Particle size effect of Moringa oleifera Lam. seeds on the turbidity removal and antibacterial activity for drinking water treatment

The treatment of drinking water using Moringa oleifera (MO) Lam. seeds is gaining popularity as a sustainable alternative to synthetic chemicals. However, there is limited literature on the effect of particle size of the ground MO seeds on their coagulation characteristics, which is revealed in this study. To investigate the impact of the particle size, the sun-dried MO seeds were ground and sieved into five distinct sizes ranging from (i) <0.25 mm, (ii) 0.25-0.4 mm, (iii) 0.4-0.8 mm, (iv) 0.8-1.25 mm, and (v) 1.25-2.0 mm. The seed protein for the experiment was then prepared by stirring a 2% (w/v) solution of the five different seed powders in tap water. Six different protein doses between 100 and 350 mg/l were added to separate glass beakers featuring a synthetic solution of 80 nephelometric turbidity units (NTU) turbidity. The experimental results revealed that the MO seed particle sizes of 0.8-0.4 mm and 0.4-0.25 mm demonstrated superior coagulation characteristics compared to the other size categories tested. Specifically, a dose of 200-300 mg/l was found to be effective in reducing the turbidity to 5 NTU and eliminating similar to 100% of E. coli after 3 h of settling. The surface characterisation showed a heterogenous surface and the presence of functional groups, which may have aided coagulation and caused the reduction in turbidity and microbial load. Statistical analysis revealed a P value <0.05, indicating that the results were highly consistent with no >5% variation. The study is also extended to explore the mechanism of coagulation of MO seeds, and the potential application of the research at a domestic scale is also discussed. Overall, the resulting water treated with MO met the WHO criteria.