Detection of reverse osmosis membrane fouling with silica, bovine serum albumin and their mixture using in-situ electrical impedance spectroscopy

Monitoring the 'state of the process' is particularly useful in fouling control in the reverse osmosis (RO) industry. In this paper, a novel non-invasive method to monitor the fouling process of single and binary foulants on the RO membrane has been studied; that of electrical impedance spectroscopy (EIS). A typical RO crossflow cell was equipped with electrodes to allow in-situ EIS measurement of the fouling process during RO filtration. The EIS signals were converted to Nyquist plots of the negative imaginary impedance versus the real impedance, and used as a convenient means for characterization of fouling. Different forms of the Nyquist plot were obtained for different types of foulant. Also a significant shift in the Nyquist plots for silica, BSA and their mixtures occurred corresponding to the buildup of a foulant layer on the membrane surface. During the early stages of fouling, the Nyquist plots shifted noticeably while the transmembrane pressure (TMP) showed negligible increase. If EIS could perform on-line in plant operation, it could be a sensitive monitoring tool to detect early fouling in RO membrane filtration.