Effects of Al speciation of polyaluminum chloride (PACl) coagulant on the organic matter removal and corresponding residual aluminum after sedimentation
|關鍵字:||混凝;聚氯化鋁;殘餘鋁;腐植酸;coagulation;polyaluminum chloride;residual Al;humic acid|
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.
|Appears in Collections:||Thesis|