Tom had to re-do some fencing and clear the site for the bio-digester. He calculated that with the amount of manure we are getting (around 30kg per day), we need a 5 cubic metre bio-digester, which will give us around 1 1/2 cubic metres of gas per day. 

Outlines of the bio-digester

Lead up time to get the gas going will be around 60 days once we start filling the bio-digester. But we are not there yet, and here I have documented the start of the project.

We got a lot of questions about how we dealt with council etc. Since this is for private use and we are not selling the gas commercially, there are no hoops we need to jump through. So we cleared the site and started digging.

The dig started, with Tom operating his excavator to make things easier and quicker.

Tom drew where he needed to dig on the ground, whereupon he used the excavator to dig the round hole (2.8 diameter), plus a square hole which will be part of the outlet. He also marked out where the inlet will be (small round circle on the right). He had to regularly check levels, to ensure the bottom was level and the sides of the hole were straight.

Completing the hole by hand

The hole was then further dug out by hand, ensuring the levels were correct and walls were straight. Tom then put a pole in the middle and measured the inner radius, thus determining where the bricks would need to go.

A pole in the middle to measure the inner circle (inside of the bio-digester). The outer circle will consist of the double brick wall

A tarp had to be placed over the hole, since we were experiencing some wet weather, and we needed a dry area to pour the concrete and did not want the hole to fill up with water.

A tarp placed over the hole to keep out the rain. Bricks to be used for the walls in the background.

Deeper outer circle for better foundation.

To ensure a good foundation, the outer circle (where the bricks will be for the walls) was dug out deeper. This way there is more concrete under the wall to hold its weight, which makes it stronger. We were lucky, there was only a little bit of water in the bottom of the outer circle, which meant that water had only just been struck. This was of no concern at this time, but strategies will be put in place to divert water past the bio-digester in wetter times.

Rio mesh put down (all materials apart from cement is second hand).

We put down rio mesh and then the concrete was poured. The post stayed in the middle so that we could still measure where the bricks were supposed to go. Once the concrete was hard, Tom attached some wire to the centre post which was as long as the inner radius, and then measured out where the bricks had to go. He marked the concrete with blue pencil and laid the bricks out so everyone could see where they were supposed to go and how they needed to be laid.

Starting the concreting, constantly leveling the concrete to ensure a straight and level floor.

Concrete laid, with the pole in the middle

Wire attached to pole to measure inner and outer circle, so the bricks would end up on top of the thicker concrete

Bricks marked out and put down, ready to be cemented in.

Double layer of bricks, how they need to be laid.

They laid one layer of bricks that day. In the coming weeks we will add some more layers of bricks until we have a wall about a metre high. Then we can start the second stage of the bio-digester: The dome!

To be involved in the next stage of the bio-digester, "The Dome", please click here for dates and to book.