How to design a metal/masonry incineration toilet that vents outside?

Septic tanks and leech fields are not affordable for everyone.
Flushing toilets need water, inconvenient for arid areas like the Mojave and Arizona-Sonora deserts, and RVs.
These calls for housing and RV designs that do not discharge black water.

While gray water can be discharged as landscape irrigation,  human waste must be sanitized.
There is already several incineration toilets on the market, but they are far from affordable.
Given we already know the design of masonry heaters, how to build heat-resistant masonry incineration toilets?

Let's say, we use electric heat to dry and ignite human waste and discharge the stinky gas up the flue.
I guess the part that have contact with both wet human waste and fire must be sheet steel. Other parts can be masonry.
How to design such metal/masonry incineration toilets? Any existing designs to copy from? Is an ash drawer necessary?

Hi Douglas,
Before delving into the complexities of your plan, have you ever tried a much simpler bucket compost method?
An internet search for "humanure” willbring up lots of good information.

Douglas this thread has instructions for making the compost toilet:

https://permies.com/t/57553/Homestead-Income-Tips

Also, the benefits of a compost toilet are so you can have something for your compost pile and for black soldier flies.

You may have a great idea for an incinerating toilet.

Heat your butt and the outhouse at the same time!

I made an incinerating bucket toilet. Follow the instructions for a sawdust bucket-toilet, but use a steel bucket instead of plastic. When full, swap it with a clean bucket, take the full one, and set it on a (very sturdy) rocket stove to burn. It would be best if this is done outside!!! I prefer to turn it into biochar, so I have a ventilated lid that goes on the metal bucket. At some point I'll probably rig up a tube so the vapors are fed back into the fire.

At least, that was the theory. The contents of the bucket have been breaking down so completely that I haven't had to do a burn yet. I'm only out there twice a week when the weather is warm, and not at all in the winter. If this was for everyday use, you'd definitely need to do a burn periodically.


I've also had an idea for a stationary incinerating toilet, but haven't tested the idea yet. Basically, have 2 tanks, similar to septic tanks but smaller and made of metal, that the toilet could alternate between. When one needs burned, switch the feed to the other one. Then open the valve between the tank and the chimney, and start the fire under the tank being burned. By having the incinerator be the tanks and not the toilet, you simplify a lot of the logistical problems. And by switching between two tanks, you don't have the problem of "I gotta go but the tank is too hot still".

Again, that's just a very rough idea I had. It needs a lot of the details worked out before it can be tested.

Industrially, solids are burned using a fluidised bed. Dry the slurry, crush it to power or lumps. Tip it into a vertical tube, and blow air into the bottom. You are aiming for just enough velocity to suspend the particles to be burned without blowing them out of the top. You obviously need a source of ignition as well.

This system if done properly is clean burning and robust, but needs to be designed well and would be sized for large scale use. Think, toilet waste from a medium sized community. Not and individual toilet. You run into all sort of problems of scale trying to burn tiny masses of material - heat loss to the fabric of your incinerator etc... You would need to supply large amounts of external energy (heat) and have a super insulated system to ensure a clean and safe burn. Way beyond the technical capabilities of a typical cheap DIY system.

We have used composting system here with great success. Incredibly low tech - literally a few plastic buckets and some sawdust free from the local sawmill. Look up the "Humanure Handbook" - available as a free pdf.

Gerry Parent wrote:Hi Douglas,
Before delving into the complexities of your plan, have you ever tried a much simpler bucket compost method?
An internet search for "humanure” willbring up lots of good information.

Thanks for mentioning this, Gerry. Unfortunately, compost toilet is culturally incompatible with many residents and regulatory bodies. While desiccating and incineration is widely known as a reliable way of disinfecting, composting is not.

Michael Cox wrote:Industrially, solids are burned using a fluidised bed. Dry the slurry, crush it to power or lumps. Tip it into a vertical tube, and blow air into the bottom. You are aiming for just enough velocity to suspend the particles to be burned without blowing them out of the top. You obviously need a source of ignition as well.

This system if done properly is clean burning and robust, but needs to be designed well and would be sized for large scale use. Think, toilet waste from a medium sized community. Not and individual toilet. You run into all sort of problems of scale trying to burn tiny masses of material - heat loss to the fabric of your incinerator etc... You would need to supply large amounts of external energy (heat) and have a super insulated system to ensure a clean and safe burn. Way beyond the technical capabilities of a typical cheap DIY system.

We have used composting system here with great success. Incredibly low tech - literally a few plastic buckets and some sawdust free from the local sawmill. Look up the "Humanure Handbook" - available as a free pdf.

Allow me to calculate the energy cost of incineration here:
Average urine production in adult humans is around 1.4 L of urine per person per day, and 0.4 kg of feces.  For simplicity, we assume this is 1.8kg of water.
specific heat capacity of water is 4.184J/gram/Celsius , plus 2260 J/gram for vaporization.

Boiling 1.8kg of water to vapor from 24C room temperature costs (76*4.184+2260) * 1800 = 4640371 J = 4.64MJ = 1.29 kWh

So it use 1.29kwh per day. The capital cost for generating this power is around 200W of solar panels. If it costs $3/w to install solar panels, the capital cost for energy is $600 per habitant, which is much cheaper than septic tank + leechfield system.

