The Petchey Academy
A manual for building a small scale anaerobic digester.
COW is a project with Year 9 GCSE students supervised by Peter Harms at the Petchey Academy in Hackney, East London, to design & build an anaerobic biodigester. School dinner left-overs go in one end and biogas and plant fertiliser is produced at the other - just like it does in a real cow!
The project aimed to bring closed-loop cycles to life in a school environment. With student participation, we built a 60-litre anaerobic digester (AD) to connect different school activities such as recycling, design & technology, food growing, science and geography, and actively demonstrate integrated closed-loop thinking. This prototype included gas storage and cooking facilities, enabling it to be used for cooking classes and community events. It will be an important feature in helping the school reduce its carbon footprint, by engaging staff and students with waste to energy solutions, circular economy principles, and nutrient recovery.
The project also supported the integration of AD into the school environment, giving students a hands-on understanding of the technology, and the potential to develop further components as the project progresses.
Anaerobic digestion (AD) is an established technology, a type of composting that transforms all organic waste (except wood) into useful by-products. Microorganisams digest the waste emitting methane and carbon dioxide in the process. This biogas is captured for use as a clean, renewable fuel. The remaining material can be utilised as a nutrient-rich liquid fertiliser. When food waste goes to landfill, the nutrients are lost and the gases escape into the atmosphere causing climate change.
AD can create a closed-loop cycle and reduce waste miles by: managing organic waste on-site (food waste, manures, soft green waste), generating clean, renewable energy, recovering nutrients to produce a quality liquid fertiliser, supporting local food growing
Education and engagement
Waste will become a valuable resource as we move further into the 21st century and anaerobic digestion is one of the technologies that will enable transition to a more sustainable future. Digesters offer educational opportunities for schools, universities, businesses and the general public. Seeing the technology at a human scale helps people understand its benefits and place within the circular economy, which can support behavior change around waste and recycling. AD can be linked to science, citizenship, design and technology, food growing, and geography curriculums. LEAP offers a 6 -12 session educational programme that can include construction of a working AD system