Moringa oleifera f-sand Filters for Sustainable Water Purification

The purpose of this work is to determine parameters for the design of a Moringa seed sand filter for water purification. Moringa oleifera seeds containing cationic antimicrobial proteins have been used as natural coagulants for the removal of turbidity; however, a low removal efficiency and high residual organic levels limit their applications. In this work, Moringa seed extracts were used to reverse the charge of sand (f-sand) to 10 mV at a seed dosage of 5.6 g of seeds/m² of sand. This f-sand filter demonstrated ∼4 log removal of 1 μm polystyrene particles and >8 log removal of Escherichia coli compared to <0.1 log removal for bare sand. Enhanced removal for particles and E. coli was dominated by attractive electrostatic interactions. Clean bed filtration modeling predicts a sticking coefficient (α) of 0.8 for f-sand compared to a value of 0.01 for bare sand. This α was further validated under a wide range of filtration conditions. Preliminary scale-up analyses suggest a point-of-use f-sand filter that requires a very small amount of seeds annually. The outcome of this work presents the scientific basis for the design of a water purification solution for developing regions, requiring only locally available resources and no use of synthetic chemicals or electricity.