Overview of relevant economic and environmental aspects of waste-based activated carbons aimed at adsorptive water treatments

The production of waste-based activated carbon (AC) for application in adsorptive water treatment is a hot research topic. The use of residues as AC precursors is generally presented as a promissory option because they are free of charge and allow for the minimization of non-renewable resources depletion. Despite waste-based AC being usually labelled as low-cost and environmental-friendly adsorbents, few studies involve cost estimations and even less assess the environmental impacts associated to their production and application. In the last few years, there has been a growing awareness about the search for greener processes, resulting in the increase of publications on the cost estimation and the life cycle assessment (LCA) of waste-based AC. Still, to the best of the authors' knowledge, a review focusing on the distinct approaches and conclusions carried out by different authors does not exist. Therefore, the aim of this work is to present an overview on relevant aspects of the economic and environmental costs of waste-based AC for application in water treatment. Overall, published studies show that the price of the precursors, the energy required for production (which can be optimized at industrial scale) and the properties of the produced material largely influence the AC final cost. As for LCA studies, they generally evidence that producing AC from wastes is an interesting management route that may present important energy and resource savings when compared to the production of AC from fossil resources. Moreover, literature points out that attention must be paid to regeneration of waste-based AC to sustainably post-pone their end-of-life. This review stresses the necessity of assessing the economic and environmental costs of waste-based AC in order to avoid vague and unsupported conclusions on their sustainability.