Optimisation and Adsorption Modelling of Chromium (Cr\(^{3+}\)) Removal from Brewery Effluent Using Sustainable African Pear (Dacryodes edulis) Seed-based Activated Carbon: An Experimental and Predictive Modelling Approach

Abstract

The astronomical rise in global industrial activity has led to an exponential surge in wastewater containing toxic heavy metals, posing serious risks to public health, aquatic ecosystems, and the environment. Brewery effluent, in particular, carries elevated levels of Chromium (Cr3+), a harmful pollutant that threatens water quality and aquatic life. Effective wastewater treatment is therefore essential for environmental sustainability, with adsorption standing out as one of the most reliable removal techniques. This study investigates activated carbon produced from African pear seeds (Dacryodes edulis), an abundantly available agricultural by-product, as a low-cost, locally sourced adsorbent for the removal of Cr3+ from brewery wastewater. The activated carbon (APSAC) was prepared by carbonising the seed material at 500°C, chemically impregnating it with 30% H₂SO₄, and activating it at 600°C for two hours. Proximate analysis, FTIR spectroscopy, and scanning electron microscopy were employed to evaluate its physicochemical properties, functional groups, and surface morphology. Batch adsorption experiments assessed the impact of contact time (15–75 min), Cr3+ concentration (5–25 mg/L), and adsorbent dosage (0.5–2.5 g) on % Cr3+ removal performance. An optimal chromium removal efficiency of 99.98% and adsorption capacity of 5.9988 mg/g were recorded at a concentration of 15 mg/L, a dosage of 0.5 g, and a contact time of 45 minutes. Equilibrium data were best represented by the Sips isotherm model (R² = 0.6812), with surface adsorption and chemisorption identified as dominant mechanisms. Kinetic analysis revealed that the pseudo-first-order model provided the best fit, confirming surface diffusion as the prevailing transport mechanism over intra-particle diffusion. These findings confirm APSAC as a highly effective adsorbent for heavy metal removal from industrial wastewater.