Combined natural organic and synthetic inorganic coagulants for surface water treatment

The purified coagulant from Moringa oleifera obtained by simple ion exchange purification was used for the removal of turbidity, dissolved organic carbon (DOC) and bacteria from surface water. The natural coagulant was used as a primary coagulant and as a coagulant aid with metal salts. Different water quality and operational parameters such as pH, turbidity and mixing conditions were investigated. Characterization studies using fluorescence excitation emission matrix indicated that the coagulant protein from M. oleifera was a tyrosine-like protein. Turbidity and bacteria (Escherichia coli) removal efficiency of the purified M. oleifera and metal coagulants were similar. While the removal of bacteria by metal salts was mainly due to coagulation/flocculation, the removal by M. oleifera coagulant was as a result of both coagulation and growth inhibition, which is expected to improve sludge microbiological quality. Among the operational parameters, slow mixing time significantly influenced performance of natural coagulant. At optimum dosages, the crude extract increased the DOC of the treated water significantly whereas the purified coagulant showed a significant removal of fulvic-like DOC fraction. When used in combination with metal salts, adding of M. oleifera before the metal salts showed better turbidity and DOC removal than adding it after the metal salts.