The Evaluation Of Hydraulic Characteristics Of Clearwell And Its Study Of Optimization For Disinfection Efficiency

Efficient and safe disinfection methods can prevent all kinds of waterborne diseases effectively, guarantee the security of water quality and maintain human health. In disinfection process, clearwell is an important reactor of waterworks. Based on dealing with all kinds of raw water quality conditions widely, optimization of clearwell hydraulic efficiency can improve the disinfection efficiency effectively. The article researches about the hydraulic characteristics of clearwell and the influencing factors of hydraulic efficiency through the tracer experiments with the purpose of enhancing the hydraulic efficiency of clearwell lowering the dosage consuming and disinfection byproduct(DBPs). The investigation is also carried out about the process and the effect of disinfection of different hydraulic characteristics using chlorine dioxide as the disinfectant. The CFD 3D modeling technique is applied to the study on the hydraulic characteristics and the disinfection process of the clearwell to explore the reasonable parameter settings so as to evaluate the feasibility and reliability of the optimization of clearwell by using CFD technology.In this study, the concept of Tio is proposed, and the hydraulic efficiency is evaluated by tio/Tio. The pilot model is designed with 1/7.6 scale of prototype clearwell. The tracer experiments is performed in different conditions to study on flow, water depth, residence time, perforated baffles and other factors influencing the hydraulic efficiency for evaluating hydraulic characteristics. Six piece of perforated baffles are set up in the import, export and corridor around the corner in clearwell to improve the hydraulic efficiency. The result of the test shows that:(1) hydraulic efficiency η increases with the increase of the flow rate during the operation of clearwell. The influence caused by flow rate change is more obvious when the water depth is larger. The hydraulic efficiency η decreases while the water depth is increasing. The influence caused by depth of water change is more obvious when the velocity is small. (2) The hydraulic efficiency η decreases with the increase of the retention time, and the hydraulic efficiency decreases quickly when the residence time is over 60 minutes. (3) Setting perforated baffles can improve the water flow obviously, rise the hydraulic efficiency thus improve the effect of disinfection. The consumption of disinfectants and the DBPs formation reduces at last. The perforated baffles with the perforation rate of 5%,10% can be respectively improved 5% and 15% of the hydraulic efficiency in clearwell.The raw water of Yellow River in winter is to be dealed with disinfection treatment using chlorine dioxide as disinfectant. The study discusses formation mechanism and conditions of DBPs. The disinfection experiments are made on improving working conditions by additional perforated baffles in clearwell and also compare with the formation of disinfection efficiency and DBPs on different hydraulic efficiency under the same conditions. The result of the test shows that:(1) The drinking water standards can be reached by adding dose 0.3mg/L. (2) It has built a positive correlation between DBPs and initial dosing concentration or retention time. (3) The improvement of hydraulic efficiency caused by additional perforated baffles in clearwell can promote the reaction of disinfectants and reduce DBPs effectively. The longer retention time is, the more raising disinfection efficiency after adding perforated baffles is, the greater the proportion of reduction of DBPs is.The three-dimensional CFD simulation results validate the conclusions of tracer experiments more rigorously and accurately. Using DPM and species transport model simulate tracer experiments to obtain the corresponding function of retention time distribution and values of tio/Tio-The simulation of species transport model by increasing a source item to prove the diffusion and consumption of chlorine dioxide in the clearwell. The three-dimensional CFD simulation obtains the loss of pressure considering vertical head changes. The variation tendency of loss pressure in clearwell is analyzed as a reference for future designs. The result of the test shows that:(1) DPM model simulation has a similar result with tracer experiments. When the flow is higher than 2.0m3/h, the error rate is about 3%. (2) The order of accuracy of DPM model simulation is greater than species transport model, both of the simulation results reflect the regularity of tracer experiments. (3) The visual analysis shows that during disinfection process clearwell has less dead zones and retention areas with the average concentration distribution. It proves that there is a better water-hydraulic characteristics in the clearwell, which is conducive to conduct the disinfection process.