A humanure compost bin such as this one is where the contents of your compost toilet are transformed into top quality compost. This simple set up totally eliminates the need for costly and polluting plumbing infrastructure, sewerage stations and septic tanks.
Here are a few of the tools we used. The metal brackets are for holding the frame of the compost bin together with screws. The pillars and planks can be cut with a hand saw if you’re brave or have no electricity. Fortunately we had electric saws etc to speed the work up. The t-square, level and a long builder’s metal rule are used to make sure the various levels and angles are right. We built the whole structure at a slight incline backwards towards the gutter so that the liquids will drain easily in that direction.
Our bin is 1m50 x 1m50 and 1m25 in height, so David cut the posts and beams to size. Ideally it should be 1m60 squared, but the lengths of plank we’d bought made that too difficult. If you make your bin too small the thermophilic bacteria necessary for converting the pathogens into nutrient-rich compost won’t have enough volume to get going with their important job. The compost must ideally reach temperatures of 62 degrees centigrade (143.6 degrees F), or a slower decomposition heat at 43 degrees centigrade (109.4 degrees F). For checking this on a regular basis it’s good to have a compost thermometer.
Strong metal brackets were attached to support the cross beams at a height to create legs (the legs were later increased in length owing to the bin’s change of location).
Here you can see a close up of how the brackets are placed at all the joins of the beams. Very few screws were needed because once all the planks are in place, the structure holds itself together snugly.
Here is a view of the completed under-structure as it was built initially. You can see the slope of the whole bin. David thought that the back feet weren’t necessary and used metal brackets instead. As it turned out, this mistake turned to our advantage when we had to shove the whole structure back a meter where it rested on the back wall of the trench as you’ll see in the following photos.
Three planks were nailed to the bottom beams to support the sheets of metal corrugated roofing. When we bought the sheeting it was quite thin so we added a couple more planks after this for extra support before we laid it on.
David cut the corrugated sheets to fit the size of the bin, with an overlap at the back so that it jutted over the back gutter. The green metal brackets attached to the front pillars will be explained later, they are part of the system for slotting in the front planks.
Here is a side view where you can see the compost underneath the bin from our second abortive attempt…
The first planks are nailed around the lower edges… However, the side edges and corners will leak onto the courtyard if they remain like this because of the gaps…
So the cracks were filled up with cement to prevent the leachate from seeping out where it isn’t supposed to.
For the front gap, as we wanted all the front planks to be removable, David screwed/stuck a narrow plank perpendicular to the bottom front plank to cover the slit and act as a mini ‘roof’. We hope that as this is at the high end of the slope and the contents of the buckets always get thrown to the center of the compost when emptying them, there will be little risk of leaking even with rainfall. This way, when the compost is ready to be removed, all the front planks can be removed including this bottom one which is attached with screws rather than nails. If it doesn’t work we’ll just cement that bottom gap up like the rest and make do with pulling the compost over this little ledge.
And the rest of the planks go up… In this photo below you can see the evacuation holes created by the corrugated roofing where the leachate will drain out of the compost bin and into the gutter.
In the next photo you can see the system David used for the front planks so that they can be easily removed. They are slotted between a vertical plank at the front and a metal bracket at the back.
1cm deep wedges are placed between the planks as they are attached in order to create airholes. Once the planks are nailed in place the wedges can be removed, apart from for the front planks, because as they are not attached with nails but slotted in, one on top of the other, they need permanent wedges attached to their bottom edges so that the planks can sit on one another with a 1cm gap.
This is how the back of the compost bin looks, with the corrugated base jutting over the gutter so the leachate can run off into the drain. We will eventually attach a more closed gutter system so that it is neater and less exposed.
Here below is our compost, it has moved around so much that all the little compost critters must think it’s a travelling circus… After putting it in, I pulled this straw and compost away from the center and towards the edges, to leave a small depression in the middle of it, in preparation for the contents of my full buckets from the compost toilets. This creation of a hole in the middle of the compost’s mass can be done with a pitch fork. After each time you throw in the contents of your buckets (which is the only time you ever get a waft of smelliness in the whole compost toilet process) fresh straw is then layed on top of it as a cover material to stop any odors getting out, to prevent flies, as well as being the perfect material to create small air pocket layers inside in the compost so that it breathes, ferments and heats up efficiently.
To this mix it is good to add kitchen scraps, dead leaves and vegetation to create the optimum environment for all the little compost creatures to do their work. As this compost is not exposed to soil, we will buy compost worms from the local gardening shop as well as maybe an organic compost activator if we suspect it’s not heating up and compacting down fast enough.
Voila! The completed humanure bin. We will put metal covers on the four exposed tops of the corner posts to prevent them from rotting before the rainy season begins. People here do this the simple way by placing empty tin cans over them. However, David will cut out some small non-rust metal squares and fit them on top of the posts neatly. We will also get some chicken wire mesh to cover it with just in case any rogue animals ever want to get in there.
And chuck their contents into the very center of the compost where I’d created a dip with a pitch fork for it to fall into without spilling towards the edges. This is the only time ever that you will get a smell from your buckets, as the contents, kept odourless by the cover material while in your loo, become exposed and slosh out into the bin. (The photo below was taken before we dismantled the whole thing and redid it with slotted-in front planks…). As you can see I’m in my very scruffy work clothes. However, if you want to empty your compost buckets in your high heels and fancy town get up, feel free…
I give the bucket a rinse with water from my butt using a watering can which is useful for efficiently rinsing the bucket.
And I give it a final rinse to get the soap off. For two buckets you don’t need to use more than a total of, say, eleven or twenty litres depending on how efficient your cleaning method is.
A final wipe down…
If the plastic bucket begins to be a bit smelly after a period of time, either leave it outside for a day in the fresh air or, as it’s only the base that can start to smell slightly, put sawdust into it right after cleaning and this immediately stops any odour.
…where I put it back in my avant-guarde toilet and admire the view….as well as bask in the joys of being free from the water grid…