Rejection of NOMs in Kin-men Raw Water by NF Membrane
Date Issued
2007
Date
2007
Author(s)
Chen, Yu-Wen
DOI
en-US
Abstract
The drinking water quality standards in Taiwan are becoming more stringent in the future. However, parts of water treatment plants in Taiwan still employ the conventional treatment processes which are hard to meet the standards. Besides, the natural organic matters (NOMs) are the main precursors of the disinfection by-products (DBPs) during the disinfection process. In this investigation, the Tai-Lake raw water in Kin-men Water Treatment Plant in Taiwan was selected to analyze the NOMs by resins and by molecular weight distribution. The NF270 membrane was characterized to evaluate its performance for reducing the NOMs and then to determine the optimum operating conditions.
The DOC concentration in Kin-men raw water was found to be approximately 6.54 mg/L, SUVA254 value was about 1.70 L/mg m and the hydrophobic NOMs (58.4%) were the major components. The molecular weight distributed broadly, i.e., lower than 1K (30%), 1K to 5K (32%) and larger than 5K (38%). This study utilized the polyamide thin-film composite (TFC) nanofiltration membrane (NF270) to treat the water samples and investigated the effects of the transmembrane pressure (75 to 150 psi), the cross-flow velocity (0.08 to 0.60 m/s) and the pre-treatment process (SF and UF) on the rejection ratios of NOMs.
The results displays that the permeate flux declines obviously with increasing the transmembrane pressure. On the contrary, increasing the cross-flow velocity could ease off the permeate flux declined. The DOC rejection ratio was not affected by changing the cross-flow velocity (0.08 to 0.60 m/s) but the reduction ratio of UV254 decreased with increasing the cross-flow velocity. On the other, DOC and UV254 reduced efficiently with increasing the applied pressure. However, while the pressure was over 100 psi, the reduction ratio was tended to be constant. During operation, the solute might accumulate on the membrane surface and resulted in the permeate flux declined causing by resistance. Increasing the pressure resulted in the membrane structure became more compact and the solute could hardly pass through the membrane. Hence, the rejection ratio increased. Further, with increasing the cross-flow velocity, the permeate flux increased but the flux declined decreased, due to the reduction of the concentration polarization effect.
By comparing the pre-treatment process, the UF-NF processes could obtain the higher permeate flux. The UF membrane process rejected more hydrophobic NOMs than by the rapid sand filter (SF) process and decreased the permeate flux declined. But the SF-NF reduced the NOMs more efficiently than the UF-NF. The SF-NF was the proposed treatment process because it can remove the NOMs effectively with lower energy consumption.
Subjects
奈米薄膜(NF270)
天然有機物
掃流式過濾
自來水處理
Nanofiltration (NF270)
Natural organic matters (NOMs)
Cross-flow
Water treatment
SDGs
Type
thesis
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