DIY hot bin for fast composting.

I'm making humanure so I want to get as hot as possible in as little time as possible. This is part of a variety of composting methods I use but the hot bin is very useful for my needs.

Supplies

Insulating material - Kingspan / Recticel etc, anything you can get free or cheap from Gumtree etc & building works.

Foil tape - To seal the joints of the bin from the inside (Aluminium non conductive ideally) £10 / roll. I had some leftover

Lashing material - Something to secure the outside sections of the box. I used an old 700c innnertube which was beyone repair & a 2 bungee chords chained together. Ratchet straps etc would be ideal.

Screws / Pegs - I had some old 9'' screws left over. You could use dowel or steel rod. Anything which is thin but rigid.

A rock - To weigh down the lid & make sure it does not blow away!

Step 1: Insulation Material

I got this super cheap from gumtree from a completed building project someone had done. It was really expensive in hardware stores so avoid that. This stuff is totally waterproof so I got it cheap as it had discouloured in places.

I chose this because it has lines on it to make the cuts easy, it's really light & you cut it with a good edge & not release millions of bits of polysytrene into the garden.

I got the 10mm thick stuff which will be easily insulated well enough to make the compost hot.

Step 2: Building Your Bin

This bit was really easy & the whole project took an afternoon. It took longer to plan it & get the stuff then the assembly. I designed this so it is easy to disassemble in case I need to move it or upgrade it in the future. This is the prototype / proof of concept but it's turned out well.

Your bin will need to;

Insulate the composting materials inside to get them hot

Have an accessible lid into which new materials can be added

Have an opening at the front near the base where you can remove the compost from

Using the insulating material with the squares drawn on it makes life really easy you don't have to measure. Just count the squares & cut to suit. In my design I cut an 8 x 8 square for the base & boxed the back & sides in. Take your time with the design.

When assembling the sections together use the screws or rods (which ever you choose will be fine) to punch halfway through the panels. You can then push the exposed screw into the joining section & they'll gently hold together. Next take the foil tape & seal the join from the inside. At first it feels a little flimsy but when you have 2 or 3 joints made up the box will start to feel really sturdy.

Step 3: Securing the Box

When the structure is rigid I moved the whole box into place.

The base of my box is not fixed onto the structure so I can easily move it in the future without having to wrestle something which will potentially weigh 200Kg.

Use the lashing material (the innertube was surprisingly adept at this) to secure the sides together. With the pegs inserted, the foil tape & the lashing, the box will easily be strong enought to fill.

For the front panel section I used 2 half panels with the bottom panel secured using 2 bungee cords chained together loosely. This means I can easily remove the lower front panel anytime I want. The inner tube would be a pain to access round the back so the bungee cord is ideal for this.

Step 4: Almost Finished

If you look at this picture again you can see that the bottom lashing is different to the top. The bottom lashing secures the opening to remove material. The top part is fixed in place. You'll have to consider how you're going to get around this problem.

It has to be sealed as much as possible but also accessible at any time.

Modifications;

In the future I'll get some more tape to seal up the exposed segments on the outside edges

& find a meat thermometer to install to see how hot it gets

otherwise I think that's good compared to how expensive a brand new shop bought was. I spent about £60 on this idea, if you're craftier then me you could easily do it better & cheaper than I did. This will make a new batch of compost every 3 - 4 months.

Step 5: Some Results

I checked the bin after 90 days & it is definitely working. The mass has sunk by about half & looks nice & loamy. It surprisingly doesn't smell at all (I'm in the North of England which is quite cold) & was giving off some heat when I opened the lid. I think this will be good to use as compost in spring 2021, I have a little doubt as to how much e coli will have been killed off but I'm absolutely happy to use this compost in flower beds. With some very crude maths I believe I've saved 4096 litres of potable water. I'm on a water meter so the project has paid for itself already. I'm now wondering how I can upscale this & will it be possible to provide all of my compost needs from my own waste?