Analysis on a vibration character of a hollow fiber membrane for MBR using a high-speed camera and an accelerometer

Abstract

The dynamical character of the membrane vibration, which relates to membrane fouling phenomena in membrane bioreactors (MBRs), had not been well analyzed by the direct measurement for the motion of the hollow fiber membrane (HFM) in the MBR system. In this study, we aimed to develop the membrane vibration measurement method using an accelerometer (ACM) attached on an HFM to apply the measurement in an invisible MBR tank due to high turbidity. A single string HFM of 80cm length with different looseness (0%, 1%, 2% and 3%) was set in a transparent plastic tank, in which turbulence jet flow was induced from a submerged pump, to compare the vibration data using a high-speed camera (HSC) and ACM. Each obtained time series data of the membrane displacement by the HSC was sequentially processed by a low-pass digital filter and a derivative digital filter to obtain each velocity data and each acceleration data. And it was found that the membrane with the larger looseness showed the smaller value in the standard deviation (SD) of acceleration data, which means the average amplitude of acceleration in the random vibration, though the SD of the displacement and that of the velocity was larger. Moreover, the relation between the looseness of the membrane and the SD of the acceleration obtained by the ACM was just the same as the relation obtained by the HSC. Also, both power spectrums of the acceleration in the frequency domain by the ACM and the HSC presented a similar tendency in the relation with the looseness.