The evolution of pore-blocking during the ultrafiltration of anaerobic effluent–like mixtures

• Ultrafiltration of anaerobic effluent produced two stages of fouling.
• The standard blocking stage was limited by chitosan deposition.
• The incidence of matrix vesicles in fouling layers was linked to biomineralization.
• Biomineral seeds increased the fouling mass in low/intermediate CaCO3 loads.
• Structure was more important than mass in AnMBR fouling.

The global market for membrane bioreactor technology (MBR) is growing fast. Membrane biofouling hinders the broader application of MBR because it reduces permeate yield. The main goal of this manuscript was to identify the arrangement of fouling mechanisms during the ultrafiltration (UF) of suspensions comprising extracellular polymeric substances (EPS) and inorganic colloids (IC). Standard blocking (SB) was the main operative fouling mechanism in the early stages of filtration, which eventually shifted to cake filtration (CF). Longer SB stages were observed in UF experiments with a slight electric charge density ratio (ECD). CF was the predominant fouling mechanism with a higher ECD and led to the formation of mineralized-EPS-building blocks (MEBB) within the cake. MEBB accumulation in the membrane produced sharp reductions in filtration performance after 0.5 and 1.5 mM CaCO3 were added. Non-covalent interactions fostered the development of irreversible fouling and biomineral seeds on membranes.