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Composting toilet guide: this article describes the nature of composting toilets, how they work, how they are used, where they can be used, usage restrictions, and different composting toilet types and features. We define & describe just about every composting toilet type, feature, methods of operation, & maintenance requirements as well as costs. We list sources of various models of composting toilets and compare composting toilet model features, uses, and costs. We include a table of composting toilet supplies, uses, properties & prices.
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What is a Composting Toilet?
A composting toilet is a self-contained unit (not connected to a septic or sewer system) which breaks-down and dehydrates human waste to a compost which can be added to soils. The toilet will consist of a place to sit (which is likely to look a lot like any other toilet), a composting chamber which breaks down and sanitizes the sewage, and a drying chamber or tray which permits moisture to escape, reducing the sewage volume.
Composting toilets come in models which use a little water or no water at all, and in electric (heated and power-vented) models and non-electric models. Some models include electro-mechanical mixers which mix waste in with a mulch product to speed and improve the composting process. Properly designed and installed the toilet is vented so that there are no abnormal toilet odors. Periodically the compost must be emptied and on occasion toilet components are cleaned.
People use the toilet in a normal manner, and modern composting toilets in fact look pretty familiar, resembling water-based toilets in general shape and comfort. Waste is mixed with a "starter mulch" to begin the composting process. Composted waste is emptied from the toilet at intervals ranging from one or two months to 12 months depending on level of usage and toilet design.
Composting toilets which do not mix new human waste with material already being composted produce a compost which is easier and safer to handle. This is a reason that some models use multiple containers or compartments, though there are other solutions to this problem. If the visible portions of the toilet need cleaning, normal household cleaner and toilet brush are used.
Composting Toilet Selection Question List
The following questions one asks when considering installing a composting toilet are addressed in the article below:
Composting Toilets may be used where the water supply is limited or not available at all, or where a building owner for other reasons wishes to conserve water use. Other wastewater treatment will still be required for handling graywater from sinks and showers. Shown above is the SunMar compact composting toilet. SunMar composting toilets and toilet models by other manufacturers are described below.
The buyer should consider carefully their intended maximum usage level of the toilet before choosing a composting toilet model.
Full time composting toilets are intended to serve as the main toilet in a full-time occupied building (more than 5 days continuous use, for example).
Part time composting toilets are intended to serve buildings which are not occupied full time (that is less than 5 consecutive days) or by some manufacturers, these models are intended for use during limited hours per day (10 or less).
Electric models include heaters to aid the composting, possibly a power ventilation system, possibly a system which mixes air in with the compost to improve the aerobic bacterial breakdown of waste, and possibly a mixing mechanism to mix sewage with mulch to aid the composting process.
Non-electric composting toilets may also be vented but will lack a heater and power mixing.
Composting toilet models vary among waterless, low water, and foam flush units. Obviously a water-model requires a water source.
Composting toilet models also vary between models requiring electricity (typically 110V), battery operated (12V), possibly solar powered, and models which use no electrical power. Features such as automatic mixing, aeration, and vent fans will require electricity
A fully automatic composting toilet will typically control a heater, ventilating fan, and a mixer to mix sewage and mulch together. A fully automatic toilet mixes each time the seat is lowered.
A semi-automatic composting toilet will still use a thermostatically controlled heater, fan. But the sewage-compost-mulch mixer is manual, typically providing a handle that is turned a few times after each use of the toilet.
[Click to enlarge any image]
The compost process involves biological breakdown of the waste - a process that needs oxygen (air) heat, and some moisture. Waste/compost/mulch mixing (the traditional "turning of the compost pile") is used to improve the aerobic breakdown of waste pathogens, to macerate the waste (which aids breakdown), to be sure that all parts of the sewage are heated and treated, and to speed the composting process.
Not all composting toilets use a compost/sewage/mulch mixing mechanism, and composting toilet manufacturers do not all agree on whether or not mixing is required. The Humanure Handbook by Joseph Jenkins has an article discussing this topic [www.jenkinspublishing.com] [Envirolet has posted his article at their website].
Shown at page top is the SunMar Excel™ composting toilet. SunMar provides low water and no-water composting toilets. Image courtesy of naturalhome.com and SunMar.
Smaller composting units, especially smaller units which do not use heaters and aerators, because they risk unwanted liquid accumulation, insects, and nitrification of the waste, will require more maintenance and care than units which provide an aerator fan, heater, and compost mixer.
Because some folks don't want to look into the sewage/compost in a self-contained composting toilet, and also for odor control and sanitation, all composting toilets have some method of closing off the bottom of the bowl from the waste line or composting receptacle.
Some composting toilet models use an automatic trap closing mechanism which appeals to people who don't want to operate any unfamiliar controls on their toilet.
