Valorization of Citrus Aurantium Dulcis Peels Biomass for Industrial Wastewater Treatment: Optimization, Kinetic and Isotherm Studies

This research investigates the removal of Methylene Blue dye (MB) from both synthetic and real wastewater using locally sourced Raw Orange Peel (ROP) waste biomass. The granulometric analysis showed an even distribution of the biomass microparticles. The investigation into surface charge revealed a pHzc of 4.5. By optimizing the adsorption process using Central Composite Design (CCD) modeling, the study identified optimal conditions of 38.5 mg/L for MB concentration, 306°K for reactor temperature, and 115 min for contact time, resulting in a maximum yield of 78% and a maximum adsorption capacity (Qmax) of 150 mg/g. The kinetic and isotherm studies demonstrated that adsorption occurs through diffusional mass transport on non-porous materials. Additionally, the Elovich model indicated a low Polanyi energy, suggesting an exothermic and spontaneous physisorption process. SEM micrographs displayed biomass particle swelling post-MB adsorption, while FTIR analysis indicated an increase in the crystalline order of ROP cellulose chains. Furthermore, applying these optimal conditions to real industrial wastewater revealed simultaneous adsorption when the ROP was acid-activated and selective MB adsorption when the ROP was base-activated. This work stands out for its transition from laboratory-scale reactors (in mL) to real industrial-scale wastewater applications (in L) and for assessing the biomass’s affinity for Methylene Blue in a mixture containing similar dyes, showcasing its selective/simultaneous adsorption abilities.