Selection of Greywater Reuse Options Using Multi-criteria Decision-making Techniques

On-site reuse of treated greywater for non-potable purposes such as toilet flushing, garden irrigation and car washing is one of the alternatives to meet the increasing water demand and to reduce the load on sewage treatment plants. However, no studies have been reported on selecting the most appropriate reuse option among the different reuse options available. In the present study, multi-criteria decision-making (MCDM) methods TOPSIS, VIKOR, ELECTRE and PROMETHEE were used to rank the greywater reuse alternatives. The main criteria considered included acceptability, adaptability and the risk involved with the reuse option along with technical and economic considerations. Alternative uses considered in the study were household reuse, public reuse, industrial reuse, groundwater recharge and agricultural reuse. Based on expert opinion, the weightage of criteria and relative importance of each alternative to criteria were determined using the defuzzification method. Kendall's coefficients of concordance and Spearman's rank correlation coefficients were used to compare the ranks, while sensitivity analysis was performed to find the least impacted results. Results show that domestic reuse is the best alternative for greywater reuse, followed by public reuse. Kendall's concordance value suggests more than partial agreement between the ranks obtained by different MCDM techniques. Sensitivity analysis showed that technical consideration was the most sensitive criterion.