Background to the project

Sludge char project 2018–2020

The sludge char project carried out in 2018–2020 was a joint project between HSY, Gasum Ltd and the Natural Resources Institute Finland examining the sludge char produced from sewage sludge by pyrolysis and its properties.

In the project, we investigated how the conditions of the pyrolysis process affect the quality of the end product and its suitability for applications that promote nutrient recycling, such as in soil conditioning, as a compost accelerator or nutrient filtering material. We studied the effect of the pyrolysis process on organic harmful substances, heavy metals and microplastics in sludge, as well as the structure of the char produced from the sludge.

The aim of the project was to promote the safe and energy-efficient utilisation of the nutrients and carbon contained in wastewater sludge. The project, carried out in a practical operating environment, provided authorities with valuable information that was lacking on pyrolysis issues, as well as reliable information for the product end users on the quality and safety of the products created. The project started in the autumn of 2018 and ended in November 2020. The final report of the project will be published soon.

The project was funded by the Ministry of the Environment as part of the programme to promote the recycling of nutrients and improve the condition of the Archipelago Sea.

Previous projects

At HSY, the roots of the sludge char project extend back to the Resource-Wise Helsinki Metropolitan Area (REPA) project carried out in 2015–2017, which explored new ways of utilising sewage sludge. The project compared several methods, of which pyrolysis proved the most suitable in the case of Ämmässuo. The project received funding for innovative public procurement from Business Finland.