Carbonaceous material from agricultural waste for treating colored wastewater: characterization and adsorption performance evaluations

Agricultural wastes such as crop residue, livestock waste, agro-industrial waste, and aquaculture waste contribute globally to a massive quantity of municipal solid waste accumulation. Therefore, in recent years, several studies have been directed toward using agricultural waste. They revealed a high carbon content, which contributes to producing an adsorbent with excellent chemical properties, adsorption efficiency, and low ash content. In this study, two types of agro-industrial wastes, banana peel, and avocado seed have been used to develop absorbents. Their adsorption performance for the removal of mixed dyes in an aqueous solution was investigated. The adsorbents' surface morphology and chemical composition have been characterized and compared. The effect of operational parameters, including initial pH, contact time, adsorbent dosage, and initial dye concentration, was also studied to identify the optimum operating condition for efficient adsorption. The adsorption data were fitted to isotherms and kinetics models. The adsorption study revealed that the hybrid adsorbent had the highest color removal of 70% and a maximum adsorption capacity of 46.1 mg/g using 0.8 g of adsorbent at alkaline pH under optimized conditions. The adsorption equilibrium data are better fitted to the pseudo-second-order kinetic and Freundlich and Langmuir isotherm models. The kinetics study reflects that the adsorption is governed by chemisorption, suggesting that chemical reactions occurred between the dye ions and the adsorbent, resulting in strong covalent bonds. In summary, our findings indicate that the agricultural waste-based adsorbent synthesizes from banana peel and avocado seed can be a promising candidate to replace conventional adsorbent from a sustainability perspective.(GRAPHICA, ABSTRACT)