Grey water footprint intensity and technology-swap simulation: A benchmarking framework for sustainable wastewater treatment

Wastewater treatment performance is often assessed using removal efficiency metrics that do not account for plant scale or local environmental standards, obscuring true sustainability. This study introduces an integrated benchmarking framework combining the grey water footprint (GWF), a normalized intensity metric (GWFI), and a technology-swap simulation. Applied to nine plants across Iran, Czechia, and Spain, the framework isolates the effects of treatment efficiency, plant scale, and process design. Statistical analysis revealed that pollutant type was the dominant factor governing removal efficiency. Organic pollutants and suspended solids were removed with >95% efficiency, while nutrients controlled the residual burden, with total phosphorus (TP) emerging as the limiting pollutant. The GWFI metric resolved the scale-efficiency paradox, showing that large, efficient plants can exert the highest per-unit intensity (up to 5.01 m 3 GWF/m 3 wastewater). Technology-swap simulations identified advanced biological nutrient removal as the most effective strategy for reducing phosphorus-driven impacts, with potential reductions exceeding 80% for some plants. These findings support intensity-based evaluation and targeted nutrient control in wastewater policy, directly contributing to sustainable development goal (SDG) #6.3.