The presented work was motivated by the search for a low-cost and efficient adsorbent for dye removal from wastewater [1]. Raw materials from agricultural and forestry activities, such as coconut shells, olive stones, almond shells, and cork residues, were used, as collected from the field, for dye removal from wastewater. These raw materials also served as precursors for the production of activated carbon (ACs), using KOH as an activating agent, at 973 K. The adsorbents were characterized physically and texturally. It was observed that natural adsorbents have lower carbon content, surface area, and porous volume and higher acidic surfaces than their respective ACs.

Although ACs in general have superior performance in removing pollutants (dyes, pesticides, drugs) when compared to their precursors, to improve the properties of ACs and their performance in methylene blue (MB) removal from water, these were subjected to a modification process involving the introduction of nitrogen into their matrix during the activation procedure.

Screening a diversity of low-cost, available raw materials allows for the identification of those that present a high adsorption capacity, directly or after being converted into ACs, for MB removal from water. These were proposed for use in pollutant removal from water used for human consumption, especially in developing countries, where wastewater is taken from lakes, wells, and rivers and consumed without any previous treatment. This work allows us to valorize subproducts from agricultural and forestry activities, removing them from landfills and obtaining adsorbent materials that are successfully used in the treatment of water that can even be used for consumption, thus closing the cycle of the circular economy.

[1] Cansado, I.P.P., Geraldo, P.F., Mourão, P.A.M., Castanheiro, J.E., Carreiro, E.P., and Suhas. Utilization of Biomass Waste at Water Treatment. Resources, vol. 13, no. 3, Mar. 2024, doi: 10.3390/resources13030037.