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Development Of Photocatalytic Reactor For Treatment Of Centralized Air Conditioning Cooling Water

Posted on:2013-08-09Degree:DoctorType:Dissertation
Country:ChinaCandidate:L J PanFull Text:PDF
GTID:1102330467451829Subject:Occupational and Environmental Health
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With the economic development and living standards rising in China, hotels, shopping malls, office buildings were equipped with central air conditioning and ventilation systems to improve the living and working environment. Central cooling water system was an important part of the central air conditioning and ventilation systems. Due to the long-running, the cooling water systems caused corrosion, scaling, the formation of biological slime and Legionella contamination. Legionella could cause the Legionnaires’disease, which had most serious health effects on the surrounding population (according to the WHO reports, the mortality rate of Legionnaires’disease is up to20%). Therefore, the study of the control tmethods of the cooling water Legionella contamination had become urgent. At present, the most direct and effective method of killing the cooling water Legionella was disinfection. The most commonly used disinfection method was dosing chemicals. However, the chemical disinfection could not effectively solve the Legionella contamination, and would increase the concentration factor and sewage of the cooling water system. Fortunately, TiO2-nickel foam photocatalytic oxidation technology could not only effectively solve the above problems of the chemical disinfeciton technologies, but also degraded the organic nutrition of the cooling water to reduce the growth of legionella. However, because of the lack of substrate data such as photocatalytic degradation reaction kinetics of pollutants, the inefficiency of existent TiO2photocatalytic reactors, as well as the influence of cooling water quality, water quantity fluctuations, the TiO2-nickel foam photocatalytic oxidation technology in cooling water treatment was limited. Therefore, we carried out the following works in the photocatalytic oxidation treatment of cooling water using TiO2-nickel foam:(1) the development of efficient photocatalytic reactor (Chapter Ⅱ). In this chapter, cylindrical photocatalytic reactor model was simulated to reduce pollutant methylene blue and E. coli, in order to optimise the photocatalytic reactor performance. Through optimizing the UV light intensity (16w), the TiO2-nickel foam packing density (the cylinder diameter of7cm) and installation of the UV light intensity enhancer (aluminum), a new type of photocatalytic reactor was developed. In the new type of photocatalytic reactor, the degradation efficiency of methylene blue was67.97%after120min reaction, increasing80%comparing with the efficiency before optimization. the kill rate of E. coli was6.28log after20min reaction. The photocatalytic degradation of methylene blue in the new type of photocatalytic reactor was a first-order reaction and met the Langmuir-Hinshelwood first-order kinetic equation. The higher initial concentration of methylene blue, the more effective photon energy absorption by the solution, the degradation rate constant decreased. The results also showed that the death kinetics of E. coli in the new type of photocatalytic reactor performance was a reaction that meets the Langmuir-Hinshelwood equation kinetic equation. In this experimental condition, the results of orthogonal analysis showed that the most effective disinfection factor of the photocatalytic reactor was the source power, followed by ultraviolet light intensifier, the concentration of methylene blue.(2) In Chapter Ⅲ, the actual cooling tower water sample was treated in the new type of photocatalytic reactor. The total number of bacteria of the cooling water was used to evaluate the disinfection performance. The impacts of cooling water influent flow rate and water quality on the new photocatalytic reactor were studied. The results showed that the average disinfection rate of microbes decreased from2.89log to the2.35log when the water flow rates increased from25L/h to50L/h, which was in consistent with the simulation results of the photocatalytic sterilization kinetic equation (y=0.192x-0.096) in Chapter Ⅱ. This indicated that the disinfection rate will reduce with the increase the flow rates in the same conditions. The greater the turbidity of influence, the lower transmittance of water, the less the number of photons reach the surface of the photocatalyst, and thus the photocatalytic reaction rate reduced, the processing efficiency fell. The results also show that the impact of water quality on the degradation of methylene blue had an apparent rate constant Kl of0.004mg (L min)-1, which was half of an apparent rate constant when studying pure water impacts. This indicates that the cooling water quality have a major impact on the degradation rates of methylene blue.(3) In Chapter IV, the wire was set as the anode in the new type of photocatalytic reactor to protect the cathode of TiO2-nickel foam from corrosion. In the coolingwater temperature was around30~40℃, the results show that with the cathodic protection, the corrosion speeds of the TiO2-nickel foam decreased from0.165g/(m2·h)~0.661g/(m2·h) to-3.122g/(m2·h)~-0.538g/(m2·h), the corrosion rate decreased from1.81~7.242mm/a to-3.480~-0.600mm/a. According to the metal loss classification standards, the TiO2-nickel foam changed from high to low corrosion metal in cooling water before and after cathodic protection. This indicates that the cathodic protection method can effectively slow down the corrosion rate of TiO2-nickel foam in the cooling water, to extend its service life and improve the economic efficiency. The results also show that the cathodic protection had little effect on the sterilization properties of the TiO2-nickel foam, and had no effect on the degradation performance of methylene blue.
Keywords/Search Tags:Treatment, Central cooling water system, photocatalytic reactor, TiO2-nickel foam
PDF Full Text Request
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