Analytic Hierarchy Of Process Scheme And Practice Of Engineering Design In The Urban Wastewater Treatment Plant

Comparasion and selection of process scheme is one of most important stages in the construct of urban wastewater treatment plant, which decides investment cost, running cost, effluent quality, operation supervision and so on. In the fact, because of no forming a complete set of evaluation method, cost of budget estimate and subjective know of designer are crucial factors of election of process scheme in the feasibility study of our country.By inducting Analytic Hierarchy Process (AHP), grey relatinal analytical method of fuzzy mathmatics and definition of weight, an optimized evaluation model ofplanning of urban wastewater treatment plant is established. Comparing with current selection of process scheme which is decided by economic datd, the model can reflect objectly complete influence of system factors and make evaluation result more reasonable, which offer better scientific reference for selection of cortrol scheme of pollution source. Commonly, evaluating indicators of scheme include quantitative and qualitative indicator, the multiple objectives decision-making screening model arrived at the hybridtype quantification indicator-synthesis relational level u by making qualitative indicator quantified and integrating two kind of indicators. The size of u decided that the scheme was good or bad, so selection of process scheme was more scientific and practical.The model was applied to comparasion and selection of process scheme of Chengdou 2nd urban wastewater treatment plant. The level of adult degree of process, capital cost and treament cost was bigger than that of operation supervision and effluent staility, and the level of floor space and removal of N and P was the smallest. The result of optimized selection was as follows: A/O process was the best scheme, and Anaerobic/Oxic process was second.Some questions in the design of urban wastewater treatment plant also were discussed. The effect of low inflow quantity and concentration on practical running should be emphasized. In primary treatment of urban wastewater treatment plant, the setup of thin bar screen was important, and vortex desilting basin was applied in more urban wastewater treatment plant. Whether preliminary sedimentations tank was set need to be considered in traditional activated sludge treament system; German put forward a new method about design of second sedimentation tank, which overcome some effect ofsubjective factor.The paper will provide reference to selection and design of process scheme of urban wastewater treatment plant.