Efficiency of Biochar Obtained from Cashew Nut Shells as a Potential Adsorbent of Heavy Metals from Eleyele Dam, Ibadan

Abstract

Most industrial effluent is characterized with heavy metal contamination and other toxic, non-biodegradable pollutants which can endanger both aquatic life and human health. Traditional treatment methods are often costly and produce harmful secondary waste, highlighting the need for sustainable alternatives. This study explores the use of Cashew-nut Shells (CNS), an abundant agricultural by-product, to produce biochar as a low-cost and effective adsorbent for removing heavy metal ions. Cashew nut shells were pyrolyzed at 600–700 °C and physically activated using superheated steam to enhance porosity and adsorption capacity. The resulting biochar was incorporated into a down-flow filtration column containing sand, biochar, and gravel layers. The collected wastewater from Eleyele Dam, Ibadan, was digested with nitric acid and analyzed using Atomic Absorption Spectrophotometry (AAS). Physicochemical parameters and concentrations of Pb, Cd, and Fe were compared before and after treatment based on National Environmental Standards and Regulations Enforcement Agency (NESREA) standards. Although pH remained slightly acidic, heavy-metal removal efficiencies were 97.14, 64.29 and 43.75% for Fe, Pb and Cd respectively.  Post-treatment concentrations of Fe (0.09mg/L) and Cd (0.009) met NESREA effluent discharge standards of <0.01 and 5 mg/L respectively, while Pb reduced from 0.28 to 0.10mg/L, a value higher than 0.05mg/L permissible limit. Physically activated CNS biochar is an efficient and environmentally friendly adsorbent, demonstrating excellent removal of iron and satisfactory reduction of cadmium. Although lead removal was substantial, further optimization such as increased biochar dosage, longer contact time, or multi-stage filtration is required for full compliance with effluent discharge standards.