Comparison of purified and crude extracted coagulants from plant species for turbidity removal

Abstract

The coagulation properties of crude extracts and purified proteins of seeds of Moringa stenopetala and tubers of Maerua subcordata, which are locally used for purification of turbid water in Ethiopia, were studied. The turbidity removal effectiveness was compared using synthetic turbid and natural river water where the initial turbidity of synthetic water was approximately 260 NTU, whereas, for river water, the initial turbidity was 30 NTU. The active coagulants from the extracts were purified by the single-step and the two-step ion exchange (IEX) chromatography technique using 0.1, 0.3 and 0.6 M concentrations of NaCl solutions. The protein quantification of a single-step purified active coagulant eluted using 0.6 M showed that the protein content of the M. stenopetala extract was 1016 µg/mL, whereas the concentration of the M. subcordata extract was 700 µg/mL. The dose for coagulation using crude extracts and purified proteins of M. subcordata on surface water was 4 and 2 mg/L, respectively, with 85% of coagulation activity. In the case of M. stenopetala, 14 mg/L dose of crude extracts, which was seven times higher than that of the purified protein, was needed to obtain the desired residual turbidity (5 NTU). The results also indicated that in the two-step purified coagulants, the sludge volume was reduced compared to crude extracts and alum. In conclusion, active coagulants from seeds of M. stenopetala could be scaled up and used in water treatment technology, whereas purifying the extracts from M. subcordata is not required as the crude extracts performed equally well.