Study On Treatment Of Microplastics In Drinking Water By Coagulation-Sedimentation Process

As a new pollutant,microplastics exist widely both in water environment and water treatment process,but it hasn't an unified detection method because of their different shapes and sizes.Microplastics pose a threat to aquatic organisms and even human health,so the removal methods of microplastics have gradually attracted attention in the field of water treatment.Coagulation-sedimentation is an important part of the drinking water treatment process,and its results have a significant impact on the follow-up process and the final effluent safety.The control of the coagulation process can improve the water treatment efficiency,effluent quality and save management costs,which is of great significance.In this paper,taking 5 ? m polystyrene particles as typical microplastics,starting with exploring the properties of its solution,the relationship between microplastic particles and typical pollutants kaolin and humic acid in water is studied by beaker experiment.It is found that both kaolin and humic acid can adsorb microplastic particles,and they have synergistic effect.Then,by comparing the detection results of scanning electron microscope,fluorescence microscope and particle counter,the fluorescence microscope is determined as the detection method of microplastics.Based on these,the simulated sand filtration experiment is carried out,and it is found that the removal rate of microplastic particles by sand filtration was only 56.9% to 87.9%,so it is clear that it was necessary to regulate and control the water quality before filtration.Then,the law of floc morphology in the flocculation stage in the coagulation-sedimentation process is explored,and the key parameters regulating the flocculation process are average particle size,geometric fractal dimension and growth fractal dimension.Among them,the change of the average particle size and geometric fractal dimension of the coagulation system with microplastics in the fast stirring stage of the flocculation process is more gentle than that without microplastics,and the fractal dimension of flocculation growth fluctuates more greatly.At the same time,it is found that the removal rate of microplastics can reach 88.9% by single coagulation process.Using three-dimensional DLCA model for simulation,the characteristic parameters affecting the shape of virtual flocs are corresponding to the factors affecting the actual flocculation process,and the actual flocs growth process is analyzed.The factors affecting the flocculation process and results were studied by investigating the characteristic parameters such as the number of single flocs with different particle number,the length characteristics of flocs,the rotational fractal dimension,the porosity of flocs and so on.It is found that the more initial particles,the slower the change of floc size,the larger the floc at the end of flocculation;the smaller the particle diameter,the smoother the change of the average rotation fractal dimension of flocs,and the higher the density of the final flocs.Finally,the flocculation process can be controlled and the removal rate of microplastics can be improved after coagulation-precipitation.