Apart from my tribe of lesbian brothers (who are off-grid cabin enthusiasts) I was not surprised that few of my circle have experienced a composting toilet. When I show pictures of my homemade toilet only then have people wondered how they work. There is a high tech expectation that a composting toilet has some internal ability to disappear what is put in it. And while there are sophisticated ones that reduce the solids to a decomposed form through the use of a hand crank, fan and heater, the collection chamber must still be emptied.
In a large house the chamber can be under the floor with an access door to the outside. There is no need to address the after life of poop for a year or so at which point it is no longer poop. But in a tiny house on wheels the process is much more intimate. In a homemade bucket toilet such as mine, my poop (and all my friends' should they gift me with a deposit) is with me for a week to a month lying quietly in a bed of sawdust and toilet paper. I admit that even I had some qualms about this fact. It felt like hoarding of the most extreme variety. And I must quickly avert my mind to the value of engaging in this cycle of nature that turns digested waste into soil and in turn to food again. And the comforting thought that humans carry all the essential minerals in bodily excreta to create soil to grow food that then provides us with essential minerals. This means we carry with us the ability to bring back fertility to a depleted planet. (This life saving factor aptly demonstrated in the movie The Martian.) How wondrous is that? What a complete package we humans are.
Thankfully the poop removal job has been made virtually odorless by the separation of solids from liquids. Modern composting toilets have caught on to this factor. So there are two containers to empty and process, one for liquids and one for solids. The urine being enclosed in a container with a screw top is easily carried out. Some toilets even divert the urine to a container outside for ease of emptying.
Urine being rich in nitrogen and phosphorous and having the benefit of being sterile is immediately useful for fertilizing plants. It must first be diluted with water at least 3 to 1 or it will burn the plant. From my workshop at an eco farm I learned that if mixed with a cup of sugar or molasses, diluted urine is made more accessible to plants. Urine can also be added to the compost pile which would help to keep it moist while the nitrogen and phosphorous is preserved in the resulting compost. Seen here is a urine toilet I visited recently at an eco village that used sawdust to absorb the liquid which was then dumped into a compost heap.
Then there is the removal of solids. In a homemade toilet this consists of removing the bucket inside the toilet and taking it to a dedicated compost container in your backyard. (You can also line the bucket with a plastic bag and pitch it, bag and all, in your garbage can as people do everyday with dog poop.) Commercial composting toilets can be more difficult to empty if they have no removable bucket. The one seen on Tiny House Nation called Nature's Head ($960) requires that the whole toilet be unscrewed from the base and taken outside. Granted the hand crank prompts more decomposition and drying and shrinkage before it needs to be emptied so not quite as vivid an experience (but the toilet paper may still be visible). Such details of compost removal is never demonstrated or even mentioned on the show I've noticed. I suspect it would disturb the viewer and scare off advertisers.
A dedicated compost pile or container for humanure composting is the rule. Rest assured that such a compost pile when done correctly will heat up to the high temperatures required to kill off pathogens. It is the size of the pile that determines if it heats up enough. About a cubic yard will do it. Leaving it for a year will also allow for the digestion of any pathogens by microbes, bacteria and earth worms. The weak link of this system is the rinsing out of the bucket. This must be done over the compost pile warns the Humanure Handbook whose author is amusingly verbose in the history and science of humanure composting. (A boiled down 12 page manual is available here.) Lining the bucket with a compostable bag which is then deposited in the compost pile could work too. I was also intrigued by this research paper by the Natural Resources Conservation Service on composting dog poop on a large scale that describes the process in a few pages of concise instruction.
If you cannot face this poop removal lifestyle there are other tiny house toilet systems to consider. For the complete overkill experience there is a toilet called the incinolet for $1849 that zaps the poop to ash with a jolt of high wattage electricity. Or if you like neat packages another toilet called the DryFlush Laveo for $590 plus disposable liners uses diaper pail technology to wrap each deposit in plastic after all the air is squeezed out. Needless to say both these options fall short for the eco minded and frugal.
Humanure composting has entranced me since I first learned about it in the '90s. It made using clean drinking water as a vehicle for transporting poop to a giant central processing plant seem absurd especially considering the difficulty of getting that clean drinking water drinkable in the first place. Plus all the chemicals added to the sewage sludge to render it "safe" before it is trucked out to farms to be laid on fields as fertilizer under the banner of organic matter. (The nerve.) This chemical interference which includes all manner of poisons thrown into sewers (informative blog devoted to the topic here) and rendering our soil ever more harmful and our food less nutritious. The nitrogen leaching out into our waterways has also caused algae blooms that have rendered beautiful lakes and ponds green and dead. A complete fiasco especially considering that depletion of phosphorous in soil is now a world crisis.
And when I learned from my construction technology class how our sewage is processed locally in huge open tanks which can overflow into the bay after a heavy rainfall, the yuck factor made a composting toilet seem much the simpler safer alternative. (Additional tanks can be built to take care of this overflow from processing plants, but I doubt if this has been a priority in our municipality.)
The flush toilet is so much a part of our society that to contemplate using anything but water to flush our poop off site far away seems heretical. When people balk at composting toilets I see how our modern technologies have so obfuscated natural processes that we no longer understand what is actually safe and what our elaborate centralized systems have done to throw nature out of balance.
Composting was a way to take myself off this land intensive, water wasteful, chemical system and return to a basic, localized mellow process that would improve the very soil around me. In fact my fondness for compost is such that it may have been one of the reasons I have so eagerly embraced the tiny house lifestyle.