Exploring the synergistic effects of Moringa oleifera seed and Opuntia ficus-indica cladode extracts for heavy metal removal from real mine-impacted water via the coagulation-flocculation process

Abstract

Contamination of water by heavy metals (HMs) presents critical environmental and public health challenges due to their persistence and non-biodegradability. The coagulation-flocculation method is commonly used for HMs removal due to its efficiency and cost-effectiveness; however, it produces significant amounts of toxic, non-biodegradable sludge associated with the use of chemical coagulants. This necessitates the exploration of safer, economical, and environmentally friendly alternatives. In this study, the synergistic effects of Moringa oleifera seed (MOS) and Opuntia ficus-indica cladode (OFIC) extracts for the sustainable removal of HMs (As, Cd, Pb, and Zn) from the mine-impacted water by the coagulation-flocculation process were investigated. The coagulants/flocculants were characterized by Fourier transform infrared spectroscopy (FT-IR), proximate/elemental (P/A), and Zeta potential (ZP) analyses. The experiments were conducted using the jar test, and the key operational parameters (pH, total MOS and OFIC dosage, MOS:OFIC ratio, and settling time) were optimized. The results of the study showed that the combination of MOS and OFIC demonstrated excellent synergistic effects, achieving removal efficiencies of 97.7% for As, 99.3% for Cd, 98.9% for Pb, and 95.9% for Zn under optimal conditions. P/A, FTIR, and ZP analyses validated charge neutralization and inter-particle bridging were the dominant mechanisms. The costs of MOS + OFIC production are lower than those of alum. Additionally, the sludge produced by MOS + OFIC is biodegradable, non-hazardous, and 82.87% lower in volume compared to alum treatment, which demonstrates the potential of MOS + OFIC as a cost-effective and sustainable alternative to alum in wastewater treatment.