Better Farming Series 32 - Biogas 2: Building a Better Biogas Unit (FAO, 1986, 47 p.) Putting in the waste The waste materials The starter Putting waste in this biogas unit After the waste is in

Better Farming Series 32 - Biogas 2: Building a Better Biogas Unit (FAO, 1986, 47 p.)

Putting in the waste

The waste materials

78. You have already been told that this biogas unit is very much like the one that you learned how to build in Booklet No. 31.

79. Since your new biogas unit is much the same as your old one, you can use the same kind of wastes in the same way. Items 58 to 66 in Booklet No. 31 tell you how to prepare them.

Use wastes

80. With the new unit, as with your old unit, you put in all of the waste at one time when you begin. Then, when all of the gas is made, you take out all of the waste, use it for fertilizer, and begin all over again.

81. However, be especially careful to mix the waste and water well. Once this kind of unit is closed you should not open it until all of the gas is made.

82. You cannot stir it or add more water if the waste becomes too thick as you could with your old unit (see Items 94 to 96 in Booklet No. 31).

83. So, the waste and water mixture for the new biogas unit should be thin enough to pour easily.

84. It should be about as thin as the paint or the whitewash that you use to paint your house.

The starter

85. If your old unit is working, take 4 litres of waste from it to use as a starter when you begin.

86. However, if you do not have any waste to use as a starter you will have to make some. Items 67 to 70 in Booklet No. 31 will tell you how to do it.

Putting waste in this biogas unit

87. When you are ready to add the waste, unscrew the plug in the waste hole and put it carefully aside. Put a large funnel in the hole.

Put a large funnel in the hole

88. Open the valve so that when you add the waste the air that is inside the drum will be forced out through the gas outlet.

89. You have not yet been told to attach the gas line and you should not have done so (see Item 75 in this booklet).

90. Put three buckets of waste and three buckets of water in a large container and mix it well (see Item 84 in this booklet ).

Mix waste and water

91. When the waste and water are well mixed, dip out a bucketful and pour it through the funnel into the oil drum.

Pour waste through the funnel

92. If it does not flow through the funnel, add a little more water to the waste mixture in the large container.

Add water

93. Then try to pour another bucketful through the funnel. If the mixture is thin enough to go through the funnel, pour the rest into the drum.

94. Again put three buckets of waste and three buckets of water in the large container and mix it as before.

95. Pour this mixture into the drum. Then take out the funnel. Put a pole long enough to reach the bottom of the drum into the waste hole and stir all the mixture well.

96. Continue in this way until the waste in the drum is about 10 centimetres from the top. Now put in about 4 litres of starter and stir it well.

Pour in starter

97. The starter, which has already begun to work, will help you to make gas sooner.

After the waste is in

98. Close the waste hole tightly and turn off the valve. After about two weeks, open the valve and let out all the gas that has collected in the top of the drum.

99. While you are letting the gas out, be very careful not to have fire near the biogas unit.

100. Listen as the gas escapes. When you hear the sound of the gas stop, turn off the valve quickly. This is to keep air from getting into the drum.

Keep air from getting into the drum

101. Now you can untie the fold in the centre of the short gas line that runs to the inner tube gas holder. When you see the tube begin to swell, you will know that gas is being collected.

102. If you find that gas is leaking from the top of the drum after the unit has begun to work, seal the leaks with tar, mastic or paint as you were told to do in Item 47 in this booklet.

103. If gas is leaking around the gas outlet, T- piece, valve or inner tube, tighten them.

Note
A good way to check for leaks after the biogas unit has begun to work is to put soapy water on the drum and on the joints of the parts and lines. If you see bubbles anywhere you will know that there is a leak. Seal all leaks as you have been told to do.

Bubbles