Field applicability verification of a piezoelectric convergence high-sensitive membrane integrity test

Abstract

This study proposes a piezoelectric sensor-based method for detecting membrane unit damage to enhance the effectiveness of integrity monitoring. The sensor can identify changes in the dynamic stiffness of the host structure and estimating internal pressure variations within the air injection pipe by measuring the electro-mechanical impedance of an air injection pipe. During the pressure decay test (PDT), resistance differences were observed in damaged regions during the gas-liquid conversion phase. However, these differences were subtle, with the rate of pressure rise to the preset PDT value ranging from a minimum of 0.015 to a maximum of 0.059 kPa/sec. As a result, conventional pressure gauges failed to accurately detect such changes. To validate the proposed method, both a pilot-scale single membrane test and a full-scale membrane unit test were conducted. The signal output from the piezoelectric sensor varied according to pipe pressure and demonstrated higher sensitivity in detecting pressure changes compared to traditional pressure gauges. This allowed for the detection of minute pressure changes caused by air leakage in damaged membranes. The use of the Cross-correlation coefficient index in relation to pressure variations reduced the diagnostic time and improved sensitivity in comparison with conventional PDT. Furthermore, the amount of leakage was reduced by up to 48% through turbidity monitoring of the permeate water. These findings indicate that the proposed method offers an efficient and reliable approach for membrane integrity testing of unit membrane systems.