| 摘要: | 聚電解質加強過濾程序(PEUF)在長時間的操作下，薄膜表面會因為聚電解質累積而造成阻塞。現有的文獻證實在PEUF掃流系統中加入固體顆粒，可以有效的改善薄膜阻塞問題，所以本文章將PEUF結合由化學還原程序所產生之銅顆粒，探討此方法是否可以降低薄膜阻塞之影響，因此本實驗之薄膜掃流系統分為兩個部分:PEUF及PEUF結合化學還原程序產生之銅顆粒。本研究以臨界通量(critical flux)比較在不同的過濾程序中，薄膜阻塞的程度。臨界通量之定義為薄膜在未發生阻塞的條件下，所能操作的最大通量。本實驗使用之聚電解質聚及還原劑分別為乙烯亞胺(PEI)及連二亞硫酸鈉(sodium dithionite)。實驗系統利用bleeding pump將系統內之含銅廢水抽出，使PEI在長時間操作下達到穩定的濃度，此時的濃度稱為最終PEI濃度(ultimate PEI concentration)，簡稱uPEI。
結果顯示PEUF臨界通量隨著uPEI濃度增加而減少， 所以uPEI濃度會影響薄膜之廢水處理量。此外在PEUF系統中，可操作的PEI最高濃度為35 mmol/L，若超過此濃度會導致薄膜系統不會有通量產生。而在PEUF結合化學還原程序中，於相同uPEI濃度下，其臨界通量比單獨PEUF程序測得的值還低，顯示此時薄膜表面產生嚴重的阻塞。此阻塞是由化學還原所產生的銅顆粒沉積於薄膜表面所造成，其原因可能為薄膜表面及銅顆粒間之不同表面電荷所產生之吸引力所致。為了減少銅顆粒沉積於薄膜表面，PEUF結合化學還原程序中加裝沉澱槽，用來蒐集較大的銅顆粒。然而在相同條件下，臨界通量仍小於PEUF程序。為了減少薄膜系統中的顆粒量，建議之後的研究中，將還原程序移至沉澱槽中，使銅顆粒於槽中還原並沉澱，探討銅顆粒對於薄膜阻塞之影響。
In polyelectrolytes enhanced ultrafiltration (PEUF) process, the membrane is easily fouled by accumulation of polyelectrolytes on membrane surface during a long time operation. According to previous research, silica particles was added to mitigate membrane fouling in cross-flow filtration. In this study, copper particle produced by chemical reduction is investigated for mitigation of membrane fouling. The objective of this study is comparison of membrane fouling for PEUF system with or without incorporation of chemical reduction is investigated.
Critical flux, i.e., membrane can be operated without fouling for maximum membrane flux, was used to evaluate membrane fouling. The ultimate PEI concentration (uPEI), i.e., stable PEI concentration during a long time operation, was controlled by bleeding pump. Polyethylenimine (PEI) and dithionite were used as polyelectrolyte and reductant, respectively. Cu(II): PEI: dithionite molar ratio of 1:1.5:3 was fixed.
For PEUF system, results showed that critical flux decreases with increasing uPEI concentration, and the highest PEI concentration of 35 mmol/L can be operated for PEUF. For integration of PEUF and chemical reduction, the critical flux was lower than that for PEUF without incorporation of chemical reduction, showing severe membrane fouling. The membrane fouling might be due to the generation of attraction force between membrane surface and copper particles causing copper particle deposition on membrane surface.
To eliminate copper particle deposition on membrane surface, sediment tank was used to collect big particle produced by PEUF incorporation of chemical reduction. However, the critical flux was still lower than PEUF without chemical reduction at the same condition. To minimize the amount of particles in the membrane system, system with copper particles produced and collected in sediment tank is investigated for the influence of membrane fouling for future experiment. |
