Experimental Study On The Characteristics Of Grid Vortex Coagulation Flocs

Coagulation is the basic treatment unit in the whole water treatment process,and its importance is self-evident.The effect and efficiency of coagulation process will directly affect the treatment accuracy and difficulty of subsequent treatment units.In recent years,flocculation technology based on the core principle of vortex coagulation has been gradually developed and applied.The core principle is to make the large-scale vortexes in the flow field evolve into small-scale vortexes suitable for coagulation as far as possible in a certain way.Therefore,this paper takes the swirl flow field as the main research object and achieves the purpose of improving the coagulation effect by adding different forms of grid-type vortex generators in the flow field.The structure combination form of the grid-type microeddy generator is optimized by orthogonal design test and the optimized result is verified.Then the treatment effect of the grid-type microeddy flocculation is compared with that of traditional mechanical agitation flocculation.The floc morphology is evaluated by floc size,particle size distribution,floc shape ratio and floc fractal dimension as indexes.At the same time,flow field characteristics of the two flocculation modes are analyzed by combining numerical simulation experiments.Finally,the treatment effect of different water volume and water quality conditions on the grating micro-eddy flocculator is investigated.The research results and conclusions are as follows:Firstly,orthogonal test with 4 factors and 3 levels is designed.Four influencing factors,i.e.shape of grille,arrangement distance of grille,thickness of grille and combination of height of grille,are selected as objects of study.With turbidity of outgoing water and fractal dimension of floc as evaluation indexes,the influencing factors are obtained as follows:A（shape of grille）>D（combination form of grille）>C（thickness of grille）>B（spacing between grilles）.The optimum form of combination of grille structure is"triangle+3mm grille+single hole spacing+’100+200+400+600’height combination".On this basis,particle size,floc morphological characteristics and flow field characteristics of grating micro-eddy flocculation and mechanical agitation flocculation were analyzed.Under the condition of the same input power of flow field,the final floc size of mechanical agitation flocculation was 106.76μm,the shape ratio is 2.29,the fractal dimension is 1.83,the average G value ranges from 0.68 to 3.52 s^-1,and the maximum turbulent kinetic energy reaches 2.62E-4 at position 9.Floc size of grille microeddy flocculation is 315.79μm,the shape ratio is 2.33,the fractal dimension is 1.94,and the G value finally stabilizes between 7-8 s^-1.The maximum turbulent kinetic energy can reach5.56E-4 at position 1.The energy distribution in the mechanical stirred flow field has little difference in the whole flow field,and the whole flocculation process can only be matched by adjusting different rotational speeds,while the flow field in the grating field matches the flocculation process better in terms of time and space distribution of energy.Finally,the treatment effect and floc morphological parameters of micro-eddy flocculation under different raw water conditions were analyzed.Under different inflow flow conditions,the mean fractal dimensions of each characteristic section were 1.820,1.870,1.873 and 1.915 respectively,and the mean fractal dimensions of grain size were 1.407,1.502,1.368 and 1.420 respectively.Turbidity of 1000NTU raw water increased by 48.92%,44.95%and 42.71%respectively compared with 300NTU.The shape ratio of flocs under the conditions of particle concentration in raw water has similar changing rules,and the size relationship is as follows:φ500NTU<φ1000NTU<φ300NTU;The fractal dimension of flocs under the conditions of particle concentration of raw water has similar change rule,and its size relation is D_f300NTU<D_f500NTU<D_f1000NTU.