Dynamic Model For Straining-dominant Deep Bed Filtration Based On Percolation Theory

Deep bed filtrat ion technology is widely used in modern water supply and drainage engineering,deep bed filtrat ion and related theoretical research for optimizing the process,cost savings ha ve significant pract ical significance.The exist ing theoretical model of deep-bed filtrat ion often lacks the dynamic descript ion of the whole process of filtrat ion,especially neglect ing the change o f the pore size caused by the pore filling of the filter bed,result ing in the concentrat ion of the effluent and the pressure drop of the subsequent suspended part icles,result ing in the deviation between the realit y and the simulat ion.Deriving from the experiment and taking the percolat ion theory as a tool,the dynamic simulat ion of deep-bed filtrat ion procedure was constructed on the basis of filtrat ion theory.In order to simulate the experiment,a deep-bed filtrat ion experiment was carried out before construct ing the dynamic model of deep-bed filtration process.The data of the experiment are used as arguments to construct the model of the filter media.Compared with the experimental results,the permeate concentrat ion of suspended particles and the pressure drop of the filtrat ion column are analysed and validated.The pore network model and the flow field of the filter bed are constructed by the percolat ion theory and the informat ion of the part icle locat ion and radius of the filter body in the model.In this paper,the trap mechanism is used to capture the informat ion of pore filled in the simulat ion process,and the state of the pore network and flow field are constantly refreshed to form the dynamic process simulat ion.To get the simulat ion results more closer to that of the experiment’s,we use the percolatio n theory to guide the judgment of the degree of blockage and to be amended.The effluent concentration and pressure drop of the suspended particles at each time point are stored and outputted,and the curves of the effluent concentrat ion and the pressure drop of the suspended part icles are obtained.The size distribut ion of the suspended granules and the pore size distribution of the filter bed have impressive impact on the results of simlulation: From the perspective of the size of the suspended part icles,if the suspended part icles are larger,the filter bed will be blocked more quickly.And the polydisperse suspended particles will block the filter bed more quickly than mo nodisperse part icles.The more descrete the part icle size’ distribut ion is,the lo nger t ime is required for the filter bed to reach full blockage.And the sensit ivit y analysis of the simulat ion results and the pore-size parameters indicates that the change in the size of pore chamber will bring huge impact to the simulat ion results.The output of the simulation is accord with the deep-bed filtrat ion experiments.The paired T-tests between simulat ion results and the the results of the deep-bed filtrat ion experiments show that at the significant level o f 0.05,there’re no significant difference between the results of experiments and simulat ions.The results of this project are of pract ical sign ificance.The model can be used to est imate the part icle size range of suspended solids,the predict ion of the concentration of suspended solids and the choice of backwashing t ime in the design and operation stage.