|Better Farming Series 32 - Biogas 2: Building a Better Biogas Unit (FAO, 1986, 47 p.)|
108. If the temperature where you live often falls below 15°C, you can keep the waste mixture warm by covering this biogas unit with plant materials such as leaves, grass, straw or maize stalks.
Protect the drum oil
109. However, as you were told in Item 28 in this booklet, you must not put this unit underground as you could with your old unit or you will not be able to shake it to break up the scum