聚氯化鋁物種混凝去穩定水中濁度顆粒及溶解性有機物行為之研究

Abstract

聚氯化鋁(PACl)混凝劑成份與溶解性有機物特性均會影響混凝效能，台灣水庫之天然原水中同時存在天然有機物、藻類有機物以及濁度顆粒，水庫中存在藻華現象，這會使得淨水場在使用PACl混凝劑進行混凝程序時，造成混凝效能及操作上的困難。 本研究目的為藉由PACl主要成份為聚合鋁或膠體鋁對模擬水庫原水水樣進行瓶杯試驗，以了解PACl混凝劑成份對水庫原水混凝去穩定之行為。以腐植酸與藻類有機物代表天然有機物，濁度顆粒使用高嶺土水樣；藻類有機物來源為實驗室自行培養，將藻類有機物分離成藻類胞外有機物與藻類胞內有機物，藻類胞外有機物代表水庫發生藻華時，藻類快速生長代謝產生；藻類胞內有機物表示藻華發生之藻類死亡，從藻體釋出有機物。控制水樣pH值在中性條件，實驗選取兩種不同鋁物種成份之PACl混凝劑，分別為PACl-H與PACl-C，鋁物種分佈(Ala/Alb/Alc)依序為22/53/25、46/11/43，並且改變加藥量進行試驗。以雷射粒徑分析儀與影像顆粒分析儀量測、觀察慢混膠羽成長狀況，再藉由螢光激發/散射陣列光譜儀與高效能粒徑排除層析儀分別分析混沉前後有機水樣螢光性有機物組成成份及有機物分子量分佈。 研究結果顯示，只有腐植酸與濁度顆粒存在水體中，兩種PACl混凝劑去除有機物效能都相當不錯(>75%)，其中PACl-C去除濁度顆粒與溶解性有機物效能表現較PACl-H良好。當藻類有機物進入水體後，兩種PACl混凝劑混凝去穩定有機物效能均變差(將近33%)，但PACl-H與PACl-C對於去除濁度顆粒依然保持良好去除效能(>90%)。對於天然有機物與藻類有機物，兩種PACl混凝劑對大分子有機物(> 1k Da)有良好的去除效能，但對小分子有機物(< 1k Da)並沒有明顯的去除效果。PACl-C形成之慢混膠羽擁有較大的碎形維度(Df >2)，PACl-H慢混膠羽之碎形維度相對較小(Df <2)，再加上PACl-C膠羽粒徑(300~900 μm)也比PACl-H之膠羽粒徑(200~850 μm)大。這些膠羽特性結果可以得知PACl-C慢混膠羽較為密實且大，而PACl-H形成之膠羽較為鬆散且小。以上實驗結果可以得知，PACl混凝劑主成份若含有較多的Alc可能會比有較多Alb之PACl混凝劑對於水中有機物有更良好的去除效能。

The Al speciation of PACl coagulants and the characteristics of organic matter (OM) in raw water critically affect the removal of OM by coagulation. In general, Taiwan’s reservoirs frequently contain high amount of natural organic matter (NOM) and turbid particles. Additionly, when algal blooming occurs, it may cause the rapid increase of algogenic organic matter (AOM) contributing to the NOM water pool. The eutrophication of algae not only deteriorates water quality but also causes numerous operational problems toward water treatment plants. This study aimed to investgate the effects of Al speciation on the destabilization of OM and turbid particles by coagulation of water simultaneously containing NOM and AOM. Humic acid extracted from a synthetic humic substance powder was used to represent for NOM. Turbid particles were kaolinite samples. Two AOM origins were isolated as extracellular organic matter (EOM) and cellular organic matter (COM) from the stationary phase of Chlorella sp.. Two kinds of PACl coagulants, which were PACl-H (Ala/Alb/Alc=22/53/25) and PACl-C (Ala/Alb/Alc=46/11/43), were used to evaluate the effect of Al speciation on destabilization of organic matter samples with turbid at neutral pH (pH=7±0.1) by jar tester. PACl-H has strong ability of adsorption and charge neutralization. Meanwhile, PACl-C has strong ability of adsorption and sweep flocculation.The formation of flocs was analyzed via Mastersizer 2000 and FlowCAM. Finally, the composition and molecular weight distribution of organic matter determined by EEM and HPSEC methods. The results showed that AOM had insignificant negative effects on the removal (>90%) of turbid particles (10 and 100 NTU) for both of PACl coagulants. However, its removal rates by two PACl coagulations were relatively low (>33%) for both NOM and AOM. PACl coagulants had a great removal performance for high molecular weigh matter (> 1k Da), and had a poor removal in low molecular weigh matter (< 1k Da). In formation of flocs, the flocs aggregating by PACl-C had higher fractal dimension (Df >2) than the flocs aggregating by PACl-H. It means that the flocs aggregating by PACl-C were denser than the flocs aggregating by PACl-H. In addition, the flocs fromed by PACl-C (300~900 μm) was bigger than those fromed by PACl-H (200~850 μm) as well. The experimental results found that for the raw water including AOM, PACl containing high amout of Alc species has the high removal of OM than PACl containing Alb species. Moreover, PACl coagulants have great removal rates (>90%) in turbid particles.