A direct observation method has been used to study fouling deposition and removal during the filtration of solutions modelling MBR foulants. The method enabled in-situ observation tangentially to the surface of hollow fibre membranes, so that cake height during filtration and cleaning could be clearly quantified, and the dynamics of backwashing on foulants during their removal could be observed. Exciting phenomena occurred during fouling removal, the backwashing force and crossflow shear caused cake expansion followed by fluidisation of the fouling layer. While solution turbidity remains a limiting factor in its application, this non-invasive direct observation technique offers significant potential for further MBR studies, such as filtration of activated sludge, and effects of filtration mode and of bubbling.

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