Evaluation of Vernonia amygdalina and Senna alata as Low-cost Plant-based Coagulants and Antibacterial Materials for Water Treatment

Abstract

Access to safe drinking water remains a critical challenge in many Nigerian communities, where reliance on untreated surface, well and borehole water increases exposure to microbiological and physicochemical contaminants. This study evaluated the phytochemical composition, antibacterial activity and coagulation potential of Vernonia amygdalina (Ewuro-ijebu) and Senna alata (Asunwon) as low-cost plant-based materials for raw-water pre-treatment. Healthy leaves of both plants were collected, shade-dried, milled and extracted separately using ethanol and distilled water. Water samples were obtained from surface water, hand-dug wells and boreholes within the study locality. Qualitative phytochemical screening showed abundant saponins in both plants, with moderate-to-trace levels of flavonoids, alkaloids and carbohydrates; steroids were detected only in S. alata, whereas phlobatannins were detected only in V. amygdalina. Antibacterial susceptibility testing using the agar well diffusion method showed that the ethanolic extracts inhibited five of seven bacterial isolates (71.4%) at 150 mg/mL, whereas the aqueous extracts produced no measurable inhibition. Jar-test evaluation using plant powders produced variable changes in turbidity and other physicochemical properties, while total hardness decreased substantially in treated samples, including a reduction from 350 to 100 mg/L in well water treated with S. alata. Total viable bacterial counts were also substantially reduced in some treated samples following the settling period. These reductions indicate treatment-related decreases in total viable bacterial load but do not, by themselves, establish drinking-water microbiological safety or potability, particularly because residual microorganisms remained after treatment. Accordingly, plant-based treatment should be followed by filtration and an appropriate terminal disinfection step. Based on these findings, a multi-barrier household treatment approach incorporating plant-based coagulation, sedimentation, sand filtration and terminal disinfection is proposed. The findings indicate that V. amygdalina and S. alata have potential as locally available, low-cost pre-treatment materials, although further dosage optimisation, safety assessment and pilot-scale validation are required before household-scale application.