Impact of Tween-80 modified foam iron combined with spatial magnetic field on methane production from medicinal herb residues in anaerobic digestion

This study investigated the impact of non-ionic surfactant (Tween-80) modified foam iron combined with a spatial magnetic field (T80-FI + SMF) on methane production during the anaerobic digestion of trichosanthes kirilowii pericarp residue. Using single-factor experiments and Box-Behnken design optimization, the optimal process conditions were determined as follows: a modified foam iron dosage of 2.9 g/L, a Tween-80 modification concentration of 8.3 g/L, and a spatial magnetic field intensity of 14.4 mT. Mechanistic analysis revealed that T80-FI + SMF effectively increased the concentrations of volatile fatty acids, iron ions, and cytochrome C, facilitated metabolic balance between Methanosarcinales and Geobacterales. This promoted efficient direct interspecies electron transfer and maintained a dynamic equilibrium between Fe2+ and Fe3+, leading to a rapid methane production peak. As a result, the cumulative methane yield reached 642.3 ± 13.7 mL/g VS, representing a significant 33.2 % increase compared to the control group. In semi-continuous mode, the maximum organic loading rate improved from 2.0 to 2.67 g VS/L/d. The energy conversion efficiency reached 75.6 %, with a payback period of 6.39 years. This study offers a novel technological pathway for the resource-efficient treatment of organic waste and enhanced methane production.