Experimental investigation of anaerobic digestion under an external static magnetic field.

Despite the numerous advantages of anaerobic digestion (AD) for biofuel production and waste reduction, its performance is often constrained by operational limitations, including slow kinetics and process instability. Magnetic induction of AD has emerged as an enhancement technique by influencing microbial activity. This study evaluated the effect of mid-range static magnetic field intensities ranging between 86 and 215 mT on AD. The experimental results were used for further analytical computations, including chemical oxygen demand (COD) balance, kinetic modeling, and energy-efficiency analysis. The results showed that the 215 mT assay achieved the greatest energy efficiency and the highest methane yield of 217.6 mL CH₄/g VS, which is 12.7% higher than the control, whereas the 118 mT assay resulted in the highest COD (55.1%) and soluble COD (66.1%) removal. COD balance confirmed that magnetic exposure promoted higher COD conversion to methane and microbial biomass. The greatest VS removal efficiency of 47.7% was achieved through applying an intensity of 86 mT. The findings indicated that static magnetic fields within the medium-intensity range can enhance AD performance without excessive energy demand or microbial inhibition. The kinetic simulation revealed that the Stannard model, which incorporates the shape factor, had the lowest error and highest R-squared value, at 1.2% and 0.994, respectively. This study bridges the research gap between low- and high-intensity magnetic applications, providing valuable insights for optimizing magnetically assisted AD systems.