Toward Greener and More Sustainable Manufacture of Bauxite-Derived Adsorbents for Water Defluoridation
The bauxite-derived adsorbent, activated alumina (AA), has a current annual global market of over 600 million USD, and of this, more than one-third of AA is used for defluoridation of fluoride-bearing water. The commonly used Bayer process for production of AA suffers from thermodynamic inefficiency, thereby raising costs, and also causes significant environmental damage. Here, we evaluate three other bauxite-derived adsorbents as alternatives to AA for water defluoridation: mildly processed bauxite, thermally activated bauxite, and acid-treated thermally activated bauxite (ATAB). We first determine the energy intensity and resource efficiency of these three new adsorbents throughout their (future, anticipated) manufacturing processes and compare their defluoridation performance in the laboratory. Then, we quantify the carbon footprints of the three adsorbents via the product life-cycle approach, from their manufacturing to their applications in defluoridation. The results reveal that these three adsorbents exhibit less energy intensity and higher resource efficiency, thereby lowering their carbon footprints by 2–20×, relative to an equivalent amount of AA. We also estimate the operating costs of manufacturing and potential revenues from carbon offsets for each of the three adsorbents. Replacement of about 33 000 tonnes per year of AA currently used for wastewater treatment with equivalent ATAB could annually reduce annual manufacturing costs by 4.7 million USD and additionally generate 79 200 tonnes CO2 offsets. This study supports decision-making on selecting a greener and more sustainable approach for wastewater defluoridation.