Influence of Mechanical Mixing Rates on Sludge Characteristics and Membrane Fouling in MBRs

Abstract

The influence of shear intensity (G) induced by mechanical mixing on activated sludge characteristics as well as membrane fouling propensity in membrane bioreactors (MBRs) was investigated. Four MBRs were operated at different mechanical mixing conditions. The control reactor (MBR₀) was operated with aeration only supplemented by mechanical stirring at 150, 300, and 450 rpm in MBR₁₅₀, MBR₃₀₀, and MBR₄₅₀, respectively. It was found that the MBR₃₀₀ demonstrated minimum rate of membrane fouling. The fouling potential of the MBR₃₀₀ mixed liquor was lowest characterized by the specific cake resistance and the normalized capillary suction time (CST_N). Moreover, it was found that the mean particle size reduced with an increase in the shear intensity. These results reveal that membrane fouling can be significantly mitigated by appropriate shear stress on membrane fibers induced by mechanical mixing condition.