This article was originally published in the January/February 1996 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online January/February 1996
Centralized composting toilet systems have individual toilets connected to a central tank, usually located outdoors or in a basement. This photograph shows a single toilet connected to the tank.
Using a composting toilet is an especially sensible way to conserve. This type of toilet uses little or no water and transforms human waste to valuable humus. It has its own waste treatment system, so it doesn't need a conventional septic system. Below the seat (or, in some cases, outside the bathroom) is a large externally vented container in which aerobic (oxygen-hungry) microbes break down waste materials. The compost has no odor, unless there is insufficient oxygen, as in an unturned compost pile. As the material is broken down, its volume is reduced by 90%, leaving a light, dry, odorless humus that can be used in a garden or in potting soil for houseplants.
The composting process requires warmth and air flow, both to evaporate water in waste and to aid in the composting of solid waste. The toilet works best at 70F or higher. Although temperatures below 50F slow the process considerably, they won't disrupt it; decomposing activity will resume when the chamber warms up (the composting process generates heat-as anyone who's seen steam rising from a compost pile can attest).
Composting toilets are available as self-contained units or centralized systems. Self-contained units require no plumbing or water connection, are easy to install, are more suited to winter operation because they're easier to keep warm, and require no approval by the National Sanitation Federation (NSF) because they can evaporate all liquids. Central composting systems can be used with a waterless or 1-pint flush toilet (the extra water helps keep the compost moist). They can accommodate more than one toilet, are placed under or outside the bathroom, and often need an NSF approved facility where unevaporated liquid can be collected or drained.
Figure 1. This cut-away schematic shows a self-contained composting toilet. These units both process and store waste, and can be installed in almost any location.
In all models, the compost chamber draws in fresh air and exhausts air to the outside. The vent stack should be insulated if it passes through any unconditioned spaces, since the warm, humid air moving through the stack could condense on the cold vent wall and drip into the compost chamber. The floor under the toilet should also be well insulated.
One type of self-contained toilet is made from fiberglass and high grade stainless steel (see Figure 1). It has three chambers: the composting chamber, which contains a drum that should be rotated about every third day to aerate and mix the compost; the compost finishing drawer, from which compost can be removed; and the evaporating chamber, into which any liquids not absorbed by the compost are drained and evaporated. All of these chambers are sealed to prevent leakage of liquids or odors. Toilet users don't even have to see the waste until it has turned to humus, since the toilet's compost cover opens only when the seat is pressed down.
Composting Toilet Manufacturers and DistributorsAdvanced Composting Systems
195 Meadows Road
Whitefish, MT 59937
550 N Sam Houston
P.O. Box 592
San Benito, TX 78586
Biolet U.S.A. Incorporated
Concord, MA 01742
Clivus Multrum Incorporated
104 Mt. Auburn
Cambridge, MA 02138
Clivus Multrum distributor:
Restroom Solutions Incorporated
3646 E Ray Road
Phoenix, AZ 85044
140-30 Milner Ave.
Canada M1S 3R3
5370 South Service Rd.
600 Main St.
Tonawada, NY 14150-0888
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