Production of activated carbon from macadamia nut shell waste for phenol removal using a partial-bed adsorption system

Phenolic compounds, commonly found in industrial wastewater from oil refining and petrochemical processes, pose significant environmental and health risks due to their toxicity and resistance to biological degradation.Among the various treatment methods, adsorption is particularly effective owing to its high efficiency and low generation of harmful by-products.However, the widespread use of commercial activated carbon is limited by its high cost.In this study, macadamia nut shells -an abundant agricultural waste -were utilised to produce low-cost macadamia nut shell activated carbon (AC-M) via CO activation.The optimal activation conditions (200 mL/min CO flow, 950 C, 240 minutes) yielded AC-M with a high BET surface area of 1,363.75m/g and predominantly featuring micro-to mesopores in range of 2.06-2.36nm.Batch adsorption experiments revealed optimal conditions for phenol removal at an initial concentration of 200 mg/L, contact time of 600 minutes, pH 6 (favourable hydrophobic interaction), and 25 C, indicating an exothermic process.Equilibrium data closely followed the Langmuir isotherm (R > 0.97), with a maximum adsorption capacity of 588.24 mg/g for the best-performing AC-M (AC-M 200 240 ).A key innovation in this study is the application of a partial-bed column system, which periodically replaces saturated adsorbent to maintain an active mass transfer zone.Compared to a traditional fixed-bed column, the partial-bed significantly extended operational time and improved performance.At a 6 cm removal height, the partial-bed achieved 124 hours of operation lifespan in the third cycle over three times longer than the 39 hours observed in a 10 cm fixed-bed column, while enhancing adsorption capacity to 246.70 mg/g, a 44% increase in efficiency.These findings demonstrate that the integration of low-cost AC-M with a partial-bed column system offers a promising, sustainable, and highly efficient solution for continuous phenol removal from industrial wastewater.