Berlin botanical garden develops carbon-friendly organic waste recycling

The TerraBoGa research project developed a ‘closed-loop’ organic material recycling system at Berlin-Dahlem Botanical Garden in which all organic waste is converted into biochar – charcoal used to increase soil fertility – and compost. The goal was to create a ‘carbon-negative’ waste management system – one that absorbs more carbon dioxide than it emits – so as to positively influence climate change.

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The TerraBoGa research project at the Berlin-Dahlem Botanical Garden developed a ‘closed-loop’ organic material recycling system in which all its organic waste is converted into biochar and compost. © TerraBoGA The TerraBoGa research project at the Berlin-Dahlem Botanical Garden developed a ‘closed-loop’ organic material recycling system in which all its organic waste is converted into biochar and compost. © TerraBoGA

" In the Berlin-Dahlem Botanical Garden, large amounts of biological waste are produced every year and have typically been disposed of by conventional means. The TerraBoGa project aimed to close the garden’s material cycles by examining biological waste with a view to recycling it, and prepared it for re-use in line with the garden’s needs using biochar technology and a climate-friendly composting process. "

Robert Wagner, Department of Earth Sciences, Free University of Berlin

A carbonisation plant was installed at the garden to produce biochar from stem wood and pruning waste, and to provide energy for heating. Other nutrient-rich waste was composted with biochar in small, triangular windrows.

The resulting product meets German federal requirements on nutrient value and pollutant limits. In addition, use of the technology has enabled the garden to achieve a negative carbon footprint for its organic waste management.

Plant nutrient and carbon storage

As an effective means of long-term storage of plant nutrients, water and carbon, biochar has great potential for accelerating moves towards carbon-negative organic waste management in urban areas, while increasing the horticultural value of plant residue. Moreover, the energy generated during carbonisation can replace fossil fuels.

Inspiration for the development of biochar technology comes from Terra Preta do Indio, an artificial soil found in the Amazon basin which owes its dark colour to its charcoal content. It was a key ingredient in a successful pre-Columbian waste management system in which organic matter was combined with charcoal to improve soil fertility.

Berlin-Dahlem Botanical Garden produces around 2 100 m³ of green waste, pruning waste, grass cuttings and wood annually. Previously, most of it went unused and was disposed of in expensive and energy-intensive ways, while some 250 m³ of compost and peat had to be purchased each year.

Optimising waste re-use

TerraBoGa identified conversion of plant waste into biochar to produce high-quality compost. The system has significantly improved compost management and quality regarding factors like moisture and odour. It has enabled the garden to cut costs as it no longer has to buy compost.

Greenhouse gas emissions from waste management at the garden have been reduced by up to 43 % and leaching of plant nutrients such as nitrate, phosphorus and potassium from compost has been reduced. Furthermore, disposal of green waste has been minimised, thus achieving the desired closed-loop recycling system.

The botanical garden has continued to use biochar technology since the completion of TerraBoGa in 2015. Thanks to the project, the method has become well-known both throughout Berlin – with many individuals and small firms applying it in domestic gardens and at business premises – and internationally through conference presentations, lectures, seminars and publications.

Berlin and other German cities are discussing wider deployment of the technology and municipal representatives from countries including Norway, Sweden and Denmark have asked to be taken on tours of the garden to learn more about it. Implementation is being investigated at Tierpark Berlin, one of the city’s two zoos. The TerraBoGa concept and results are being introduced into vocational training for gardeners, cooks and environmental engineering assistants.

Total investment and EU funding 

Total investment for the project “TerraBoGa” is EUR 2 005 097, with the EU’s European Regional Development Fund contributing EUR 1 002 548 through the “Berlin” Operational Programme for the 2007-2013 programming period. The investment falls under the priority “The environment”.

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