Exploring strengths and synergies in greywater treatment

Greywater reuse is a critical solution for water scarcity in arid regions like Egypt. This study presents a multi-criteria evaluation of treatment technologies tailored to local conditions. Using a TOPSIS framework and expert-weighted criteria, systems were ranked across six indicators, including CAPEX/OPEX and efficiency. Ultrafiltration (UF) emerged as the top standalone technology ($Ci* = 0.653$), validated through Monte Carlo simulation. However, a synergistic hybrid system combining Coagulation & Sedimentation (C&S) with UF offers the optimal practical solution. This configuration leverages low-cost pre-treatment to mitigate membrane fouling and reduce operational expenditures, balancing technical superiority with economic feasibility. This validated matrix serves as a rigorous decision-making tool for authorities and engineers to select sustainable treatment solutions.