In situ monitoring of membrane fouling in spiral-wound RO modules by UTDR with a sound intensity modeling

Abstract

ab s t r ac tThe ultrasonic time-domain reflectometry (UTDR) technique with a new signal analysis protocolsound intensity calculation and modeling was developed to detect the calcium-sulfate fouling in a commercial spiral-wound reverse osmosis (RO) membrane module. The fouling experiments were carried out with 2.0 g/L calcium sulfate solution. A 2.25 MHz focused transducer was used and mounted on the outside of the module housing. Results show that the ultrasound is capable to penetrate through the multiple layers of membrane. The systematic changes on the ultrasonic reflected signals with fouling time were observed by UTDR. The total sound intensity of the response signals obtained declined with the fouling time and reached a minimum at about 25 h of fouling, and then increased in the following time. The changes in the total sound intensity were correlated to the deposition and formation of the fouling. The entire acoustic spectra were divided into three sections according to the arrival time. The subsection sound intensity indicated that the fouling layers deposited on the membranes in regular order from inner to outer of the spiral-wound module. Gravimetric and scanning electron microscopy (SEM) analyses revealed the membranes near the pure water tube of the module suffered from much severely fouling. Overall, this study demonstrates that the UTDR with a suitable signal analysis protocol can provide valuable insight concerning fouling in a spiral-wound membrane module.

Inorganic Scaling in Membrane Desalination: Models, Mechanisms, and Characterization Methods

“…In principle, information on the thickness of the scaling layer can be obtained. In addition, sound intensity, which is related to the sound pressure, sound velocity, and medium density, is used to analyze the formation of inorganic scale precipitates and the cake scaling layer . The relative sound intensity decreases because of the growing precipitates absorbing or scattering the echo sound signal.…”

“…In addition, sound intensity, which is related to the sound pressure, sound velocity, and medium density, is used to analyze the formation of inorganic scale precipitates and the cake scaling layer. 278 The relative sound intensity decreases because of the growing precipitates absorbing or scattering the echo sound signal. The following increase after the minimum in relative sound intensity results from the formation of the scale cake layer, which has a higher density and ultrasonic impedance than those of polymeric membrane materials (Figure 9B2).…”

Effects of concentration polarization, temperature and pressure on ultrasound detection of inorganic fouling and cleaning in a spiral-wound membrane module

“…Zhang et al [16] and Chai et al [17] were the first investigators to apply UTDR to monitor calcium sulfate scaling in a commercial 2 1 = 4 -inch (5.6 cm) spiral-wound RO module. Recent applications of UTDR to monitoring calcium sulfate scaling in a commercial 4-inch (10.2 cm) spiral-wound module have been done by An et al [18,19]. Calcium sulfate scaling has been studied using UTDR for flat sheet NF membranes by Zhang et al [20] and Cobry et al [21], and calcium carbonate scaling by Li et al [22].…”