Comparative assessment of magnetic pretreatment across low to moderate intensities for enhancing anaerobic digestion of sewage sludge

This study investigates the effect of static magnetic field (SMF) pretreatment at different field intensities on the anaerobic digestion (AD) of sewage sludge. Three SMF intensities (10, 20, and 50 mT) were applied through tubular magnetic polarizers under varying numbers of magnetization cycles (NMC) to assess their impact on biomethane production. The 20 mT condition with a single NMC yielded the highest improvement, increasing methane production by 21% compared to the untreated sludge. Lower (10 mT) and higher (50 mT) intensities produced modest enhancements, suggesting a nonlinear correlation between SMF strength and methane generation. Volatile fatty acid analysis indicated that pretreatment at 20 mT enhanced hydrolysis and acidogenesis. Microbial investigation further showed that moderate SMF exposure reshaped the sludge community, enriching fermentative and syntrophic taxa that promote organic matter degradation and efficient methanogenesis. Unlike energy-intensive pretreatments, the proposed SMF system operates passively, using permanent magnets to generate magnetic exposure without external power input. Preliminary economic analysis suggests that this energy-neutral approach can lower sludge management costs while improving overall energy recovery.