Updated May, 2020
Three leading brands of self-contained composting toilets are Sun-Mar, Envirolet, and Biolet. These claim to convert human waste (with peat moss/wood shavings added) to a product resembling dirt, suitable for putting on a compost pile or even to be used directly on flower beds or trees. A comparison of the mechanics of these three toilets, along with on-line user feedback, indicates that Sun-Mar toilets are more likely to perform as expected. The Sun-Mar rotating drum seems to give better control of liquid contents than seen with Envirolet and Biolet devices. Non-electric versions of these toilets often cannot keep up with liquid evaporation, so a functioning liquid overflow tube is essential.
User satisfaction seemed highest with “urine-diverting” toilets, such as Nature’s Head, Air Head, C-Head, and Separett. Urine is directed to a storage container or a grey-water drain. Solids drop into a bucket where they are typically covered with peat moss. Disposing of the relatively dry solids perhaps once a month is straightforward. This type of toilet may be useful in regions of the world that cannot afford plumbing and sewage systems: urine is rich in nitrogen and phosphorus and is nearly sterile, and thus could be used directly as fertilizer, while disposal of the solids alone is easier than dealing with combined liquid and solids.
Fully-Composting Small Toilets
– Sun-Mar, Envirolet, and Biolet
Customer Experiences with Biolet, Envirolet, and Sun-Mar Self-Contained Composting Toilets
– Nature’s Head, Air Head, C-Head, and Separett
User Experiences with Urine-Diverting Toilets
Bucket/Compost System: Loveable Loo
Some Global Takeaways
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A key discovery of nineteenth century science was that diseases can be transmitted via pathogens in human waste. In regions of high population density, this can lead to epidemics if adequate sanitation facilities are not available. A milestone in epidemiology was the 1854 cholera outbreak in London. A physician named John Snow analyzed the incidence of the disease and concluded that the Broad Street public water pump was the source of infection. Even though he had no explanation in terms of germ theory at that time, he persuaded the authorities to remove the handle of that pump. This stopped the cholera epidemic. The well from which this pump drew had been dug a few feet away from an infected cesspool. A replica of this pump still stands in London:
Improved sanitation in the West and in prosperous areas of the rest of the world led to a dramatic decrease in deaths by disease, especially among children. Using water to sluice wastes to a septic tank or to a central treatment plant has proven an effective means to handle these wastes, for single homes and for vast urban population centers. However, an estimated 2.5 billion people, about a third of the world’s population, still lack access to basic sanitation. Those living in rural settings may cope by relieving themselves in the woods or fields, but many live in crowded urban slums and are too poor to install flush toilets with their requisite water supply and sewage piping and treatment facilities. Microsoft founder Bill Gates has attempted to address this problem. The Bill and Melinda Gates Foundation has initiated the Reinvent the Toilet Challenge, to support the development of a “next-generation” toilet which:
- Removes germs from human waste and recovers valuable resources such as energy, clean water, and nutrients.
- Operates “off the grid” without connections to water, sewer, or electrical lines.
- Costs less than US$.05 cents per user per day.
- Promotes sustainable and financially profitable sanitation services and businesses that operate in poor, urban settings.
- Is a truly aspirational next-generation product that everyone will want to use—in developed as well as developing nations.
These are lofty goals for the humble commode. Some of the technologies put forward to meet this challenge involve high cost or high tech components whose maintenance could be problematic. For instance, here is one of the prototype sanitation units developed in response to the Gates challenge:
While I salute the enterprise and ingenuity embodied in this device, my guess is that any viable sanitation solution for the masses will likely involve some much lower-tech approach. Here we examine a suite of small composting toilets whose descriptions are available on the internet. In North America these devices are sold primarily for use in vacation homes or on boats. We will evaluate them for these purposes, based mainly on online comments. From an engineering point of view, we will examine the key materials-handling aspects of these different models, and attempt to predict which features might be most useful in a “global toilet”.
Fully-Composting Small Toilets
There are a number of composting toilets sold where the compositing unit is located on a floor below the actual throne. These “remote” composting toilets include the venerable Clivus Multrum and the newer Phoenix. These are large and fairly expensive (typically over $5000) units, sometimes servicing commercial establishments. Sun-Mar, Envirolet and EcoTech offer remote composting toilets for around $2500-3000 for full-time family use. (All prices here are approximate).
Several manufacturers offer compact or “self-contained” composting toilets where the composting chamber is built into the toilet itself. These toilets are the focus of this review. These units typically include apparatus for stirring the wastes to promote aeration. The higher-capacity models use electric heating and air flow to evaporate urine. To handle excess liquid accumulation, an emergency liquid overflow tube leads to some outside drainage spot such as a gravel-filled hole. These liquids are fecal-contaminated “black-water”, so they require careful disposition.
Forced-air ventilation to the outside serves to promote urine evaporation and mitigate odors. Final composted product is removed from a tray or drawer situated below the main chamber. This may or may not require further composting.
