Transition of major components in irreversible fouling of MBRs treating municipal wastewater

• Different components caused irreversible fouling depending on the duration.
• Humics first conditioned the membrane surface.
• Polysaccharides started to accumulate after the conditioning.
• The study was based on operation of a pilot-scale MBR.
• Powerful analytical techniques such as NMR/FTIR were used.

Evolution of irreversible fouling in pilot-scale membrane bioreactors (MBRs) treating municipal wastewater was studied. Three membrane modules were sacrificed to analyze foulants after they had been used for different durations (1 day, 8 days, 24 days). The module used for 1 day reflected fouling occurring at the initial stage, whereas the module used for 24 days reflected the later stage of fouling. After each module had been used for the predetermined period, it was disassembled and subjected to powerful chemical analysis such as Fourier transform infrared (FTIR) analysis. It was clearly shown that components involved in evolution of irreversible fouling gradually changed depending on the duration. The initial fouling (conditioning of membrane) was caused by humics, whereas later fouling was mainly caused by polysaccharides. A model for evolution of irreversible fouling in MBRs and implications for fouling control are discussed.