Coupled fouling dynamics of particulates and dissolved organic matter in digestate treatment: Insights from real-time optical coherence tomography

Abstract

Membrane fouling remains a major obstacle in membrane bioreactor (MBR) treatment of food waste digestate, primarily driven by complex interactions between particulates and dissolved organic matter (DOM). This study systematically investigated how varying levels of particle removal—achieved by centrifugation at 4000, 7000, and 10,000 rpm—affect fouling behavior and structure. A real-time Optical Coherence Tomography (OCT), combined with flux monitoring, SEM-EDS, FTIR, and Raman spectroscopy, was employed to characterize the fouling dynamics and structural properties. Results revealed that higher centrifugation speeds led to slower but more compact and irreversible fouling. At 10,000 rpm, despite a 22 % reduction in protein and polysaccharide content, Raman analysis revealed a ∼200 % increase in disulfide bond signals and ∼81 % increase in C–O–C linkages, indicating enhanced molecular cross-linking by low-molecular-weight DOM. OCT tracking confirmed a shift from reversible surface deposition to irreversible internal fouling with increased particle removal. These findings suggest that excessive pretreatment may aggravate internal fouling and underscore the need for an optimized particle removal strategy. Real-time OCT is shown to be a promising tool for monitoring fouling dynamics and guiding adaptive pretreatment in high-strength organic wastewater treatment.