Some models are aimed at sites with only solar electricity. These toilets would have 12-volt motors for the ventilation fan, and no electric heating of the main toilet. Non-electric models are also made. These rely on natural convection up a vent stack to move air through the toilet.
Three leading manufacturers of these devices are Sun-Mar, Envirolet, and Biolet (Mulltoa). We will describe the workings of these devices, and note the positive and negative comments and reviews from the internet.
Sun-Mar Self-Contained Toilets ($1850 for Excel model)
The signature hardware feature of Sun-Mar units is their drum-shaped composting chamber, as shown in the figures below. Shown on the left is the Excel, which is their most popular model. This is claimed to service up to four people full-time. Like the other manufacturers, Sun-Mar makes units of varied sizes and capacities.
Waste drops into the drum through an inlet port on the top side. A bulking peat moss/ wood shaving mixture is also added daily. Liquid drains from the drum through a screen down to the evaporation tray, which can be electrically heated. Every few days the user turns a crank to rotate the drum, to aerate and distribute the contents. The unit is designed to maintain the optimal moisture content (40-60%) for composting. The door over the inlet port is automatically closed during rotation. Every few months, depending on usage, it is time to drop some material from the drum to the finishing tray. This is done by releasing a locking switch and rotating the drum backwards. The material then sits on the finishing tray for at least a month to finish composting and to dry off. If all goes well, the final product is dry and ready to be strewn upon flower beds:
Envirolet Self-Contained Toilets (e.g. MS-10 $2400)
Envirolet claims their main AC-powered MS-10 model can handle six full-time users. Their 12-volt and non-electric models have lower capacity, since they cannot evaporate liquids as fast.
With the Envirolet self-contained toilet, the user opens a trap door, does his business, and closes the trap. The waste drops onto a perforated holding tray. Warm air is blown across this tray to evaporate liquids. Peat moss (daily) and Compost Accelerator (weekly) are added to aid composting. About once a week the upper handle on the front is pulled back and forth to move “mulcherator” metal blades through the contents in the holding tray, for distribution and aeration. The contents are emptied several times a year. From the operation manual, the procedure for emptying is as follows: (a) Don’t use the toilet for 2-3 days. If contents still look wet, add dry peat moss and stir and wait. (b) Remove the bottom panel in front. (c) Work the lower handle (Rake Bar) back and forth a few inches to get material to drop down from the bottom of the main chamber to the emptying tray. Keep checking that the tray is not getting overfilled. (d) You may need to remove more than one tray-full. Ideally the product is dry and finished, similar to the Sun-Mar product. The material can be left for several weeks on the emptying tray within the toilet to dry further, as long as the material in the main chamber is not so wet that liquids drip onto the emptying tray below.
Biolet Composting Toilets ( $1800 for Biolet 10 [3 users], $2800 for Biolet 65 [4 users] )
The Swedish Mulltoa toilets are sold as Biolet in the U.S. and Ecoethic in Canada. Waste drops into a main compost chamber. Warmed air is circulated across the top of the chamber to evaporate liquids. Mixing arms attached to a central shaft distribute and aerate the contents. The trapdoor sealing the opening down into this chamber is normally closed, but opens mechanically when the user sits down on the seat. Thus, the user typically does not see the contents of the chamber. The toilet is initially loaded with several gallons of a special mulch mixture sold by Biolet, and another half-cup is added after every fecal use. The user manual gives a recipe if you want to make your own mulch. It is mainly fine (peat moss) and coarse (wood shaving) fibrous material, plus a little soil, molasses, perlite, and grain hulls.
After each use of the toilet, the mixing shaft is rotated, by hand or automatically by electric power. With each mixing event, some material filters down through holes in the bottom of the composting chamber and onto the humus tray below. Excess liquid will also accumulate with the solid material on that tray. The user needs to monitor the dampness of the material in the chamber, and adjust the heater thermostat accordingly. If the heat setting is too low, the material will be too wet to compost well and be hard to stir, and fecal-contaminated liquids will make a sloppy mess on the bottom humus tray and possibly overflow the tray into the base of the toilet. If the heat setting is too high, the material will dry out and become too hard to turn the mixer.
Every six months, or sooner if needed, the humus tray is emptied. It is recommended to first spread out a plastic sheet on the floor. If the liquid level inside is high, the humus on the tray is likely to be wet, and it may be necessary to carry the toilet outside to empty it. Wet or merely moist, this product should be placed in a compost pile for further stabilizing.
Biolet also offers the BTS 33 ($1200), which seems to be the essentially the same as the EZ-Loo Air and the Biolet 30 NE. This has few moving parts, and is aimed at sites with no electricity. The human waste is deposited in a bin in the toilet. Mulch is added regularly. The bin is changed out or emptied when it gets full. Air is drawn through the unit and up a vent pipe by natural convection. Liquids that overflow the bin are drained through a drain nipple.
Customer Experiences with Biolet, Envirolet, and Sun-Mar Self-Contained Composting Toilets
The vendor websites provide plenty of testimonies from satisfied customers, so these devices do work for some people. However, there are a number of complaints to be found on more neutral sites like Amazon. (I will assume these comments are genuine, although they could be the work of trolls or shills).
