In recent years I became quite obsessed by thermophilic composting, as an effective method to safely recycle our excreta. Obtaining high temperature in (fecal) compost at household scale is not so trivial. This was my impression when I started using a dry toilet back in 2016, and was confirmed by a survey of dry toilets in France published in 2019 (https://doi.org/10.1007/s11356-017-0604-z).
I am experimenting with different designs for household-scale composting, and over the past two years I have managed to obtain very high temperatures up to 79°C by modifying the geometry of the composters, the timing of compost onset, and the "recipe" to make microbes really happy.
Experiments from 2024 and 2025 have shown that a static pile without any turning or mixing can get very hot at the core, but the bottom mostly remains too cool, so that coliform tests (indicator micro-organisms for fecal contamination) were positive at the bottom.
This new design below should help solving most the problem. It is a compartmented outdoor composter, built and first tested this year (June/July 2026). The idea is to have the toilet material (ie. feces + litter, the latter being a mix of wood shavings, dried leaves and dried grass) at the core of the compost pile, physically separated from other stuff that I compost from the garden. The periphery also composts and serves as a warm insulation blanket to keep the core (inside the blue bin) as hot as possible. There is a hole at the bottom of the bin, serving as air inlet and leachate outlet. The leachate, if any, is collected in the small blue receptacle at the bottom. The whole thing is under a roof (it's me who decide how moist the compost should be, not the weather!), and I put a foam insulation lid to keep the bin as warm as possible.
The design (together with good management) is successful to reach very high temperatures of up to 79°C at the core, and about 55°C outside within 10cm of the bin. Being compartmented, it is easy to mix the compost material and bring the (cooler) bottom to the top without disturbing the geometry of the pile or contaminating the periphery. I mix it with a screw (visible on the second photo) which involves a bit of exercise, but ok. Mixing also helps get all the material equally moist.
I am experimenting with different designs for household-scale composting, and over the past two years I have managed to obtain very high temperatures up to 79°C by modifying the geometry of the composters, the timing of compost onset, and the "recipe" to make microbes really happy.
Experiments from 2024 and 2025 have shown that a static pile without any turning or mixing can get very hot at the core, but the bottom mostly remains too cool, so that coliform tests (indicator micro-organisms for fecal contamination) were positive at the bottom.
This new design below should help solving most the problem. It is a compartmented outdoor composter, built and first tested this year (June/July 2026). The idea is to have the toilet material (ie. feces + litter, the latter being a mix of wood shavings, dried leaves and dried grass) at the core of the compost pile, physically separated from other stuff that I compost from the garden. The periphery also composts and serves as a warm insulation blanket to keep the core (inside the blue bin) as hot as possible. There is a hole at the bottom of the bin, serving as air inlet and leachate outlet. The leachate, if any, is collected in the small blue receptacle at the bottom. The whole thing is under a roof (it's me who decide how moist the compost should be, not the weather!), and I put a foam insulation lid to keep the bin as warm as possible.
The design (together with good management) is successful to reach very high temperatures of up to 79°C at the core, and about 55°C outside within 10cm of the bin. Being compartmented, it is easy to mix the compost material and bring the (cooler) bottom to the top without disturbing the geometry of the pile or contaminating the periphery. I mix it with a screw (visible on the second photo) which involves a bit of exercise, but ok. Mixing also helps get all the material equally moist.
There is also the insulated compact composter which I introduced in a previous post. I tested it without feces for a first try in May/June 2026, but I will make a real batch with feces very soon.
Further developments:
- These designs use a 120L bin which fills rather quickly, forcing me to start a new compost every 2-3 weeks. So I also made a new one like on the photos above, but with a 220L bin.
- Mixing with screw is a bit cumbersome and somehow imperfect. I have an idea to further improve that. To be followed...
Further developments:
- These designs use a 120L bin which fills rather quickly, forcing me to start a new compost every 2-3 weeks. So I also made a new one like on the photos above, but with a 220L bin.
- Mixing with screw is a bit cumbersome and somehow imperfect. I have an idea to further improve that. To be followed...
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