Reduction of natural organic matter by nanofiltration process

The objectives of this investigation were to characterize natural organic matter (NOM) in Kin-men raw water, to evaluate the performance of the nanofiltration (NF) membrane process for NOM removal, and to determine the good engineering practice (GEP) of the NF 270 membrane filtration performance. Three different samples: (1) raw water collected from the Tai Lake in Kin-men, Taiwan; (2) ultrafiltration (UF) pre-treated water; and (3) sand filtration (SF) treated water after the coagulation and sedimentation processes were employed in this study. The hydrophobic component (58%) was the predominant NOM fraction, and the NOM molecular weight was distributed broadly, i.e., lower than 1 kDa (30%), 1-5 kDa (32%) and larger than 5 kDa (38%). Hydrophobic NOM easily accumulated on the NF membrane surface and resulted in flux decline. The SF-NF was the proposed treatment process because it can reduce the NOMs effectively with lower energy consumption than UF-NF. It was noted that the dissolved organic carbon (DOC) rejection ratio was not affected by changing cross-flow velocity. However, at lower cross-flow velocity (0.15 ms(-1)), the reduction of organic matter in water sample was higher than that at higher cross-flow velocity (0.30 ms(-1)). By integrating the experimental results, it was concluded that a transmembrane pressure of 690 kPa and a cross-flow velocity of 0.30 ms(-1) exhibited the GEP, yielding about 94% of both DOC and UV(254) reduction.