Sugarcane Bagasse Biochar as a Sustainable Adsorbent for Cadmium Removal from Wastewater
Abstract
With rapid industrial expansion, effective wastewater treatment has become an urgent environmental priority. Industrial effluents contain diverse pollutants, including toxic heavy metals, organic and inorganic contaminants, and microplastics. Among these, cadmium (Cd) is a persistent, non-biodegradable heavy metal released through electroplating, mining, and agricultural activities, posing severe ecological and human health risks. This study evaluates the efficacy of chemically unmodified sugarcane bagasse biochar as a sustainable adsorbent for removing Cd from aqueous solutions. Sugarcane bagasse biochar was prepared via slow pyrolysis in a muffle furnace at 550 °C at Pir Mehr Ali Shah Arid Agriculture University, Rawalpindi, and surface functional groups were characterized before and after adsorption using Fourier Transform Infrared Spectroscopy (FTIR). Batch adsorption experiments evaluated the effects of solution pH (2–12), initial Cd concentration (5–100 mg/L), adsorbent dosage (0.5–3.0 g/L), and contact time (10–180 min) on Cd removal efficiency and adsorption capacity. Optimal removal was achieved at pH 10, an initial Cd concentration of 25 mg/L, an adsorbent dose of 3.0 g, and a contact time of 90 min, yielding removal efficiencies of 98.6% (at pH 10) and up to 99.8% (at a 3.0 g dose). Equilibrium data were modeled using the Langmuir and Freundlich isotherms; the Langmuir isotherm provided the best fit (R² = 0.999), confirming monolayer chemisorption on a homogeneous surface with a maximum adsorption capacity (qmax) of 24.45 mg/g. Desorption experiments using 0.1 M CaCl2 and 0.1 M HCl demonstrated that CaCl2 achieved higher desorption efficiency (67.98% vs. 60.46% at 100 mg/L) due to the stronger competitive displacement of divalent Ca2+ ions compared with monovalent H+ ions. These findings demonstrate that unmodified sugarcane bagasse biochar is a low-cost, chemical-free, and sustainable adsorbent for cadmium remediation.