Comparative coagulation performance study of Moringa oleifera cationic protein fractions with varying water hardness

Extracts containing cationic proteins from Moringa oleifera seeds are used to reduce drinking water turbidity in developing regions where the plant grows. To identify the active components in the seed extract, high performance liquid chromatography was employed, and eight M. oleifera cationic protein fractions were isolated. The protein fractions were characterized using gel electrophoresis (native molecular weights range from 12 to 48 kDa, reduced molecular weights range from 7 to 30 kDa), dynamic light scattering (radii of strongly cationic fractions are 1.2 to 1.5 nm), and circular dichroism (strongly cationic fractions are mainly comprised of alpha helices). Coagulation performance experiments were conducted using a coagulation micro-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. Ionic strengths of the model freshwaters ranged from 2.29 to 18.33 mM, and protein fraction concentrations ranged from 0 to 20 μg/mL. A combination of the weakly cationic fractions did not show coagulation activity. In diluted soft through moderately hard water, the individual strongly cationic fractions were effective at low dosages across a narrow range. Combinations of the strongly cationic fractions, of all cationic fractions, and of all cationic and non-cationic fractions were effective across broad ranges that encompassed low and medium dosages. The range of effective coagulant concentrations broadened for all individual fractions and combinations as water hardness increased. In model hard water, kaolin is inherently unstable, so protein additives are unnecessary to induce flocculation.