Electrical Sensors for on-Line Monitoring of Fouling in Hollow Fibre Membranes

摘要

Membrane fouling has been recognized as the main problem of using membranes for liquid separation. Fouling leads to flux decline, higher energy demand for maintaining a constant permeate flux and eventually requires the filtration process to be stopped for physical or chemical cleaning [1]. Monitoring of fouling on-line would allow optimization of the operation of the membrane separation plants. Ultrasonic reflectometry is one of the examples of non-destructive techniques for this purpose [2]. This method has been proposed for on-line detection of membrane scaling or fouling but has not been implemented industrially at this stage. Electrical impedance spectroscopy (EIS) of the membrane using a small AC signal has recently shown to be a successful method for predicting the fouling of reverse osmosis (RO) and nanofiltration (NF) membranes[3,4]. Flat RO and NF membranes are commonly used in the last stage of water treatment, but hollow fibre membranes are increasingly used in early stages of water treatment process. EIS of hollow fibre membranes is more difficult to perform because of the geometrical constraints. The best results for flat membranes have been obtained using two electrodes on each side of the membranes, i.e. feed and permeate. In the case of the hollow fibre membrane, there is no limitation on the number and location of electrodes outside the fibre but it is not practical to fit two electrodes inside the fibres.