A composting toilet uses aerobic decomposition to compost human waste. This system is faster than the decomposition in septic tanks and is often used in place of septic tanks or sewers that flush waste into treatment plants. But there are sometimes problems with odor and disposing of the compost. Composting toilets are relatively new on the market, and comparisons other than self-serving reviews written by competing manufacturers are scarce.
BioLet has a trap door that opens when you sit on it. This is good for females, but males have to artfully push on the seat with their foot to open the trap door. The compacting chamber uses electricity to heat and evaporate waste; it is located directly under the toilet. The compost it produces can sometimes be dry, making it difficult to stir the compost using the external stirring rods. Good for three or four people.
Sun-Mar is the best known composting toilet in the United States and Canada. The toilet goes inside the bathroom; the composting chamber and vent pipe are outside. The composting chamber rotates like a clothes dryer, adding air to the waste which speeds up decomposition. A separate "finishing drawer" stores the finished compost. Despite isolated complaints about odor, the National Sanitation Foundation International has certified Sun Mar as containing a minimal amount of odorless fecal matter in its finished compost. Good for three or four people.
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An Echo Tech system usually has four chambers that are rotated when they are full, a process that takes from 2 to 6 months. The composting chamber is usually in the basement with a vent pipe running up through the wall or roof. This system is good for a family in a cabin or vacation home. Since no fresh material mixes with older waste, more pathogens are destroyed, resulting in cleaner compost at the end. Good for a large family using it continuously.
The Clivus Multrum requires a basement or other large, accessible space below the toilet. An automatic moistening system, connected to water, moistens the compost as gravity moves it down a ramp. An electric pump moves the liquid from the composter to a storage tank. This is a complex, expensive system, best suited for municipal or industrial use.
There have been complaints about odor in models without fans to carry away the odor. Some nonelectric models use a partial vacuum to spirit odor away. Composting toilets designed for boats and recreational vehicles are usually not suitable for cabins and vacation homes.
Too much urine can also turn aerobic decomposition into anaerobic composition that smells. Some models spirit urine away to separate tanks. Others recommend adding dry material to balance the urine. You need to take this into account when buying a composting toilet.
You need to remove the finished compost promptly. You can make this easier by using peat moss for dry matter in your toilet.