Study On The Effects Of Organic Matters On Floc Morphology And Inter-particle Forces Of Cohesive Sediment

The suspension fine sediment in the estuarine and coastal areas will flocculate and settle under the turbulence,which plays an important role in the channel deposition,pollutant transport and sediment transport.However,there is a large amount of organic matter in the suspended particles,which has an important impact on the flocculation processes and floc characteristics of cohesive sediment.Therefore,it is very important to study the effect of organic matter on the flocculation of cohesive sediment.In this study,the effects of organic matter on the morphology and the inter-particle forces of polystyrene latex particles are studied,and the mechanism of collision,aggregation and breakup of flocs are revealed considering the organic matter.By culturing the polystyrene latex coated with humic acid organic film,the floc morphology and the interaction forces between particles with the organic film were measured.Furthermore,according to the fitting formula of the interaction forces between particles,a lattice Boltzmann model was established to study the effect of organic matter on the flocculation of cohesive sediment.The main results are as follows:(1)The experiment of the growth of the organic film on the latex particles.After 121 days,a kind of colloidal and translucent organic film to wrap polystyrene microspheres was formed due to the sodium humate,and the average particle size of the microspheres would increase firstly and then decrease with the increase of organic matter content.(2)The experiment of the interaction force between polystyrene particles with attached organic matter was carried out.it can be seen that the organic films formed by humic acid reduce the total repulsion force when two particles are close to each other,which promotes the flocculation.Comparing the measured inter-particle force with the colloidal XDLVO force,the XDLVO forces are modified considering the influence of organic film.(3)Based on the measured return force between particles it is found that the organic matter will increase the shear stress for separation of two bonded particles,thus increasing the stability of floc.According to the measured data,the floc strength formula considering the influence of organic matter film is obtained.(4)A three-dimensional lattice Boltzmann model was established to simulate the flocculation of cohesive sediment considering the influence of organic matter.The numerical simulations show that organic matter can promote flocculation and increase the floc particle size.With the increase of organic matter content(within the range of10-60 mg / L),the floc particle size increases.