This article will explain and feature the composting toilet, an eco-friendly and permaculture-compliant alternative to flush toilets. Different settings of composting toilets will be compared, and both advantages and limitations discussed.
Composting toilets are almost certainly an ancient technology that predates literate society. The simplest composting toilet design possible may involve a hole in the ground to collect human waste, and a supply of carbon nearby, such as sawdust, to assist in aerobic composting. Once composted, the result is sometimes called ‘night soil’.
Composting toilets save water and reduce the requirements for cleaning chemicals at water treatment facilities, and so are eco-friendly. However, the biggest saving lies in constructing houses or even housing complexes from scratch that are intended to be designed around their use.
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The Science of Composting Toilets
Composting toilets utilize the principle of aerobic composting, which is where oxygen is involved in the process of decomposition.
Generally, human waste contains a high concentration of nitrogen, which, when deposited outside of the body, is ready to undergo anaerobic decomposition, or decomposition in the absence of oxygen.
However, anaerobic decomposition takes a long time, and has the side effect of stinking, because bacteria involved in anaerobic decomposition produce methane as a byproduct.
Anaerobic decomposition also happens at a lower temperature than the temperature at which aerobic bacteria thrive, and the anaerobic decomposition process produces pathogens that may contaminate any water nearby, including groundwater.
Instinctively, we learn from an early age to keep anything we consume away from where we excrete, in order to avoid infection and illness.
This can all change when a source of extra carbon is added to the excrement pile. when the pile reaches sufficient size, such as 36 cubic feet, the pile can now undergo even more efficient aerobic decomposition. When done correctly, this can produce a pathogen-free environment and usable soil after some time has passed.
An aerobic pile allows more air flow, which allows oxygen to take part in the chemical reaction. The decomposition involving carbon and nitrogen at an ideal ratio, such as 30:1 carbon to nitrogen by mass, accelerates the chemical reaction, producing more heat, and killing off the bacteria that thrived in lower temperatures.
This decreases the concentration of pathogenic bacteria and allows benign bacteria to proliferate.
The aerobic pile now produces more carbon dioxide instead of methane, so the pile doesn’t stink, and composting toilets used correctly actually stink far less than a traditional flush toilet restroom does immediately after use.
This makes it much more pleasant both to use and to maintain the composting toilet, and allows the waste products to be used productively after some time has passed.
Once a waste receptacle is full and has been emptied outside, it is advisable to wait a minimum of one year before using the ‘night soil’ in any way that would incur a contamination risk.
Where to build them
Composting toilets can be built outside or inside a house, depending on what you prefer. Generally, the main limitation of their construction is that that have to be built on, near, or just below ground level, as there are significant disadvantages and expenses incurred when building them on the second floor or above.
If you are building a house from scratch in DIY fashion, you can consider using composting toilets in place of flush ones entirely. When done correctly, you may not even need a septic tank or sewer connection (local regulations differ on this point, so be sure to check with your local governments,) saving you potential construction costs.
Most jurisdictions do tend to require at least one flush toilet per dwelling. If you’re located in such a jurisdiction, you can, at minimum, install the smallest required septic tank system as all the other toilets will not be connecting to it.
The classical outhouse model of a composting toilet is one of a purpose-built structure in the back yard. One advantage of this method is that it can be built in most yards or properties without modifying your existing house.
Another is that you can use recycled materials to build it, including materials such as tires or plastic bottle eco-bricks that you might prefer to avoid in dwellings.
Possible dimensions for an outhouse can be 4 feet by 4 feet, and ideally, the outhouse is 7 ft high. Most outhouses feature a raised platform inside to sit on or squat above the hole, and then have a gap behind the outhouse to remove the excrement container when it is full. The outhouse is usually built from wood and has a large door for easy access.
Some outhouses have multiple large buckets and multiple holes, so that one can be in use while the other is undergoing its year-long composting process. If the outhouse is a secondary toilet and won’t be used often, you probably won’t need multiple bucket holes, although you will most likely need multiple buckets.
It is also convenient for the outhouse to feature shelves for toilet paper storage, sawdust storage, and hand sanitizer. The outhouse can also feature a sink outside or inside for hand washing.
The most inexpensive and least obtrusive way to build a composting toilet may be inside an existing restroom. You will need a cabinet high enough to sit on – 2’ should be high enough.
The cabinet can be placed against a wall, and have a hole drilled into the top. If you are looking to install a standard toilet seat on it, you can make the hole the same dimensions – 16 ½ inches is the standard round hole diameter in the US.
Don’t forget to order multiple buckets so that your toilet isn’t out of order for months at a time. Also, it is necessary to keep a supply of sawdust within arm’s length of your new toilet cabinet. This will help to prevent unwanted odors. Use your bathroom sink as normal.
Finally, the most cost-effective way to integrate composting toilets into your life is to design your off-grid house around them while your house is under construction, so that you may save the cost of connecting to a sewer or a septic tank, or if this is not permitted, you can build the smallest septic system that is allowed.
