In the May Biogas course, we built some pillars in the biodigester with leftover bricks, on which plywood was placed, cut to size to fit perfectly the diameter of the pit. This would then support soil to form the base on which to pour concrete for the dome.
Tom, students and helpers ensured the plywood was stable and then they proceeded to pile soil on top of it, keeping it slightly wet and shaping it as a dome. On top of the soil, sand was patted down so the cement wouldn’t stick to it. Once that was done, they mixed the cement and gently shaped and padded the cement in place, smoothing it out as they went. A good 10 days of cool and damp weather was perfect to cure the concrete without cracks. On the top of the dome Tom needed to build a brick tower to house the gas pipe, which he did after the concrete dome had set.
Once the cement had dried, Tom had to remove the plywood to drop the soil into the pit, and shovel it out of the confined space. This took most of one day (and a lot of sweat!!).
The next stage of the biodigester is building the inlet and outlet, and if time permits starting on the toilet which will feed into the biodigester as well. This will be done as part of the next biogas course and runs from 19 to 23 August. Please email info (at) permaculturesunshinecoast.org for more information or to book.