Abstract Variations in water quality of waste water treatment plant (WWTP) effluent complicate ultrafiltration of this feed water. Traditional parameters do not provide sufficient information to explain the fouling of membranes during ultrafiltration of WWTP effluent. New parameters for measuring and monitoring the fouling potential of feed water for ultrafiltration membranes need to be developed. The normalised membrane fouling index for ultrafiltration membranes (MFI-UFn) can be used as such and is according to the cake filtration theory calculated from the ratio of filtration time and filtration volume as a function of the filtration volume. MFI-UFn can be calculated from both experiments with constant Trans Membrane Pressure (TMP) and from experiments with constant flux. This parameter can also be calculated independent of the scale of the experiment. Results show that differences in fouling potential can be measured for various feed waters using the same membrane type and for various membrane types using the same feed water. Variation in feed water quality leads to a deviation of the MFI-UFn, as was found especially for WWTP effluent. The applied TMP influences the value of the MFI-UFn, indicating cake compression when applying a higher TMP. MFI-UFn can be used to identify the effect of pre-treatment methods, which is useful when using WWTP effluent as feed water for an ultrafiltration processes.

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