Elaeis guineensis-activated carbon for methylene blue removal: adsorption capacity and optimization using CCD-RSM

The activated biochar is a carbonaceous material obtained from thermal degradation of biomass with high adsorption potential. On the other hand, the high production cost has still limited its use in large-scale, so that low-cost raw materials derived from biomass have been encouraged. For instance, waste from palm oil industry, such as palm endocarp (Elaeis guineenses), has shown high potential to produce cheaper activated carbon since high amount of palm residues are annually generated worldwide. Moreover, as far as we know, Elaeis guineensis-biochar activated by ZnCl2 has not been tested as an adsorbent for methylene blue (MB) removal. In addition, optimization studies on activation variables focused on maximizing MB removal are still scarce. This work aims to investigate the adsorption capacity of the Elaeis guineensis-activated carbon for MB removal and to find optimized conditions. Thermo-chemical activation was carried out using ZnCl2. Temperature ( $$T$$ ), activation time ( $$t$$ ) and particle size ( $$PS$$ ) were the variables evaluated through a full factorial design. The optimal condition was obtained based on central composite design (CCD) and surface response methodology (RSM) techniques. Kinetic and equilibrium studies were also carried out. CCD and RSM predicted an optimal MB removal of 93.2% adopting 0.05 g of activated biochar, PS = 65 mesh, $$T\hspace{0.17em}$$ = 700 °C and $$t\hspace{0.17em}$$ = 3 h. Kinetic and adsorption equilibrium results agreed to pseudo second-order model and Langmuir’s model, respectively. Finally, Elaeis guineensis showed to be a promising feedstock to produce activated biochar aiming MB removal from water and wastewater.