140. The biogas unit that you learned to build in Booklet No. 31 and the biogas unit that you learned to build in this booklet are both small units that use one drum for the waste holder.
141. With both of these small units you put in all of the waste when you first began. Then, when all of the gas was made, you cleaned out the unit, used the waste as fertilizer and started all over again.
142. By building and using either or both of these units you learned a lot from your experience.
143. Now, let us look at still another biogas unit that you can build using what you have learned to help you.
144. This unit is bigger and better than your first two units. It is also more difficult to build and to use.
145. This kind of biogas unit can also be built using oil drums with the same kind of pipe fittings that you used before.
146. However, it can be built much bigger than your old units. You can use several oil drums instead of only one. So, you can make more gas than you did before.
Another kind of biogas unit
147. This kind of unit is also filled with waste when you first begin.
148. Then, after the unit begins to make gas, you continue to put in waste from time to time. You may do this every few days or you may do it every week.
149. However, when you put new waste into this kind of unit, an equal amount of waste is pushed out of the unit.
Put in waste material
150. With fresh waste material always moving through the unit, it will make biogas for a much longer time.
151. You will learn more about this bigger and better unit in a later booklet in this series.