Zero Excess Sludge Production in a Thermophilic MBR System: Performance and Energy Consumption Evaluation

Water utilities are looking for creative solutions that can lower sludge output while maintaining process dependability and environmental compliance due to the increasing operational and regulatory difficulties related to managing sewage sludge. In order to minimize sludge, this study presents the first full-scale implementation of a thermophilic pure-oxygen biological process integrated with ceramic ultrafiltration (UF) membranes in Europe. The system uses thermophilic conditions (50°C–55°C) to treat thickened municipal sludge, and membrane separation ensures complete biomass retention. Long-term monitoring (2024–2025) revealed high biodegradation performance, with VS removal exceeding 85% and very low biomass yields (0.01 kg VS kg−1 COD_removed). COD removal efficiencies were slightly lower due to the selective permeation of soluble organic matter, which is beneficially reused as an external carbon source for downstream denitrification. Oxygen- and energy-based indicators confirmed that process efficiency was strongly influenced by membrane hydraulic performance, particularly membrane fouling, permeability decline, and the associated membrane maintenance requirements. Despite higher energy demand compared to conventional mesophilic processes, the substantial sludge reduction and recovery of soluble COD make the system economically competitive in a regulatory context where sludge disposal options are increasingly limited. The results demonstrate the robustness and sustainability of thermophilic UF-based sludge reduction and highlight its potential as a strategic solution for modern wastewater treatment plants seeking resilient, circular, and regulation-proof sludge management pathways.