Evaluating the role of polyelectrolyte in effluent treatment process at water treatment plants for balancing water resources (case study: Iran: water treatment plants of Tehran)

The use of technology in drinking water treatment plants can be employed to reduce the uncertainty between urban water supply and demand. This study introduces the application of effluent treatment in drinking water treatment plants to reduce the generated effluent and balance groundwater resources. To achieve this, poly-electrolyte compounds were employed to treat the generated effluent in drinking water treatment plants, resulting in significant sedimentation of the Effluent volume and increased availability of water to meet the demands. In the drinking water treatment plants of Tehran city, to compensate for aquifer deficits, 50 million cubic meters of water per year were discharged as effluent from the cycle. However, by modifying the recycling process and utilizing poly-electrolyte, it is possible to reintegrate this water into the cycle. This water volume can be utilized as a substitute for exploiting groundwater resources. To assess the effectiveness and prioritize water allocation, three technical, economic, and social criteria were defined and calculated for each water treatment plant. To evaluate the impact of this process change on the groundwater level, a hybrid model called ANN–WOA was utilized. Based on this, four variables, including groundwater level, recharge, precipitation, and groundwater discharge, were defined as input variables to the model. 10 years was used for training, and 2 years was used for testing the model. Ultimately, the quantitative improvement of the groundwater was assessed the downstream of each water treatment plant using an appropriate index of desirability. The economic index value for allocation and the level of social satisfaction based on stakeholders' perspectives were completed. Ultimately, in the SWARA–COPRAS multi-criteria decision-making model, the prioritization of allocation for each water treatment plant was determined. The results demonstrated that by substituting this water volume, the desirability index increased by an average of 23%, which can be effective in balancing groundwater resources. Furthermore, the results indicated that the priority for allocation was given to the industrial sector, followed by the nearest green spaces available. The findings of this study illustrate that the use of new technologies in effluent treatment plants can be effective in reducing the exploitation of groundwater resources and achieving groundwater balance.