| dc.description.abstract | 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. | en_US |