Jan C. Schippers ~b alnternational Institute for Infrastructural, Hydraulic and Environmental Engineering,

T he influent feedwater to the Rhine River and I jssel Lake RO pilot plants still contained p articles after conventional pretreatment, as o bserved by the measured MFI-UF values of c irca 2000 and 5000s/L 2, respectively. The resp ective MFI045 (and SDI in the case of the Rhine R iver plant) for the influent feedwater were circa 4 00-1400 times lower as smaller particles are n ot retained and measured in these tests. F or the Rhine River plant biological activated c arbon filtration significantly removed particles i n the size range measured in the MFI-UF test. L ittle or no removal was found for ozonation. S SF was the most successful pretreatment p rocess in reducing the particulate fouling p otential, with 90-=100% particle removal m easured by both the MFI-UF and MFI045. In c ontrast, the SDI gave variable results for the r emoval efficiency of a pretreatment step, e.g., 4 0->90% for SSF. The MFI-UF of the final RO f eedwater after extended pretreatment was close t o the detection limit, and hence the fouling p otential was very low. T he Ijssel Lake plant feedwater was a factor 2 .4-2.9 times more fouling, according to M F I U F measurements, than the Rhine River plant f eedwater. However, UF significantly reduced t he fouling potential of the feedwater: circa 90% a s measured by the MFIo.45 and 80% by the M FI-UF. The UF removal efficiency was lower t han expected due to operational problems at the p ilot plant during the period of the MFI-UF m easurements. High particle counts were m easured in the UF filtrate due to leakages and b acterial regrowth which resulted in the higher M FI-UF of the UF filtrate. Thus, the lower UF r emoval efficiency is not considered representat ive of normal operating conditions. A significant i ncrease in particle counts was found after acid a nd antiscalant addition to the UF filtrate (RO f eedwater). The net result of these additions was a n increase in the MFI-UF. Calculations showed t hat acid addition was responsible for this i ncrease, most likely by the introduction of s maller particles and/or by acid degradation into p articles smaller than 0.05 gin. R esults of particle counts for the feedwater to t he MFI-UF test membrane showed that initially = 40% and finally 90% of particles in the smallest c hannel range (0.05-0.10gm) of the particle c ounter were captured and thus measured in the M FI-UF test, whereas for the larger size c hannels (0.1->0.2gm) particle retention was i nitially 70% and close to 100% at the end of the e xperiment, I n conclusion, the MFI-UF was found to be a p romising tool for measuring the particulate f ouling potential of a feedwater. Moreover, it can b e used alone or in combination with the MFI0.45 o r MFI0.05 to compare the efficiency of various p retreatment processes for the removal of s elected particle sizes. Future work focuses on p redicting flux decline in the MFI-UF test for m embrane filtration systems.