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.

At Loowatt, we built a 1-cubic meter digester in the UK in 2010. This photo was taken the first day our digester produced gas. It has been producing gas ever since.

Digesters can be built at any scale, and there are many established methods and configurations. In this example, the biogas drum floats up and down inside the digestate.

This means that the pressure is created by gravity – the weight of the floating drum. Small-scale digesters like these are commercially available in India.

In 2011, we brought a digester and 5 prototype toilets to a Marina in West London,
where houseboat residents and Loowatt staff used the toilets and ran the digester for
several months.

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.

We believe that waterless toilets and clean energy are a winning combination.