It is important to probe the cause of membrane fouling from the aspect of water qualities. The resultant technical findings on membrane foulants enable the development of low-fouling membranes and reflect a streamlined process for water purification with stable productivity. This study shows the relationships between the fouling rate of PVDF microfiltration (MF) membranes and NOM characteristics in Lake Biwa (Japan) detected by DAX fractionation and GPC-TC. The amount of the specific NOM (hydrophilic acid: HiA from DAX fractionation) is correlated with the increasing rate of filtration resistance, and the membrane foulants consist of aliphatic carboxylates and calcium ions. From the GPC-TC measurements, the specific NOM around 2,000 Da partially remains on the membrane to indicate a primary ingredient of foulants, while the high-molecular weight NOM (MW > 40,000) is removed without trace by the backwashing process.

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