AWWA MTC57543

The objectives of this study were to identify foulants and to investigate fouling mechanisms associated with the nanofiltration (NF) membrane for a pilot unit fed with conventionally treated water and conventionally treated ozonated water during spring and fall seasons. Generally, membrane fouling depends on a combination of physicochemical and hydrodynamic conditions. This study focused on the effects of bulk natural organic matter (NOM) type, NOM concentration, and ozonation on the membrane fouling. Other factors that affect fouling such as membrane material, solution chemistry (pH, ionic strength), and operating parameters (transmembrane pressure and cross-flow velocity) were maintained constant during the test period. Pilot scale fouling experiments were carried out with four NF200 (DOW Filmtec, Minneapolis) membrane elements (two series of two stages) fed with sand filtered water (SFW, without ozonation) and sand filtered and ozonated water (SFOW, with ozonation). The 2nd stage membranes were not subjected to analysis due to the relatively lesser degree of fouling compared to 1st stage membranes even though feed concentration was higher for the 2nd stage. The operating conditions provided a system pressure of 5-15 bar, a recovery of 12%, a pH of 6.9 (with sulfuric acid addition), antiscalant addition of 2.1 g/m3 (blend of polycarboxylate and phosphonic acid). Three month period tests were conducted during two seasons (spring and fall, 2001). Feed water samples were characterized according to dissolved organic carbon (DOC) and UVA254 by a total organic carbon analyzer (TOC 800, Sievers) and a UV-visible spectrophotometer (UV-160A UV/Visible Spectrophotometer, Shimadzu) with a 1 cm quartz cell, respectively. NOM fractionation was performed by XAD-8/-4 resin adsorption. The concentrations of major cations and anions were measured using a Liberty-Series II ICP-AES Spectrometer (Varian, TX) and a Dionex ion chromatograph with an auto sampler (with an IonPac AS-SC column). A DS-130 (AKASHI, Japan) scanning electron microscope (SEM) was used to determine the deposit morphology of fouled membranes. An energy dispersive spectrophotometer (EDS, EDAX PV9900, PHILIPS) was also used to characterize inorganic foulants on the membrane surface. To identify the functional groups of foulants, spectra were collected with a Nicolect 752 Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectrophotometer using a KBr pellet or membrane specimens. Includes 19 references, tables, figures.