;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.