Effect of chemicals combination and mixing strength on particle destabilization in coagulation process - A pilot study

• Main Authors: Hung, Ming-Yu, 洪銘佑
• Other Authors: Huang, Chih-Pin
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/ehz9pn

碩士 === 國立交通大學 === 環境工程系所 === 101 === The velocity gradient (G) and duration (t) in rapid-mixing process for water treatment plant (WTP) predominate the formation of floc formed by coagulation. However, the performance of particle destabilization and floc growth are also significantly affected by the strategy of coagulant dosing and the quality of raw water. This study aims to understand the relationship between the removal in particle and the characteristics of floc formed with various rapid-mixing strength in the coagulation of different natural turbid water. In this study, a pilot-plant with water supply capacity of 100 CMD in Linnei WTP has been continuously operated to evaluate the performance of particle destabilization by PACl coagulation with and without the addition of PolyDADMAC or FeCl3, where the size and fractal dimensions of flocs were analyzed by particle sizer and floc image colorimetric analyzer (FICA). In addition, the coagulation with various rapid-mixing strength was conducted to evaluate the effect of velocity gradient and duration in rapid-mixing on particle removal by sedimentation. The results of pilot-plant test has indicated that the reduction in turbidity after coagulation-sedimentation process can be effectively improved by increased rapid-mixing strength for low-turbidity water (<100 NTU) when PACl coagulation is performed with and without the addition of PolyDADMAC. With increasing rapid-mixing strength, the flocs become larger and compact, while the standard deviation of RGB measured by FICA system increases with the size of flocs. For high-turbidity water (>100 NTU), the reduction in turbidity by PACl coagulation and sedimentation process cannot be effectively improved by increased rapid-mixing strength. When PACl and FeCl3 were simultaneously added at the initial rapid-mixing in the coagulation process, the particle destabilization and floc formation can be effectively improved by increased rapid-mixing strength, which reduces the residual turbidity of supernatants. At low-turbidity water (<100 NTU), the residual turbidity of supernatants can be substantially reduced with increased rapid-mixing strength for PACl coagulation when Gt is less than 2×104, while the removal in particles becomes worsen with increased rapid-mixing strength for PACl coagulation with the addition of FeCl3 when Gt is higher than 2×104. At high-turbidity water (>100 NTU), the residual turbidity of supernatants increases with increased rapid-mixing strength for PACl coagulation with the addition of FeCl3 when Gt is higher than 4×104. However, the removal in particles is insensitive to rapid-mixing strength for PACl coagulation.