聚氯化鋁混凝劑鋁物種分佈對沉澱後有機物去除和殘餘鋁之影響

Abstract

混凝劑種類及有機物特性均會影響混凝效能，此外，有機物存在於水中也會使鋁溶解度增加，造成水中殘餘鋁含量增高。本研究之目的為探討PACl混凝劑之鋁物種分佈對混沉程式去除腐植酸及上澄液殘餘鋁含量及形態之影響，瞭解有機物特性對自來水混凝沉澱過程造成鋁殘留之影響。首先在中性pH條件下，以瓶杯試驗評估混凝過程中各鋁物種對腐植酸去穩定之影響，實驗中將選取三種不同鋁物種分佈之混凝劑並改變加藥量。以portable flowCAM分析膠凝後膠羽之結構。此外，藉由螢光激發/發散陣列光譜儀和高效能粒徑排除層析儀分析混沉處理前後腐植酸官能基及分子量大小，並通過XAD-2離子交換樹脂分離出有機錯合鋁，探討混沉上澄液中有機鋁錯合物含量及分子特性對水中殘餘鋁量之影響。 研究結果顯示，在中性pH條件下，PACl中膠體鋁(Alc)含量相同時，PACl混凝劑中聚合鋁/單體鋁(Alb/Ala)比例越高，電性中和能力越強，混沉去除 DOC之效能越好且混沉上澄液殘餘鋁量越低。同時，發現聚氯化鋁混凝劑與類腐植酸的錯合反應程度較為明顯，且聚合鋁/單體鋁(Alb/Ala)比例高時，鋁物種對類腐植酸的錯合反應速率比類黃酸錯合反應速率快。另外，PACl混凝劑主要去穩定類腐植酸之大分子有機物，在低加藥量(Al/DOC≤0.4)時，Al-HA complex 分子較小，不易被混沉去除，殘餘鋁較多，殘餘鋁成分主要為溶解鋁，且有機鋁佔溶解鋁之比例超過80%以上；高加藥量(0.4<Al/DOC≤0.8)時，Al-HA complex分子較大，殘餘鋁較少，易被混沉去除，殘餘鋁成分主要為顆粒鋁。

The types of coagulant and the characteristics of organic matter can strongly affect the performance of coagulation. In drinking water treatment, organic matter would lead to the increases in aluminum solubility and residual Al. This study aims to investigate the effects of Al speciation on coagulation of organic destabilization and residual Al in supernatants after coagulation and sedimentation. Three kinds of PACl coagulants were used to evaluate the effects of Al species on the destabilization of humic acid (HA) at neutral pH (pH 7±0.2) by coagulation with jar test. The formation of flocs was analyzed via flowCAM for each trial. Moreover, the composition and molecular weight distribution of organic matter were determined by EEM and HPSEC methods. Finally, the separation of organically-bound Al was conducted by XAD-2 ionic exchange method. The results have shown that PACl with higher ratio between polymeric Al and monomeric Al (Alb/Ala) has stronger ability of charge neutralization to effectively destabilize HA and improve the reduction in residual Al. For coagulation with PACl containing high Alb/Ala ratio (Alb/Ala=64/14), the reaction between Al speciation and humic acid-like substances was dominant and faster compared to fulvic acid-like substances. Therefore, the humic acid-like substances with large molecular weight was more effectively destabilized by PACl coagulation than fulvic acid-like substances. At low dosage (Al/DOC≤0.4)，the Al-HA complex was not large enough to be removed by sedimentation, thereby the residual Al in supernatant was composed of dissolved Al, where the amount of organically-bound Al is more than 80% of total dissolved Al. While increasing the dosage (0.4<Al/DOC≤0.8), the Al-HA complex became larger so as to it is easily removed by sedimentation.