Studies On The Key Factors Influencing The Radiation Field And The Application Of Vacuum Ultraviolet In UV Disinfection Process

In recent years,ultraviolet technology for water disinfection is applied increasingly in our country due to low cost,high efficiency,easy operation,no addition of chemicals.Advanced oxidation process?AOPs?involved ultraviolet also attracts both industrial and academic attentions.In practical operation,the disinfection/treatment effect is fundamentally decided by UV dose.The effect would drop seriously when UV dose is not enough.On the other hand,UV disinfection has an obvious drawback:there is possibility for UV-inactivated microorganisms to reactivate in appropriate circumstance.The key factors influencing the radiation field and the application of vacuum ultraviolet in UV disinfection process were studied in this thesis,and the following conclusive remarks were reached:?1?The radiation model,the manner that the light beam leaves the light source,is one of the most important issue for numerical simulations to calculate radiation field.In this work,three radiation models,i.e.,radial model,specular model,diffuse model,were evaluated.The calculation results were compared with experimental measurements.The results indicated that the evaluation results of the low-pressure UV lamps with different power were similar.Along with the perpendicular bisector of lamp in the scope of 0<r<4.5L,The values of the irradiance E_p on the plane which is parallel to the lamp?will be abbreviated as parallel irradiance?calculated by Radial model gradually deviated from that of the other radiation models and the experimental measurements with the increasing of radial distance r.Based on the definition of Radial model,the values of the irradiance E_n on the plan which is normal to the lamp?will be abbreviated as normal irradiance?is 0.Diffuse model,Specular model and their transformed forms incorporated geometric coefficient k were all found better than Radial model to match the experimentally measured values.At the range of r<1.5L,the parallel irradiance E_p of diffuse model with k was more appropriate to describe the radiation field under the established experimental conditions.The relative differences between the measurements and calculations are 1.8%,1.15%,4.5%for 8 W lamp,20 W lamp and 40 W lamp,respectively.?2?A method for calculating the average fluence rate in a UV reactor,which recommended by U.S.Environmental Protection Agency in 1986 and still is being used by domestic manufacturers,was analyzed by establishing models for UV reactor.Two UV reactors were theoretically set,which are the same except lamps array.It indicates that this method has been out of date and the calculation error is large,actually just an estimation.?3?Under the different circumstance of heat dissipation,the effects of temperature on the measurement of irradiance and the UV output were also studied.The results indicated that the variation of temperature had significant impact on the UV output.The UV output was reduced by about 20%with 2 degrees decrease of the relative temperature(T_air).?4?A chemical actinometer had been developed based the mechanism of chemical actinometer?KI/KIO₃?for the measurement of irradiance inside water.The chemical actinometer is a 1×1×4 cm³ sealed cell with KI/KIO₃ liquid.Based such a cell and a method proposed by IUVA,a measurement method of the UV output of monochromatic?254 nm?low pressure UV lamps in water was proposed.This method has two characteristics:?a?it doesn't deviate from the method recommended by IVUA,that used in air,and just expanded to be used in water;?b?it can precisely measure and calculate out the UV output for the lamp which is inside water.The actual measurement results showed that the chemical actinometer has good accuracy.It did not need to agitate the actinometer liquid during the process of measurement.The measurements of an 8 W low-pressure lamp were performed in two different ultraviolet transmittance?UVT254??95.5%and 89.1%?,respectively.The relative difference between two measurements was 1.73%.?5?The ability of VUV?185 nm?to inactivate microorganisms and control the reactivation of UV-inactivated microorganisms were studied by the same conditional experiments of UV lamp?only release 254 nm wavelength?and VUV/UV lamp?release both254 nm and 185 nm wavelength?.The UV lamp as well as the VUV/UV lamp could arrive at high sterilization rate in short time for inactivating the total bacteria and Escherichia coli.In total bacteria test,the test water was the effluent from wastewater treatment plant;Escherichia coli were the pure bacterium suspension purchased from the provider.Under the experimental conditions,the sterilization rate of UV lamp and VUV/UV lamp for inactivating the total bacteria reached 5.63 lg and 4.95 lg,respectively in 30 seconds.The inactivation rates of two type lamps for inactivating the Escherichia coli were found all above 5 lg in 15seconds.For the water with relatively high turbidity,the sterilization efficiency of VUV/UV lamp was better than that of the UV lamp in the early stage of the disinfection process.It was verified that the 185 nm VUV can control the photoreactivation of Escherichia coli effectively and proved qualitatively that the VUV/UV lamp can restrain the reactivation of bacteria from effluent after UV exposure.