|By pinoyfarmer | July 30, 2007|
84. It may take up to three weeks or even a month for the waste in your biogas unit to start making gas. After that, gas will be made for about eight weeks.
85. During these eight weeks, half of the gas will be made in the first two or three weeks and the rest in the last five or six weeks.
86. If you find that not much gas is being made in the last weeks, empty the unit and start again.
Cold weather protection
87. If the temperature where you are often falls below 15°C, you will have to keep the waste mixture in your biogas unit warm.
88. If you put your biogas unit under the ground or partly under the ground, this will help to keep the waste warm.
Keep the waste warm
89. You can keep the waste mixture in your biogas unit warm by putting leaves, grass, straw or maize stalks around the large drum.
Keep the mixture warm
90. You can also keep it warm by adding a bucket or two of poultry drop, pigs mixed with other waste to the waste already in the large drum. Use one part of poultry droppings to three parts of other waste.
Use poultry droppings
Stirring the waste mixture
91. Sometimes a layer of scum may form on top of the waste mixture in your biogas unit. If this happens, less gas will be made and the small drum may not rise.
Layer of scum
92. If the waste is well mixed before it is put into the unit, there will be less chance for scum to form and your biogas unit will make gas well.
93. If you use plant materials, scum is more likely to form than if you use only animal manure. You will need to stir the waste mixture in your biogas unit from time to time.
94. You can break up a scum layer by stirring or shaking the waste mixture after it is in the unit. You must do this without opening the small drum and letting out the gas or letting in the air.
95. During warm weather, the waste mixture in your biogas unit may become too thick and little gas will be made.
96. If this happens, add a bucket of water to the unit and stir the waste to thin it. If after a few days no gas is being made and the waste is still too thick, add another half- bucket of water and try again.
Add water and stir or shake
97. If a lot of very hard scum forms on top of the waste mixture and no gas is being made, take out all the waste mixture, clean the unit and start again. Do not throw the waste mixture away, use it for fertilizer.
When the gas is made
98. Do not burn the first gas that is made. It may have air in it and could explode.
99. A few days after the small drum has begun to rise, open the valve or clamp or untie the gas line and let out all of the gas that has been collected.
open the valve
100. While you are letting the gas out, be very careful not to have fire near the biogas unit.
101. To let the gas out, push the small drum back down into the waste mixture in the large drum. This will force all gas and air out of your biogas unit. Then, close the valve or clamp or tie the gas line and your biogas unit will begin to collect gas again.
Push the small drum down
102. If you have done this carefully, the next gas that is made will have no air in it and it will be safe to burn. You can burn all the biogas that is made after this. Do not open the unit again until all the gas has been made.
103. After all the gas has been made, take the unit apart and empty out the fertilizer. Keep about 4 litres of the fertilizer to be used as a starter for the next time.
Take the unit apart
Keep fertilizer for starter
104. Clean the unit and check for leaks.
Clean and check for leaks
105. Now fill the unit with new waste material and add the starter. Close the unit tightly and it will begin to make gas again.
Fill with new waste material
106. Remember, every time you start again, do not burn the first gas that is made.
Using your biogas
107. The best way to use the biogas that you make with your small biogas unit is for cooking. When your unit is working well, it will make enough gas every day to cook your evening meal.
108. You can use biogas with almost any ordinary gas- burner, if you adjust the burner so that the right amount of air is mixed with the biogas.
Adjust air mix
109. If there is too much air, the flame will be blown out and the biogas will not burn. If there is not enough air, the flame will be yellow, the biogas will not burn well and will not give enough heat.
110. When there is the right amount of air and the biogas is burning well, it will burn with a blue flame. By letting more or less air into the burner, try to make the flame as blue as you can.
111. Sometimes the flame may begin to turn yellow after it has been burning well. This may mean that the burner has become full of a black material called soot.
112. If this happens, clean the burner very carefully and clean all the holes in the burner with soap and water. Dry the burner well. This may help your biogas
113. If the flame is not steady, or if it is weak when there is still gas in the unit, this may be because there is water in the burner or the gas line.
114. Shut off the gas at the small drum and take off the burner. Empty out any water that is in the gas line or in the burner. Then put the burner back, turn on the gas and light the burner again.
Shut off gas
Empty out water
Using the fertilizer
115. You have already learned that when all the gas has been made, the material that is left in your biogas unit is a very rich fertilizer.
116. It does not have a bad smell, and the parasites that were in the animal wastes and the weed seeds that were in the plant wastes are no longer harmful.
117. You can spread this new fertilizer on your fields to help your plants grow well.
Put fertilizer everywhere
118. Do not put the fertilizer all in one place. Put a little of it everywhere on your fields. In this way, all of your plants will grow better.
Taking care of your biogas unit
119. Always be very careful when you are near a biogas unit because gas may be leaking.
120. Never build a fire near the unit, smoke, or even light a match near the unit, because If gas la leaking It may explode.
Never build fire near the unit
121. It biogas is leaking and you breathe in too much of it can make you very sick.
122. Check your biogas unit and gas lines often to be sure that there are no leaks. Items 49 to 57 and items 82 and 83 have told you how to find and stop leaks.
123. After some time, rust will start to appear on the inside of your unit.
124. Once a year you should take the unit apart and clean and paint the metal gas holder and all other metal parts.
Clean and paint
125. You can use paint which is used to protect metal or coat the metal parts with tar.
Making more biogas
126. After you have made biogas a few times with your small biogas unit, and have used it for cooking, you may find that you could use more gas if you had it.
127. The easiest way for you to make more biogas is to build one or more biogas units just like your first one.
128. If you can get more oil drums, pipe, valves and gas lines, and if you have enough waste materials, you can build and run several small biogas units and get gas from all of them.
129. When you have several biogas units, you can connect them to your gas line by using T- pieces. The drawings show you a t- piece and how to connect several units to the same gas line.
130. When you have several biogas units fill them with waste at different times so that when all of the gas in one unit has been made, you will still get gas from another unit which is working.
131. In this booklet you have learned how to build a small biogas unit and how to make your own biogas. You have also learned that you can make more biogas by building several small biogas units.
132. But there are still other ways to make more biogas. You can build an improved small unit or you can build a different kind of unit which is bigger and better and will give more biogas.
133. You will learn about these ways in a later booklet.
Source: Better Farming Series 31 – Biogas: What it is; How it is made; How to use it (FAO, 1984, 52 p.)