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Común Tierra presents…
How to build a low cost BioDigester
Filmed at the Tierra del Sol EcoCenter Instructed by agronomist Walter Carvallo
I’m Walter Carvallo, from Bolivia. I come from the state of Chuquisaca…
We're here in Oaxaca since a week ago, giving practical courses and trainings on
the design and implementation of Integral Farms.
What is a Biodigester?
The biodigester functions similarly to a stomach,
‘digesting’ animal manure to produce Biogas (Methane).
The Biogas can be used to power a stove, lamp, heater, etc.
It’s constructed with simple materials, making it a great source of
alternative energy for the world.
'We can say that there are biodigesters made of all kinds of different materials.
The Dimensions
The size of the biodigester is determined by 2 factors:
*The amount of manure available *The energetic needs of the place
The minimum length is 5 meters, which can produce 2-3 hours of gas every day.
According to it’s size, the biodigester requires a daily input of manure and water.
In this video we document the construction of a biodigester 7 meters long,
which requires 30 liters of manure, and 60 liters of water everyday.
This same amount is also produced from the other end of the biodigester in the
form of foliar fertilizer, ready to be applied to crops.
‘Another benefit is that it gives us an abundance of foliar fertilizer.
Three buckets, at least, we can say at least 60 liters of foliar fertilizer… every day!'
The Construction
The construction of the Biodigester is simple, but requires attention to many
details during the process.
Before construction, you have to build the pit, which is the structure that
protects the Biodigester.
The pit should be totally flat, smooth, and free of rocks or roots
that could break the Biodigester. The size The size of the pit follows the size of the Biodigester.
At Tierra Del Sol in Oaxaca, we constructed a 7 meter long Biodigester.
We started by preparing the plastic that forms the main structure.
In this case, we had one big plastic, so we measured it in 3 parts of 10 meters,
and then very carefully cut it into 3 pieces.
When the plastic was ready, someone had to pass inside of the plastic,
to insert one inside of the other forming one circle with two layers
Then we passed another plastic inside of these two,
forming 3 layers of strength in the structure, forming a type of bag.
This part requires paying a lot of attention that the plastic adjusted exactly without
breaking.
The next step is to prepare the gas exit valve.
One person went inside the bag, to cut a hole from inside.
Then we reinforced the area with plastic, and connected the exit pipe, sealing both
sides and tightening from the inside.
'There it is. Now, place this, and start tightening!'
When this step was ready, we were ready to place the bag in it’s place,
in the pit that was ready for it, making sure the exit valve was
right in the middle, facing up.
The two sides of the bag enter into tunnels on either side,
and were tied on the outside so that solid and liquid materials could pass through.
We used pieces of old tires to tie here.
On one side, we began filling the bag with air by connecting to the exhaust of a car.
On the other side, we began filling the bag with water,
until the water covered the two tunnels, sealing the inside.
In the gas exit we placed a T, which works as a security valve,
reducing pressure when it gets too high.
The T connects to an extra gas exit that opens in a container filled with water.
Why this security? Precisely because it assures us no gas will escape,
because of the water.
But when there is too much gas, it starts to bubble here, releasing pressure.
That’s why this has to be the most carefully prepared part.
'Full of water?' It always has to be full of water.
As long as it has water, we can be sure that gas is not escaping anywhere.
Only in the case there is excess.
The valve should be closed. From here we run a tube to the kitchen.
There in the kitchen we can install an L valve
in the connection to the kitchen.
When we want gas, we can leave this one open and the other one closed, and when
we open it, there's gas.
The construction process took about 4 hours, and the structure was ready to
receive the first load of manure.
It will take about 30 days of adding manure to begin producing Biogas.
This model of Biodigester can easily last 10-15 years without problems
with good maintenance.
It's recommended to build a roof above the biodigester
to protect it from rain, sun, and birds.
This can be a very simple structure built from straw, palm leaves, or black plastic.
Important: Don’t build a biodigester without the help of someone who has done it before.