A serious problem is that the liquid overflow drains are prone to plugging with goo and fine mulch material, which can lead to fecal liquids dripping out onto the floor: “When the drain clogs you never know it till you walk in the bathroom and the floor is covered with brown stinking pee/crap soup. Its horrible”. The user might need to regularly reach deep inside the unit to proactively keep the entrance to the drain cleared. Also, it is important to ensure the drain tube is sloped downhill over its entire length.
Biolet and Envirolet products seem to come in for the most criticism. There are many passionate and seemingly well-grounded complaints about these units, e.g. at Compare The Brands , at The Poop Report , and (regarding the Biolet 30 NE) at Amazon. For instance, a commenter at The Poop Report wrote:
I also have an envirolet self-contained electric model. Two of my neighbors do as well. We all have frustrations with these units. Just as poop’n steve mentioned, you need to use a stick to move the poop around. The mulcherator doesn’t work well. The unit needs to be emptied frequently, and because it’s a continuous composter, you always get fresh, uncomposted poop mixed in with the stuff you’re trying to get rid of. Flies get in, but if you screen the vent to keep flies out, the unit leaks water back inside and makes a mess. The rake bar usually gets stuck, so you can’t use the nifty emptying tray, and instead you need to empty the unit with a trowel, mixing fresh poop in with your composted poop. I have a PhD in ecology, and I’ve been composting out in the garden for 20 years. But I still find this toilet incredibly fussy. Either it gets too dry, and the poop turns into rocks and stops composting, or else it gets too wet, and turns anaerobic. Toilet paper doesn’t break down. On and on. Don’t get me wrong–I’m all for composting toilets. But get a remote model! And get a batch model, so that your poop can compost separately before you empty the unit. Continuous, compact models don’t work.
Liquids management seems to be a key challenge. It may be that the users are not following all the instructions carefully. Just pulling out a product tray without taking care and time (up to several days of avoiding toilet use) will likely result in wet, nasty product. However, the design of the Envirolet and Biolet toilets allows liquids to easily get out of balance. These systems rely on warm air circulation to evaporate moisture from the solids. Perhaps these vendors should devise an electronic sensor for the moisture level in the compost in the chamber, which would then automatically adjust the heater to maintain the desired moisture. Another problem seems to be unrealistically high claims for the number of full-time users; probably these units cannot actually evaporate the liquid fast enough for four to six people, even with electric power. The capacity of the non-electric versions will be even lower, especially in humid regions where liquids will not naturally evaporate well. These versions will be especially dependent on functioning overflow drains.
User satisfaction seems higher for Sun-Mar toilets than for the other two vendors. The drum design gives good aeration without trying to force mixer blades though the solids, and allows excess liquids to immediately drain away from the solids. Having a tray dedicated to liquid evaporation allows its heater setting to be automatically controlled. The isolated product tray allows material to sit there for weeks while finishing and drying out. Also, Sun-Mar seems to rate the capacity of its units more realistically. Nevertheless, even Sun-Mar units require attention and adjustments, are subject to occasional mechanical failures and insect infestations, and have a few deeply-dissatisfied customers (especially for the 12V or non-electric models).
A remote composting toilet allows a much bigger waste-handling unit to be located on a floor below. Most of these remote units have similar moving parts as the compact versions, but with greater capacity to evaporate liquids. Ecotech offers a batch “Carousel” model, which has four separate compartments into which the waste drops. When a compartment is filled, it is rotated away to quietly compost for several months, and a new compartment is positioned beneath the throne.
Regarding the compact units in general, Toilet-Composting.com opines:
Because of their small size, self-contained composting units only have a limited capacity. If there are more than two individuals using the toilet year round, a self-contained composting toilet system is not for you. In fact, even two individuals may overburden many models, and you need to choose your model carefully if for more than one individual. Self-contained composting toilets are probably most ideal for occasional usage in cottages or seasonal and vacation homes, or for year around usage by a single individual.
Another class of small waterless toilets solves the problem of liquids by separating them at the source. Part of the waste opening is occupied by an inclined tray which directs the urine to a different destination than the solids. The solids typically drop into a mulch-filled container, which is stirred with a crank to mix the solids with the mulch. Four such toilets are discussed here. The first three units were initially developed for use on boats, so they are compact.
Nature’s Head ($950)
Two views of the Nature’s Head toilet are shown above. The lower chamber is initially filled with 2 gallons (1 U.S. gallon= 3.8 liters) of composting material, such as dampened peat moss or similar material. Urine runs to the front of the toilet, and drains into the liquid waste vessel. Reportedly, the urine-diverting feature is not hard for users (men or women) to get used to. Some mindfulness is required regarding one’s positioning.
The trap door is opened with a lever for solids deposition into the lower chamber. After use, the crank is turned several times to mix the solids into the peat. The unit comes with an electric exhaust fan installed. The user runs the vent line to the outside as part of the installation. Air flow through the unit flow prevents smells, and provides fresh air for the composting process and for drying the solids (which shrinks their volume). Below is a view down into the lower chamber, showing the agitator which is turned with the crank.
