Last week I helped out in the construction of the roof over a biodigestor. According to Green Empowerments blog, a biodigestor is:
… The ultimate in closed-cycle resource use. You put cow manure in one end and get out usable cooking gas and organic fertilizer. The odorless gas is piped into the kitchen where it can be burned for 4-5hrs a day, replacing the need to collect firewood. The liquid fertilizer is rich in nutrients to boost crop production. And, the patio is no longer littered with cow manure. Biodigestors are relatively simple to construct and made with cheap local materials. It’s basically a huge plastic bag laying on top of straw, insulated between adobe walls and covered with a roof.
This is in fact a nice technology. The materials are not expensive, the construction is not essentially complicated and in operation it is very simple, if slightly unappealing for many people. It is after all, animal shit that you have to put into it. But it so happens that animal waste is a big source of greenhouse gases in the atmosphere and using it like this, burning it to the advantage of heating or cooking is an excellent way of reducing greenhouse gases.
Anyway, our task was to help in the construction of the roof. As you can see in the photo on the left hand side, the actual biodigestor is practically ready by now. It is really “just” a plastic bag in the ground with some tubing (although I do not want to diminish the engineering ingenuity of the designer!). We decided to go for a roof design of plastic over PVC tubes in a sort of semi-circle design. It is basically a big iglo-tent (for those familiar with camping).
We faced two big challenges: how to keep the PVC tubes standing up right and how to connect the plastic without ripping it to pieces. We more or less succeeded in both challenges, although a perfectionist would certainly manage to find some flaws in our work. In the process we included a nice wooden platform on one of the entrances (extra stability, but we really needed it to fix the line to the PVC).
After some 5 hours of hard work under the burning sun we were done. The photo on the right is about 30 minutes before finishing. Today I heard that the dean of the environmental engineering faculty was very pleased with his biodigestor in general and that he liked the roof. Of course this answer was solicited, so we are not entirely sure about the sincerity, but that doesn’t in fact matter. We are proud of our work and that counts for more.