TLDR: Methane is flammable. It is a gas that comes from compost during decomposition (also in farts). If you catch it, you can cook with it like you would propane. Thus if you compost in a container, you have unlimited free fuel.
NOTE: Methane Digesters are also called Biogas Digesters.
So there are a shitload (pun intended) of options and styles to choose from or you can design your own Biogas Digester. Youtube has all different scales and budgets.
Mine uses a permanent system similar to a hot tub dug into the ground partially. I use gravity to add waste and remove old compost and a rubber diaphram to pressure gas into my kitchen.
The process of using the gas and making sure you are safe in doing so will be Part III of this series. In Part II I'm only going over the digester itself.
YouTube Videos about Methane Digesters:
One guy's build: www.youtube.com/watch?v=xAkIKxA3Jm0
How it works: www.youtube.com/watch?v=TXXfLwvjO5k
How to build a Digester from a IBC: https://www.youtube.com/watch?v=Cwm5Rm8uIsk
You have 3 connected compartments.
Inlet- This is where you put compost, manure, anything to be broken down. (Plus water to create slurry and help with the process.
Biogas Digester- This is the main compartment where the breakdown occurs. The microbes, slurry, water, waste products all churn here and decompose over time creating gas. The top of this chamber has a rubber diaphram so that it can expand with the production of gas and also provide pressure to push the gas into the hoses towards your kitchen stove.
Outlet- After the slurry has been churning in the digester it produces less and less methane (because it'll be completely broken down. At this point you don't want the compost in your methane digester anymore. So you design it so that when you add some to the inlet, it pushes some of the old stuff out of the outlet. The easier you design this to be, the better. Otherwise you have to scoop and scrape and thats not a fun task.
I recommend using gravity so that the inlet is higher than the outlet. When you add some, the rasied water level will pour some old stuff out through PVC pipes into your drip irrigation system. Only do this if you have wide enough pipes/hoses in your drip irrigation to handle larger pieces that may make it into them. Also will need a separate system for removing solids.
Watch this video for a really cool video on building one of these bad boys for yourself and get yourself all the free off grid fuel you could want.
This one is above ground, non-permanent, portable, and relatively cheap and simple to build but will work wonders for you and your family.
Let me know if you have any questions.
Written by: Page Ollice
Founder of Good Old Fashioned, Page has spent over 7 years researching off grid and sustainable living techniques to design one master project: A self reliant homestead in New Mexico that takes into account shelter, water, fuel, food, waste management, heat/cooling, and electricity. He is putting all his notes online open source for public use so that anyone can follow his plans to building their own autonomous, self-reliant homestead.
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