FertiCycle representation at the 1st Swedish Conference on Sewage Sludge Biochar

By Maja Rydgård (ESR 12) and Clara Kopp (ESR 6)

Biochar can bind carbon for a very long time, providing a climate benefit by ensuring that this carbon is not released to the atmosphere. Researchers and companies with an interest in biochar produced from sewage sludge gathered in Malmö in October for the 1^st Swedish Conference on Sewage Sludge Biochar. FertiCycle ESRs Clara Kopp and Maja Rydgård participated and presented their research at the conference.

The conference covered topics related to biochar properties as well as the production technology: pyrolysis. Pyrolysis is the term for heating of organic material to high temperatures (usually at least 500°C) in an oxygen-free environment. When sewage sludge is pyrolyzed, organic pollutants and microplastics are degraded. Another benefit is that when pyrolysis is performed at sufficiently high temperature, cadmium is evaporated and can be collected and separated from the biochar. Thus, the technology could provide a solution to recycle the phosphorus in sewage sludge to agriculture in a safe way, with a lower risk of harmful contaminants.

In a session about biochar characteristics, Clara Kopp presented her research on how the phosphorus in biochar can become more easily available for plants to take up, by treating the biochar with an acid or a base. Making the phosphorus more plant-available could potentially make it more appealing to farmers to apply biochar to their fields.

To give an overview of the total environmental impact of pyrolysis technology and the application of biochar in agriculture, Maja Rydgård presented insights from a life cycle assessment study. The conclusions support the climate benefit of pyrolysis of sewage sludge when compared to the current sludge management practice, identifying reduced emissions of carbon dioxide, nitrous oxide and methane throughout the life cycle as key contributors to the reduced climate impact.

After two days with presentations and discussions about biochar properties and pyrolysis technology, the conference was ended with a full day study visit to Fårevejle wastewater treatment plant in Denmark, where the first full scale sewage sludge steam dryer and pyrolysis plant recently has been installed.