Compost Toilets

Milkwood Permaculture, Australia.

“Wendell Berry once said if you eat, you’re involved. He was talking about agriculture, but if you ask me, he really meant humanure. Getting your outputs sorted is a big and necessary task. For us, that meant designing and implementing a composting toilet system based on wheelie bins.

I thought I’d better give out the details of our compost toilet bin system, as we’re receiving many emails asking for the specifics of how the system fits together. It’s a simple design, but one that we’re very happy with. Here’s how the bins work:

The whole point of having these bins as our composting toilet system was to remove the need to handle the humanure until it had gone through its composting process and was safe to handle. We’re fine with handling open buckets of our own family’s sawdust-covered poo within a small humanure toilet system, but when we have a course here at Milkwood we can have up to 70 people on the farm each day. And though I value their presence (and their poo) I prefer not to process their collective contributions while they’re fresh, if i can avoid it.

So the bins are our solution. When one fills up, you roll it out, stand it aside in the sun, roll another empty in, lock it into place and continue on. No bucket handling, no processing. And a year later, each full bin has transformed into a rich, safe humus, ready to be added to the rootzone of our food forest trees. We label each full bin so we have a full inventory of when each lot of humanure will be ready to use.

The bins we’re using are normal 200 litre wheelie bins, used for household rubbish in Australia. We add a vent at the top of the back panel, a tap outlet at the bottom of the back panel, and a grate inside the bin. Each bin takes about 1 hour to prepare all up, and are best done as a batch. Once a bin is adapted, you’ve got it adapted for life, so it’s a worthy time investment.

The Grate
Each compost toilet bin has a home-made grate in them which sits about 5cm off the bottom of the bin. This grate provides a permeable barrier between the solids and woodchips coming into the bin, and the bottom of the bin reservoir. Any liquid (and there isn’t much, as the woodchips absorb most of it) moves through this grate and fills the bottom of the bin, and then drains out the bottom through the tap.

The grates were made by cutting a piece of galvanised steel mesh to size, and then adding a polyethylene surround (19mm low density irrigation pipe) to the mesh and wiring it on. A shadecloth cover is then tied to the grate to filter finer particles. The finished grate is wired to 4 bar chairs (the little plastic cones that support rebar while concrete is being poured), which raise it off the bottom of the bin. The completed grate can then be placed inside the bin, and can be removed easily when the humanure is used at the end of it’s composting cycle.”

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