Monitoring of Long-Term Irreversible Membrane Fouling of Pilot-Scale Drinking Water Ultrafiltration Systems Using Fluorescence Excitation-Emission Matrix Analysis

Ultrafiltration (UF) membrane treatment systems are increasingly used in the production of drinking water as an effective mode of removing particulate matter as well as reducing natural organic matter and water-borne disease causing organisms. This technology is however impeded by membrane fouling, which contributes to increased operational costs associated with decreased membrane permeability, higher trans-membrane pressure and the need for frequent chemical cleaning, as well as shortened membrane service life. Characterization of natural water species that contribute to UF fouling is therefore essential for improving our understanding of membrane fouling in drinking water treatment applications. Implementation of effective and reliable foulant characterization techniques could also be utilized for developing fouling control strategies that have applications in industrial-scale membrane filtration systems. In this study, the feasibility of fluorescence excitation-emission matrix (EEM) approach together with principal component analysis (PCA) to assess the long-term hydraulically irreversible fouling of two pilot-scale UF systems, equipped with full-scale hollow fiber membrane modules, for the production of drinking water from lake water was investigated. The UF systems were operated with frequent cycles of permeation, and a combination of back-pulsing, scouring and chemical cleaning over several months of operation. The principal component (PC) scores generated from the PCA of the fluorescence EEMs were related to humic substances (HS), protein-like and colloidal/particulate matter content as previously observed for laboratory scale UF systems and river water. Multi-linear regression analyses between the measured permeability and the PC scores related to HS-like, protein-like and colloidal/particulate matter were developed to understand the individual and the synergistic contributions of major natural water species groups to long-term hydraulically irreversible UF fouling.  This analysis revealed that both HS- and protein-like matter played a significant role in long-term hydraulically irreversible fouling, with protein-like matter generally showing the greatest contribution. The colloidal/particulate matter contribution to hydraulically irreversible fouling was however not significant. The addition of the coagulant, polyaluminum chloride to the UF feed appeared to have a positive impact in reducing hydraulically irreversible fouling. The proposed approach has applications in quantifying the individual and combined contributions of major foulant species groups present in natural water to irreversible UF membrane fouling and could have application in controlling UF irreversible fouling in the production of drinking water.