Methane is a versatile, sustainable gas that can be used to perform everyday tasks like heating water and cooking food with surprising simplicity.
Unfortunately producing it and using it at home may seem messy, but below we have a simple DIY instruction on making a biogas digester.
All grazing animals have bacteria that are needed for creating methane in their guts, with cows being the most efficient creators of the gas. For those of you who can’t get hold of cow manure on a regular basis, there are other options as horse or sheep manure can function effectively too.
That being said, manure is needed to start the process and maintain this particular method of producing methane. However, only using manure is not the most effective method of continuously producing methane. Adding chopped up plant materials that grazing animals naturally turn into methane such as grass produces a great yield. Leaves and rotting vegetables are also options for feeding a biogas digester and creating methane, once the system has been established.
Another advantage of this is that careful creation and management of the biogas digester allows for stacking functions. Once a biodigester is built for the creation of methane, the semi-liquid substance left behind is a great fertilizer.
Creating a basic bio digester does not have to be an expensive endeavour.
Only a few items are needed, and the concepts behind creating one are simple.
That being said, the gas produced won’t be pure methane. Cow manure yields about 60% methane while the rest is carbon dioxide with a touch of hydrogen sulfide. There are ways of extracting that, but it is a far more complicated design that requires biogas scrubbing. As a first timer, it’s best to try and easy do-it-yourself biogas digester with the following materials.
● Two drums – One drum must be slightly smaller than the other so that the smaller one can be fitted into the larger one.
● Manure suited to creating the needed anaerobic bacteria culture.
● Input pipe and funnel for pouring in processed food waste.
● Output pipe for draining waste for fertilizer.
● 3 uniseals.
● Valve for controlling gas out flow.
● Pipe for connecting outflow valve to burner Gas Burner
● Chicken wire & cable ties to make a cage for the biodigester.
● For cold climates and winter – black spray paint (if drums aren’t black) and/ or aluminum tape or other outdoor insulation materials.
Ensure that the drums fit tightly enough to prevent oxygen getting in and methane escaping, but not too snug so that the smaller drum doesn’t slide. The smaller drum should still slide down on it’s own due to its own weight so that there here is pressure from the smaller drum on the gas that is created.
Three holes need to be cut into the two drums. The solid’s input pipe and the gas outflow valve must be cut into the top of the smaller drum, while an output pipe for the leftover digested mass is needed at the bottom of the larger drum in order to drain the excess material for fertilizer. Cut holes suited to the size of the three holes and insert the appropriately sized uniseals. It will be necessary to seal these holes to ensure that gas doesn’t leak out and oxygen doesn’t get in and ruin the digestion process.
As a rule of thumb, your input pipe would be much larger than your outflow valve as the food going in would take up more volume and the smaller space for the outflow pipe will add to the pressure needed for effectively using the bio gas. Make sure that they are effectively sealed by putting the drum in some water. If it seeps through and into the drum, it’s not well sealed and a lot of gas will be lost. Lastly, the input pipe must have a sealed closure so that it is not left open after manure or vegetation matter has been added.
Create a cage for your drums that will prevent the top from popping off. Chicken wire shaped to give enough space for the small drum to rise would do the trick. Don’t drill holes into the larger drum to secure it though. That would allow oxygen in. Remember, the cage needs to allow access to the input and output pipes.
The manure needs to be diluted with water at a 1:1 ratio and stirred into a slurry like consistency. Then, pour it into the bottom of the larger drum carefully.
Insert smaller drum into larger drum and give the bacteria some time. After about three weeks to a month, adding in some cut grass is a good way to build up the system. Don’t add too much plant matter that is high in sugar such as grains, fruits and vegetables. First let the bacteria establish themselves and the correct pH level with the kind of plant matter that grazing animals very effectively turn into methane. After a while, any leftover vegetables can be added along with cut grass. Manure is needed from time to time to maintain the bacteria count.
Maintain the temperature. If you live in a cold climate, you may need to provide added insulation to your biogas digester system. The temperature needed by the bacteria ranges between 32 and 37 degrees Celsius or about 90 to 99 degrees Fahrenheit. If it drops below 15 degrees Celsius or 60 degrees Fahrenheit the bacteria will no longer be active.
A few tips for keeping the container insulated would be:
● Spray paint the container black for it to attract as much heat from the sun as possible.
● Bury the container in order for the earth to insulate the heat generated by the bacteria.
● Cover the container with aluminum tape or another insulation material that may be available to you that is suited to the outdoors.
Hook up your burner to the pipe you have attached to the outflow valve and reap the rewards of your gas production.
Here is a series of great illustrative videos courtesy of Tom Kendall, https://diyfoodandhealth.com/.
Illustrations by: Aerialist Joe Art