AWWA WQTC63981

The objective of this study was to assess the influence of both hydrophobic-hydrophobic and chargeinteractions on the rejection of selected trace organic pollutants. In order to experimentally generate the rejection values, bench-scale laboratory experiments werecarried out. Trisep 4040 TS80-TSF spiral-wound nanofiltration membrane elements were used for all experiments. In order to investigate the influence of solute-hydrophobicity on the rejection, three differentcategories of uncharged solutes were selected, based on their log K_ow-value: hydrophilic molecules(log K_ow<1), hydrophobic molecules (log K_ow>3), and a category of solutes of intermediatehydrophobicity (1<log K_ow<2). Compounds of increasing molecular weight were chosen, to constructrejection curves in function of molecular weight. Some interesting trace organics (e.g. NDMA andMTBE) however, were also included in the testing.In order to investigate the influence of charge, several pharmaceuticals were selected, based on theirmolecular weight and charge. Positively and negatively charged pharmaceuticals were selected, aswell as some neutral pharmaceuticals. All organic contaminants were analyzed by GC/MS (gas chromatography, combined with massspectrometry) or LC/MS (liquid chromatography, combined with mass spectrometry). The feed watermatrix for the filtration experiments with the neutral compounds was Milli-Q water. For thepharmaceutical experiments, surface water from the Weesperkarspel treatment plant in Amsterdam(DOC-content 5 mg/l) was used. Compounds were spiked into the feed waters in concentrations of 2µg/l. A bench-scale, cross-flow membrane filtration test unit for 4040 membrane modules was used in thisstudy. The unit utilizes a multi-impellor centrifugal pump (Grundfos CRN 3) capable of providingpressures of up to 25 bar at a flow rate of 3 m³/h. Temperature of the feed tank was kept constant at20ºC using a cooling system (Tamson TLC 10B). Feed, permeate and concentrate flows weremonitored by rotameters. The bench-scale NF experiments were carried out at a recovery ofapproximately 10%. All test unit parts in contact with the solution are made of stainless steel tominimize adsorption of the organic solutes used.Bench-scale filtration experiments were performed at a constant cross-flow rate (Qf = 1500 l/h,cross-flow velocity = 0.2 m/s (which correspond to a concentration polarization factor of 1.02)) andtransmembrane pressure for 4 days at 20ºC and pH 7-8. Experiments lasted for 4 days toreach saturation of the membrane with the compound of interest, so no overestimation of the rejectionwas obtained. Samples of feed and permeate streams were taken for analysis of organic solutesconcentration.Before use, membranes were rinsed for 2 hours with tap water (to remove the preservation liquidspresent in the membranes) and characterized for MgSO₄-rejection with a 500 ppm MgSO₄-solution inMilli-Q water. Includes 12 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2006

Number of Pages:

9

File Size:

1 file , 350 KB