This simple biogas digester at ECHO can create cooking gas from cow manure. A family of four can cook for months on the gas from just one drum of manure sludge. Methane is created by the anaerobic composting of manure by methane-producing bacteria. Harnessing this process replaces the need for firewood. Great appropriate technology for the developing world. The biogas pressure tank is simply an inverted drum in a barrel of water, held in place with an innertube strap that provides pressure as the gas rises. Amazingly simply but highly engineered.