Hydrothermal carbonization and pyrolysis of dairy processing sludge for improved nutrient management in agriculture: Current state-of-the-art

This paper summarises advances in hydrothermal carbonization and pyrolysis of dairy processing sludge. Since municipal wastewater treatment plants are the primary source of sludge, thermochemical treatment processes were initially studied and applied to municipal sewage sludge. Research on dairy processing sludge can build upon the insights gained from sewage sludge studies. This article begins with a summary of the current state of the art for both technologies as applied to sewage sludge. It then presents an overview of dairy processing sludge properties, which in some cases differ significantly from those of sewage sludge. This review discusses the properties of all products derived from hydrothermal carbonization and pyrolysis of dairy processing sludge, identifies knowledge gaps, and explores the potential for integrating these two processes within wastewater treatment plants in dairy processing facilities. The integration of hydrothermal carbonization and pyrolysis presents a transformative approach to valorizing dairy processing sludge, aligning with global goals for climate resilience, nutrient recycling, and sustainable agriculture. The review highlights critical knowledge gaps and proposes strategies to accelerate industrial adoption and policy integration.