AWWA WQTC60679

This study examined the effects of conventional pretreatment and conventional pretreatment with ozone and biofiltration (O₃/BF) on organic fouling of reverse osmosis (RO) membranes. Project goals included assessing the effects of O₃/BF on natural organic matter (NOM) and how changes to NOM affect RO fouling. NOM was characterized using ultrafiltration (UF) size fractionation with ultraviolet absorbance at 254 nm (UV₂₅₄) to produce the following size fractions: >10 kDa, 10-3 kDa, 3-1 kDa, and <1 kDa. Salt rejection, specific flux, and differential pressure data were used to evaluate RO membrane performance. Fouled RO membranes were analyzed with scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS). Results showed conventional pretreatment produced lower average turbidity and silt density index (SDI) than O₃/BF, although average SDI values for both pretreatment processes were higher (>3.0) than recommended for RO membranes. NOM size distribution varied substantially between samples from the same location, preventing an assessment of the effect of O₃/BF on NOM and RO fouling. SEM revealed visual morphologies indicative of colloidal and organic fouling. EDS identified aluminum silicates and silica as sources of colloidal fouling, particularly after O₃/BF. FTIR-PAS indicated O₃/BF caused more fouling and identified proteins, polysaccharides, and aluminum silicates as the primary foulants, although overlapping polysaccharide and aluminum silicate spectra obscured the relative contributions of these materials. Overall, conventional pretreatment yielded better RO performance and less fouling than O₃/BF pretreatment. Enhancing NOM characterization techniques, evaluating alternative NOM characteristics, or reducing interference from colloidal fouling could improve future studies on organic fouling of RO membranes. Includes 11 references, tables, figures.