Optimal wastewater allocation with the development of an SECA multi-criteria decision-making method

The aim of this study is to develop a multi-objective decision-making method, named Simultaneous Evaluation of Criteria and Alternatives (SECA) for optimal ranking of wastewater allocation alternatives. This multi-objective decision-making method is for the continuous environment, meaning that experts can choose the best solution among the solutions obtained. The SECA multi-objective non-linear programming method has three objective functions: (i) maximization of the overall performance of alternatives, (ii) minimization of the deviation of criterion weights from reference point based on the within-criteria variation information, and (iii) minimization of the deviation of criterion weights based on the between-criteria variation information as well as two limitations for the weights of criteria. First, 15 criteria from different fields, including economic, socio-cultural, technological, and environmental, and six alternatives were determined for reusing wastewater, including reuse in the industrial sector, for recreational consumption, supplying environmental demand, artificial aquifer recharge, agricultural irrigation, and landscape irrigation. Then, decision-making matrix was constructed and reference points were calculated. By programming the SECA code in Lingo software and considering different beta values, different weights for criteria and alternatives were ranked. In the other words, determining the best value for beta was the most important step, so different values for beta from 0.1 to 10 were examined. Results showed that in the value of beta equal to 4, the maximum value of the objective function was obtained as 0.6926. Therefore, it was the best value for beta and the weight of the effects on water resources criterion was equal to 0.0957 and was the most important criterion, and the allocation alternative in the environmental sector with a score of 0.8575 was the best wastewater allocation alternative. Followed by the environmental sector alternative, landscape irrigation, industrial sector, artificial aquifer recharge, agricultural irrigation, and recreational consumption were placed. Therefore, water supply for the environmental sector by considering the effect of wastewater on water resources is the best alternative for optimal allocation of wastewater.