| Summary: | 碩士 === 國立交通大學 === 環境工程系所 === 104 === Polyaluminum chloride (PACl) is one of most frequently used coagulant for particle destabilization in water treatment. The speciation of PACl coagulant strongly affects the coagulation performance and residual Al species in the supernatant. The aim of this study was to investigate the effects of hydrolyzed Al species on the removal of particles and speciation of residual Al after sedimentation. Three kinds of PACl coagulants with different fraction of monomeric Al (Ala), polymeric Al (Alb) and colloidal Al (Alc), namely PACl-1 (Ala/Alb/Alc=14/64/22), PACl-2 (Ala/Alb/Alc=47/31/22) and PACl-3 (Ala/Alb/Alc=56/22/22), were used in jar testing to evaluate the performance of coagulation with and without FeCl3 dosing. For coagulation with dual dosing, the ratio between PACl and FeCl3 dosing is 2:1. The composition and speciation of residual Al in the supernatant after sedimentation for coagulation with various PACl coagulants were determined with and without dual dosing.
The result has shown that PACl coagulant with high ratio of Alb/Ala possesses strong charge neutralization ability to effectively destabilize particles at the optimum dosage of 2 mg/L as Al, which lowers total residual Al as well as dissolved Al in the supernatant, even though dual coagulation (PACl dosing mixed with FeCl3 coagulant). At such conditions, the average size and fractal dimension of flocs formed by mixing with PACl coagulants with high ratio of Alb/Ala are much smaller compared to PACl coagulants with lower ratio. The dissolved residual Al in the supernatant increases with Ala/Alb ratio of PACl coagulants regardless of dosage. With increasing PACl dosage, the quantity of Ala decreases and Alc increases in the supernatant after PACl-2 and PACl-3 coagulation, while Ala increases and Alc decreases after PACl-1 coagulation. The quantity of Alb in the supernatant increases with Alb/Ala of PACl coagulant.
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