Research On Coagulation Sedimentation Process Enhanced Technology Based On Particle Morphology Control

Presently, the conventional coagulation-sedimentation-filtration-disinfectionprocess is still used as the drinking water treatment process in most water plants ofour country. Coagulation sedimentation process is an important part of theconventional water treatment process, and plays an important role in particles’migration, transformation and removal. Therefore, studies on coagulationsedimentation process still have significant application value. At the present stage,most studies on coagulation sedimentation process are based on static experimentsand use the turbidity of effluent as the unique index to evaluate the effects ofcoagulation sedimentation process. Because the particles’ size distribution andmorphological characteristics are neglected, these studies are only suitable fortheoretical analysis and the results are much different from actual water treatmentprocess.In this research, a continuous flow reactor simulating actual coagulationsedimentation process is built.to resolve the problem above. Operation parametersand conditions are optimized to make sure that reactions of the particles in thisreactor are similar to the actual coagulation sedimentation process. In theexperiments, size distribution fractal dimension, average particle size and geometricfractal dimension are used as analysis indexes to research the changes of particles’morphological characteristics in coagulation sedimentation process. Meantime, theeffects on effluent caused by these changes are analyzed.Control the particles’ size distribution and morphological characteristics bymechanical method, research the breakage and regrowth process of flocs andanalyze the effects on effluent quality caused by this process. In this research, wefind that in a low breaking strength scale range (200~300rpm), the broken flocs canpartly or absolutely regrow to the formation before broken. In these cases, thesettling performance of theses regenerative flocs is improved. And then, turbidityand particle number of effluent are remarkably reduced and the efficiency ofcoagulation sedimentation process is enhanced. On the others side, if the breakingstrength increases to an excessive degree (300rpm), the broken flocs cannot regrowto the previous formation in same hydraulic retention time. Turbidity and particlenumber of effluent are increased and the efficiency of coagulation sedimentationprocess is reduced.250rpm is determined as the optimal mechanical breaking scaleof the experiment. Then, control the particles by hydrodynamic method, and asimilar conclusion is gained in the hydrodynamic breaking experiment. The optimal hydrodynamic breaking scale is18.9-18.910-3m/s.In this research, it is proved that two preconditions should be satisfied for thepurpose of enhancing the efficiency of coagulation sedimentation process. Oneprecondition is that the breaking scale must be limited into a low range, and theother one is to make sure the broken flocs can regrow to previous size distributionand morphological characteristics before broken.