For two people with full-time use, the liquid waste vessel (2.2 gallon capacity) is emptied about every two days and the solid waste needs to be emptied every 1-2 months. As feces dry down and decompose, their volume decreases considerably. After waiting at least 6 hours from the latest use of the toilet for solids, the top half of the toilet is removed and set aside. The bottom half is carried outside and emptied by inverting with a plastic bag over it. In use, the agitator mashes the solid waste in with the peat moss, so it is aerated, partly dried, and gets a start on the composting process. The material inside the lower half of the unit appears much like plain peat moss, with an “earthy” smell. It should be dumped into an outdoors composting bin to finish it. On a boat, the product can be stored until landfall, then thrown in a dumpster, as one might dispose of soiled diapers. After emptying, the toilet is put back in its place (no need to specially clean it) and refilled with peat moss.
Air Head Toilet ($1000)
The Air Head toilet is very similar to Nature’s Head.( In fact, the Nature’s Head appears to be a heavily-marketed knockoff of the original Air Head). The urine container is easier to remove – -you can just pop it off, without opening the top half of the unit. To prevent soiling the toilet bowl, many users put down a disk of paper (shaped like a coffee filter but flimsier material), make their solids deposit on that, and then open the trap door to let it all drop into the lower compartment. A comparison of Air Head and Nature’s Head features appears on the Wooden Boat Forum . There is an Air Head vs. Nature’s Head vs. C-Head discussion at Cruiser Forums, and also one at the Boat Galley . For any model you are interested in, you can find reviews on YouTube.
A realistic video on use of the Nature’s Head, showing what is involved to carry the unit out of the RV to dump solids, and discussing women’s issues, is here. A similar realistic assessment of the Air Head is here. With both these units, there will be occasional fecal smears in the upper section, which are cleaned off using wipes. Also, a spray bottle of water/vinegar is used to help wash down the urine and deodorize it. Women typically need to move forward a bit to urinate, and shift backward to defecate, in order to get the liquids and solids going where they should.
C-Head Toilet (About $600)
The C-Head has operational similarities to Nature’s Head and Air Head, but is constructed differently. It looks more like a piece of furniture and less like a marine head, and comes in several versions. Pictures of the C-Head are shown below. The black crank handle shown lying on the floor is inserted through the hole at the back of the toilet seat to rotate the compost agitator. Various customized sizes and shapes and finishes (e.g. wood-grained) are available. The “shorty” model can slide into a low space.
Urine is collected in a standard one-gallon plastic jug. Solids go into a 5-gallon (20 liter) bucket, partly filled with peat moss or similar material. The C-head is stirred after use, but the agitator action is different from the other two toilets. The agitator is a small, single-bladed sloped paddle rotating on a vertically-oriented shaft. Rather than mashing the feces, this agitator mainly stirs the peat moss and turns it over, coating the feces and forming them into 2-3 inch spheres whose surface quickly dries out to minimize odors. This form-factor of the solid waste can be advantageous in disposal. For emptying the solids, the internal 5-gallon bucket is removed and dumped into a composting area or into a longer-term storage bucket. Unlike any of the other composting toilets discussed here, the C-Head does not necessarily need a ventilation hose hook-up. Thus, it can be easily moved around. It does not need to be anchored in place. Folks in small RV’s sometimes stash a C-Head in a cabinet, and just slide it out to do their business.
The liquid capacity is about half that of Nature’s Head or Air Head toilets, so for two people it may need emptying every day. This involves raising the top of the unit and lifting out the one-gallon jug. Filled jugs can be stored or emptied as appropriate. One or two full jugs could be discreetly carried in a cloth grocery bag into a public restroom for disposal down the toilet there. Rinsed-out milk or water jugs from the grocery store can be used as additional containers, so fresh containers are easily available. An external urine diverter can be installed to drain the urine to an external tank or to a gravel-filled pit, obviating the need to swap out jugs.
The Swedish-made Separett sends the urine to a drain tube. Forced ventilation of the toilet is required to eliminate smells and to aid solids drying, using AC or 12-volt power.
Normally a trap door covers the opening to the solid waste container, so the user is spared the sight of its contents. When the user sits down on the seat, this flap is automatically opened and the solid waste container below is incrementally rotated so it fills evenly. The user experience is like using a conventional toilet. There is no regular mulch addition and no working of levers before, or stirring of contents afterward. As with the C-Head, the target hole for feces looks larger than for Nature’s Head or Air Head, making it less likely to miss the target and then have to wipe a smear.
The solid waste container is a bucket, lined with a biodegradable plastic bag. After perhaps two months (for two full-time users), the toilet is opened and the waste container is lifted out. It is taken outdoors, some dirt is added on top of the waste, and it sits for six months with a loose lid on it to inactivate any human pathogens. Then it can be added to a mulch pile for final composting or discarded elsewhere. Thus, there will always be several containers aging in the back yard. Or, as with the other urine-diverting toilets, the solids could put in a dedicated composting setup or securely wrapped in plastic and thrown into the regular trash.
