Research On Advanced Treatment Of Secondary Effluent From Sewage Treatment Plant By O₃/UV

In recent years, with social development, water treatment technology has been widely applied to all walks of life, and tertiary treatment process of urban sewage treatment plants has been to be paid more and more attention. In this paper, the pilot plant of the ozone and ultraviolet combined process was designed and processed, secondary effluent of a sewage treatment plant in Hefei as the research object, using the ozone and ultraviolet combined process for advanced treatment, separate O3, UV, VUV and O3/UV combined process on the removal effect of organic matter CODCr in water was first studied and the impact of different experimental conditions on the process was analyzed. The synergistic mechanism of the ozone and ultraviolet combined process, including oxidation of ozone mass transfer in secondary effluent, the inhibition experiments of adding sodium carbonate as inhibitors to inhibit hydroxyl free radical as well as the catalytic experiments of adding iron ions as catalyst to stimulate hydroxyl free radicals was then analyzed. Finally, with the conclusions of the above experiments, according to the water quality characteristics of sewage treatment plants, the design scheme of depth treatment process was optimized. The results showed that:(1) A wavelength of254nm UV and ozone for advanced treatment process on organic matter in water had a synergistic effect, processing more effective than ozone alone or ultraviolet technology alone. The effect of VUV on the degradation of COD is obvious better than that of UV photolysis, the treatment effect of the high wattage UV is better than that of the low wattage UV, the same as UV, the treatment effect of the high wattage VUV is better than that of the low wattage VUV. The removal rate of CODCr can reach72.2%after50min when the ozone dosage was at2L/min and VUV was at15w. There was a great impact between different reaction conditions and the ozone and ultraviolet combined process on the removal effect of COD, when pH was at7and the water was in the neutral condition, the degradation effect of COD was the best, and there was a positive correlation between the initial concentration of the influent and the removal rate of COD.(2) Under the experimental conditions in this paper as well as the overall process of the ozone reactor used, the ozone mass transfer coefficient KLa is0.32min-1, chemical reaction enhancement factor E as the contribution of chemical reaction on the absorption rate can be approximated as one.(3) The degradation effect of organic matter and inhibitor concentration of sodium carbonate showed a negative correlation. In the condition of PH7.0, the accession to the sodium carbonate to some extent weakened the degradation efficiency of O3/UV, when the sodium carbonate dosage was at100mg/L, the removal rate of CODCr was only15.78%. But whether or not to add sodium carbonate as well as add high or low concentration of sodium carbonate, the appearance point of dissolved ozone did not change significantly. According to the water quality characteristics of secondary effluent of Wang Tong sewage treatment plant,when the addition dosage of Fe2+was at0.3mg/L Fe2+on the catalytic effect of the ozone and ultraviolet combined process showed the highest and the removal rate of CODCr reached68.25%after30mins.When the concentration of Fe2+was less than this concentration, with the increase of the Fe2+dosage, the removal efficiency of the CODCr in the water body increased; the concentration of Fe2+continued to rise, when up to0.5mg/L, the treatment effect decreased instead.(4) In the ozone and ultraviolet combined process, the optimal action time of ozone was30min, to prolong action time can not effectively improve the removal rate of organic matter. From an economic and energy point of view about the urban sewage treatment plants, the author suggests that the ozone and ultraviolet combined process which Wang Tong sewage treatment plant in Hefei used can be optimized, that is, through the change of UV lamp time point and UV lamp action time on the ozone and ultraviolet combined process optimization, intermittent UV light can be used to open, using interval of3min, the results can still achieve the desired requirements.