原水濁度對快濾池空氣閉塞之影響

Effects of raw water turbidity in rapid filter air occlusion

王建智(Chien-chih Wang)

指導教授 ： 秦靜如

國立中央大學/工學院/環境工程研究所/碩士(2014年)

摘要

石門水庫為因應颱風暴雨時期，原水濁度暴漲導致淨水廠難以處理，在水庫區設置分層取水工程，取用高程較高濁度較低之原水，但淨水廠以分層取水作為水源時，曾在淨水廠快濾池操作上發生嚴重空氣閉塞的問題，使快濾池濾程嚴重縮短，進而影響出水水量。本研究探討藉由提高濁度的方法，增加水體中顆粒的濃度，提供水中溶解性氣體異相成核的機會，使溶解態的氣體生成氣泡，進而從水體中釋出。原水利用碳酸氫鈉模擬氣體過飽和，並以高嶺土調配不同的濁度，觀察不同濁度的氣體過飽和原水混凝的情形及其對水中溶解性氣體量的影響，並探討對後續快濾單元的水頭損失與濾程之關係。
從瓶杯試驗的結果發現，混凝劑的添加量越大並不會使除氣的效果越好，反而在最佳加藥區間因為其混凝的成效較佳而有較好的除氣效果，且初始總溶解氣體量的變化也會影響膠羽的結構特性，初始溶氣量高所生成的膠羽較大且具有較多孔隙，形成相對膨鬆的結構，影響膠羽的過濾性及沉降性。模廠快濾槽因為水中溶解氣體過飽和，氣體在濾床中累積，造成空氣閉塞現象，使快濾槽的濾程縮短，配合以調整不同的初始濁度，觀察並記錄各模廠單元的水質變化情形及混凝的成效，探討不同濁度的情況對於濾程及TDGP的影響，改善快濾槽濾程因空氣閉塞而縮短的情形。由結果發現，雖然提高濁度有助於釋出水中溶解性氣體而增加濾程，但形成的膠羽易有上浮的現象，且濁度提高不是無限制，過高的濁度會增加混凝程序的負擔，使混凝的成效降低，沉澱水的濁度降不下來，增加後續快濾單元的負擔，使濾料表層快速累積顆粒形成濾餅，造成壓力水頭急遽升高。

關鍵字

濾程 ； 總溶解氣體 ； 模場試驗

並列摘要

Due to extreme high turbidity during typhoons or heavy rains, which resulted in difficulties in potable water treatment, the water intake well was built in the Shihmen reservoir to draw water from upper levels of the reservoir. After drawing water from the intake well, it was found that the rapid sand filter was severely clogged, the head loss increased dramatically, and the filtration run-time was seriously shortened, which are because of supersaturation of gas in the raw water. In this study, degas is proposed by adding turbid particles, which provide nucleation sites for dissolved gas so that the bubbles could be easily formed and removed. To simulate the supersaturation of total dissolved gas, sodium bicarbonate was added into the kaolin particle suspensions. The effects of turbidity on the coagulation and degas efficiency when the water is supersaturated with gas was investigated by kaolin particle suspensions were investigated. The influences of turbidity on the head loss and filtration run-time of rapid filter were also studied by pilot-scale experiments.
From the jar test, it is found that the efficiency of degas is not necessary increased with increasing dosage of coagulant. The optimal degas occur at the coagulation dosage. The amount of the initial total dissolved gas (TDG) may also affect the structure of flocs. Higher the initial TDG, looser and larger the flocs are, which further affect the settability of clos and the filterability. In the pilot study, kaolin particles and sodium bicarbonate were added into the raw water directly draw from a water treatment plant to investigate the degas of supersaturated water by increasing initial turbidity. It was found that although adding turbidity may help to release dissolved gas, ease the clogging of filter, and increase the filter run-time, the floating flocs are easily observed. Also, when the dosage of coagulant was too high, because the coagulation efficiency was poor and the flocs were unable to settle, filtered loading of rapid filtration increased instead. As the consequence, the flocs accumulated on the surface of the filter sand and the head-loss increased rapidly.

並列關鍵字

filtration run-time ； total dissolved gas ； pilot-scale experiments

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