With rare use, the septic tank itself will need less maintenance and result in lower costs.
For example, one county in central Texas has the injunction that composting toilets are allowed, but that kitchen sinks still need to connect to a septic tank because of the contamination potential of meat preparation.
So, in this county, if you were planning to skip the cost of a septic tank, you would need to design an alternative kitchen sink system as well as installing composting toilets.
This is a reason that you should always research your local state, county, or city regulations that may support or hinder your off-grid building plans, and be sure to talk to other off-grid building enthusiasts about their experiences in compliance with building codes.
They may have useful tips or workarounds that keep you fully compliant while supporting your off-grid ambitions.
If the path of designing your new home around composting toilets sounds right for you, then it may make sense to design your ground-level restrooms for composting toilets. You can do this by setting your toilet seat on a ledge inside, and by having the bucket that receives the deposits stationed outside, below the toilet seat.
This allows for easy maintenance while keeping your ablutions conveniently indoors. It also doesn’t require multiple bucket slots, as you can use wheelie bins and move one bin out when it is full and move another bin into the space. It is best if you keep a bin unused for six months before dumping it into the compost pile for cleaning.
One last aspect of the construction of composting toilets worth mentioning is that of urine diversion. While urine diversion is not necessary for correct use of composting toilets, many homestead residents may also like to use their urine for fertilizer due to its high nitrogen content.
Avoiding urination into a composting toilet does have the benefit of speeding up the chemical reactions inside the pile and make them smell a little less, because the compost pile is drier.
Urine diversion requires setting up a section of the toilet bowl for urine capture, which is easier to achieve for men and much more difficult for women. It is advised that urine should stand for no more than about five hours before collection.
After collection, dilute the sample 1:5 with water and used liquid fertilizer. Urine is sterile at the time of excretion, but if it stands for more than five hours, it runs the risk of pathogen contamination.
How to Use Composting Toilets
When it comes time to sit on a composting toilet and use it for its intended purpose, you may use toilet paper as normally, and deposit this in the bucket as you would down a conventional flush toilet.
However, the main difference is that instead of flushing the toilet with water, you need to pour sawdust or another source of carbon into the waste collection bucket.
Alternatives to sawdust include paper waste from shredders, coffee grinds, wood shavings, pine needles, chopped straw, peat moss, or wood ash. Wood ash might be the most effective at odor removal, but be warned that if you use wood ash, the bucket can be much harder to clean.
Toilet paper should be used as normal, as toilet paper is compostable. Some commercial toilet papers contain bleach, which homesteaders may like to keep out of their compost because of its antimicrobial properties. For this reason, readers may like to order ‘camping’-style toilet paper instead.
Composting toilet setups are known for sometimes having multiple buckets per unit. This is commonly seen in two settings – one where buckets are very small, which means that they become filled quickly and would require more maintenance. The other setting is more likely in an outhouse on a farm, where farmers may like to use large amounts of compost regularly.
Setups that use composting toilets do require some maintenance. In the video below, David Omick describes how to maintain composting toilets by making sure to have one bucket not in use at any given time.
His buckets have a volume of 55 gallons, and he uses an aeration cranking device every two weeks to speed up the chemical reaction and reduce odors.
How to use ‘Humanure’ safely
If you are using composting toilets, it is recommended that you have a special outdoor composting area dedicated to the processing of human waste, or ‘humanure’.
The site should be located on well-drained, flat soil that is not upstream of or nearby to any vegetables that you may be growing. The site should be prepared thickly with straw, within arm’s length of a straw pile, and within range of a hose pipe.
Once a bucket has been filled, set it aside and mark the date that it was filled. Add some straw to the bucket, leave it outside, and place a screen over the container to keep flies out, and mark the container or area with signs so that visitors avoid any contamination risk.
The site of the compost pile and bucket can be fenced off, preventing access by children, pets, or wildlife. Also, the site can be marked as being for humanure so that visitors know to avoid it. Ideally, homesteaders can use a shovel specifically marked as being only for humanure use, which can be kept in a safe place, such as in a locked shed.
When new humanure is ready to be deposited outside, first make a hole in the center of the pile, and then pour the humanure in. This keeps the night soil aerated without having to turn the pile. Turning the pile is discouraged because this brings more bacteria to the surface of the pile.
While you are working with humanure, gloves and safety goggles are recommended, as well as is wearing an apron and old farm clothes. Having a hosepipe with medium pressure nearby is also useful to help clean any humanure buckets, or any areas where humanure has been spilled.
To clean the bucket, hot water and soap are used to wash humanure off, and the bucket can later be disinfected by bleach or alcohol. This is especially important to do if the bucket is going to be placed inside again.
If the bucket will be placed in your house, leave it outside in the sun for a day first after disinfection.
