Effects Of Adsorption Of Organic Matter On Particle Surface On Coagulation And Settling

The model organic matters including humic acid and polyacrylic acid of different molecular weights were selected to investingate the adsorption of organic polymer on particle coagulation and settling by in situ and improved particle image velocimetry technique, including floc strength, floc fractal structure, the dynamic processes of floc growth-breakage-regrowth, and the effects of floc intrapermeation on the floc settling velocity.The structural changes in diffusive electrical double layer on kaolin particle surface resulted from the adsorption of humic acid and polyacrylic acid of different molecular weights. The zeta potential of kaolin particle surface after adsorption of polymer was characteristics of concentration saturation and acid-base buffering balance. The adsorption of organic polymer resulted in more negative electrophoretic mobility and higher energy barrier so that promoted the particle mobility in the processes of drinking water.The polymer molecular weights and solution chemistry including pH, ionic strength, and ionic valence affected the surface structures on particle surface by the adsorption of organic matterThe adsorption of organic polymer on particle surface resulted in the variation of light scattering and affected the accurate measurement of the sample turbidity under low turbidity condition. The extent of turbidity fluctuation had close relationship with pH, ionic strength, and ionic valence. The presence of Na+, Mg2+ and ozone could result in turbidity fluctuation because of the turnovers of molecular morphologies.The presence of organic molecules significantly affected the dynamic processes of particle coagulation. The dynamic processes of coagulation were divided into three characteristic phases with increasing coagulant dosage: compact electrical double layer, sensitivity of zeta potential, and stability of zeta potential. The zeta potentials of particle fluctuated obviously in the phases of sensitivity of zeta potential. The coagulant dosages at which the turbidity started to be removed increased with the increasing humic concentration. The coagulation mechanisms of kaolin particle coated by humic acid and polyacrylic acid included the bridging flocculation and sweeping flocculation other than the charge neutralization for naked kaolin particle.The effects of adsorption of organic polymer on the floc rupture and floc surface erosion and recoverability after high shear have been evaluated. The initial formation rates of floc and floc strength increased in the presence of organic matter. The floc sizes during the steady phase of growth were smaller, and the regrowing capability decreased because of the steric rebulsion from organic polymer. The recoverability was closely relative with floc breakage modes. The regrowing capability increased after floc rupture, and decreased after floc surface erosion.The fractal dimensions had close relationship with the floc sizes. The decreases in fractal dimensions resulted from the presence of organic molecules. The fractal dimensions were reversible during floc rupture, and irreversible during floc surface erosion. The reversibility of floc structure indicated at least two-level floc structure.The porous and fractal structures indicated that the fluids could penetrate into the flocs. The settling velocities of the fractal flocs were larger than the predictions from Stokes'law for impermeable flocs in the presence of intraflow. The settling performance of the flocs from the humic-coated kaolin particle got worse than that of the flocs from the naked kaolin particle. The settling velocities of flocs were in a good agreement with the fractal dimensions. The larger fractal dimensions, the faster settling velocityes of flocs, the smaller intrapermeation ratio. The increases in fluid collection efficiencies resulting from the intrapermeation were in good agreement with predictions from the cluster-cluster fractal model.