<i>Moringa oleifera f</i>-sand Filters for Sustainable Water Purification

The purpose of this work is to determine parameters for the design of a <i>Moringa</i> seed sand filter for water purification. <i>Moringa oleifera</i> 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, <i>Moringa</i> seed extracts were used to reverse the charge of sand (<i>f</i>-sand) to 10 mV at a seed dosage of 5.6 g of seeds/m<sup>2</sup> of sand. This <i>f</i>-sand filter demonstrated ∼4 log removal of 1 μm polystyrene particles and >8 log removal of <i>Escherichia coli</i> compared to <0.1 log removal for bare sand. Enhanced removal for particles and <i>E. coli</i> was dominated by attractive electrostatic interactions. Clean bed filtration modeling predicts a sticking coefficient (α) of 0.8 for <i>f</i>-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 <i>f</i>-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.