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The effects of coagulant residuals on nanofiltration (NF) fouling wereinvestigated. Experiments were carried out with a pilot microfiltration(MF)-NFplant and a laboratory-scale MF-NF setup. The pilot influent was drawn from asedimentation basin after poly-aluminum chloride (PACl) coagulation. In the pilot,MF (PVDF membrane nominal pore size, 0.1 m) permeates were transferred tothe NF modules (nominal NaCl rejection 55%; polyamide), which was operatedwith constant flux (0.6 m/day) and water recovery (95%) by adjusting the feedpressure. In the laboratory-scale experiment, groundwater was pretreated withPACl, alum, or ferric chloride in-line coagulation and MF; then the MF permeatewas pumped to an NF cross-flow cell with 0.6-m/d flux and 10% raw waterrecovery.The trans-membrane pressure of the NF in the pilot doubled in the 6 months ofoperation, although the mean silt density index of the NF feed water was 2.25,suggesting an absence of severe fouling by particulate matter. The aluminumconcentration in the NF influent was not high (average 30 g/L), but analysis ofmembrane foulants revealed excessive accumulation of aluminum (46 mg/msup2/sup)as well as silicate (30 mg/msup2/sup), suggesting that aluminum residuals probablycaused the membrane fouling by forming alumino-silicates or aluminumhydroxide. In the laboratory-scale experiments, the permeability of NF declinedwhen the feed water contained residual aluminum at 18 g/L or more, but notwhen the aluminum concentration was lower than about 9 g/L. Thermodynamiccalculations and elemental analyses of the foulants recovered from themembranes indicated that the majority of inorganic foulants were compoundscomposed of aluminum, silicate, and possibly potassium. Includes 4 references, tables, figures.

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Edition: Vol. - No. Published: 03/01/2007 Number of Pages: 8File Size: 1 file , 400 KB