Influence of operating parameters on turbidity removal by coagulation with Moringa oleifera seeds

A model turbid water was treated with Moringa oleifera seeds as a natural coagulant and various phenomena like coagulation flocculation and sedimentation were observed in detail using jar-test equipment under laboratory conditions. Influence of pH, temperature, cation concentration and anion concentration of test water was studied. Also investigated was the effect of intensity and duration of rapid mixing as well as slow mixing on turbidity removal. Experiments were conducted at optimum dosage of a crude 5% (wt/v) water extract of dry non-shelled Moringa oleifera seeds. It was found that variation of pH, cation concentration, anion concentration and rapid mixing did not significantly affect the coagulation activity of Moringa oleifera seeds, while temperature and slow mixing did. Lower temperatures increased the residual turbidity, and in case of slow mixing, an optimal intensity and duration of 40 RPM and 40 minutes respectively were found, which corresponds to a velocity gradient G equal to 25 sec(-1) and a product Gt value of 6 x 10(4). Hence, for best results in turbidity removal in coagulation with Moringa oleifera seeds, only slow mixing is recommended at the optimum intensity and duration. Longer sedimentation time should be provided when treating colder waters.