Biogas Plant What is Biogas? How Biogas plant made? How to Use biogas plant? Part 2 of 3
What waste materials to use
58. Animal manure from cows, pigs and chickens, and crop and plant wastes are good materials for making biogas.
Materials for make biogas
59. You can use animal manure alone or plant materials alone or you can use both mixed together.
60. Straw which is mixed with manure, which you may have where you keep your pigs or chickens, is usually a good mixture of animal manure and plant material for making biogas. Be careful to chop it fine before you use it.
Straw mixed with manure
61. When you first begin, it is best to use only animal manure or a mixture of animal manure and very little plant material. Later when you have learned more about how your biogas unit works, you can use more plant materials.
62. When you do begin to use plant materials, remember that dry plant materials must be chopped or shredded very fine and fresh plant materials must be left outside to rot for 10 days or more before you put them into a biogas unit.
How to use them
Rot 10 days
Rot 10 days
63. Whether you are going to use animal manure or plant materials in your biogas unit, you must mix them with water. Use one bucket of water with every bucket of animal manure or plant material.
Animal manure and plant material
64. Plant materials which are not mixed well may not make gas later. When you mix plant materials with water, they pack together.
65. If you are using plant materials, break them apart and stir them well so that they will be well mixed.
66. Mix the animal manure or the plant material with water until the waste mixture is easy to pour. The waste mixture will work best if it is like a thin paste.Making a starter
67. About two months before you are ready to use your biogas unit for the first time, put 2 litres of animal manure and 2 litres of water in a bucket and mix well. You can also add some finely chopped plant material such as grass.
68. We call this mixture a starter. A starter helps the biogas unit to make gas sooner.
69. Pour the starter mixture into a container which holds a little more than 4 litres. You can use a bottle or a jug but do not close it, leave it open.
Pour starter into a container
70. Keep the starter warm and shake the container three or four times each week to mix the contents. In about two months it will be ready to use.Putting waste into your biogas unit
71. Now you are ready to put the waste into your biogas unit. Put the large drum open end up where you want the unit to be. Put the small drum next to it with the gas outlet up.
72. Now put the waste and water you are going to use into the large drum. Put 3 buckets of waste and 3 buckets of water into the large drum and stir it well.
Put waste and water
73. Now put another 3 buckets of waste and 3 buckets of water into the large drum and stir all of the waste mixture again.
74. Put more waste and water into the large drum, stirring well each time, until the waste mixture in the large drum is level with the top of the small drum. The drawing on page 29 will show you how.
75. Stir the starter you have made, (see Items 67 to 70) into the waste mixture in the large drum. The starter which has already begun to work will help you to make gas sooner.
76. Now open the valve or clamp or untie the gas line of the small drum to let out the air. Push the small drum down into the waste mixture until it touches the bottom of the large drum.
77. The small drum must be full of waste mixture. It must be full to the top so that there will be no air in it.
78. You can be sure that the small drum is full to the top if you can see that the waste mixture inside the large drum rises a little above the top edge of the small drum when it has been pushed down.
Small drum full
79. If it does not rise above the top edge of the small drum, take the small drum out and put a little more waste and water into the large drum. Then put the small drum back and push it down into the waste again.
80. When you are sure that the small drum is full of waste mixture to the top, close the valve or clamp or tie the gas line so that you will keep out air and begin to collect gas.
81. You can tell that the waste mixture in your simple biogas unit has begun to rot and make gas when the small drum begins to rise. This means that gas is being collected.
82. If you find that gas is leaking from the small drum after the biogas unit has begun to work, seal the leaks with tar, mastic or paint. If the gas is leaking around the gas outlet or valve, tighten the outlet or valve again and coat the joints with tar, mastic or paint.
83. A good way to check for leaks after the biogas unit has begun to work is to put soapy water on the small drum and on the joints of all the parts and lines. If you see bubbles anywhere, you will know that there is a leak. Seal the leaks as you were told in items 53 and 54.
Source: Better Farming Series 31 – Biogas: What it is; How it is made; How to use it (FAO, 1984, 52 p.)