Influence of immersion depth of membrane on filtration performance of anaerobic membrane bioreactor

Abstract

Membrane fouling is still the main obstacle that hinders the development and implementation of anaerobic membrane bioreactor (AnMBR). In conventional upflow anaerobic reactors, sludge at different height usually presents certain differences in characteristics in terms of particle size, etc. The immersion depth of membrane modules in anaerobic reactors can also influence the fouling of membrane. Thus, it is of great interest to investigate the fouling mechanism with the membrane installed at different heights in reactors. The filtration performance and sludge properties were investigated at different heights of AnMBR. The fouling of membrane in the middle position was severer than that in the top and bottom positions. The total resistance of membrane in the top, middle, and bottom positions was 27.31 × 10¹¹ m⁻¹, 34.67 × 10¹¹ m⁻¹, and 25.29 × 10¹¹ m⁻¹, respectively. By comparing the characteristics and structure of bulk sludge and cake layer at three heights, the bulk sludge in the middle position presented higher content of soluble microbial products (SMP) and finer flocs, and the cake layer was also denser. The results obtained in this study indicated that small size of sludge flocs as well as adhesion of SMP might be the major factors governing membrane fouling at different height in the AnMBR.