Green yet constrained: Reassessing Moringa oleifera's role in drinking water and wastewater treatment

A comparative bibliometric analysis using Web of Science and Scopus reveals a growing research shift from alum to Moringa oleifera (MO) as a green coagulant for decentralised water treatment. The coagulation efficacy of MO is attributed to its high molecular weight cationic seed proteins, rich in amino, hydroxyl, carboxyl, and amide groups, which destabilise colloids via adsorption and charge neutralisation. Extraction in saline medium (0.5–1.5 M NaCl) enhances protein solubility and coagulation, achieving > 90 % turbidity reductions and 1–3 log removal of E. coli and coliforms at doses 50–300 mg L⁻¹ for drinking water and 400–4000 mg L⁻¹ for wastewaters. Optimal coagulation requires rapid mixing (∼130 rpm, 2 min) followed by slow stirring (∼30–40 rpm, 15–40 min) to promote floc growth. Compared to alum, MO generates 3–5 times less sludge, with potential for residue reuse as fertiliser. This review aims to address existing knowledge gaps by consolidating available studies and identifying the conditions under which MO is most effective, as well as the limitations that may hinder its sustainable application. The paper offers a novel synthesis by integrating case studies with sustainability assessments, providing one of the few comprehensive evaluations of MO’s performance across both drinking water and wastewater treatment contexts. Our findings indicate that while MO is a viable, low-cost option for household-scale drinking water treatment, its slower coagulation kinetics (1–2 h) and high dosage requirements restrict its suitability for treating highly contaminated wastewaters. In addition, MO is ineffective at turbidity levels below 10 NTU and exhibits limited removal of organics and heavy metals. Because MO is an organic coagulant, its use may increase BOD, COD, and TOC, and interactions with chlorine can lead to the formation of carcinogenic trihalomethanes. Future research should focus on elucidating toxicological implications, optimising treatment processes, and assessing commercial scalability to support the responsible and sustainable use of MO in water treatment systems. • Bibliometric analysis from 1984 to 2025 shows that MO is the most studied coagulant between 2011 and 2021. • MO offers a low-cost, natural, alternative for drinking water treatment at domestic scale. • Up to 3 log E. coil removal and 99 % turbidity elimination but limited removal of heavy metals. • High dose requirement for wastewater restricts its application to drinking water only. • Further studies are needed to analyse the toxicology and health impacts of MO water treatment.