| As an important part of the conventional water treatment process, the treatment effect of coagulation and sedimention process directly determined the operating load, treatment efficiency and operating costs of the following process,So the studies on coagulation and sedimentation process still have a great significance. Currently, traditional research methods commonly use static jar test as a means of basic research, but it’s extremely limited, and can’t meet the needs of the actual process,So we combine the simulation of the flow field and coagulation-sedimentation continuous-flow experiments to further optimize the coagulation and sedimentation process.Numerical results are applied to guide the design of experimental equipment to optimize the operation conditions,inversely,the experimental results could further validate the accuracy of the numerical simulation.Firstly, the three-dimentional flow field in the continuous flow mechanical flocculation tank was numerically modeled with Computational Fluid Dynamics(CFD) under different hydraulic conditions such as paddle types, installation positions and break power. The velocity distribution, turbulent kinetic energy k, the turbulent dissipation rate ε,cycle time and stirring power are obtained by numerical simulation to investigate the influence of flow state in flocculation tank on the characteristics of floc size distribution and floc growth under different hydraulic conditions.The results indicated that the proper paddle types and operating conditions can effectively improve the flow state in reactor, increase the collision frequency of particles and accelerate the growth ratio of flocs.Besides,the two-dimentional flow field in a variable speed and two layer inclined plate sedimentation tank is also simulated with CFD software and the flow state in reactor is further studied, which provides the theoretical foundation for the following experimental study.The study shown that the sedimentation tank modified the hydraulic conditions to form a dynamic suspension layer, which can improve the uniformity of water distribution compared with the ordinary two layer inclined plate sedimentation tank.Increasing the number of inlet increases the concentration of the suspension layer and further strengthen the contact flocculation. This optimization measures improved the uniformity of water distribution, and provide better flow state for particles settling.The modified contiuous flow coagulant-sedimentation equipment composed of mechanical flocculation tanks and a variable speed and two layer inclined plate sedimentation tank. In order to simulate the natural water, small amount of humic acid added in the kaolin stock solution to prepare for the raw water. Poly aluminium chloride(PACl) was used as the flocculant.The on-line turbidimeter and particle counter are used to monitor the characteristics of floc size distribution and turbidity change in flocculation and sedimentation process, and get the same conclusion with numerical simulation.The result shows that the suspension layer was existence in the transition area between the upper and lower inclined plate,which significantly improved the removal efficiency for small particles. The appropriate operating conditions can increase the thickness of the suspension layer, such as an appropriate dosage, break power and so on. In addition, under shorter residence time in sedimentation tank, effluent water quality has no obvious deterioration, indicating that the equipment has strong resistance to impact load for the flow rate. |
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