The flagship Separett Villa 9200 model costs about $1300 in the U.S. The Villa 9210 model (about $1100) is the same except it has a less-powerful fan which can run off 12 volts DC or a 120 volt AC converter.
Separett now offers the stripped-down Weekend 7010 model for about $700. It is smaller-sized to fit in smaller spaces. It has no moving parts except for the fan (no sliding trap door or bucket rotation), so when you lift the lid to use it you get a view of the uncovered feces in the bucket.
RV users of the Separett pipe the minuscule urine flow to the black water tank, or to the gray water tank for dilution. Pulling out the plastic bag lining the poop bucket for solids disposal is an easy task compared to regularly churning the other models and every few weeks carrying the unit outside (for Nature’s Head and Air Head) and tipping it upside down into a disposal bag, and sometimes having to clean out the entire solids container.
User Experiences with Urine-Diverting Toilets
In on-line forums and reviews, user reports on all four of these devices have been overwhelmingly positive. They perform exactly as they claim. The handling of a clear liquid stream and of a fairly dry mulch/solids accumulation is straightforward. These toilets can handle visits from a beer-swilling crowd, as long as the host keeps up with emptying the urine collection vessel. For a fixed application like a vacation home, the chore of emptying the urine can be eliminated by installing a drain tube for the liquids. Because this stream is clear liquid with few pathogens, it can be hooked up to a gray-water drain system, or drained to a small gravel-filled pit. A heater for the outside portion of the drain line might be needed to prevent freezing in winter.
There are differing opinions on handling used toilet paper with these commodes. North Americans are used to dropping all used toilet paper down to be flushed away. In much of the rest of the world, used toilet paper goes into a little separate trash can with a swinging lid and lined with a small plastic bag. Whatever you add to the solids bucket will force you to change it out sooner, and most toilet paper (apart from special RV paper) does not compost as quickly as the human waste. There are some reports of long strands of used toilet paper getting wound around the stirrers of some of these toilet models. Users often have a separate waste container for the TP, such as the little trash can with a lid, or a plastic jar with a very wide lid (e.g. from Costco mixed nuts).
With the C-Head, the TP may just float on the surface of the medium – – not harmful, but not mixing in. The C-Head site notes, however, that “flushable” wet wipes can be disposed in the device; because the wet wipes have higher density, they get pulled down into the dry solids medium, and they will compost eventually. Such wipes are available in bulk for about 3 cents apiece at Walmart, and may provide an intrinsically more comfortable wiping experience.
A fold-up urine-diverting toilet is available for camping or emergencies. With this Rescue Kit, liquids go into a tube which can drain into a jug or a hole in the ground, while solids go into compostable bags. A do-it-yourself kit is also available:
Urine-diverting toilets are also made for use in a squatting position, which is common in southeast Asia.
Bucket/Compost System: Loveable Loo ($50 – $300)
The “Loveable Loo” has a following among the ecologically conscious. Popularized by “humanure” apostle Joseph Jenkins, it consists of a wooden box with a toilet seat on top, and a large (e.g. five-gallon) plastic bucket within. There is a bin of sawdust nearby, with a scoop in it. After you do your business, you throw a scoop of sawdust on top of it. There is reportedly almost no odor, if sufficient sawdust is used. The use of peat moss is frowned upon, since that is not a sustainable material (peat is cut from bogs far faster than it can regrow).
About once a week, a new bucket is swapped in. The full bucket is covered with a lid and carried to an on-site composting station. A typical composting station might occupy about 4 feet by 13 feet, consisting of two composting bins (one for this year’s waste, the other digesting last year’s waste) with a roofed sawdust pile in the middle. The bucket’s contents are dumped on the active pile, and more sawdust is added on top. The bucket is then rinsed out. After sitting for a year, the humanure is transformed to clean, fertile compost.
For $299, including shipping, all this can be yours:
Many users make their own toilet box, and just purchase a toilet seat and some buckets. Most user comments for this toilet are enthusiastic. The folks who install this system are typically self-reliant and are proud of living out a commitment to sustainability. The danger of spreading infections is low if humanure compost is used only on one’s own family garden.
However, the carrying and emptying of the filled buckets is not a task that a small or frail person can do comfortably and safely. Many people are averse to handling the waste of non-family members. A writer at Toilet-Composting.com recounts his experience with this system in an eco-village in Missouri:
A rotational system was put in place whereby each member had a shift for emptying and cleaning the five gallon buckets into the humanure compost bins. It is probably no surprise that this rotation was not very popular in the village. Many members came up with often quite elaborate excuses to get out of the humanure rotation when their turn came up, and it was a source of considerable tension in the village…During the hot summer months, the compost buckets became quite foul smelling and also very liquid in nature, so it was difficult to empty them into the bins without having quite a bit of fecal matter splashing onto your clothes and body.
