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Passive Solar Toilets

Credits: ©2005 Long Branch Environmental Education Center

Passive solar composting toilets offer an alternative, on-site waste recycling system that reduces pollution and creates safe and nutrient-rich fertilizer for gardens and farms. The typical flush toilet consumes approximately half of a household's consumption of water. This is about 12,000 gallons of water per person per year to carry 165 gallons of body waste to the place of disposal. The negative results of water-based flush toilets include:

- Large amounts of valuable and scarce pure drinking water are used

- Ground water and surface water are polluted

- A useful, natural fertilizer is lost

- Energy-intensive and costly waste-treatment plants must be constructed

- The disposal of sewage sludge causes further pollution problems


ELoo Solar Toilet

The Enviro Loo, although not a composting toilet, provides the right environment to treat and stabilize human waste by the natural processes of dehydration and evaporation. The waste is reduced into an inoffensive and harmless, dry ashlike material, which is then disposed of according to county, state, and Federal regulations. ©2009 Southwest Septic Loo, Inc

What Is It?
The waterless composting toilet is an alternative solution to these water pollution problems. It uses no water, thus eliminating massive water consumption used with flush toilets. The self-contained system protects ground and surface waters from contamination, and valuable nutrients are converted into a pathogen-free, sanitary rich humus that can be applied directly to the orchard, ornamentals, and the garden. With solar features, it needs no additional or outside source of energy to complete the decomposition and there are no mechanical moving parts. Because of this, it needs very little maintenance and requires no additional expenses after the original installation. Water conservation equals energy conservation in that no energy is needed to pump, store, or purify waste. Recycling human wastes will also reduce the need for chemical fertilizer production. (Three pounds of composted human feces equals approximately one pound of 10-10-10 commercial fertilizer.) Composting toilets are a part of an appropriate technology in that they reflect a low-cost solution to local resource management problems. They are simple to build and maintain; and can be constructed from locally available materials.

How Does It Work?
The toilet consists of a concrete block vault with a sloping "air staircase" system (see diagram). The organic wastes move down the staircase at a rate that will ensure aerobic decomposition by the time they reach the final storage chamber. Aerobic decomposition means that the organic materials are breaking down in the presence of oxygen. The compost pile is aerated in three ways: first the incoming air stream is preheated by the flat plate solar hot air collector (eliminating the need for an additional power source), and brought underneath the "steps" of the air staircase so that the air can circulate from the bottom and on up through the pile. Second, the air is conducted thouth the slotted and perforated four inch PVC pipe ducts that run through the center of the pile. Third, air flows over and across the pile, evaporating excess moisture and pulling off the carbon dioxide. The solar chimney drives of the air circulation for the composter by allowing the sun to heat the air in the black vent stack, thus causing a natural draft. The warm air rises by natural convection and in turn pulls more air through the collector and throughout the compost pile, and the cycle goes on. Also, it's important to add after each use a generous scoop of "dry flush" material rich in carbon, such as grass clippings, sawdust, leaves, peat, and/or wood chips. You're building a working compost pile here so you need enough fibrous material to mix with the wastes to keep the pile loose so air can circulate through. All odors are released through the solar chimney which ensures the bathroom is free from odors at all times. The humus that results is only five to ten percent of the original volume as ninety to ninety-five percent will be transformed into carbon dioxide and water vapor and released through the vent. It will take approximately two years for the first decomposition period, then with the continuous process, three to ten gallons of humus will be produced per person per year.

Where Can They Be Applied?
The compost toilet is appropriate for urban, suburban, rural, and vacation-type settings. It is appropriate for recreational and commercial facilities and backcountry camp sites, as well as in residential locations. It can be used seasonally or on a continuous basis in any type of climate. One of the benefits of composting toilet systems is that they can be installed in houses that sit on steep rugged land which would normally be unacceptable for septic systems. This enables good, flat, productive land to be used for agricultural purposes, and marginal land for housing purposes. So utilizing good water conservation technology can also lead the way to the conservation of agriculturally productive land.


eLoo Solar Toilet (Texas, USA)

EnviroLoo Solar Toilet (Texas)

Humanure Handbook: Guide to Composting Human Manure

Solar Composting Toilet at Dunton Family Farms

Composting Toilets for Sustainable Living

Passive Solar Composting Toilet (North Carolina, USA)