In situ investigation of fouling behavior in submerged hollow fiber membrane module under sub-critical flux operation via ultrasonic time domain reflectometry

This study described the extension of ultrasonic time-domain reflectometry (UTDR) for monitoring the fouling profile in a submerged hollow fiber membrane module under different operation conditions including aeration rate, fiber length and operational flux. Five 10 MHz ultrasonic transducers employed were mounted along the tubular test module with a single hollow fiber membrane evenly. A polyethersulfone hollow fiber membrane with inside and outside diameter of 1.0 and 1.6 mm was employed to treat 5 g/L yeast suspension. The experimental results showed that the fouling could not be completely prevented under the operation of the sub-critical flux, and still deposited at the upper part of the submerged hollow fiber membrane. The progress of foulant deposition onto the membrane surface gradually migrated from top to bottom and reached the plateau finally. Further, the increase of aeration and curtailing fiber length could only slow down fouling and reduce deposition rate to some extent, but could not fully avoid the membrane fouling. Moreover, UTDR technique was successfully employed to measure the relationship between the operational flux and particle deposition on the membrane surface so as to obtain threshold flux, under which could obviously alleviate membrane fouling.

► UTDR technique was used to monitor fouling distribution under sub-critical operation.
► The increase of aeration could not completely avoid membrane fouling.
► Curtailing fiber length is not an effective method to control membrane fouling.
► Critical flux represents relative rather than absolute value of fouling control.