Microbiological and Physicochemical Interactions in the Formation and Control of Fouling in Anaerobic Membrane Bioreactors Treating Urban Wastewater

This study investigated fouling formation in anaerobic membrane bioreactors for urban wastewater treatment through an integrated analysis combining operational assessments, physicochemical characterizations, and molecular microbiological characterizations. Operational results, including resistance and permeability tests, indicated that the cake layer was the main factor increasing the filtration resistance, whose reversibility was limited by the stratified nature of the deposit. This was detailed by the presence of biopolymers (proteins, fatty acids, extracellular polymeric substances, and polysaccharides) and inorganic elements such as iron and aluminum, which coexisted in a complex matrix. Biomineralization was demonstrated by the persistence of iron and aluminum complexes with protein residues, even after rigorous chemical cleaning, giving the fouling layer a robust and partially irreversible nature. Scanning electron microscopy analysis corroborated the dense structure of the fouling layer, confirming its partially irreversible character. Microbiological characterization via ribosomal gene sequencing indicated high similarity between the mixed liquor and biofilm communities, with enrichment of genera associated with anaerobic digestion and methane production, such as Methanosaeta, Methanobacterium, Syntrophobacter, Syntrophus, and Clostridium, as well as sulfate-reducing bacteria like Desulfomonile. Additionally, the genus Pseudomonas stood out, being identified in high abundance in the membrane sample after cleaning, suggesting a crucial role in adhesion and fouling consolidation.