A proof-of-concept study on continuous side-stream low-intensity magnetization during anaerobic digestion of sewage sludge

Municipal wastewater treatment plants face increasing pressure to improve energy recovery while reducing sludge volumes and operational costs. In this context, low-input process intensification strategies are of growing interest. This study evaluated a continuous side-stream magnetization strategy applied during 44 days of mesophilic anaerobic digestion (37 ± 2 °C) of sewage sludge, where digesting sludge was continuously recirculated through a tubular rare-earth-material magnetic polarizer generating a low-intensity static magnetic field (20 mT). The experimental results revealed a substantial increase in AD performance, with the SMF-exposed reactor achieving a 48.3% increase in specific biomethane production and a 15% higher reduction in volatile solids compared to the control reactor. Additionally, the digestate exposed to the SMF showed an improved dewaterability, evidenced by a 26.8% reduction in capillary suction time compared to the non-magnetized digestate. Microbial community analysis at the end of the AD process indicated that continuous exposure to SMF significantly enhanced the abundance of key methanogens, including Methanosarcina and Methanobacterium, which contributed to the higher biomethane production observed during AD. These findings indicate that continuous SMF exposure during AD can significantly enhance biomethane production and can be regarded as a promising approach to improve energy recovery from sewage sludge.