AWWA ACE65397

The most commonly used indices for determining the suitability of feedwater for reverse osmosis (RO) treatment are the silt density index (SDI) and the modified fouling index (MFI). These indices, especially SDI, are not considered to be a representative measure of the particulate fouling potential of RO feedwater in all cases. In this study, a cross-flow sampler (CFS) has been developed to select the particles that are most likely to deposit and cause fouling. Combined with the upstream CFS, the SDI/MFI was systematically measured to detect the fouling potential of various feedwater with different pretreatment techniques. Results showed that the SDI and MFI values obtained with the CFS system were not proportional to standard SDI and MFI indices except when tight microfiltration/ultrafiltration (MF/UF) pretreatment was used. Because the CFS system was operated at similar hydrodynamic conditions as in a RO process, the SDI and MFI measurements obtained using the CFS system could serve to be a more appropriate method to measure fouling indices. As part of future work, the indices obtained after CFS system would be compared to flux decline behavior of various source waters to determine the sensitivity in measurements and, hence, predict RO flux decline. Includes 10 references, table, figures.