Study On Ozone Dissolved Air Flotation Technology In Advanced Sewage Treatment

At the Globalization background of serious shortage of water resources, recycling of water resources has become one of the important solutions to the current water crisis. Municipal sewage as the second water source of the city was not only stability, but also having good economic benefits and a very bright future for the development.The Ozone Dissolved Air Flotation wastewater advanced treatment technology was studied in this subject, aiming at the defects existing in current commonly used coagulation-sedimentation technologies, such as long treatment process, large area, poor removal rate of residual organic pollutants in sewage and so on. The subject mainly included as follows: (A)The experimental study of ozone-coagulation wastewater advanced treatment. The impacts of removal effects of the organic matter in the secondary effluent using different coagulant type and dosage, and the impacts on coagulation process when adding ozone were studied through statistic tests. The flocculants role of ozone was investigated. (B) The experimental study of Ozone Dissolved Air Flotation wastewater advanced treatment technology. The feasibility of the Ozone Dissolved Air Flotation technology in reclaimed water reuse was studied through the research of treatment effects applying the Ozone Dissolved Air Flotation technology in the sewage plant secondary effluent, and the research of treatment effects by using different coagulant type and dosage, ozone dosage and ozone content in the dissolved airflow.The experimental study of ozone-coagulation wastewater advanced treatment showed as follows:(1) The best coagulant was PAC, the best dosage of ozone needed was 3.0mg/L, and the best contact reaction time was 10 min under the conditions of the test.(2) Adding ozone could intensify the coagulation effect. The best coagulant dosage of PAC (calculated with Al₂O₃) without adding ozone was 6mg/L. After adding the ozone of 3mg/L, the dosage (calculated with Al₂O₃) could be reduced to 0.8mg/L to achieve the same treatment effect.The experimental study of Ozone Dissolved Air Flotation wastewater advanced treatment on the basis of statistic test showed that:(1) The ideal conditions of Dissolved Air Flotation were as follows: dissolved air pressure of 4.2 bar, dissolved gas-water ratio of 20%, technology reflux ratio of 40%, hydraulic retention time of 15min.(2) Turbidity, color, UV₂₅₄ and COD_Cr were chosen as verifying parameters in the experiment, and the best coagulant dosage of PAC was confirmed as 0.5mg/L.(3) The test ensured that the Ozone Dissolved Air Flotation system had good removal effects on the turbidity, color, UV254 and COD_Cr at the ozone dosage of 2.76mg/L, the removal rates could be achieved to 24.67%, 51.83%, 22.56% and 33.96% respectively, and the technology effluent indicators of the turbidity, color, UV₂₅₄ and COD_Cr could be reduced respectively to 3.97NTU, 7.007 degrees, 0.127l/cm, and 35mg/L, which fully met the "Miscellaneous Domestic Water Quality Standard" CJ 25.1 -89 requirements.(4) In the Ozone Dissolved Air Flotation technology, the ozone content in the dissolved gas flow was also one of the important operational parameters. Test showed that the dissolved ozone concentration in airflow had a negative impact on micro-bubbles when it was too high, while efficient help of ozone oxidation and coagulation effects could not be exerted when the ozone concentration was too low. Integrated various targets, the best general removal efficiency for different pollutants could be achieved at the ozone content of 17.42mg/L.