Thermophilic Digestion in the Nordic Region

Requirements for sludge sanitisation are something that water and wastewater operations will likely need to address within the next 5–15 years. One proposed option for sanitisation is thermophilic digestion at 55°C, with an exposure time of 8 hours.

AN NSVA PROJECT One advantage of thermophilic digestion compared to, for example, pasteurisation, is that the use of high-grade energy for heating can be avoided. If low-grade energy can be used to meet future hygiene requirements, high-grade energy can be allocated to other uses, contributing to more sustainable and efficient resource management. Other potential benefits include higher gas production and a reduced risk of methane emissions from digested sludge.

A challenge is that thermophilic digestion is moderately widespread in Sweden, with approximately 14 facilities in the water and wastewater sector. Experiences have been mixed, with reports of both positive outcomes and issues associated with thermophilic digestion. Isolated negative experiences can lead to the discrediting of the technology, while long-term positive experiences risk being overlooked. Therefore, there is a knowledge gap that needs to be addressed for thermophilic digestion to reach its potential as a resource-efficient and climate-smart alternative for sludge sanitation.

In this project, 11 water and wastewater organisations currently using thermophilic digestion are collaborating, along with four others that see thermophilic digestion as a key option for their future sanitation needs. The project collects and compiles operational experiences, process results, and the conditions for thermophilic digestion of sewage sludge. Surveys and interviews with representatives of Nordic facilities are supplemented by literature reviews to gather current experiences. These findings will be processed and structured into an SVU report in collaboration with the participating water and wastewater organisations.

The results, in the form of an SVU report and a knowledge base of useful key performance indicators from thermophilic digestion facilities, are expected to disseminate knowledge and provide better support for water and wastewater operations in utilising thermophilic digestion.

Project manager: Safa Hadi, Envidan, sah@envidan.se