混凝程序中加藥組合及攪拌強度對顆粒去穩定之影響 - 模廠試驗

Abstract

淨水場混凝操作之快混攪拌強度(G及t值)的選擇與混凝膠羽之形成密切相關，而天然濁水之水質及混凝加藥組合會影響混凝去穩定顆粒的程度及膠羽生長特性，故本研究主要即為探討在不同天然濁水濁度條件下，調整快混攪拌強度對不同混凝加藥組合之混沉除濁效能及膠羽生長特性的影響。本研究引用林內淨水場天然濁水以最大處理水量100 CMD之模廠進行連續式混凝試驗，並使用膠羽影像色彩分析裝置(FICA)及小角度雷射光散射粒徑分析儀分析混凝膠羽粒徑與碎形維度，以評估在單獨聚氯化鋁加藥、聚氯化鋁搭配PolyDADMAC加藥及聚氯化鋁搭配氯化鐵混凝加藥組合下，混凝去穩定顆粒之成效。此外，藉由調整混凝操作之快混攪拌強度，評估攪拌強度對混沉除濁效能之影響。 模廠混凝試驗結果顯示，使用單獨聚氯化鋁加藥及聚氯化鋁搭配PolyDADMAC加藥混凝處理低濁水(<100 NTU)時，增加快混強度可使混沉上澄液殘餘濁度降低，明顯提昇混沉除濁效能，且隨攪拌強度增加會使混凝膠羽增大且結構更為密實，而FICA系統監測之膠羽影像RGB標準偏差值亦會隨膠羽粒徑增加而上升。但當單獨使用聚氯化鋁混凝劑處理高濁水(>100 NTU)時，增加快混強度對混沉除濁效能並無明顯提昇，而採聚氯化鋁搭配氯化鐵同時加藥混凝時，增加快混強度可提高顆粒去穩定及膠羽生長的效率，並降低混沉上澄液的殘餘濁度。在低濁水(<100 NTU)條件下，使用單獨聚氯化鋁加藥混凝，於快混Gt值小於2×104的範圍內，增加快混攪拌強度可明顯降低混沉上澄液殘餘濁度，而當以聚氯化鋁搭配氯化鐵加藥混凝時，增加快混攪拌強度至快混Gt值大於2×104會造成濁度去除效率下降。此外，在高濁水(> 100 NTU)的條件下，以聚氯化鋁搭配氯化鐵同時加藥混凝，在快混Gt值大於4×104時增加快混攪拌強度將使混沉上澄液殘餘濁度升高，但採用單獨聚氯化鋁加藥混凝時，調整快混強度對混沉除濁效能影響不顯著。

The velocity gradient (G) and duration (t) in rapid-mixing process for water treatment plant (WTP) predominate the formation of floc formed by coagulation. However, the performance of particle destabilization and floc growth are also significantly affected by the strategy of coagulant dosing and the quality of raw water. This study aims to understand the relationship between the removal in particle and the characteristics of floc formed with various rapid-mixing strength in the coagulation of different natural turbid water. In this study, a pilot-plant with water supply capacity of 100 CMD in Linnei WTP has been continuously operated to evaluate the performance of particle destabilization by PACl coagulation with and without the addition of PolyDADMAC or FeCl3, where the size and fractal dimensions of flocs were analyzed by particle sizer and floc image colorimetric analyzer (FICA). In addition, the coagulation with various rapid-mixing strength was conducted to evaluate the effect of velocity gradient and duration in rapid-mixing on particle removal by sedimentation. The results of pilot-plant test has indicated that the reduction in turbidity after coagulation-sedimentation process can be effectively improved by increased rapid-mixing strength for low-turbidity water (<100 NTU) when PACl coagulation is performed with and without the addition of PolyDADMAC. With increasing rapid-mixing strength, the flocs become larger and compact, while the standard deviation of RGB measured by FICA system increases with the size of flocs. For high-turbidity water (>100 NTU), the reduction in turbidity by PACl coagulation and sedimentation process cannot be effectively improved by increased rapid-mixing strength. When PACl and FeCl3 were simultaneously added at the initial rapid-mixing in the coagulation process, the particle destabilization and floc formation can be effectively improved by increased rapid-mixing strength, which reduces the residual turbidity of supernatants. At low-turbidity water (<100 NTU), the residual turbidity of supernatants can be substantially reduced with increased rapid-mixing strength for PACl coagulation when Gt is less than 2×104, while the removal in particles becomes worsen with increased rapid-mixing strength for PACl coagulation with the addition of FeCl3 when Gt is higher than 2×104. At high-turbidity water (>100 NTU), the residual turbidity of supernatants increases with increased rapid-mixing strength for PACl coagulation with the addition of FeCl3 when Gt is higher than 4×104. However, the removal in particles is insensitive to rapid-mixing strength for PACl coagulation.