The basic bucket can be used with an even smaller footprint, by placing a toilet seat directly atop it. For short-term use, the Luggable Loo (about $30) gets favorable reviews. Users typically line it with a plastic bag and add material such as lightweight (preferably not clay) kitty litter or peat moss which absorbs essentially all the liquids. The used bags are often thrown in the trash, although they could be emptied onto a compost heap. This is not meant for extended use by large families, but seems to work fine for a weekend of camping. Toilet paper can be dropped into the bucket.
This bucket system can work well on a car trip where you carry along some solid litter, and you pass trash cans where you can dispose of your bags of waste. Urinating into some small container and dumping that in the woods or in a sink, as appropriate, can reduce the liquid load on the main bucket. Adding a tablespoon (15 ml) of a gellifying powder like Reliance Products Bio-Gel Waste Gelation will absorb a lot of liquid, which can reduce consumption of solid litter.
A boater who did not have space for any of the composting toilets described above reported success (e.g. no odors) using the simple 5-gallon bucket approach, adding sawdust after each use. He uses sawdust from compressed pine pellets. For a typical couple, the plastic bag lining the bucket is to be removed every few days, and sealed, stored and later thrown in a dumpster (which is legal) or possibly composted at home.
Some Global Takeaways
Even gadget-savvy North Americans can be challenged to make in-situ composting toilets work for them. This suggests that these devices would not translate well to more traditional cultures. It remains to be seen whether a novel, more fool-proof small device can be developed which economically performs desired transformations on human waste within a user’s home. Positive results for Latin America are claimed for larger, remote-type composting toilets built to serve large families or small neighborhoods, and serviced by professionals.
Collection of combined (liquid and solid) waste by low-wage workers, and careful composting at central locations by highly-trained workers, seems like a viable model for sanitation in very low-income areas. To kill off all pathogens in human waste requires certain combinations of temperature and time for the compost, and care to not mix fresh waste in with aged material. Because of the high nitrogen content of urine, additional cellulosic mulch must be added to achieve the optimal carbon:nitrogen ratio for composting.
If the users can adapt to them, urine-diverting toilets offer some advantages. This Wikipedia article describes projects using urine-diverting toilets in Haiti, South Africa, and elsewhere. The urine is typically directed to a pit, leaving a greatly reduced volume of the solid waste to deal with. The solids are collected to be composted, or to be dried down to kill pathogens.
The major nutrients in plant fertilizer components are nitrogen, phosphorus, and potassium. Urine contains most of the nitrogen and potassium, and about half of the phosphorus, produced in human waste. Urine is relatively sterile, although this is not guaranteed. With proper precautions, the separated urine can be directly applied as fertilizer, as described in Scientific American (“Gee Whiz: Human Urine Is Shown to Be an Effective Agricultural Fertilizer”). This usage would accomplish at least some of the goals set out in the Gates Toilet Challenge.
Some time after writing the article above, I was asked to recommend an economical toilet for someone to install in a makeshift apartment section of their house, where a visiting couple might use it several days a week and where no existing plumbing was available. This forced me to revisit this topic and delve into some of the finer differences among the urine-diverting toilets. This type of toilet was the only one I considered, since it seems far superior to the non-diverting toilets like Sun-Mar or Envirolet: besides being less expensive, the urine-diverters are less problematic to operate and take up less space.
For a toilet in a fixed dwelling that needs to service more than two people full time, the Separett provides a number of advantages. No monitoring and emptying pee containers, no special instructions for guests beyond watching where they aim, and no adding extra composting material. The main Separett model costs significantly more than the other brands. Since the feces are not covered by any composting medium, it absolutely requires installing forced ventilation to the outside, as well as running the urine tube to some external pit or separate tank. The ventilation dries down the poop volume, which, together with the absence of added medium, makes for fairly long times between changing out the poop bucket. The Separett looks classy, much like a regular toilet.
However, the Separett may be overkill for just two people on a limited budget. This leaves the three toilets which were originally designed as “heads” for use on boats (Air Head, Nature’s Head, and C-Head). In general, users report very high satisfaction with all of them, so it is hard to choose among them. As noted above, the Air Head and Nature’s Head are extremely similar, and are perfectly good products with enthusiastic users.
However, after sifting through a lot of user comments and reviewing the product specifications, I ending up leaning towards the C-Head for this particular application. The 1-gallon (4 liter) pee container change-out is easy and foolproof, even though it is more frequent than with the 2-gallon liquid containers for the Air Head or Nature’s Head. (C-Head does offer a larger custom 1.5 gallon urine tank).
Likewise, emptying the C-Head solids container is very trivial. This involves lifting out a lightweight bucket about 30% full of dryish solids (a one-handed task) and pouring into a bag or a 5-gallon holding bucket. In contrast, the Air Head and Nature’s Head require disassembling the unit, and carrying the whole bottom half of the unit to a safe area, fitting a trash bag over the top, and flipping it all over to dump the contents into the bag. It would not bother me to do this, but I think it would stress my wife if she had to do it in my absence. The C-Head solids have to be changed more frequently than with the other two, but in my opinion, the ease of emptying more than compensates. That seemed to be the consensus of the C-Head users in this long and useful compilation at the Boat Galley of comparative comments by boaters who had installed either Air Head, Nature’s Head, or C-Head toilets on their crafts. See also positive comments and practical tips here and here by other C-Head users.
