| 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.
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