Journal of Applied Physical Science International

This research investigated watermelon rind (WMR) powder and biochar as sustainable biosorbents for the removal of selected heavy metals, namely Cu, Pb, Cd, Ni, and Zn, from produced water. Watermelon rind samples were collected and pretreated, then transformed into biochar by charring, followed by modification of the char to obtain a highly effective biosorbent. Produced-water samples were analysed using an atomic absorption spectrophotometer (AAS) before and after passage through the column, and the influences of pH and contact time were investigated. The results indicated that all analysed heavy metals showed removal at the tested optimum pH and contact times. The optimum pH and contact time for the most effective removal of Zn²⁺, Pb²⁺, and Cu²⁺ ions from the produced water were 6.2 and 30 minutes, respectively, when modified WMR biochar was used as the biosorbent, with >99.0%, >99.0%, and 52.72% removal efficiencies, respectively. Modified WMR biochar at pH 6.2 and a contact time of 60 minutes gave optimum removal of Cd²⁺ ions (>99.0%). Similarly, modified WMR biochar at pH 6.2 and a contact time of 180 minutes gave optimum removal of Ni²⁺ ions (73.04%). This research demonstrates the advantage of using modified WMR biochar as a biosorbent over unmodified WMR powder, owing to the presence of active sorption groups, a higher surface area, greater porosity, and carbonisation. The result suggests that watermelon rind biochar is a low-cost, efficient, eco-friendly, and reusable sorbent capable of removing dissolved metals from produced water before its safe release into the environment and could also provide a means of converting this agricultural waste into a useful resource. Increasing the contact time further could lead to higher Ni²⁺ removal from produced water.