Because the C-Head solids are emptied more frequently and because the feces tend to empty more thoroughly (because they are in the form of chunks instead of being smeared around, and because the C-Head chamber has fewer nooks and crannies), the C-Head is less liable to insect infestation. Also, the chunky solids with the C-Head can be scooped out with a big kitty litter scooper and disposed separately, if you are on a long cruise and really want to minimize the volume of your waste disposal and the amount of fresh peat moss to add.
The C-Head design seems less prone to fecal smears inside the “bowl“ than its competitors. All the parts of the C-Head are contained within the outer, leak-proof shell, so even if there is some odd user error that causes a drip or overflow, it would all be contained within that shell. In contrast, the Air Head has no catch tray under the urine container and the Nature’s Head has only a partial catch tray, and there have been instances of users getting the solids mixture in an Air Head or Nature’s Head too wet, and having fecal fluid drip out the side, through the bearing for the agitator.
Besides all this, the C-Head is several hundred dollars cheaper, and reviews show that you can probably get by without installing a fan if the toilet sees only moderate usage (e.g. most of the time only used by two people), especially if the “bathroom” has reasonable air movement. Providing a powered fan and running a vent line out through an exterior wall may or may not be a big chore. See here for an entertaining and educational video of amateur Jason Wynn’s five-day ordeal in installing a powered vent line in his RV for a Nature’s Head. Boaters with a C-Head often run the attached vent hose out through a nearby bulkhead and just let the breeze provide ventilation.
Anyway, for what it is worth, this was my thought process for recommendation of a low-cost, low-effort installation of an auxiliary toilet.
Update May, 2020: After further reading and reflection, I still find the C-Head to be the most attractive of the urine-separating toilets. However, a number of writers on the internet claim that the simple 5-gallon bucket (Luggable Loo or similar versions) works perfectly well, if you add enough dry medium and change out the liner bag when it gets much more than half full (say 3.2 gallons or 12 liters of waste plus medium). There is reportedly no offensive odor, even though the urine and feces are mingled. (In terms of biochemistry, the addition of plant cellulose can inhibit the enzymatic reactions that produce objectionable odors, and the aerobic conditions and short residence time in the bucket may prevent anaerobic bacteria from generating foul sulfur gases). The single bucket makes for an easier user experience. It eliminates all the fuss over precise positioning of private parts and wiping smears of feces and menses and spraying with vinegar, and turning cranks and disposal of toilet paper and cleaning out poopy solids containers. It does not require a ventilation hose to be installed and a fan to run 24/7 (although some ventilation in the bathroom is probably a good idea). Users mainly just have to sprinkle in the appropriate amount of medium after each use.
The practicality of the single bucket may depend on how much it is used, how much the users eat and drink (i.e. whether the bag must be changed out every day or every two days or every three days), and how easy it is to dispose of these heavy bags of moist waste. Full time usage would entail steady consumption of stout plastic bags as well as a lot of the solid medium. As noted above, users can practice a low-tech version of urine separation by peeing into a separate container for separate disposal, in order to reduce the load on the main bucket. This is straightforward for men to do. I am told on good authority that it is possible for women as well, though it may not be something that one would ask a casual visitor to do. Or, have two buckets-with-toilet-seats side by side, one for solids and one for urine (assuming users have reasonable control; when in doubt, use the solids bucket, to keep the urine bucket always uncontaminated with solids). Again, the practicality of this separate liquids handling would depend on whether there is a convenient and responsible place to dispose of it.
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A Separett equivalent
I noticed on the C-Head web site that they offer a “churnless” version, with no solids stirrer. The solids container is just an empty bucket, which can be lined with a compostable or non-compostable bag, depending on whether the solids will be disposed into a composter or into the regular trash. The assumption here is that the user will sprinkle composting medium over the solids after each deposit. This is a reasonable approach, and has various pros and cons compared to using a hand-cranked stirrer to cover the feces. There are less moving parts, and this makes it easy to drop toilet paper down into the solids container, although then the solids will likely have to be changed out sooner.
However, if you install forced ventilation on a “churnless” model to ventilate the solids container per the C-Head Owner’s Manual , there should be no need to regularly add medium to the solids container. The feces will dry out faster, with no odor in the bathroom. If you also used the optional external urine diverter to run the urine to an external gray-water system or pit in the ground, you would have a toilet which is functionally equivalent to a Separett Model 7010 for about the same price. The only maintenance would be to remove and dispose of the bag of solids maybe once every 2 months. The Separett looks sleeker, but the C-Head has the advantage that it could be readily reconfigured to use a urine collection container and to do stirring of the solids container, if a different application is desired later.
