Human waste + Anaerobic digestion = Biogas + Fertilizer
Anaerobic digestion (AD) is a biological process in which organic waste is consumed by micro-organisms in oxygen-free environments. It is used for industrial or domestic purposes to manage waste and to release energy. As it decomposes, the waste releases biogas.
Biogas is composed of methane (CH4, 65%), carbon dioxide (CO2, 33%) and other trace gases (2%). For comparison, the natural gas supplied to ordinary gas stoves and boilers is about 80% methane. When biogas is burned, the methane converts back to CO2 and water vapor, so the gas is clean burning.
Fertilizer is the other by product of AD. The microbial process homogenizes the nutrients making them easier for plants to access. The output is a semi-liquid manure that is easily separated into liquid plant food and fiber-rich manure that’s perfect for digging in under newly planted crops.
AD around the world
In most of the world, not to mention your stomach, AD is happening. Some believe that humans have used AD for gas production since the ancient city of Ur—a hypothesis that’s difficult to prove. Today, in parts of India and China, AD is widespread on a household scale, treating a combination of animal, human and food waste. In Germany and Austria, there are towns that run completely on biogas sourced from farm digesters in the outskirts of town.