Extraction of natural coagulants from Maerua subcordata and Moringa stenopetala for use in turbid water treatment

Natural coagulants, especially those from Moringa oleifera Lam., have been employed since ancient times (200 B.C.) in the treatment of drinking water. The aim of this study was to extract natural coagulants from tubers of Maerua subcordata (Gilg.) DeWolf and seeds of Moringa stenopetala (Baker f.) Cufod, both native to Ethiopia, and to examine their potential utility in water treatment in the future. The coagulation activity of the extracts was measured in natural turbid river water and synthetic water made of a kaolin clay suspension. The turbidity removal efficiency was tested using a jar test and spectrophotometric-based assays. Proteins from the extracts were visualized by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and gel staining. Relevant parameters affecting the effectiveness of coagulation (pH, extraction time, type/concentration of the extracting solvents, and storage duration/conditions) were also investigated. A wide range of abundant proteins, with molecular weights of 10, 15, 35, and 40 kDa, were found in the crude extracts. However, only the proteins with molecular weights of 10 and 15 kDa were resistant to prolonged heat at 95 degrees C for 5 h. Interestingly, using synthetic turbid water, the tuber extracts from M. subcordata showed 90.5% coagulation activity within 3 h of contact, whereas the seed extracts from M. stenopetala showed only 83.5% coagulation activity. The removal efficiency of M. subcordata and M. stenopetala in turbid river water was 80% and 83%, respectively. Both the M. subcordata and M. stenopetala extracts showed the most efficient coagulation activity at pH = 8. Increasing the extraction time negatively affected the removal efficiency of the coagulation. In conclusion, coagulant proteins from these native species could provide a means of water treatment for communities living in rural areas, enabling access to adequate supplies of safe drinking water.