| Due to the increasing complexity of the pollutants in wastewater treatment plant effluent and improving of recycled water quality requirements, conventional treatment process(coagulation-sedimentation-filtration) become more and more limited in wastewater reclamation recently. In the need for a higher water quality, conventional treatment process should add the treatment process of pre-oxidation or activated carbon, which made the process becomes tedious. For this, the processing technology of dissolved ozone flotation(DOF)has been invented. Including ozone oxidation and Air flotation, the DOF simplified processing flow and improved the water quality. However, DOF process was restricted by dissolved ozone ratio so that the amount of dissolving ozone was limited. As a result, a waste of undissolved ozone was inevitable and treatment effect is not stable. Dual-step ozone induced flotation(DOIF) process based on the thinking of utilizing the undissolved ozone for extra ozonation after flotation. This process included two process: DOF and extra ozonation. Based on this, tertiary wastewater treatment of city and dyeing wastewater were selected to analyze the efficacy of treatment and technique economics. Analyzing the effluent organic matter characteristics will provide the theoretical and application basis for the practical application of the process.In this paper, tertiary wastewater treatment of domestic wasterwater was conducted in pilot scale at Xi’an using DOIF to find the optimum condition of the coagulant dose. Operating conditions: polymeric aluminum chloride(PAC) as the coagulant, influent flow is 1.5 m3/h,retention time is 30 min, ozone dose is 20 g/h. Research results show that, the best condition was under the 160mg/L of PAC dose, it could achieve a very high removal of TP, TOC, UV254, turbidity, color as well as effective inactivation of total bacteria. Three dimensional fluorescence analysis and molecular weight distribution analysis were studied in this paper. As a result, ozone is mainly reacted to the functional groups of humic acid and reduced the molecular weight of water as well. By comparing the treatment effect of the upper and lower layer of the device,t he extra ozonation zone using undissolved ozone could further remove TP, UV254, color and total bacteria. Further, DOIF process also applied to the dyeing water recycling treatment. The COD and color of the effluent met the water requirements of the workshop.In summary, the DOIF process utilizes the undissolved ozone for extra ozonation. It was an integrated process for coagulaton, separation, organic matter removal and disinfection. The effluent water quality meets the requirement of recycling, and the operation and maintenance of the equipment is simple. The DOIF process will be shaped to achieve high efficient sewage recycling and safety insurance of water quality and has a good economic and social benefits. It has a wide range of application prospects. |
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