Simultaneous optimization of activation conditions of alperujo (two-phase olive mill waste) using a desirability function: Production of porous carbons for adsorption and energy storage

Valorization of agro-industrial waste is considered an essential step towards a circular economy. The potential reuse of these byproducts in practical applications requires feasibility assessments and optimization of variables in order to be profitable. In the present study, an abundant and problematic residue from the olive oil industry, “alperujo” (two-phase olive mill waste), was used as precursor material for activated carbons. A simultaneous optimization methodology was applied to maximize two response variables: energy storage capacity and lead (Pb) removal efficiency. The simultaneous optimum conditions were 3.66 g of KOH per g of carbonized residue and a temperature of 650 °C for 120 min. The result was a microporous activated carbon with an energy storage capacity of 252 F/g and a lead removal from aqueous solutions of 68.8 %. These values are comparable with those offered by commercial activated carbons, evidencing that porous materials obtained from alperujo using unique activating conditions for both applications present a remarkable performance. The novelty of the present study lies in the application of a useful statistical methodology for simultaneous optimization through the “desirability function”, resulting in a reduction in cost and time. Our results have demonstrated that it is possible to generate activated carbons with the highest performance for two different applications using the same combination of activation variables.