Removal of dyes by Moringa oleifera seed extract. Study through response surface methodology

BACKGROUND: The effect of pH and initial dye concentration (IDC) on dye removal by coagulation/flocculation process with Moringa oleifera seed extract has been studied. The study was carried out by using the response surface methodology (RSM) in an orthogonal and rotatable design of experiments. Three types of dye were studied: anthraquinonic (Alizarin Violet 3R); indigoid (Indigo Carmine); and azoic (Palatine Fast Black WAN). RESULTS: The interaction level of the two variables studied is higher in the case of azo dye, while it is almost null in the case of anthraquinonic dye. Indigoid dye presents an intermediate situation. pH has a negative influence on dye removal, and by raising IDC q capacity tends to be higher. Polynomic regression of the surface plot was carried out and the adjusted r2 found for each case, this being 0.99 in the case of anthraquinonic dye, 0.94 in the case of indigoid dye, and 0.74 in the case of azoic dye. CONCLUSIONS: Moringa oleifera is an interesting natural coagulation agent for use in dye removal. pH should be taken into account in the cases of indigoid and azo dyes, while its influence is rather small in the case of anthraquinonic dye.