【作者】 张光辉；

【导师】 顾平；

【作者基本信息】 天津大学 ， 环境工程， 2007， 博士

【摘要】 突发性公共卫生事件引起的安全问题,以及化学消毒副产物对水环境和人体健康的潜在威胁,引发了水处理领域消毒技术的革新。UV消毒因具有广谱高效、无二次污染的特点,逐渐受到人们的青睐。与此同时,近年来随着膜材料价格的下降和性能的改善,MBR在水处理领域得到迅速推广,而MBR出水非常适合UV消毒。在此背景下,本文首次对UV消毒MBR出水及CFD模拟反应器的流场和基于CFD计算UV剂量进行了研究。UV对MBR出水中的指示微生物具有良好的灭活效果。不考虑光活化的影响时,17 mJ/cm2的UV剂量可以将污水中的细菌、大肠菌群和粪大肠菌群全部灭活。研究光强范围内UV强度的变化和MBR出水浊度在小范围(< 3 NTU)的波动,对微生物的灭活率没有影响。UV消毒后的水在3 h内未发现暗修复,但在日光灯和太阳光照射下均发生了光活化。采用UV对医院的MBR出水进行消毒,污水中残余的微生物数量能够满足《医疗机构水污染物排放标志》(GB 18466-2005)的要求。反应器的水力特性是影响UV消毒效果的重要因素。增大雷诺数,反应器的水力特性逐渐接近理想推流,水流的拖尾现象也随之被弱化。反应器的长细比较大时,径向尺寸的影响基本可以忽略,进出口垂直或相切于反应器主体、以及位于反应器的同侧或异侧,对水力特性的影响并不明显。与示踪试验比较,CFD技术能够较好地模拟反应器的流场,二者的差别主要是由于示踪试验的实际条件偏离理想条件所造成的。采用CFD对反应器进行优化,在其进出口设置导流孔板后,雷诺数增大到一定程度后能够明显改善其水力条件。分别采用Radial模型和PSS模型分析简单UV消毒器和大型UV消毒系统的光强及其分布规律。为克服PSS模型手工计算量大的缺点,探讨用介质的吸光度对空反应器的光强进行修正,该方法计算量小、相对误差小,理论上是可行的。利用CFD中的DPM模型模拟微生物在其内部的运动规律,以PSS模型计算UV强度,提出了计算反应器UV剂量的新方法。与近似方法和常规方法相比,理论上CFD离散方法的计算结果更接近实际值,并能减少不必要的能源浪费。该方法尚未在一定的UV消毒系统范围内得到验证,目前仍处于探索阶段。更多还原

【Abstract】 Water and wastewater disinfection technology is innovated by the safety problems caused by emergency of public health and threats of disinfection byproducts to water environment. Ultraviolet (UV) disinfection has been widely concerned by many researchers as broadband inactivation of microorganisms and little influence on treated water or wastewater. In the mean time membrane bioreactor (MBR) are also widely used in the field of water or wastewater treatment with decreasing price and increasing performance of membrane, and MBR effluent is very fit for UV disinfection. As a result MBR effluent disinfection by UV, reactor characteristics and UV dose calculation based on computational fluid dynamics (CFD) were studied for the first time in this dissertation.UV has good effects on inactivation of the indicator microorganisms in MBR effluent. When photoreactivation is not considered, all the bacteria, coliform group and fecal coliform group in MBR effluent could be inactivated with 17 mJ/cm2 of UV dose. Removal effects of microorganisms are little affected by the variation of UV intensity within the test range and MBR effluent turbidity in a narrow range less than 3 NTU. When MBR effluent samples irradiated by UV were put in dark, dark repair was not found in three hours. However, photoreactivation occurred when the samples were placed under a fluorescence lamp or in the sun. When a pilot UV reactor was used for disinfection of MBR effluent from a hospital, residual microorganisms in treated wastewater could meet the requirements of Discharge Standards of Water Pollutants for Medical Organization (GB/T 18466-2005).Reactor hydraulic characteristics are the main factor for water or wastewater disinfection. Hydraulic characteristics were gradually close to plug flow with increasing Reynolds number, and tailing effect was also weakened. The influence of radial size could be neglected at a high ratio of axial to radial length. Additionally that the inlet tangent or perpendicular to reactor, and the inlet and outlet located in the same or opposite direction, has little effect on the reactor hydraulic conditions. In comparison with tracer test, CFD technology could simulate the flow field in the reactor to a better extent. The major difference between CFD simulation and tracer test was cause by the deviation of the practical operation condition from the ideal. CFD simulation results showed that when perforated plates are installed near the inlet and outlet for optimization of the reactor, and Reynolds number rises to a certain extent, hydraulic conditions would be improved obviously.Calculations of UV intensity in a simple annular reactor and complex disinfection systems were made based on Radial Model and Point Source Summation (PSS) Model. In order to reduce the amount of calculation with PSS model, a method that absorbance of media was used to revise the UV intensity in empty reactor was discussed. This method is theoretically feasible for little amount of calculation and relative error. In addition, with the help of Discrete Phased Model in CFD for simulation of microorganisms’trajectories, a new method for calculation of UV dose based on CFD was put forward. Compared to the approximate method and ordinary method, this new method could reduce some unnecessary energy consumption, and the calculation results were more close to the true values in theory. However, this calculation method based on CFD is still in exploration and has not been verified in the UV disinfection systems yet.更多还原