Integrated Agro-Waste Binary Biochar for Heavy Metal Remediation and Sustainable Soil Management

Abstract:

This research investigated the potential and effectiveness of agro-waste biochar composites derived from empty palm fruit bunch and coconut husk (EPFBB–CHB) and palm kernel shell and coconut shell (PKB–CSB) in immobilizing metals (Fe, Cu, Cr, Ni, Pb, Zn, Cd, and As) to alleviate contaminated soils. Soils were collected, air- and oven-dried, sieved, and artificially spiked to 100 mg/kg for each metal. The metal levels in soil were determined spectroscopically before and after treatments. The biochar was synthesized via pyrolysis at 500 °C, and two composites were prepared: EPFBB–CHB and PKB–CSB. Ten grams of contaminated soil were treated with 5% w/w biochar and incubated for 72 hours and characterized for surface physicochemical parameters. The findings indicated that the untreated soil exhibited significant contamination levels of Fe (160.8 ± 10.50 mg/L), Cu (166.05 ± 10.30 mg/L), Cr (153 ± 9.41 mg/L), Ni (135.35 ± 8.17 mg/L), Pb (107 ± 7.93 mg/L), Zn (158.495 ± 10.12 mg/L), Cd (163.35 ± 10.61 mg/L), and As at 0.35 ± 0.0001 mg/L (unspiked environmental concentration). Treatment-A (EPFBB-CHB) exhibited greater effectiveness in the removal of Cu, Pb, and Cd, achieving removal efficiencies of 73.35%, 85.39%, and 22.52%, respectively. In contrast, Treatment-B (PKB-CSB) demonstrated slightly higher efficiency in removing Fe, Cr, Ni, and Zn, with removal efficiencies of 97.24%, 24.47%, 84.81%, and 53.67%, respectively. The findings indicate that EPFBB–CHB was more effective for Fe, Cu, Pb, and Ni, but PKB–CSB had superior performance for Zn and Cr. Both composites effectively immobilized arsenic, while cadmium remained stable for an extended duration. Functional group analysis revealed adsorption-promoting aromatic, phenolic, and oxygenated compounds, but also indicated persistent organic pollutants, highlighting potential environmental risks. The study concludes that agro-waste biochar is a low-cost, sustainable method for reducing heavy-metal mobility in contaminated soils, and recommends optimization, repeated applications, or combined remediation strategies to achieve regulatory compliance and restore soil health in metal-contaminated soils.