Intermittent low-strength ultrasonication enhances magnetite retention in anaerobic granules to mitigate washout in upflow anaerobic sludge blanket (UASB) reactors

초록

Direct interspecies electron transfer (DIET), promoted by conductive materials such as magnetite, provides a thermodynamically favorable pathway for anaerobic digestion. However, continuous magnetite washout during long-term operation limits practical application. This study proposes intermittent low-strength ultrasonication to enhance magnetite retention in upflow anaerobic sludge blanket (UASB) reactors. Magnetite (0.1 g/L) was applied during granule formation at hydraulic retention times of 8 h for H₂ granules and 24 h for pre-formed CH₄ granules, with ultrasonication at 0.1 W/mL for 1 s/min. SEM–EDS and ferrozine assays confirmed improved magnetite retention, with insertion into developing H₂ granules increasing by ~76% and attachment onto mature CH₄ granules improving by ~8% compared with non-sonicated controls. Ultrasonication also promoted more uniform magnetite distribution, indicating enhanced permeability and dispersion. Overall, intermittent low-strength ultrasonication mitigates magnetite washout and may support DIET-related syntrophic metabolism. © 2026 Elsevier Ltd

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