Enhanced coagulation-flocculation of domestic wastewater using sustainable plant-based material: A comparative study of nopal, agave, and eucalyptus

Abstract

This study addresses the critical challenge of sustainable wastewater treatment by investigating and valorizing agro-industrial residues as high-performance, zero-waste coagulants. The scope of this engineering investigation was the optimization and comparative assessment of 4 readily available materials – bentonite (BN), eucalyptus leaf powder (ELP), agave powder (AP), and the novel nopal fibrous residue powder (NFRP) – as alternatives to aluminium sulphate (AS) for urban wastewater treatment. The core novelty and innovation lie in the successful utilization of the discarded fibrous residue of the nopal cactus; this approach fundamentally shifts the paradigm from complex, resource-intensive extraction of nopal mucilage to the direct, simple use of a high-volume waste product. This leverages the lignin- and tannin-rich components, which are shown to be responsible for bio-flocculation, making the process intrinsically simpler, cheaper, and scalable, relative to state-of-the-art mucilage-based technologies. The statistical analysis confirmed significant differences in pollutant removal based on the material (p < 0.01). Agave powder (AP) was statistically superior for clarity, achieving a maximum turbidity removal percentage (TRP) of 97.76 ± 2.180% at an optimal dose of 20 mg/L, statistically outperforming AS. Conversely, for the removal of organic pollutants, the chemical standard AS was superior in single-dose trials, with COD reduction (CODR) ≈ 88.5%. However, the synergistic combination of NFRP (100 mg/L) and BN (60 mg/L) achieved the highest CODR ≈ 92.13 ± 0.398%, successfully exceeding the performance of AS. Furthermore, AP demonstrated high effectiveness in ammoniacal nitrogen removal (≈ 75%), highlighting its multi-pollutant capacity.