Identifying artifacts in EDS of fouled RO membranes through Raman and ICP-MS analysis

Abstract

Fouled reverse osmosis (RO) membranes, primarily characterized by Scanning Electron Microscope and Energy Dispersive X-ray Spectrometer (SEM-EDS), face several limitations including spectral inaccuracies and misidentification of elements caused by automatic peak assessment software. This work addresses the latter by analyzing fouled polyamide membranes from community RO plants of Rajasthan treating brackish groundwater. Initially, EDS analysis revealed unexpected elements including Sc, Ti, V, and Cr, alongside anticipated foulants like Ca, Mg, Al, Si, Fe, and Mn. However, upon manual reassessment guided by spectral libraries and elemental likelihood, the peaks originally identified by the software as Sc, Ti, and V were reattributed to Ca and Ba, emphasizing the importance of careful peak assignment. Further, Raman spectroscopy of the same membranes detected calcite, dolomite, and molybdenum-bearing minerals. A peak initially assigned to Mo by the software was reinterpreted as interlayer carbonate, supported by literature on hydrotalcite structures. Subsequent ICP-MS analysis of the deposited salts showed that both Sc and Mo were below the detectable threshold, validating the reassessed findings. This study underscores the challenges of accurately identifying the inorganic scales to develop the right descaling approach by emphasizing the importance of integrating multiple analytical methods for comprehensive analysis and effective membrane cleaning solutions.