When humanure has matured for its recommended year-long period, as a final precaution, you can avoid using it anywhere near food you may want to eat (vegetables and herbs) and instead use humanure mostly with bushes, hedges, and larger trees, so that there won’t be contact between any edibles and the soil.
Construction of toilets is strongly regulated in some states and less in others. In general, humanure itself is legal to produce, as long as you keep it on the property it was produced on, and do not sell or give it away.
This means you can only practically produce humanure if you have space for composting, and shouldn’t try to do so in an urbanized setting unless you have private outdoor space.
Frequently Asked Questions
This section will contain some questions that readers may have, along with attempts to answer these questions.
Can you urinate in a composting toilet?
Yes, although it will make the chemical reaction take longer, and the deposits may have a harsh odor. Some composting toilet owners prefer using urine diversion, which then produces nitrogen-rich fertilizer for the garden.
Do composting toilets smell bad?
If used correctly, a composting toilet should not smell bad. Urine diversion may result in less smell, and using a fine, carbon-rich source of additive is more effective at removing odors.
Can you use toilet paper with a composting toilet?
Yes, it is recommended that you use toilet paper. If you prefer clean composting, then buy unbleached toilet paper.
Do you have to empty composting toilets?
Yes, emptying composting toilet containers is required. Humanure is best kept for at least 6 months inside a container before being dumped out and used in a secondary compost pile. This usually necessitates having multiple buckets.
How often do you dump a composting toilet?
This depends on the size of the container and how many containers you have. For a small family, 2x55gallon buckets seems to be plenty to always have a composting toilet in use, while keeping the other one in composting mode for at least six months.
Are composting toilets safe?
Yes, provided sensible guidelines are followed. All regular occupants of the site need to know where the composting toilet is and how to use it correctly. Young children who may use the toilet should be supervised, and pets kept clear.
All occupants should know where composting buckets are stored, which shovel is dedicated to humanure, and where the compost pile with the humanure is. Those whose job it is to clean and aerate the buckets should use safety equipment, such as gloves, an apron, and eye protection.
Do I need a septic tank if I have a composting toilet?
In most situations, the answer is yes. The best way to take advantage of cost-saving in these locations is to buy the smallest possible septic system that is connected to the fewest possible wastewater sources, such as by installing the fewest number of flush toilets on the site that is legally permissible.
How much does a composting toilet cost?
Composting toilets bought commercially tend to cost a minimum of $ 1,000 and less than $ 10,000, depending on their complexity, bucket size, and any added features, such as wash basins, extra buckets, or outhouse structure.
If you have necessary tools such as an aeration crank and a saw, and can repurpose an old cabinet and have access to 2-3 five-gallon buckets, your composting toilet can be very cheap indeed.
The composting site may also require fencing and straw, and you will most likely need to buy a shovel specifically for it. Unless you happen to have the exact materials on your site ready to use, you will probably spend an absolute minimum of $ 150, even if you perform all the labor yourself.
Do composting toilets need water?
Water is necessary for hand-washing when using the toilet, and for use in cleaning composting toilet buckets and disinfecting them.
How big is a composting toilet?
It can be as small as a wooden cabinet that you sit on (2’x2’x2’) or as large as a 4’ x 4’ x 7’ outhouse.
Are composting toilets legal?
No state or federal law is known by the author to disallow composting toilets outright, but some states may require installation by licensed professionals only.
However, there are individual municipalities that prohibit any backyard composting, which would include necessary processing from composting toilets, so in those municipalities, composting toilets are not legal.
This section is intended for educational purposes only, and nothing in this entire article constitutes or may be construed as legal advice.
Are composting toilets sanitary?
Well-designed, regularly aerated, and correctly maintained composting toilets allow informed users to dispose of human waste in a sanitary way. Following the proper guidelines of their use and maintenance helps to keep sanitary conditions comparable with conventional flush toilets.
Not everyone has the means or appropriate property to set up composting toilets and use them, and maintaining them does require some physical effort. However, for those that are in the process of setting up an off-grid or self-sufficient homestead, building composting toilets is one of the most powerful way to decrease one’s reliance on the government.
Composting toilets are not especially simple to construct, coming in at an intermediate difficulty. Once constructed, they are very easy to use and quite simple to maintain, so long as you don’t mind occasional heavy lifting and taking proper safety precautions.
If you have gone to the effort to set up and maintain composting toilets correctly, your rewards will be effective night soil, lesser or possibly even no sewage costs, a cleaner water table, and reduced reliance on the grid. Happy composting!
David Dornbrack is a permaculture designer and author from the Austin area of Texas, USA. He first achieved his PDC in South Africa in 2013, and has since traveled to the world’s prototypical intentional community and ecovillage, Findhorn Foundation in Scotland. He has gardened in three different climate types – Mediterranean, Cold Temperate, and Humid Subtropical. His favorite plants are tomatoes, chilies, and potatoes. He believes that humans function best when interdependent – able to take good care of themselves so that they can be generous and giving to others. He would like to gain experience in house-building, carpentry, and solar electricity installation.