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.
Building the bricks to rest the plywood base onto to build the soil dome for the biodigester.
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.
Starting to put soil on top of the ply base
Soil is whetted down and shaped as a dome
The dome exterior is covered with sand to stop cement sticking to the soil, note the gas pipe sticking out.
Bit by bit concrete is poured and worked on top of the soil dome. It is a slow and laborious process to ensure the concrete stays smooth all around.
The finished cement dome for the roof of the biogas biodigester
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) permeco.org for more information or to book.
Author: Permeco Inc.
Not for profit organisation and charity based in Queensland, Australia, focusing on permaculture education and environmental research. Please note that all articles and recipes written under this label on this website prior to 2025 are written and copyrighted by Willa Sevenstern (previously known as Zaia Kendall).