Modified Fouling Index(ultrafiltration) to compare pretreatment processes of reverse osmosis feedwater

Existing fouling indices to measure the particulate fouling potential of re verse osmosis (RO) feedwater, the SDI and MFI0.45 do not include smaller co lloidal particles. Therefore, the MFI using ultrafiltration (UF) membranes was developed (1000-100,000 Da pore size) to incorporate and measure smalle r particles. A 13,000 Da membrane was selected as the most promising refere nce membrane for application in the MFI-UF test. This research investigates its application to (1) measure the particulate fouling potential of RO fee dwater and (2) evaluate the efficiency of pretreatment processes on particl e removal at two RO pilot plants. Where possible a comparison was made with the SDI, MFI0.45, and particle counts. Both RO plants use conventional pre treated surface water. Subsequently, the Rhine River plant uses ozonation, biological activated carbon filtration, and slow sand filtration while the Ijssel Lake plant uses ultrafiltration (150-200,000 Da). The MFI-UF of the influent feedwater was about 400-1400 higher than the corresponding MFI0.45 and SDI, due to the retention of smaller particles. A reduction in the par ticulate fouling potential, greater than or equal to 80%, was found by MFI- UF with pretreatment at both plants. For the larger particles the MFI0.45 g ave a 90-approximate to 100% reduction at the Rhine River plant, while the SDI gave more variable results: 70 greater than or equal to 90%.