Water scarcity footprint of primary aluminium

Abstract

Purpose: The cradle-to-gate water scarcity footprint (WSFP) of primary aluminium has been determined for global aluminium including China (GLO) and global aluminium excluding China (RoW). It consists of the following:the direct WSFP, based on the freshwater consumption data collected by the IAI from global bauxite mines, alumina refiners and aluminium smelters and the local water scarcity index (WSI) of each plant, andthe indirect WSFP which has been calculated using data collected by thinkstep on the freshwater consumption of the different ancillary materials, of the fuel and of the electricity needed for the production of alumina and aluminium and the relevant water scarcity indexes. Methods: The calculation of the direct WSFP follows the requirement of ISO 14046 to aggregate data of sites at locations with different water scarcity after multiplication with the local water scarcity index. For the indirect WSFP, regional averages of the water consumption and water scarcity index were used for an initial screening study to determine fields for further investigation. Results of this study demonstrate that data on evaporation of water from reservoirs of hydropower plants has an extremely high contribution to the indirect WSFP of primary aluminium (79 % of the GLO value and 92 % of the RoW value). Therefore, a plant-by-plant approach was applied for hydropower which considers the net freshwater consumption of the hydropower reservoirs and uses the local water scarcity index of each power station, individually, for the calculation of the generic WSFP of the country or region. A special treatment has been given to some multipurpose reservoirs which typically have a beneficial effect on water scarcity, i.e. they have a negative WSFP if seasonal water scarcity indices are used. Results and discussion: With this approach, the WSFP of primary aluminium has been calculated as follows:18.2 m3 H2Oe./tonne for global primary aluminium (GLO);9.6 m3 H2Oe/tonne for global primary aluminium, excluding China (RoW). Conclusions: In order to avoid distorted results of water footprint studies, in depth analysis of identified hotspots in water consumption is necessary, in this case the plant-by plant approach, in accordance with ISO 14046. Data providers are encouraged to facilitate such analysis by improving the accessibility of such detailed data.