Wastewater quality index (WWQI) as an assessment tool of treated wastewater quality for agriculture: a case of North Wastewater Treatment Plant effluent of Isfahan

Treated wastewater reuse is one of the most important ways to confront the water shortage, especially in arid and semiarid regions facing a water crisis such as Iran. This study aims to develop a wastewater quality index (WWQI) to evaluate the effluent quality of the North Wastewater Treatment Plant (WWTP) of Isfahan for agriculture. Three indices, namely overall, acceptability, and health wastewater quality indices (OWWQI, AWWQI, and HWWQI), are developed, using 23 quality parameters of the WWTP effluent. Four different aggregation functions, i.e., weighted arithmetic mean function, weighted geometric function, and two weighted mix functions, are tested. The results revealed that all aggregation functions are free from eclipsing and ambiguity. The weighted arithmetic mean function (WWQI((A))) gave the highest values of OWWQI, AWWQI, and HWWQI, whereas the lowest values were related to the weighted geometric function (WWQI((G))). The sensitivity analysis showed that the OWWQI((G)) and OWWQI((Mix1)) were more sensitive to the group quality rating values. In all aggregation functions, the OWWQI was more sensitive to groups 5 and 6, while group 1 in the OWWQI showed the least sensitivity. It is concluded that the OWWQI((G)) and OWWQI((Mix1)) were the most representative aggregation functions for the estimation of the OWWQI.