DIY Biogas digester

aka Farting machine

If you have never heard of Biogas digester or maybe have always thought of it as one of those mysterious engineering miracles (like myself couple weeks ago) then I'm about to change your world.

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Biogas in theory is any gas that is produced by breakdown of organic matter, normally it is 50-70% of Methane and rest Carbon dioxide with small traces of other gases. Methane is the gas we burn in our ovens and reason what makes biogas valuable as it can replace conventional natural gas as well as turned into electricity.

To get biogas we need to gather organic matter (food waste) and create system for it to decompose anaerobically- without access to oxygen. Opposite to aerobic composting  where pile is turned to let the air in and facilitate microorganisms that release CO2, anaerobic system requires the opposite- no air and different microorganisms that produce Methane.

Anaerobic composting is what usually happens to organic matter in landfills as there is no access to oxygen below the surface and it is one of the reasons why landfills are a such bad idea, methane is around 20 times more harmful to the environment than CO2. So either turn you pile (or landfill) or collect and use methane.

 

 To produce and collect Biogas we have to make an airtight system with a one pipe for feeding, one for collecting gas and another for removing the digestate. Anaerobic digesters are often compared to human digestion as the ideal food waste mix, bacteria and processes (including smell) are very similar to what happens in our gut, hence the "Farting machine" title. So we just need to build one good belly, sounds easy, right?

Here is my plan, I based it on these guys and adapted it where it made sense to me.

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I have designed the system around airtight container that I can recycle for this project. It is about 50 cm in height and has a barrel shape (perfect belly!). 

The first pipe is the MOUTH- where we put food waste, the middle is the BUM- where we collect biogas, and the third is THE USEFUL OPTION - where we can access the leftover digestate.

The MOUTH pipe goes all the way to the bottom of the container, but cut in a angle to allow easy flow into the barrel.

The BUM has a very small pipe to gather all the biogas that will gather at the top of the container (Methane is lighter than air so will sit at the very top).

The USEFUL OPTION pipe goes until the middle of the barrel as that's where the ready (not producing biogas anymore) digestate will sit.

Ingredients

If you get the all of the parts right then you just have to put it together keeping in mind that the system should be airtight above the food waste as it shouldn't let any biogas escape.

Here are some photos how I did it.

When you have assambled the biogas belly, it's time to feed it and wait until the bacteria starts to do it's magic!