For this simple animation describing just how simple it is to build your own biogas digester I downloaded Google Sketchup 7 and then used Google 3D Warehouse to download a model of a digester by roilbilad130 called "Biogas untuk limbah dapur" which is Indonesian for "Biogas for Kitchen Garbage". I changed the food inlet pipe and the fertilizer output pipe to reflect the way they work in the ARTI India systems we have been building in Cairo and Germany and set different sequence animation key frames in Sketchup and did screen capture in Snap Z Pro. Building real digester is about as easy as building a digital one in sketchup -- it really is just two plastic barrels, one inverted inside the other, with three pipes -- one to get the food in, one to take the liquid fertilizer out and one at the top to deliver the gas to your cookstove or generator. 1000 liter tanks should get you about 2 hours of cooking gas a day if you live in a warm climate. As shown, we intend to use psychrophilic bacteria at the bottom to increase cold weather production.
The process is very simple -- on the first day you put in about 40 kg of animal manure (horse or cow work fastest, but anything will work) and fill up the container with water. Then place the gas collector on top with the valve open so it sinks down into the bottom container, driving out the air. Then close the valve. After about 3 weeks the gas being created inside the container will be flammable. From that point on you start adding kitchen waste ground up with water in a blender (be careful not to burn up your blender!) Because methane is lighter than air, if the valve in the top container is closed it will not escape (think of a diving bell or a hot air ballon -- they are open on the bottom and no gas escapes). Even though there is open space around the sides the gas is trapped in the top container until you open the valve to bring it to the kitchen. Hope that helps!