Characterization And Intensive Control Of Mechanism Primary Flocculation Stage Of Water Treatment Process

The traditional water treatments mainly contain three units, flocculation, sedimentation and filtration, with flocculation always being the first step of these three units. In the process of flocculation, the characteristics of the flocs, such as the floc size, density and structure strength, have great effects on water quality of the sedimentation outlet and the filter outlet,the period of filter backwash cycle, and other operating parameters. Therefore, the key of flocculation is forming easily-settled flocs in the process. The flocs forming process starts with the small colloidal particles. They aggregate to small flocs, then medium flocs, finally big flocs. The stage of small flocs growing into medium flocs, being defined as the primary flocculation stage in this study, has great research significance.For learning the characteristics of the primary flocculation stage, a series of flocculation-sedimentation-rapid filtration experiments have been finished, with PACL being coagulatant, and the suspension of koalin and fluvic acid being the initial water. Through non continuous online monitoring system of water treatment, water turbidity, particle number and size distribution, the pressure of the specified location in filter were monitored. The characteristics of the primary flocculation stage, got knowledge from this study, include segmentation, the law of particle distribution characteristics, its defination effect factors, and the relation with the subsequence treatment units, diagnosis method of water in the process of each unit and the whole process, control mechanism on the subsequent process of primary flocculation stage, the strengthening mechanism of primary flocculation. These results are of major importance on the research of flocculation theory and optimization control in waterworks.First, the law of particle distribution characteristics changing with time in flocculation-sedimentation filtration process, was studied. The method of detecting particle distribution in traditional water treatment process was established, in order to quantify the efficiency of each unit. This method consists of applying water turbidity and2~5μm particle number to diagnosing flocculation-sedimentation process of solid-liquid separation effect, applying precipitation initial fractal dimension decreased rate of v to diagnosing flocculation floc settling properties, applying RSS0.5to diagnosing filtered water quality stability, applying filter head loss rate of rise to diagnosing filter hydraulic parameters. There is a good relationship between these factors (R2>0.9).Secondly, through analyzing the law of partical distribution characteristics changing with time in flocculation process, the segmentation，defination and characteristics of flocculation were studied. As the results shown, the fractal dimension of particle flocculation process could be used as the basis of flocculation process segmentation. Through the analysis of its derivative rule with the flocculation time changes, the flocculation process is divided into four stages, preparation stage, primary-flocculation stage, growth stage and stable stage. And then the definition of primary-flocculation stage was given,and its characteristics were studied by application of KaG,‘’ and Dfg comprehensive evaluation. Through the quantitative analysis of primary flocculation stage effects on each unit of water supply process, the mechanism of primary flocculation stage dominating the water supply process unit was obtained, which could provide a new method for the study of production control and automatic control of waterworks waterworks. The result shows that when flocculation speed increase1%, flocculation efficiency increase1.7%, settling properties increase4.2%, filtered water quality stability increas0.85%, and filter hydraulic parameters increas0.17%.Thirdly, two-dimensional DLA model with time parameters was set up, and used to simulate and study the floc morphologial rules with time, the effect of floc morphology kinetic parameters on the floc forming of primary flocculation stage, and the effect of floc morphology of primary flocculation stage on that of floccutation outlet. On the basis of other previous research, floc step growth model was improved, and the new model was uesd to analyze and caculate.The results shows that the floc will grow on one certain direction prior to the other ones; the flocs forming in primary flocculation stage have ‘active site’(2-4in one core); in the growth stage, the flocs will only grow at the active site, and according to different active sites grow into different patterns of flocs; the effective density of flocs could alone be effected by the effective density, particle size and quantity of active site of flocs forming in primary flocculation stage.Above all, strengthening control method of primary flocculation stage was established, whose effect on primary flocculation stage was alse studied. Through investigating the efficiency of sedimentation and filtration, the settling and adhesion properties of flocs in flocculation outlet were infered. Finally, the mechanism of primary flocculation stage strengthening control was found, which could become the theoretical basis of construction, management and research of strengthening flocculation in practice..