Biochar Production from Municipal Sewage Sludge via Pyrolysis - The Case of Gotland

Abstract: In order to keep global average temperature below 2°C it is necessary to accelerate climate change mitigation actions and reduce global greenhouse gas emissions. This can be achieved by carbon capture and storage methods such as the production of biochar. Especially its production from municipal sewage sludge could decrease emissions and disposal costs as well as act as a valuable material for different fields of application afterwards. In this quantitative study, the potential for a biochar production system was investigated for the case of the Swedish island, Gotland. Documents and grey literature were reviewed to collect the necessary information and data and experts were asked to fill in information gaps to evaluate the following: Calculate the energy and mass balance of a biochar production system from municipal sewage sludge in 2018, to find possible applications for the produced biochar by investigating the heavy metal content as well as to assess the direct carbon sequestration potential of the produced biochar. The results indicate that in 2018, 540 t of biochar could have been produced with a net heat demand of around 543 MWhth and electricity consumption of 231 MWhel. Heavy metal contents were found to be very high especially for copper and zinc, which means that the produced biochar would only qualify for the EBC-BasicMaterial certification class of the European Biochar Certificate. The annual carbon sequestration potential resulted in 97.2 t of carbon stored in the material or 356.4 t of CO2 emissions saved. Further research needs to be conducted on economic factors of a biochar production system from municipal sewage sludge.