The GREEN4SLUDGE* project introduces an innovative and sustainable approach to the treatment of tannery sludge in the Santa Croce sull’Arno industrial district. By integrating hydrothermal carbonization (HTC) with advanced mechanical dewatering, the project aims to drastically reduce sludge volume and improve its manageability. At the heart of this innovation is the B‑Sludge technology, which couples HTC treatment with a high‑efficiency filter press dewatering.

The filtration step is critical to the project’s success: by exploiting the physico-chemical transformations induced by HTC, the filter press is able to achieve dry‑solids contents above 45%, far exceeding the performance of conventional dewatering technologies. This enhanced filtration capability leads to lower transport and disposal costs and reduces energy consumption during subsequent drying.

A dedicated study assessed how HTC operating conditions — namely temperature and reaction times, initial solids concentration… — affect filtration performance. The results highlight a critical threshold for suspended solids concentration, above which the filter press consistently produces a stable and compact cake suitable for industrial‑scale operations. The analysis also identified optimal HTC parameters that improve filterability, demonstrating that controlled carbonization significantly enhances sludge structure, permeability, and water‑release behavior.