Prioritizing the best sites for treated wastewater instream use in an urban watershed using fuzzy TOPSIS

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Abstract

This study developed a new framework that prioritized the best sites for treated wastewater (TWW) instream use using fuzzy Technique for Order of Preference by Similarity to Ideal Solution (fuzzy TOPSIS), a fuzzy-based multi-criteria decision-making (MCDM) technique. We identified key criteria for TWW use based on the Driver-Pressure-State-Impact-Response (DPSIR) framework that considered technical, social, economic and environmental aspects. We also introduced triangular fuzzy numbers and conducted individual interviews to consider the uncertainty of weighting values and input data. This procedure was applied at ten sites in a South Korean urban watershed, where hydrologic modeling exercises were performed. Our simulation results for water quantity (i.e., drought flow, low flow and the days to satisfy instream flow) and water quality (i.e., BOD concentration and the days to satisfy target water quality) showed significant inter-annual variability that could be better represented with fuzzy numbers. Furthermore, the use of fuzzy TOPSIS gave different rankings of the best sites for TWW use compared to those obtained from a weighting sum method, a traditional MCDM technique. Such varied rankings with different MCDM techniques indicate the need for fuzzy-based techniques, considering various uncertainties and thus being less controversial.

Highlights

► A framework to prioritize the best sites for treated wastewater use was developed. ► Social, economic and environmental criteria were selected using DPSIR framework. ► Triangular fuzzy number is introduced for uncertainty of weights and input data. ► A fuzzy-based multi-criteria decision-making method, fuzzy TOPSIS, was used. ► Use of fuzzy TOPSIS gave markedly different rankings of the best sites.

Introduction

New approaches to the sustainable planning, design, and management of urban regions for water cycle (stream) restoration depend upon improvements in our knowledge of the spatial and temporal variations of flow regimes and pollutant loadings during the urbanization process. Worsening urban conditions related to crowding, housing shortages, and insufficient or obsolete infrastructure, increasing urban climatological and ecological problems, and issues of urban security have increased the need for effective urban water management and planning (Chang et al., 2008).

Among the various available urban water management strategies, treated wastewater (TWW) use has received growing attention over the last 30 years and is considered an important part of sustainable urban water management for stream restoration in many countries. However, TWW use has a critical disadvantage in that it leads to water quality deterioration. Highly treated wastewater (HTWW) can be used instead, but requires a tremendous budget and most countries cannot satisfy residents’ demand with such water. Thus, the trade-off between flow regime enrichment and water quality aggravation must be determined with caution.

Therefore a decision support system is urgently needed to select appropriate locations and best-fit quantities within the supply (Ganoulis, 2003). Ganoulis (2003) suggested a methodology to evaluate alternative strategies with different treatments, different disposal sites, different types of irrigation scheme and others for wastewater recycling and reuse in the Mediterranean area. Alternative strategies were evaluated by using the Multi-Criteria Decision Making (MCDM) method with the concept of sustainability, considering public health and environmental factors, economic factors and social factors.

Recently, Anane et al. (2012) have developed a methodology to rank the best sites for irrigation with TWW in Tunisia, with considering five main criteria including land suitability, resources conflicts, cost effectiveness, social acceptance and environment factor. Using fuzzy Analytic Hierarchy Process based on GIS, they were able to map and rank the suitable sites for TWW irrigation. Other reported applications of site selection have included aquifer recharge (Pedrero et al., 2011), soil waste disposal (Nouri et al., 2011) and water harvesting ponds (Al-Adamat et al., 2010). However, no site selection has been applied to TWW instream use.

In light of these issues, this study established a framework to prioritize the best sites for TWW instream use by considering both the capacity for water quantity improvement and the risk of water quality deterioration with the hydrologic modeling exercises. This study employed the Driver-Pressure-State-Impact-Response (DPSIR) framework to consider technical, social, economic and environmental aspects of TWW use, and fuzzy Technique for Order of Preference by Similarity to Ideal Solution (fuzzy TOPSIS) to consider the uncertainty of criteria weighting values and the performance of TWW use. The framework was applied to an urban watershed in South Korea, which demonstrated the value of the framework to help decision makers for ranking alternatives of TWW instream use.

Section snippets

Characterization of the study area

The Anyangcheon watershed in central Korea, near the capital city of Seoul, was selected for this study because serious water quantity and quality problems have been observed and resulted in devastating flood damage, depleted streams, and even occasional fish deaths (Han et al., 2005, Lee et al., 2008). The river is a first-order tributary of the Han River in Korea (Fig. 1). The main channel length of the Anyangcheon River is 32.38 km, draining a watershed area of 287 km2, in which 388 million

Generating alternatives

We derived ten suitable sites for TWW instream use in the Anyangcheon watershed by considering the streamflow quantity during the dry period and the sub-watershed area (Fig. 1). We divided the sites into five groups according to the watershed areas in which the sites were found (Table 2). The first group consisted of four sub-watersheds (SS, SB, WG and OJ) measuring under 10 km2 with capacities of 6000 m3/day and the second group consisted of three sub-watersheds (SM, SB1, and DJ) under 20 km2

Conclusions

This study established a framework to prioritize the best sites for TWW instream use by considering both water quantity and quality with the HSPF simulations. The DPSIR framework was employed to consider technical, social, economic and environmental aspects of TWW use, and fuzzy TOPSIS was also used to consider the uncertainty of criteria weighting values and the performance of TWW use.

The framework was applied to an urban watershed in South Korea to demonstrate the value of the framework

Acknowledgements

This study was financially supported by the Construction Technology Innovation Program (11-Tech-Inovation-C06) through the Advanced Research Center for River Operation and Management (ARCROM) in Korea Institute of Construction & Transportation Technology Evaluation and Planning (KICTEP) of Ministry of Land, Transport and Maritime Affairs (MLTM). This study was also supported by the funding from the Basic Science Research Program of the National Research Foundation of Korea (2010-0010609).

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