After the lecture of Durk Durksz on biogas, the WOT decided to build its own biodigester. The system is self-constructed and uses 3 regular liquid barrels, as seen on the drawing above.
In the main barrel a substrate of manure and food scraps is present, where anaerobic digestion takes place producing (among others) methane gas. The other two barrels store the produced gas. For this purpose the barrel floats upside-down in the other barrel filled with water, containing the gas at variable volume and about equal pressure.
The system stores up to 120 liters of biogas. At this moment production is about 150 +- 50 liters a week. This is monitored by a wifi-connected Arduino circuit, measuring the temperature of the substrate and the height of the barrel. These values over the last 7 days can be seen in this graph.