Other composting toilets use a manual valve to close the bottom of the bowl. The manufacturers of composting toilets which use a manual valve point out [Envirolet] that men who are accustomed to urinating while standing up will have to sit to urinate on toilets which provide an automatic bowl valve.
Watch out: we've come across composting toilet user reviews complaining that the bowl closing door design looked great (automatic when the seat was lifted) but proved flimsy or actually broke quickly when the toilet was in service.
Note: we have not quoted specific reviews griping about shoddy products, clogs, breaks, and snafus or poor service because of uncertinty about the review source, authority, etc. But it's worth reading a few of these when sorting out composting toilet features and maintenance and repair performance.
Composting of sewage in a composting toilet involves worm processing, micro-organism processing (bacteria, molds, and possibly other microorganisms) and dehydration by the evaporation of moisture.
The toilet manufacturer may recommend or provide a specific mulching product to aid the composting product and probably to aid in deodorizing.
A batch-system composting toilet interior contains multiple or change-out composting compartments. When a compartment (or change-out container) is filled with waste it is sealed and taken out of use to permit the sewage breakdown to continue. When the composting process is complete for a given container it is emptied (and presumably applied to soil in a legal manner) and the container is returned to use.
A non-batch, continuous composting toilet receives waste continuously into a single container. The composting procedure reduces the volume of the waste which is eventually (typically after 6-12 months) removed from the bottom of the container and is considered "fully composted material" which is then emptied (and presumably applied to soil in a legal manner).
Be sure to review the installation requirements for the composting toilet you're considering. Some models require that the toilet be installed directly over the composting reservoir and others not; some models use a large reservoir below the toilet, others may be much smaller and self-contained.
This makes a big difference if you're considering a composting toilet in a one story building built on a slab, particularly if your toilet installation space does not include space for an along-side composting tank.
In a non-freezing climate it may be feasible to add-on a shelter against a building wall to contain the composting unit, but in freezing climates where the composter needs to be protected from freeze damage (varies by model) placing the composting tank outside the building envelope increases the installation cost as well as risks of freeze damage.
When planning for space for a central composting unit (using a composting tank that is separate from the toilet itself) remember that you're not going to just jam the composter into an inaccessible crawl area. Access needs to be easy, safe, and comfortable, as regular access will be required for cleaning, emptying, and other maintenance chores.
The U.S. standard for composting toilets is NSF (National Sanitation Foundation) Standard 41. Some, probably not all, models advertised have been tested to determine if they meet this standard. In Canada, the CSA- has adopted and also certifies composting toilets to meet National Sanitation Standard (NSF-) Standard-41.
The following is from: New York State Appendix 75-A.10 Other systems
These units shall be installed in accordance with the manufacturers instructions. The units shall have a label indicating compliance with the requirements of National Sanitation Foundation (NSF) Standard 41 or equivalent. Only units with a warranty of five years or more shall be installed.
Composting Toilet Product Index & Feature Guides
BioLet Toilet Systems 830 West State Street Newcomerstown, OH 43832, Tel: 800-524-6538, Website: biolet.com
* - units that were recommended by RealGoods and which look good to us.
Table of Composting Toilet Operating Costs, Choices, Supplies - do we really need to buy mulch or sawdust or other stuff?
Reader Question: What are the operating costs & choices for composting toilets? Are consumables really required for composting toilets?
Your web site has been very useful indeed but we remain uncertain about our choice. Are you aware of a composting toilet that uses water and standard house electricity for which there are no consumables necessary? if not is there a way of comparing the on-going costs of additives for these toilets? Thanks very much - A.D. - Canada
Reply: List of Composting Toilet Supplies, Costs, Features, Functions
I am not aware of any composting toilet design for which the manufacturer recommends no consumables whatsoever. The minimum consumable required is a bulking material. Sun-Mar and some others also offer enzymes, deodorants, and compost activators that may be optional. Quoting from the Phoenix Composting Toilet System Instructions for Operation and Maintenance, and noting that opinions vary among manufacturers about the best and most easily biodegraded bulking material to use in a composting toilet:
"Anaerobic conditions" means more than just an unpleasant odor. It also means the system will lack aerobic bacterial action and biodegradation will not proceed properly nor adequately.
Keep in mind that the operating cost for a composting toilet depends not only on the cost of supplies but on the type of toilet selected (non-electric vs. electric, for example) and upon the level of usage and perhaps maintenance. That said, below we have begun a table of composting & waterless & low-water toilet system supplies, uses, & costs.
Table of Toilet Supplies for Composting, Low-Water & Waterless Toilets
The toilet supplies listed in the table below are available from the manufacturers listed in a product directory found in the article above, as well as from additional distributors located online.
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Frequently Asked Questions (FAQs) about composting toilets, choices, types, operation, use, supplies, costs, operating costs.
Questions & answers or comments about buying, using, & maintaining a composting toilet
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