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Effects of Flocculation Conditions on Aggregates Fractal Structures

LI Dong-mei~(1,2),SHI Zhou~1,MEI Sheng~2,TAN Wan_chun~3,JIN Tong-gui~4(1.School of Civil Engineering,Hunan University,Changsha 410082,China;2.School of Construction,Guangdong University of Technology,Guangzhou 510500,China;3.School of Chemical and Environmental Engineering,Changsha University of Science & Technology,Changsha 410076,China;4.School of Environmental & Municipal Engineering,Xi'an University of Architecture & Technology,Xi'an 710055,China)  
By adding cationic high molecular weight polymer into high turbid water with slit content containing 85kg/m~3,variation regularities of the following morphologic factors which can characterize fractal structural properties of aggregates under different flocculation conditions: such as aggregates sizes,efficient mass density of aggregates,aggregates free settling rate,turbid liquid layer settling velocity,residual turbidity of supernatant,are analyzed and discussed by using image analysis and settling technologies.The characteristic parameter "fractal dimension D" can be used to quantitatively control the effects of flocculation conditions such as stirring rate,stirring time,high molecular weight polymer concentration on the fractal properties of aggregates structures of high turbid water with slit content.It is found in experiment that when flocculation conditions are improper,fractal structures of aggregates will become loose and fragile and the value of fractal dimension D is low.When the flocculation conditions are proper(rapid flocculation strength and time separately is r_1=300r/min,t_1=10s;slow flocculation strength and time separately is(r_2=120r/min,) t_2=180s;polymer concentration is 0.1%),the fractal structures of bridging-flocculated aggregates reach the optimum compactness.Under this optimum conditions,aggregates have such characters as a bigger size,a faster free settling rate,a higher efficient mass density,size distribution in turbid suspended liquor uniform and the value of fractal dimension D is the highest((D_3=2.16).) Furthermore,the results testing from the static settling experiment indicate that the settling rate of turbid liquor layer is fast and the residual turbidity of supernatant is low also.The following behaviors of silt aggregates,such as coagulation properties,settling behaviors and the properties of structural compactness are all ideal.
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