Single-stage microwave-irradiated activated carbon from corncob for ammonia nitrogen removal: Batch, attraction mechanism and regeneration studies

Abstract

The existence of ammonia nitrogen (NH3-N) in water reservoirs contribute to the poor quality of water, thus affecting aquatic life and human. Therefore, the goal of this study was to treat NH3-N from wastewater using activated carbon derived from corncob (CCAC). The CCAC was produced through a single-stage microwave irradiation technique where carbon dioxide (CO2) was utilized for the gasification effect. The CCAC demonstrated a mesoporous surface area measuring 645.97 m2/g, accompanied by a total pore volume of 0.41 cm3/g. Furthermore, the average pore diameter was determined to be 2.74 nm. The equilibrium study revealed that NH3-N uptakes and NH3-N percentage removal increased (9.11–59.49 mg/g) and declined (91.10–59.49 %), respectively, when NH3-N initial concentration increased from 10 to 100 mg/L. At a solution temperature of 30 °C, the greatest adsorption capacity for NH3-N was observed, reaching 59.49 mg/g. Similarly, at a pH of 4, the adsorption capacity peaked at 71.46 mg/g. Adsorption of NH3-N onto CCAC obeyed the Langmuir isotherm model and pseudo-first order (PFO) kinetic model. It was determined that the maximum monolayer coverage, Qm was 78.05 mg/g. The investigation of the mechanism indicated that film diffusion is the rate-determining step in the adsorption process. In the thermodynamic section, the parameters of ΔH°, ΔS°, ΔG°, and Ea were computed to be −1.70 kJ/mol (exothermic in nature), 0.05 kJ/mol.K (elevated randomness at the solid-liquid interface), −18.22 kJ/mol (spontaneous) and 1.89 kJ/mol, respectively. The surface of CCAC was occupied with different functional groups namely nitro compound, aromatic compound, and phenol. These functional groups formed hydrogen bonding with NH3-N, thus aiding NH3-N removal from wastewater. In the regeneration study, CCAC can withstand up to 3 cycles before its yield dropped to 33.21 % and its adsorption capacity dropped to 10.15 %.