Hollow Fiber Ultrafiltration of Hydrophobic Natural Organic Matter (NOM) Waters using Different Pretreatment Schemes: Floatation versus Sedimentation

There has been only limited research on coagulation/flocculation/floatation as pretreatment for ultrafiltration (UF) membranes in drinking water treatment, and it has concentrated on the treatment of algal-laden waters, i.e., their natural organic matter (NOM) has a low hydrophobic fraction (HPO). The main objective of this study was to investigate the effects of pretreatment including floatation as opposed to sedimentation on the performance of a hollow fiber UF membrane system for the treatment of a surface water with a relatively high NOM concentration and a high HPO component. Multiple-day UF membrane filtration/fouling tests (constant flux with backwash and chemical cleaning) were conducted with different pretreated waters using an automated bench-scale system in both summer and winter. The pretreatment was performed at two adjacent full-scale treatment plants. Floatation performed about 10% better in terms of NOM and HPO removals. Floatation pretreatment resulted lower membrane transmembrane pressure (TMP); higher backwash efficiency (less than 10% higher) and lower resistance-in-series fouling indices (total fouling index (TFI); hydraulically irreversible fouling index (HIFI); and chemically irreversible fouling index (CIFI)) in both the late summer and winter testing. Fouling was more intensive for the winter samples presumably due to higher NOM concentrations. The superiority of floatation pretreatment seems to be linked to its greater removal of the HPO fraction, as the both the TFI and HIFI indices were highly correlated to the specific UV absorbance (R2less than 0.92).

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