Efficacy of Moringa Oleifera Proteins as Coagulants in a Sustainable Sand Filter for Drinking Water Treatment

Cationic proteins from the seeds of the Moringa oleifera tree are of interest as sustainable coagulants for drinking water treatment in regions with poor access to potable water in tropical and subtropical regions of the world. They have been shown to reduce turbidity in natural water sources as well as in various model freshwaters. To identify the active components in the seed extract, high performance liquid chromatography was employed. Eight M. oleifera cationic protein fractions were isolated and characterized using gel electrophoresis, dynamic light scattering, and circular dichroism. Coagulation performance experiments were conducted using a micro-coagulation assay that was validated by comparison to a standard jar test. Fraction coagulation performances were compared individually and in various combinations against kaolin clay suspensions in model freshwaters of varying hardness. The unfractionated protein extract was found to be effective across a broad range of protein dosages. Coagulation activity for this extract was further investigated against humic acid and mixtures of kaolin clay and humic acid in model freshwaters of varying hardness. The coagulation mechanism of Moringa oleifera proteins was demonstrated to be adsorption and charge neutralization. Adsorption isotherms were measured using ellipsometry to investigate the effects of water hardness, fractionation, and fatty acid extraction on protein adsorption to silica surfaces. The zeta potentials of the resulting protein-decorated surfaces were measured by the rotating disk streaming potential method. Sands can be effectively modified with M. oleifera proteins using small amounts of seed extract under various local water hardness conditions. Gravity sand filters packed with Moringa oleifera modified sand were constructed and shown to be effective against kaolin and humic acid. Protein layer coverage and composition did not affect filter performance. These studies may aid in the design of a simple, effective, and sustainable water purification device for developing nations.