Real-time monitoring of scale formation in reverse osmosis using electrical impedance spectroscopy

Early detection of scale Formation in reverse osmosis systems remains challenging since the bulk measurements of the operating data are not sufficiently sensitive to detect the subtle changes occurring across the membrane. Electrical impedance spectroscopy (EIS) was investigated as a tool for measuring the electrical properties in real time and to identify changes that occur during calcium sulfate scaling in a reverse osmosis system. EIS signals were obtained across a frequency range of 10(-1)-10(5) Hz during the filtration of calcium sulfate scale forming constituents in recirculation and batch modes. The measured capacitance and conductance of various electrically distinct layers were compared against the flux measurements, in order to assess their significance to indicate the scale formation. The rate of change in conductance was higher than the flux decline. Change in the conductance value around 38 Hz, corresponding to the coating layer on the active membrane surface was most suitable. From the suggested approach of monitoring the changes in conductance at 10-100 Hz, scale formation can be detected prior to observing any significant permeate flux decline. (C) 2013 Elsevier B.V. All rights reserved