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


Composting Toilets:
A Tankful of Conservation

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.
Toilet flushing accounts for 45% of indoor water use, or approximately 32,000 gallons per year for a family of four using 5-7 gallons-per-flush toilets. That's $56 a year, based on the average cost of water ($1.76 per 1,000 gallons), for those still using inefficient toilets. Communities also pay; enormous costs and energy use accompany building, operating, and maintaining supply-side pumps, pipes, and reservoirs, and waste-end sewage treatment facilities.

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.
Both self-contained and centralized toilets are available in electric and nonelectric models. Where utility power is available, electric models work best. These use a thermostatically controlled heating element to help with evaporation, and a small (25W) fan to facilitate fresh air flow and negative air pressure inside the compost chamber. This fan will ventilate the entire bathroom, in fact. Nonelectric units have a lower capacity and use a 12V fan, which draws only 1.4 watts and can run off of house electricity, a solar panel, or a 12V battery. Electric models cost about $1,300 and nonelectric ones cost about $1,000.

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.

-Nancy Hurrelbrinck


Composting Toilet Manufacturers and Distributors

Advanced Composting Systems
195 Meadows Road
Whitefish, MT 59937

Biolet Interamericas
550 N Sam Houston
P.O. Box 592
San Benito, TX 78586

Biolet U.S.A. Incorporated
Suite 4B
Damonmill Square
Concord, MA 01742

Clivus Multrum Incorporated
104 Mt. Auburn
Cambridge, MA 02138

Clivus Multrum distributor:
Restroom Solutions Incorporated
3646 E Ray Road
Suite B16-46
Phoenix, AZ 85044

San Cor
140-30 Milner Ave.
Scarborough, Ontario
Canada M1S 3R3
Tel:(416)299-4848; (800)387-5126

Sun-Mar Corp.
5370 South Service Rd.
Burlington, ON
L7L 5L1
Fax:  905-332-1315

Sun-Mar Corporation
600 Main St.
Tonawada, NY 14150-0888

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