Composting toilets are the most misunderstood element of an ecologically friendly building. There’s no need to be scared!
This introduction to composting toilet basics is adapted from the book Making Better Buildings by Chris Magwood:
Composting Toilet Basics
Composting toilets collect urine and feces — referred to as humanure in the rest of this chapter — and treat it completely on-site, until it is transformed into useful compost or humus.
This category of treatment system does not include common pit outhouses, which do not provide ideal conditions for the conversion of humanure to compost, though given enough time the material in a pit toilet can undergo this transformation.
There are three common types of composting toilet:
Bucket toilet — This low-tech version of the composting toilet uses a bucket or similar portable receptacle placed under a seat/container to receive humanure deposits. Sawdust, wood shavings, chopped straw or another form of cellulose material is used to cover each deposit in the toilet, helping to reduce odor, absorb urine and provide aeration. Once full, the bucket is emptied into an outdoor compost heap. Here the material is layered and mixed and covered with more cellulose material, providing the right conditions for the natural conversion to compost/humus.
The indoor toilet construction is usually provided with passive or active ventilation, but no water connection or flushing action is used.
Self-contained toilet — These units provide a seat over an integral composting tray in a single, self-contained structure. Humanure deposits are received in the tray and provided with the appropriate conditions for composting action within the unit. These toilets all use some form of mechanical ventilation to reduce odor. Excess urine may require a separate handling system, or heat may be used to speed evaporation. Due to limited storage capacity, these toilets normally use some form of mechanical action and/or acceleration for the composting process and are only suitable for low numbers of users or for intermittent use.
The compost tray is removed from the unit when processing is complete or when the tray is full. It is often necessary to have an outdoor compost heap to receive material from these units, as it can prove difficult to complete the composting process within the unit.
Some models of self-contained toilet use chemicals or high heat to “cook” the humanure into a benign state. The material from these toilets is not useful compost, as the biological activity that creates rich, useful soil has been killed off.
Remote chamber toilet — A toilet (dry chute or low-water flush) sits above a large, enclosed chamber that receives humanure. The chamber is of sufficient capacity and design to contain and process a high volume of completed compost.
Units handle humanure in various ways. Some use heat and/or evaporation to rid the chamber of excess urine and water and speed the composting process, while others retain and process all material. Mixing or stirring capabilities, misting sprayers and rotating trays are options offered by certain manufacturers. Vacuum flush, allowing the toilet to be level with or below the height of the chamber, is also available.
Some units gather excess urine after it has passed through the bulk material in the chamber and retain this liquid as a high-quality fertilizer. This makes best use of the potential value of all material entering the toilet, as up to 80 percent of the nutrient value in toilet waste is in the urine. Once transformed into nitrites and nitrates after passing through the biologically active compost solids, the liquid can be a safe and low-odor fertilizer.
All chamber-style toilets provide humanure with enough time and adequate conditions to fully convert to compost before being removed from the unit. These are the only units that do not require additional outdoor composting capacity.
Types of waste handled
– Black water (though most systems are waterless)
Tips for successful installation
- Understand the maintenance requirements of any type of composting toilet before committing to installation. All require some maintenance, and dealing with humanure is not for everybody. Some units require infrequent maintenance, others daily.
- Check local codes before planning for a composting toilet. They are an accepted solution in some codes but not in others.
- Check local codes for the legal status of composted humanure. Though a good deal of documentation exists to show the material is biologically benign, some jurisdictions require compost to be treated as hazardous waste.
- Some types of composting toilets require specific layout arrangements that must become part of the home design.
- Mechanical ventilation is part of most composting toilets, requiring an exit tube that passes through the roof of the building with as straight a run as possible.
- Plan for an easily accessible route from the point of removal to the outdoors, to facilitate emptying of the toilet or chamber.
- Be sure there is sufficient provision on the property for units requiring outdoor composting facilities, and that the process of finishing humanure compost outdoors is well understood.
- When using commercially produced units, follow the manufacturer’s instructions for successful installation.
Pros and cons
Composting toilets are the only form of toilet that does not treat human excrement as waste, and rather as a potentially regenerative material for amending soils and fertilizing plants. A large environmental problem is thereby transformed into a solution to soil depletion, creating more robust growing environments.
The composting of humanure is not without issues, and untreated or partially treated material can be contaminated with pathogens that are potentially dangerous to humans and animals and can contaminate soil and ground water. There is a growing body of evidence that complete composting of humanure is relatively easy to accomplish reliably, but the correct conditions must be understood and created.
Simple bucket toilets and appropriate outdoor composters can be built for as little as a hundred dollars. Complete remote chamber toilet systems can cost between four and eight thousand dollars.
Depending on the type of composting toilet, labor input can vary greatly. Other toilets do not require direct ventilation, and even the simplest composting toilet has more components and longer installation times than a conventional flush toilet.
Skill level required for the homeowner
Installation — Moderate to Difficult. Multiple components and connections can complicate installation.
Use — Easy.
Maintenance — Moderate to Difficult. Some form of regular maintenance is inevitable with composting toilets. Bucket toilets can require daily maintenance to transfer full buckets to the compost pile. Chamber units may only need monthly inspections and annual emptying.
There are many commercially available self-contained and remote chamber toilets. These are typically sold directly from the manufacturer or in specialty shops. Bucket toilets are homemade, with plans readily available online or in books.
Plumbing for any composting toilet system are standard components available through any plumbing supply outlet.
The simpler the toilet system, the greater the durability. Units with heaters and moving parts are more prone to durability issues. Consider the accessibility of parts that may need repair or replacement; if they are in difficult locations (especially if they require emptying of the toilet’s contents) they will be unpleasant to service.
Interest in composting toilets is just beginning to grow, and the technology is likely to develop rapidly in coming decades. There has been a significant shift in understanding about humanure, from a sense of revulsion and the certainty of contamination and illness to an appreciation of the simplicity and value of composting. It will be some time before this shift affects a broad constituency of builders and homeowners, but the research and experience currently being gained in this field by early adopters will be valuable contributions to a technology that is potentially transformative. There is little else in home-building practice that could so radically improve the environmental impacts of our homes.
Build and operating a composting toilet system in a low- or no-energy scenario is straightforward. The bucket toilet is an excellent example of resilient technology, as it not only replaces an energy- and resource-intensive practice, but does so in a way that gives back valuable nutrients to the ecosystem.
Resources for further research
Jenkins, Joseph C. The Humanure Handbook: A Guide to Composting Human Manure. Grove City, PA: Joseph Jenkins, 2005. Print.
Del Porto, David, and Carol Steinfeld. The Composting Toilet System Book: A Practical Guide to Choosing, Planning and Maintaining Composting Toilet Systems, an Alternative to Septic Systems and Sewers. Concord, MA: Center for Ecological Pollution Prevention, 2007. Print.
Darby, Dave. Compost Toilets: A Practical DIY Guide. Winslow, UK: Low-Impact Living Initiative, 2012. Print.
Envirolet vacuum flush toilets
Phoenix composting toilets