| 摘要: | 本研究以沉浸式過濾系統進行海水淡化前處理。比較不同程序對於濾速與出水品質的提升。使用0.45μm之PVDF膜與活性碳動態膜對模擬海水進行過濾，並探討加入凝聚程序對於整個系統的過濾性質與水質影響。其中活性碳動態膜的生成方法，是預過濾多孔性粉末狀活性碳(PAC)，使其於0.45μm PVDF膜面上形成一定量之活性碳濾餅層，此層濾餅層即稱之為動態膜。希望藉由活性碳動態膜複合式之系統，可將海水中之有機物質及無機微粒去除，以降低逆滲透程序之薄膜結垢的發生。
實驗結果顯示，用0.45μm PVDF膜過濾模擬海水，過濾初期因粒子於膜面上累積使濾速下降快速，於過濾結束後80kPa之濾速較40kPa高30%，比較使用活性碳動態膜與0.45μm PVDF膜之膜阻力可發現，於80 kPa操作下，預過濾10分鐘生成之活性碳動態膜之阻力較0.45μm PVDF膜高133%，相較於預過濾5分鐘高13%，但厚度卻增加了50%，故選用10分鐘做為動態膜預過濾時間。本研究使用5 mg/L幾丁聚醣作為凝聚劑，並以0.45μm PVDF膜過濾，其濾速會隨透膜壓差增加而提升，於過濾時間結束時，透膜壓差80kPa與60kPa相較於40kPa時濾速可提升24%與16%。因添加凝聚劑後使模擬海水中之物質粒徑分布增加，形成結構較鬆散之濾餅層，使濾餅所造成的阻力下降，因此無論使用0.45μm PVDF膜或活性碳動態膜皆可使濾速提升。最後綜合比較出水品質(COD、DOC、濁度、腐植酸濃度)與濾速之提升可知結合使用凝聚程序結合活性碳動態膜之複合系統可使上述移除率達最大，且有效使濾速提升。相較於將活性碳懸浮於海水中，使用動態膜可大幅減少活性碳用量。而使用沉浸式過濾系統生成動態膜之時間僅為掃流系統所需時間的8%，可大幅減少動態膜預過濾時間。
Hybrid submergedmicrofiltration systemsforpretreatment ofseawater desalinationwere studied. The permeate flux and water quality among different operations, such as 0.45μm hydrophilic membranes, dynamic membrane formed bypowder activated carbon (PAC), dynamic membrane coupled with coagulation operationwere measured and compared.The PAC dynamic membranes, constructed bypre-coatingPAC on the primarymembrane, were used forabsordingorganic material andinorganic fine particles in seawater to prevent the membrane fouling in following Reverse Osmosis(RO) units.
Artificial seawater was filtered using0.45μm PVDFmembrane, the filtration flux increased30% asthe transmembrane pressure increased from 40 to 80kPa. However, the flux decayed more quickly under higher pressures.The membrane resistance of the PAC dynamic membrane was133%higherthan that of 0.45μm PVDF membraneunder 80 kPa.ThePACthicknessincreased 50% with twice coating time. However the resistanceonly increased 13%. It was attributed to the large PAC particle size and loose packing structure of dynamic membrane.
Tocombine coagulationoperations withsubmergedfiltration processes, either theuseof 0.45μm PVDFmembrane or PAC dynamic membrane, the flux was improved.The flux of seawaterwithcoagulant increased with increasing transmembranepressure.However, theflux declineddramatically at the beginning of filtration, the major resistance sources werethose organic materials fouling on themembranes.Comparing the performances of different operations, the hybrid system coupled with coagulation and PAC dynamic membrane behaved the highest efficiency of pollutant removal and highest permeate flux.The quality of permeate water, COD, DOC, turbidityand concentration of humic acid, for each operation was measured.The permeate quality met the requirement of RO feed.On the other hand, compared to directly add PAC into suspensionto adsorb organic material, the use of PAC dynamic membrane significantly reduce the cost of PAC.Beside, the submerged system only cost 8% of pre-coating time by cross-flow system. |