If the heat is generated by burning propane, "combustion of propane produces about 50 MJ/kg of heat". Because propane fire is not 100% efficient, let's say 50% efficient, it uses around 0.2kg (1/15 of a gallon) of propane per day, or $0.2 per day, $73/year fuel cost.

Hello Douglas Woods. I see this post is a couple of years old. Has there been any progress regarding your idea for incinerating human waste. Ive been considering this option for some time now and have a desire to see a working version of this idea, if someone has come up with one, that will accommodate off gridders and give them an option of disposing, rather than composting. And Ellendra, have you  made any further progress with your steel bucket. My idea involves drying the waste first in a solar dehydrator before burning, hopefully reducing the waste maybe to ash? Your thoughts?

I too an ambivalent about combusting, rather than composting, humanure.

The long term loss of soil fertility which attends such a solution actually seems most pressing for those who have a subsistence lifestyle, whether on the margins of a more financially prosperous society, or otherwise.  Paul's willow feeder system, or even having enough 5 gallon buckets with tight lids that the full ones can be left to age for 6 to 12 months, seems to present minimal opportunity for infection and is quite sanitary if properly done.  An above-ground vault system, with alternating vaults, could be implemented on a communal scale at reasonable cost (though what I think is reasonable may be beyond the means even of the pooled resources of several neighbors or an extended family who are on the lowest rungs of the economic ladder).  Joseph Jenkins method presented in 'The Humanure Handbook" is a bit more hands-on, potentially presents some risk of infection (at least in theory, if not in practice), but it very inexpensive to implement.

Too, regulations are often made with little thought for how they impact those of meager means, and what options remain for them after the cheap, if old fashioned, options are precluded by edict because they aren't the "best" solutions by one cost function or another.  I suspect a lot of the crisis of lack of affordable housing could be overcome by loosening regulations; yes, some stuff would be substandard, even potentially hazardous, but living in an abandoned car isn't exactly risk-free, either.  As one who who tends to let the perfect be the enemy of the good in my own life, it's easy for me to spot it in others as well (as hypocritical as that may be).

Thus, circumstances vary, and burning potentially infective waste to dry ash may, under some conditions, indeed be the best choice.  As a case in point, when my brother was still working at Walmart, before he had obtained his contractor's license, one of his coworkers had bought an old farm.  The "sewage treatment" consisted of a pipe run to daylight in a shallow declivity adjacent the house.  The coworker wanted to put in a proper septic system.  The health department insisted that the drain field needed to be in a raised sand bed of prodigious proportions, with a lift pump, all of which would have cost a mint, just in sand and hauling fees.  So, my brother's coworker told the health department they'd just keep using it the way it was, since it was grandfathered in.  As long as they made no modifications, the health department had no say-so in the matter, since it was an existing system.  Faced with the prospect of a now-known potential source of surface water contamination, the powers that be at the heath department relented and granted an exception to permit a gravity fed system.  A Bobcat with over-the-tire tracks was borrowed (to satisfy the requirement of using tracked equipment to cover the drain field piping) and a gang of coworkers and community members got the job done on the cheap and with the look-the-other-way approval of the health department.  Problem solved.  But, if they hadn't been blessed by topography and the situation of the old farm house relative to the property boundaries, and the fact that, being grandfathered, they had some leverage - do you want the current bad situation to persist, or can you countenance a solution which is good enough, even though not "perfect" - it probably would have been a show-stopper, since this was back when our Walmart was paying somewhere near to $8/hour.  Now, I've heard they are paying nearer to $15/hr, though inflation, and the concomitant price rises which increasing the money supply beyond the growth in economic activity and productivity necessarily brings, have surely eaten into that nominal increase.

I can't find any additional development work which Erica Wisner may have done, but in 2015, she and Peter VdB worked on a version of the pocket rocket stove at Wheaton Labs which Erica dubbed the "Caddisfly":
http://ernieanderica.blogspot.com/2015/10/
This was a compact and robust clean combustor, and might be a good start for a homemade rocket-y incinolet.

The place where the commercial incinolets seem to make the most sense to me is for the short term "man camp" comfort stations, where a small army of laborers will descend briefly - a few days to a few weeks - in some remote location to bang out an infrastructure project before moving on to the next location a few miles away.  A sea can with an array of incinerating toilets inside actually seems to be a reasonable solution for sanitation under such circumstances, at least by my lights.  Temporary, portable and with a reduced chance of spread of infection amongst a bunch of unrelated persons, and often a changing and transient population as the tasks to be completed on location change as the project progresses.

okay so its the festive season , i am going to wade into this ---so to speak -- a comfortable chair to sit on --like a throne almost ----pre warmed up and all ---sit down read a book ---take in the ambiance ---finished --- clean up ---close lid ---divert valve flap ----to re route hot flue gas over the contents ---desiccate them out ---burn off the smell ---later on access the clean out chamber ---dispose of the ash. This is not my pic , and its not a toilet ---but with some modification -----add in a re routed flue ---a toilet seat and drop down chamber ---clean out grid---- perhaps some festive led light strung up--- i give you the ---christmass krapper

Whether for the purposes of this thread, or its original intended use, this thing is brilliant!

Where did you find this?  I'm sure I could do a TinEye or Google Images search, but I'd love to know a bit more about this.

sorry no idea where it came from --p interest ---most likely---heres another similar one---even a bit more stylish ----wish i had the time and skills to develop for these