Novel Monitors Enable Early Detection of RO System Fouling

Abstract

Noninvasive process monitoring methods—such as ultrasonic time domain reflectometry (UTDR) and electrical impedance spectroscopy (EIS)— provide reliable information. Coupled with a side-stream reverse osmosis (RO) fouling monitor cell that simulates plant flows, these methods could preempt fouling problems through more sensitive process monitoring. This is more desirable than crude measurements of transmembrane pressures and flows that may fail to detect incipient fouling. When the RO process is operating, another way to preempt fouling problems is to measure the water's fouling propensity with a silt density index (SDI). However, SDI is empirical and potentially unreliable. A membrane integrity sensor (MIS) can evaluate the integrity of microfiltration or ultrafiltration membranes used in pretreatment, which in turn measures the RO feed's fouling propensity. This article reviews recent MIS and UTDR developments at the Singapore Membrane Technology Centre and EIS developments at the University of Sydney.