 45-60% total water content).

Local government approval

An exemption in the relevant legislation allows you to design/build/operate your own composting toilet system, provided you satisfy your local council that you are “committed to [its] safe operation [and to] protecting public health and the environment.”


Suggested reading

Composting toilets – Wikipedia
Always a good starting point, and featuring a photo of one of our own pedestals!

The following are excellent review papers, in the form of a scientific document, but accessible for all audiences. They are hosted by the Sustainable Sanitation Alliance, who make a vast array of information available to the public.
Berger, W. (2011). Technology review of composting toilets. Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH
von Münch, E., Winker, M. (2011). Technology review of urine diversion components. Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH

Del Porto, D., Steinfeld, C. (2000). The Composting Toilet System Book. Center for Ecological Pollution Prevention, Massachusetts USA
A comprehensive guide to composting toilets, including guidelines on usage, suggested designs for DIY, and case studies. Available directly from the author, your local bookshop (ISBN: 0-9666783-0-3, 9780966678307) or from Amazon.com.

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