Analysis Of Fecal Coliform Over Standard And Techniques For Meeting Standard In UV Disinfection Of Wastewater Treatment

In present domestic sewage plant, there are serious overweight problems in UVdisinfection unit. In this thesis, a UV disinfection-CFD Model of sewage plant isestablished by studying the UV disinfection unit of a sewage plant withComputational Fluid Dynamics (CFD) software is used, and biological validationexperiments are conducted. The reasons of fecal coli form bacteria overweightproblem in UV disinfection unit are analyzed. The disinfection effects andapplication conditions of current application of UV and chlorine disinfection areexplored, and standard methods are proposed according to those reasons. Finally,several standard methods are compared, and the optimal case is verified bybiological experiments.UV Disinfection-CFD Model is established for UV unit of wastewater plant.The results of UV Disinfection-CFD Model indicate that the internal flow velocityin UV disinfection unit is relatively uniform, mainly in0.40~0.52m/s. No obviouslow velocity area is observed, and t10/HRT is high, and the flow regime in UV unitis fine. The distribution of UV light intensity inside the UV unit is not uniform, withan intensity of243mW/cm2near the UV lamp light, and dropping to10mW/cm2near the side wall, where the disinfection dose is low.The possible reasons for overweight problems in UV disinfection unit isanalyzed. The analysis reveals that a wastewater treatment plant under normaloperating conditions will not cause excessive problems. Prolonging service time ofUV lamp would cause a decrease of disinfection efficiency and had a risk ofexcessive problems. Appropriate measures would be economic and desirable toprolong the life time of UV lamps. Casing pipe deposited degree would affectdisinfection efficiency significantly. A scaling factor smaller than0.65would giverise to the overweight. The damaged UV lamp is the main reason for overweightphenomenon. The location and number of damaged UV lamps would affectdisinfection efficiency. Compared to other areas, overweight is more likely tohappen when damaged UV lamps are located at side walls. The greater number ofdamaged UV lamps, the more severe the overweight phenomenon.The study of UV and chlorine disinfection joint indicates that disinfectantscombination could guarantee the effluent quality under the conditions that theprolonged tubes are approaching their life time, and that the casing pipe depositedand lamps damage are not serious. However, if UV lamps are seriously damaged, disinfectants combination could not guarantee that the effluent meets standardplacidly.The analysis and comparative study of three standard methods reveal that,compared with disinfectants combination, vertical lamp configuration andmulti-stage lamp configuration can more effective in reducing excessive risk.Multi-stage lamp configuration is the best method in the same hydraulic conditionsbecause of its advantages of high effective dose, tube damage resistance and lowoperating cost. The results of biological verified experiments on multi-stage cascadelamps configuration and one parallel lamps configuration manifest that multi-stagelamp configuration can significantly improve the effectiveness of UV disinfection,and reduce excessive risks brought by lamp damage and casing fouling.