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GTG Composting Toilet: Recent churnless model
I just (May, 2020) became aware that Sun-Mar now offers a urine-separating toilet, called the GTG Composting Toilet, for about $620. Functionally, it is essentially the same as a ventilated “churnless” C-Head: Urine goes into a urine vessel in the front, and feces drop into a bucket in the back, with no cranks or paddles to churn the solids. The urine vessel is medium-sized (1.85 gallons or 7 liters). The solids bucket is easy to lift out, or you can line it with a plastic bag and just lift out and replace the bag. Here is a view of this device from the back, showing the vent fitting for the included ventilation fan.
To get at the urine and solids vessels, you remove the liquid/solid separation plate, as shown:
This model gets mixed reviews. It is relatively compact and simple. Unlike the other urine diverting toilets, you can’t see from the outside how full the urine vessel is, so you have to remove the separation plate/seat and peer down into the vessel to assess the liquid level. Also, removing the plate to remove the urine vessel seems a bit more hassle than lifting up a hinged top as with Nature’s Head or C-Head. A key user complaint is that the liquid/solids separation plate has only a shallow angle for liquid to collect and run into the urine vessel, so urine can easily get into the solids chamber. Men may find their private parts dragging in pee. One user improved on this by propping up the back of the unit on a 3/4 inch dowel. It seems to me that a churnless C-Head or the Separette 7010 works better than the GTG.
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Preferred composting media
Peat moss has long been a common medium to add to composting toilets. It is cheap and available in bulk at gardening stores. However, it is for practical purposes not a renewable resource since it takes so long to form in the bog. These days it is preferred to use more renewable media like coconut coir or sawdust or wood shavings. You can buy coconut coir in dehydrated, compressed blocks in most gardening stores. To use it, you break off some chunks and rehydrate it. Wood-based pet bedding such as Aspen Bedding also works well. Compressed pine pellets for horse bedding absorb a lot of liquid, and are available cheaply at feed stores. They can be moistened to soften them so they can be crumbled into sawdust.
What about diarrhea?
The urine-diverting toilets are engineered to handle regular bowel movements. But what if you (and maybe your partner, too, as a worst-case scenario) eat the wrong seafood salad or pick up a stomach virus, and spend the next 12 hours spewing liquids from the near and far ends of your gastro-intestinal tract?
For vomit, it makes sense to use a bucket or a big cooking pot, not the toilet. For diarrhea, I’d guess the Separette (or a “churnless” C-Head) would be unaffected except you’d have to change out the waste bucket sooner than planned. The Nature’s Head manual states, “Vomiting and diarrhea, if not persistent, are unlikely to affect the head function. If increased wetness of the compost results, the situation may be corrected with the addition of a small amount of dry compost medium.” If diarrhea is persistent, presumably you’d have to keep emptying the solids bucket and refilling with fresh dry medium. For the C-Head, the owner’s manual notes that, if necessary, you can remove the usual solids bucket, and line the inside of the unit with a kitchen trash bag, and defecate into that after adding some adsorbent medium.
Disposal of wastes
There seems general agreement that urine is essentially sterile, and can be poured on the ground off in the woods, or walked into any regular rest room and poured down the toilet. Putting the urine onto composting solids can accelerate the composting process and better recycle all the nitrogen and phosphorus in the urine.
Solids can be put onto a dedicated composting pile, and 6-12 months later used as compost for non-food plants. Also, people toss solid waste into pit toilets, if it is contained in appropriate compostable bags.
There is controversy over whether the solids can be disposed of in the regular trash, which likely goes to a landfill or incinerator. I have read statements that putting human waste in the trash is illegal in many jurisdictions. However, baby and adult disposable diapers are trashed by the millions. If there are such laws on the books, I suspect they would only be enforced if someone were creating a real nuisance.
I don’t think having human waste buried in a landfill (which is supposed to have containment for its runoff) would pose much of a health hazard. However, there are concerns to not expose sanitation workers to human waste during the collection phase. Thus, it would be responsible to securely double-bag the solid waste before disposal in the trash, or to permanently seal it into a 5-gallon bucket with a hammered-down lid before tossing it in the dumpster.
Here is a thorough treatment of best practices for managing human waste when hiking far from a toilet. This includes methods for packing out your solids.
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Shrink-wrapping or vaporizing your stuff
Finally – – for those who just can’t get enough of toilet technology, here are links to two oddball commodes I ran across. These push the envelope of elimination, but will likely not win any ecological awards:
( A ) On the Tiny House Blog is a glowing review of the Dry Flush Laveo toilet. Each time after you make a deposit (liquid or solid or both) into this device, you push a button and your waste is shrink-wrapped into a tidy package, which is placed into a secondary accumulation bag, which you can then throw into the trash. No odors, no mess. Comments on that Tiny House blog post include moral outrage over wrapping human waste in plastic and putting it in landfills, answered by others pointing out that this is done all the time with disposable diapers and dog poop.
( B ) The Incinolet zaps the waste at 1200 degrees F (650 C) to convert it all to vapor (mainly water and CO2, I’d guess) and a wisp of ash. It requires a vent line and a dedicated 20-amp circuit. This logo seems to say it all: