Enhanced Zn Removal from an Industrial Effluent Using Green Flocculant-Based on Cactus Formulations

In this study, three cactus formulations: cactus juice (CJ), lyophilized cactus powder (CLP), and oven-dried cactus powder at 60 °C (CDP) were evaluated for their flocculating efficiency in treating an industrial effluent loaded by heavy metals and taken from a local manufactory industry in the region of Sfax, Tunisia. Relevant concentration of heavy metals was registered in the raw wastewater such as iron (Fe), nickel (Ni), and zinc (Zn) at high concentrations exceeding thus the Tunisian standards. For their removal, conventional coagulation using alum solely showed a considerable removal just for Fe and Ni. To enhance the elimination of the third metal, Zn, three cactus bio-flocculants were added as flocculants. A lyophilized and an oven-dried cactus powders ensured a total Zn removal of nearly 100%. However, just a slight improvement in Zn elimination was found after the supplement a cactus juice as flocculant. The flocculating activity of the cactus formulations is likely to be linked to the polysaccharides. Hence, owing to the presence of hydroxyl (–OH) and carboxyl (–COOH) groups on the backbones of the polysaccharides, beside to the divalent cations like Ca²⁺, Zn elimination was carried out through both adsorption-bridging and adsorption-charge neutralization mechanisms. The salient Zn removal using the cactus formulations casts light toward the wide application of a safe and a green material-based flocculants instead of the harmful chemical ones.