The Membrane Fouling Monitored by Scanning Electron Microscopy (SEM) in a Submerged Membrane Bioreactor

Jixiang Li, Shuying He, Siqing Xia, Changquan Qiu, Yanhao Zhang, Junqi Xuan



Scanning electron microscopy (SEM) can provide high resolution images of morphology, thus it is universally used to characterize the membrane fouling. In this study, SEM was performed to visualize the morphology of membranes and further to monitor the effectiveness of different cleaning protocols in a submerged MBR. The SEM images of membrane surfaces indicated that the cake layer could be completely removed by physical cleaning, and biofilms on the surfaces could be eliminated by chemical cleaning, but the biofilm fouling could not be eliminated by physical cleaning alone. The SEM images of cross-sections indicated that the internal pores were still filled by foulants after physical cleaning, but the foulants disappeared after chemical cleaning. These SEM images were also supported by the results of nominal flux tests. Biofilm fouling, together with internal pore block fouling, constituted irreversible fouling, and dominated the operation of MBRs. These results also suggested that the fouling in MBRs should be overcome by multiple methods, including physical and chemical methods. Physical cleaning removed the reversible fouling such as cake layer fouling or concentration polarization, and chemical cleaning eliminated the irreversible fouling such as biofilm fouling and internal block, thoroughly restored the permeate flux.

Keywords: Biofilm fouling; internal fouling; membrane bioreactor; scanning electron microscopy  (SEM)