Comprehensive water footprint assessment of RO and MED desalination plants in China based on ISO method

Desalination technologies have been employed worldwide to alleviate water supply and demand disparity. Freshwater production via desalination is accompanied by the consumption of substantial energy and diverse chemicals, and the discharge of brine. Among the Life Cycle Assessment (LCA) of desalination plants, various aspects of environmental impacts have been discussed; however, their negative water-related impacts have always been overlooked. In this study, a water footprint assessment based on the ISO 14046 standard was developed to quantify the water environmental impacts of desalination plants in their operational phase. With one m³ desalinated water as the functional unit, the water scarcity footprint of and multi-effect distillation (MED) (∼10⁻² m³ H₂O eq/m³) was higher by around an order of magnitude than that of reverse osmosis (RO) (∼10⁻³ m³ H₂O eq/m³), indicating that MED contributed more to water scarcity than RO. Moreover, the water increment footprint ( WIF ) was proposed with the consideration of net freshwater increment and regional water stress, and the positive effect of net water increment was more significant in water-scarce regions on local water resources. The water acidification, eutrophication, and ecotoxicity footprint were analyzed and compared. Electricity contributed over 75 % to the water scarcity footprint of RO, and steam contributed 92 % or above to that of MED. Steam, carbon dioxide, and antiscalants were the main substances responsible for the water degradation footprint. Finally, the contribution and sensitivity analysis highlighted that optimizing the consumption of these critical substances could reduce the water footprint.