Coagulant properties of Moringa oleifera protein preparations: application to humic acid removal

Abstract

This work aimed to characterize the coagulant properties of protein preparations from Moringa oleifera seeds in the removal of humic acids from water. Three distinct preparations were assayed, namely extract (seeds homogenized with 0.15 M NaCl), fraction (extract precipitated with 60% w/v ammonium sulphate) and cMoL (protein purified with guar gel column chromatography). The extract showed the highest coagulant activity in a protein concentration between 1 mg/L and 180 mg/L at pH 7.0. The zeta potential of the extract (−10 mV to−15 mV) was less negative than that of the humic acid (−41 mV to−42 mV) in a pH range between 5.0 and 8.0; thus, the mechanism that might be involved in this coagulation activity is adsorption and neutralization of charges. Reduction of total organic carbon (TOC) and dissolved organic carbon (DOC) was observed in water samples containing 9 mg/L carbon as humic acid when treated with 1 mg/L of the extract. A decrease in colour and in the aromatic content of the treated water was also observed. These results suggested that the extract from M. oleifera seeds in a low concentration (1 mg/L) can be an interesting natural alternative for removing humic acid from water in developing countries. The extract dose determined in the present study does not impart odour or colour to the treated water.

Keywords:

• Moringa oleifera
• humic acids
• lectin
• water treatment
• natural coagulant

Acknowledgements

The authors acknowledge the financial support from the Portuguese Fundacao para Ciencia e a Tecnologia (FCT), through the post-doctoral grant SFRH/BPD/37349/2007, and the Brazilian programmes: Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), VALNATURA ALFA and the Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES).