Study On Optimal Allocation Of Urban Reclaimed Water System

Wastewater reclamation and reuse has been widely accepted in the world as an effective approach to solve various problems related to water shortage and water pollution. Although water reclamation has been adopted for a long time in China, there are still lack of researches on reclaiming water system optimal allocating. This problem results in the low rate of wastewater reclamation, and induces to not only the waste of funding but also the aggravation of water pollution to the environment.This paper introduces the research status of reclaimed water planning and optimal allocating study home and abroad, and compares the different methods applied in reclaimed water planning and regional allocating. Based on further analysis of the main problems in urban reclaimed water systems, the critical distance is introduced as a basic criterion to make proper patterns of reclaimed water. Because there are many problems in the process of the secondary pipelines system constructing, the efficiency of secondary pipelines network, expressed as the ratio of demand flow rate to pipeline length (Q/L), is an effective factor that can improve the decision-making process in constructing and laying out the secondary distribution pipeline. In addition, combining with the cost of decentralized reclaimed water project, a minimum economic scale (Qmin) is established as a criterion to choose decentralized reclaimed water project.Furthermore, this paper focuses on models of urban reclaimed water system optimal allocating. After analyzing the characteristics of urban reclaimed water system, two Multi Objective Nonlinear Planning (MONLP) models was established. To solve the MONLP model, Elitist Non-dominated Sorting Genetic Algorithm (NSGA-II) was adopted. The critical distance and efficiency of secondary pipelines network were used as two criterions for model tests.Because reclaimed water optimal allocating is a multi-attribute decision making problems, after researching on the theory of multi-attribute decision making, this paper the introducted Distance Gray Relationship Analysis (DGRA) method to evaluate configuration optimization programs, using FAHP to determine weights.The result shows that MONLP model is suitable for reclaimed water system optimal allocation. The solution from by NSGA-II could supply many flexible propositions. Meanwhile, the critical distance, the efficiency of secondary pipelines network and the minimum economic scale are proved to be useful as basic criterions for reclaimed water system optimal allocation. DGRA method is suitable for evaluating configuration optimization programs for decision-makers to make a comprehensive, practical decision.