Insights of membrane fouling under scale inhibitor synergistic condition monitored by ultrasonic phased array: Fouling spatial and density characteristics

Abstract

Achieving accurate dosing of scale inhibitors in full reverse osmosis (RO) membrane systems for industrial applications is a critical challenge due to a lack of understanding of membrane fouling characteristics. To address this, this study investigated membrane performance at different inhibitor concentrations and proposed a method using ultrasonic phased arrays (UPA) to evaluate the fouling layer's spatial and density characteristics. The study also examined the relationship between fouling reversibility and compaction, and the results showed a clear conversion process from inhibition to exacerbation of membrane fouling by scale inhibitors. Additionally, the fouling layer distribution characteristics were opposite at different concentrations. At insufficient concentrations, the scaling layer forms near the outlet and spreads to the far-end with a continuously decreasing thickness. Conversely, at surplus concentrations, the opposite effect was observed. At sufficient concentrations, the fouling layer thickness and range exhibited a discontinuous distribution. The high-density layer was dominant on the membrane surface and showed low fouling reversibility. However, scale inhibitors were found to minimize fouling density by interfering with ion deposition, reducing the ion content and significantly increasing its reversibility. These findings have significant implications for scale inhibitor efficiency evaluation and scientific application, which can improve industrial membrane system performance.