Initially, depending on the tank available, this will be the quantity of biogas produced by the digester.. Uses for this biogas could be cooking certain foods, heating a room, lighting, or simply for home projects or experiments. For the latter, a Bunsen burner would be very useful as it makes it easy to regulate the gas flow and the air-biogas mixture.
the biodigester it should be built according to the availability of resources and not try to do it with exactly the materials that I will mention below. Remember “the three Rs”; reduce Reuse and Recycle.
Materials and their description.
The reactor and the supply of materials.
- A tank or drum with a capacity of between 120 and 220 litres. They are usually blue with an airtight lid.
- Sanitary cleaning cap (4”): This is a kind of adapter with a screw cap.
- Short segment of tubing (4″): Passes through the opening and connects the “matching plug” on the outside with the reducer inside the tank. It must be short enough to allow both the reducer and the adapter-plug to imprison the wall of the lid of the tank and thus allow better adhesion and tightness Sanitary flanges glued with silicone on the tank can also be used.
- Reduction of PVC from 4″ to 3″.
- Sanitary PVC pipe (3”): From the reduction to 5cm before the bottom of the tank.
For the effluent outlet:
- Reservoir adapter (2″).
- PVC pipe (2″) for the effluent outlet pipe.
- 3 PVC elbows (2″).
- Tank adapter (1″) to connect the valve.
- PVC ball valve (1”) For low outlet of the heaviest effluents.
For the biogas outlet (in order):
- Tank connection (1/2”).
- Ball valve with thread (1/2”).
- Hose adapter.
To assemble the parts and seal:
- Solder (glue) for PVC.
- Clear silicone sealant, fungus resistant! : To seal around tank joints and prevent leaks.
( ” ) = inches.
Two side holes and two in the cover are made in the tank. One on the bottom side for the 1 inch valve; another in the middle part for the effluent outlet. On the lid, one will be for the material inlet and the other for the biogas outlet, always of the diameter of the piece that crosses it.
to store biogas a floating bell tank is used, very easy to build with two drums; a large one where the water goes and another slightly narrower one that is placed upside down inside the previous one. The pipe that comes from the digester is introduced into the larger tank and bubbles so that the gas rises and is trapped in the smaller tank, which has a valve for the gas outlet with a pipe and a water trap.
How to use a Drum Biodigester.
Don’t forget that this biodigester is above all “experimental”. What I mean is that it is a test and information gathering unit rather than a stable source of biogas for home use. For the latter, a larger capacity biodigester is recommended.
To use the biodigester, its manufacturer must first install the connections, hoses, safety valve, biogas tank and burner, as well as check the connections in order to avoid gas leaks or the entry of air into the device. Once these preparations have been resolved, it will be possible to continue filling it.
Usable organic matter.
- Fresh manure or slurry from herbivorous or omnivorous animals (example: pigs).
- Kitchen scraps and leftover food, (except citrus fruits).
- Used cooking oil (only 5%).
- Leftover vegetables from the market place.
- Freshly cut grass – mixed with other materials.
- Sawdust (sawdust) “old” -mixed with other materials.
To allow rapid degradation, all materials to be used must be crushed, shredded or crushed depending on the case, in fragments not exceeding 10 mm for the softest and less than 5 mm for the most substantial. The smaller, the better.
The filler will consist of a mixture of 20 to 25% organic matter and 80 to 75% water. Part of this water can be replaced by the treated liquid (effluent) that comes out of the biodigester, also called biol, and thus produce more biogas at the expense of obtaining less fertilizer.
Retention time and daily load.
Depending on the ambient temperature, this will be the retention time of the materials added to the biodigester. The following table shows retention time as a function of temperature.
An “air” space will be left in the biodigester of 25% (1/4) in the tank-biodigester, so only 75% of its capacity will be used, which we will call volume of work (VT). The outlet pipe will be arranged in overflow, so that 1/4 of the capacity remains for the gas phase.
The mix charge to be added daily is calculated as follows:
- TV= VAT x 0.75
- CC = VT/TR
TV: volume of work in litres.
CTT: total tank capacity in litres.
CD: daily mix load to be added.
TR: retention time in days (see table)
Example: In hot weather, for a 120 liter biodigester, the working volume will be 90 liters (120 L x 0.75= 90) and the daily mixing load will be 4.5 liters (90L/20=4.5L) .
The biodigester must initially be filled (3/4) with the mixture of organic matter and water in a few days to avoid excessive release of odours. After filling, no more mixture will be added until the production of methane is well started and then maintained for several days. After that, the calculated load for your specific biodigester will be added daily, always through the PVC cover on top of the digester.
The outlet pipe of the biodigester will be the overflow through which the liquid effluent or biol will exit each time the load is added to the device.
Regarding the amount of biogas that will be produced, there is no “magic number” for all possible substrates. It’s best to research each material you plan to use in an article or book.
Keep in mind that these are just a few guidelines and you may experience different retention times, organics, filler dilution, or other issues.
CAUTION: BIOGAS IS A FUEL. Take adequate security measures and consult a professional. The process will be faster if you live in a hot climate, as the temperature speeds up the process. However, never leave the biodigester in direct sunlight as this will create sudden temperature changes on a daily basis.
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