Sustainability assessment of wastewater reuse alternatives using the evidential reasoning approach

Abstract Wastewater reuse is a necessity especially in arid and semiarid regions. Assessing wastewater reuse applications and the required tertiary treatment technologies with regard to sustainable development issues is a multi-criteria decision making problem that involves a number of conflicting objectives and various types of uncertainties. In this study, the evidential reasoning (ER) approach which is a multi-criteria decision making method for dealing with problems having both quantitative and qualitative criteria under uncertainties, is used for prioritizing the wastewater reuse applications as well as wastewater treatment technologies. The proposed ER approach for sustainability assessment of wastewater reuse alternatives consists of five main steps: 1. Identification of potential wastewater reuse alternatives (including wastewater reuse applications and tertiary treatment technologies). 2. Determining contributing criteria in the assessment (with regard to economic, environmental, technological, and sociological/cultural aspects of wastewater reuse) and identifying the relative weights of the criteria using analytic hierarchy process (AHP). 3. ER distributed modeling framework for the identified wastewater reuse criteria. 4. Recursive ER algorithm for aggregating multiple identified wastewater reuse criteria. 5. Utility interval based ER ranking method which is designed to compare and rank the alternatives. In order to increase the precision of the assessment, life cycle costs and life cycle assessment are used as tools to assess the costs and environmental impacts of tertiary treatment technologies. To show the applicably of the proposed scheme, it has been applied to a wastewater treatment plant located at south of Tehran, Iran. Agricultural irrigation, artificial recharge of groundwater, and industrial usages are considered as the main potential wastewater reuse application alternatives and 20 tertiary treatment technologies are proposed to meet the wastewater reuse standards. Among the wastewater reuse applications, artificial recharge of groundwater, Tehran oil refinery, Shamsabad and Parand industrial parks, and agricultural irrigation are the alternatives with the highest utility numbers and priorities. Food security, lack of public acceptance, value added, and implementation cost, with relative weights of 0.33, 0.18, 0.17 and 0.17, respectively, are the criteria with the highest effect on prioritization of the wastewater reuse application alternatives. Moreover, it is known that MBR + UV, UF + RO + UV, UF + RO + DF + Cog/Floc + UV, and CW + UV are the most sustainable tertiary treatment alternatives for wastewater reuse in artificial recharge of groundwater, cooling tower & other industries, boiler, agricultural irrigation, respectively. Life cycle costs and environmental impacts of the tertiary treatment technologies with relative weights of 0.27 and 0.1978, respectively, have the highest influence in this prioritization. In addition, it is indicated that the life cycle costs for MBR + UV, UF + RO + UV, UF + RO + DF + Cog/Floc + UV, and CW + UV, range from $1799 to $5714, $3903 to $7050, $4685 to $8350, and $1171 to $1733, respectively, which make them the tertiary treatment alternatives with lowest life cycle costs. MBR + UV and CW + UV with estimated environmental impacts of 390 and 86.8 pt, respectively, are among the most suitable tertiary treatment alternatives. UF + RO + UV and UF + RO + DF + Cog/Floc + UV with estimated environmental impacts of 623 and 695 pt, respectively, have the highest estimated environmental impacts among the treatment technologies for reuse in industries, however, having better assessment grades with regard to other criteria (e.g. life cycle costs) makes them the most suitable alternatives for reuse in industries. This study shows that the ER approach provides a flexible and systematic method for sustainability assessment of wastewater reuse alternatives.