Construction of a biogas digester

Construction manual of a biogas digester by T.H. Culhane
Here is the description of the system, the basic principles  are  very  simple,  use  the  things  you
find in your surroundings. 
 

1. Cut the top off at a 2.500 liter water tank.You  have  now  made  the  stomach  of  your  “sacred  cow”.

2. Drill 2” hole at bottom of tank and 1” hole at top of tank.

3.  Put  tank  adaptors  in  holes  (threaded  pipewith rubber gasket and locking nut, sometimes
called  bulkhead  fittings  (check  aquarium shop).

4.  Fit  1”  pipe  in  top  hole  (pic  4.a)  on  outside  and 2” pipe inside tank that reaches to middle
of tank. Fit  2”  tube  outside  tank  to  elbow  going  into
tank. This is your feeding tube or the “throat of
the cow” (pic 4.b-c).

biogas digester

5.  Gas  Collector.  Take  another  tank  that  is smaller  in  diameter  than  the  “stomach”  tank you  made  (one  that  fits  inside)  but  try  to  get one as close to the first tank as possible (for a 2.500 “stomach” tank you may only be able to find a 2.000 l “gas collector” tank.  Cut holes in the bottom of this tank as shown (pic 5).

6. Cut 8 holes slightly larger than 2” in bottom.

7. Burn or drill a ½” hole in the top of the gas collector tank near the side as shown.

Put a ½” tank fitting in this hole

9. Put small stones at bottom of stomach tank as homes for bacteria, but do not block or go higher than the output of the feeding pipe.

10.  Fill  with  about  300  to  500  liters  of  water  (grey water is fine).Then  pour  in  about  100  kg  of  animal  manure (this keeps the manure from being exposed to too much oxygen.If you put manure in first you aerate it as you add water  and  that  can  kill  bacteria.  Bu  sure  and use fresh moist or wet fermented manure). Fill the stomach tank to the top until some drips out the 1” pipe.

 

11.  Cut  8    2”  pipes  slightly  shorter  than  the height of the gas collector and cut holes in them like a church organ to let food in and gas out.

12. Fix a piece of  ½” pipe (A) through one end of the 2” pipe and melt its ends so it flares out and can´t fall out of the 2” pipe.

13. Put the 2” pipe in the larger than 2” hole in the gas collector and when it is inserted, fix a  ½” pipe (B) in the other end and flare it. Nowthe  2”  pipe  can’t  fall  out  of  the  tank  when  it goes up and down. Do the same thing for the other 7 pipes. These are our “bacterial motels” or bacterial fuel rods!

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14. Place the gas collector in the stomach tank. Let it sink down until completely submerged if possible, making sure that the bacteria hotels are straight up and down (you may need to turn the tank slowly as you put it in and let the air out”.

15. Put an elbow, ½” valve and hose adaptor on the ½” tank adaptor and connect to ½”
plastic tube.
16. Wait 3 weeks or so with valve closed until gas collector starts to rise. Release all gas to air
and let it rise again. Release all gas in case it has oxygen in it.
17. The third time tank rises, try to light gas coming out. If it doesn’t light it has too much CO
2in it. Release it and let it rise again. One day it will light as CH2concentration rises.once it lights you can start slowly feeding.
18. When you connect the outcoming gas tube with your cooking place, make sure that a simple “water trap” is included, so that the pipes do not become blocked by condensing water.

download diagram

Next page Biogas Pipeline Connection fittings

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