石門水庫因颱風暴雨時期，水庫設置分層取水工程來因應淨水廠難處理高濁度原水之問題，但淨水廠以分層取水做為水源時，在淨水廠快濾池操作上發生嚴重空氣閉塞問題，進而影響出水水量，本研究探討淨水廠之原水和利用碳酸氫鈉進行水中氣體過飽和條件模擬之原水，對模廠快濾單元的影響，再藉由超音波振盪除氣方式，降低水中溶解性氣體量，探討對於快濾單元的水頭損失與濾程關係。 原水以瓶杯試驗進行混沉，比較多元氯化鋁及氯化鐵之殘餘濁度與沉降性較佳之混凝劑。首先以二氧化碳曝氣方式增加水中溶解氣體量，但是模廠試驗將pH調至6 ~ 7時，總溶解氣體量卻降低至約與大氣壓力相同，較不利於後續對於快濾池濾床空氣閉塞之模擬。以碳酸氫鈉模擬水中氣體過飽和之原水，pH條件在6 ~ 7時，在水中釋出二氧化碳，在慢混槽、沉澱槽的池壁皆有氣泡的產生，於快濾池濾床表面發現許多氣泡的附著，濾床中也出現空氣所造成的小空隙，對於快濾池之濾程經由快濾模廠試驗結果顯示，隨著碳酸氫鈉的濃度增加，快濾池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，造成快濾池濾程縮短。藉由超音波振盪方式，將氣體過飽和之原水進行振盪，減少水中溶解氣體量，改善快濾池之濾程因為空氣閉塞而縮短的情形。 Due to extreme high turbidity during typhoons or heavy rains, which resulted in difficulties in potable water treatment, the water intake well to draw water from upper levels of the reservoir was built in the Shihmen reservoir. After drawing water from the intake well, it was found that the rapid sand filter was severely clogged, the head loss increase dramatically, and the filtration run-time was seriously shortened, which are because of supersaturation of gas in the raw water. In this study, sodium bicarbonate and CO2 were added into the raw water to simulate the supersaturation of gas. Ultrasonic was then applied to decrease the dissolved gas. The head loss and filtration run-time of the pilot plant were used to investigated the efficiency of degas. It is found that although aeration of carbon dioxide can increase the total dissolved gas in the water, the total dissolved gas almost decreased to the atmospheric pressure when the solution pH increased from 6 to 7, at which is the optimal condition for coagulation. When sodium bicarbonate was added into raw water and the solution pH increased from 6 to 7, bubbles were observed in the slow mixing tank, the precipitated tank, and inside the filter bed. With increasing concentrations of sodium bicarbonate, because of the air occlusion in filter bed, the run-time of filtration decreased significantly. It is also found that ultra- sonication could effectively reduce the amount of gas dissolved in water and prolong the filtration run-time, compared to that when there were air occlusion in the filter bed.
