A substantial portion of the wastewater generated from residential and commercial properties comes from toilet flushing. In most cases, potable water is used to convey our pee and poop to a wastewater treatment facility where the human waste products are separated and biodegraded and the water is purified for disposal or reuse. However, toilets exist that use little to no water and therefore generate no wastewater that must be subsequently treated. These toilets are called composting toilets. Although mostly found at campgrounds, national parks and other locations where water supplies are limited and/or where a wastewater treatment system is not available, composting toilets are found in some buildings in urban areas.
Composting toilets use the natural processes of decomposition and evaporation to recycle human waste. Waste entering the toilets is over 90% water, which is evaporated and carried back to the atmosphere through the vent system. The small amount of remaining solid material is converted to useful fertilizing soil by natural decomposition. This natural process, essentially the same as in a garden composter, is enhanced in commercial composting toilets by manipulating the environment in the composting chamber. A correct balance between oxygen, moisture, heat and organic material is needed to ensure a rich environment for the aerobic bacteria that transform the waste into fertilizing soil.
When human waste is properly composted, the end product does not contain any pathogens or viruses (these are destroyed by bacterial breakdown). This nutrient-rich fertilizer can then be used on plants or around the base of trees, as part of the natural cycling of nutrients, reducing the need for commercial fertilizers.
A composting toilet must perform three separate processes:
- Compost the waste and toilet paper quickly and without odor
- Ensure that the finished compost is safe and easy to handle
- Evaporate the liquid
A well-functioning composting toilet requires attention to the following elements:
- isolation: The material should be left to compost in isolation, without potential contact from people, until it is fully composted and safe to handle.
- ventilation: The toilet needs a flow of fresh air, to add oxygen and remove odors. All vents should exit the living space.
- moisture: A composting toilet should not be too wet. Sawdust is used to soak up urine, or urine is diverted away from the feces. If the toilet does not divert the urine, or if a small amount of water is added, the material will need more dry material added or extra heating and mechanical mixing.
- temperature and time: The rate of decomposition is a combination of temperature and time: the hotter the compost pile, the more quickly the process happens. If a human manure (humanure) compost pile is not monitored for temperatures it should be isolated for a long time to ensure full decomposition. In a mild climate this takes a year, while in areas with cold winters it may be 2 years.
- bulking agent: In a composting toilet sawdust covers the material creating air gaps for aerobic bacteria to break down the material. Toilet paper and feces compost through the same process a household food scrap compost bin undergoes. In a dry toilet ash or lime is mixed with soil and added to create a dehydrating environment for breakdown and die off of pathogens. Dry toilets are often used in arid, dry climates where lime and ash are more available than sawdust. Toilet paper cannot be added to a dry toilet, it is usually burned or buried.
There are several options for methods and styles of composting toilets.
Some manufactured composting toilets are certified by NSF, which makes them easier to be accepted by health and building departments. Large manufactured toilets, like Clivus Multrum and Phoenix brands, can be a good option for people who can afford them and don’t want to be involved in the handling process. Small, self-contained composting toilets like the Sun-Mar or Biolet have a seat right on top of a compost container. These are designed for seasonal or cabin use but cannot handle the quantity of feces a household produces on a daily basis. Toilets such as the Separette Villa and Nature’s Head (which includes urine diversion) collect the material in a small chamber, which then must be emptied outside into a larger composting container to finish the process.
Site-Built Systems: Do-It-Yourself
A do-it-yourself ecological toilet is also an option if you’re inclined to be more involved in the process–like by emptying buckets once a week. If you need a permit for your toilet, however, a site built toilet is most likely not an option (though these laws are slowly changing). And if you also have a flush toilet, hooked up to an approved sewer or septic system, you are generally not technically breaking any laws by having a composting toilet. Many states do not have codes regarding composting toilets, nor are there regulations for backyard composting. Site-built toilets look very different from one another, but they all function on the same basic principles as the manufactured types. Composted waste is typically stored for a minimum of one year before being used as fertilizer.
The sawdust toilet is a common DIY option. It is low cost, easy to use and maintain, and produces lots of rich compost. Watch a video or view step-by-step instructions here.
In the past, home-built toilets were difficult (or impossible) to get permits for. Times are changing. Arizona has permitting requirements for composting toilets and is working on a pilot project to create site-built designs approved by the Department of Ecology. Oregon’s REACH code includes guidelines for site-built toilets.
Although North America doesn’t have a sewerless city, there are a few sewerless buildings. One example is the public restroom at the Bronx Zoo in New York City. Faced with an exorbitantly expensive sewer connection they decided to go sewerless, installing large Clivus Multrum composting toilets underneath the bathroom and using all graywater on the landscape. In downtown Seattle, the Bullitt Center, a six story, 50,000 square foot building is outfitted with Phoenix composting toilets. The San Francisco Public Utility Commission’s new office building in downtown San Francisco uses a living machine to treat wastewater, the treated wastewater is used to flush toilets in the building. This system, along with a rainwater catchment system, enables the building to consume 60% less water than similarly sized buildings. See this resource page for more info on these types of projects.
There are even high-tech toilets in development that produce nothing but ash and usable (perhaps even drinkable) water. The Bill and Melinda Gates Foundation, through their Reinvent the Toilet Challenge, is trying to address the problem of the estimated 2.5 billion people that still lack access to proper sanitation.