The Optimization And Comprehensive Evaluation Of Oxidation Ditch Wastewater Treatment Plant

The wastewater treatment plant(WWTP) is an essential public infrastructure to control the pollution and shortage of water. In the process of design and operation in WWTP. There are a lot of issues that should be give a definite answer, but now they are usually determined by the practical engineering experience, which lead to a lack of theoretical support and a certain one-sidedness and limitations. The issues that the spacing of aerator impeller and the intermediate guide wall, and eccentric position of half-width of the guide wall of bend, the oxygenation mechanism of surface aeration equipment and how to choose the right aeration equipment, comprehensive comparison of operational performance of WWTP always perplex the engineering. Fluid dynamics simulation, experiments and various evaluation and optimization methods are applied to solve the above questions, the main contexts are summarized as follows:1.The Optimization of spacing between umbrella-type surface aerator impeller and the intermediate guide wall in Oxidation ditch process. The optimal spacing between the impeller and the intermediate guide wall directly affects the hydraulic characteristics and the energy consumption of the impeller, but now the design of the parameters is based on the experience, and it must be lack of theoretical support. Based on computational fluid dynamics simulation, mean method, analytic hierarchy process (AHP)and gray correlation method(GRA) were used to evaluate the distribution of the different speed ranges, the results shows that:mean method can’t be unreasonable to evaluate the hydraulic characteristics in the Oxidation ditch; the optimal spacing range obtained by AHP contains the energy consumption of the impeller beyond the acceptable quantity; the optimal spacing range obtained by GRA is moderate,in which energy consumption of the impeller can be accepted and the area of speed in0.3-0.5m/s is maximum, so GRA method can be used to evaluate the flow field characteristics in oxidation ditch.2. The Optimization study of eccentricity of the half-width guide wall in oxidation ditch bend. In the bend of the oxidation ditch, if the eccentricity of the half-width guide wall is set appropriate, the hydraulic characteristics can be effectively improved. By the analysis of results of the FLUENT and GRA method, confirmed that the setting of half-width guide wall could improve the velocity distribution in the entire ditch, but it could also cause additional power consumption. To the same oxidation ditch,when the aeration impeller changes will affect the best eccentricity.3. The comprehensive evaluation of different aeration equipments based on life cycle cost method. Currently, the selection of the surface aeration and blast aeration equipment is difficult and has controversy. In order to solve this puzzle, two WWTPs were selected,which have the same water consumption and treatment process and different aeration, to compare the costs of life cycle.The results show that in normal operation time, blast aeration can save electricity charges about900OOOyuan compared with surface aeration every year, but the number of the total costs in20years of surface aeration are only one-half compared with blast aeration, because surface aeration has the feature of easy maintenance and long service life. Therefore, for the long-term consideration, surface aeration equipment should be selected of the first until the life of the diffuser has revolutionary update. Based on the above results, the intermittent unsteady state method was adopted to study the performance and efficient conditions of inverted umbrella surface aerator impeller, and showed that there is a characteristic curved surface and have a best matching point in the surface for each aerator, and in the point the aerator impeller has the highest power efficiency and no matter with the reducer and motor.4. The evaluation of operation performance of WWTPs based on projection pursuit. The operational performance of the WWTP behalves the technical level and the capacity for sustainable development, genetic algorithm and projection pursuit(PP) model are used to make multidimensional evaluation indexes project to the one-dimensional space, horizontal comparison of complex systems is achieved for the plants having the different processes and in different regions, and confirmed the credibility of results. Compared with the evaluation results of principal component analysis, PP model can not only achieve the sort of performance of WWTPs,optimum projection direction of PP model can also be used to improve the operation performance of WWTP with the poor performance. The results can contribute to the continuous self-improvement of the WWTP and compare operation performance of different WWTPs.The conclusion of the research can be directly used to optimize the design and operation of the WWTP to continuously improve the operational performance in the whole life cycle, so as to achieve the purpose that WWTP plays its important role in the control of water pollution.