Monitoring of colloidal fouling and its associated metastability using ultrasonic time domain reflectometry
Ultrasonic Time Domain Reflectometry (UTDR) is used to monitor the deposition and physicochemical nature of colloidal silica fouling on a polyethersulfone ultrafiltration membrane under crossflow and constant flux conditions. The fouling can be characterized by four stages based on the rate of inc...
Saved in:
Main Authors: | , , , |
---|---|
Other Authors: | |
Format: | Article |
Language: | English |
Published: |
2013
|
Online Access: | https://hdl.handle.net/10356/99940 http://hdl.handle.net/10220/11003 |
Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
Institution: | Nanyang Technological University |
Language: | English |
Summary: | Ultrasonic Time Domain Reflectometry (UTDR) is used to monitor the deposition and physicochemical
nature of colloidal silica fouling on a polyethersulfone ultrafiltration membrane under crossflow and
constant flux conditions. The fouling can be characterized by four stages based on the rate of increase of the
transmembrane pressure (TMP): (1) an initial rapid increasing rate due to concentration polarization; (2)
a slow constant rate; (3) a nonconstant increasing rate associated with metastability of the colloidal silica;
(4) a constant rapid rate associated with the foulant layer having a constant thickness. The destabilization
of the colloidal particles in the foulant layer during stage 3 is associated with an increase in the UTDR
peak amplitude. During stage 4 the foulant layer thickness reaches a plateau value that decreases with
increasing crossflow velocity. The rheological behavior of the foulant layer is described by the Bingham
plastic model for which the yield stress can be obtained from the UTDR data. When membrane cleaning
is done by switching from a fouling to a non-fouling feed solution, marked decreases in both the foulant
layer thickness and TMP are observed. However, a residual tightly bound foulant layer remains on the
membrane whose thickness, determined by UTDR, corroborates well with off-line scanning electron
microscopy analysis. |
---|