Modification of local soil/sand with Moringa oleifera extracts for effective removal of cyanobacterial blooms

•MO extracts turned local soils into flocculants for algal blooms removal.•Surface charge of local soil can be remarkably increased by MO extract.•Initial alga concentration influenced the value of cyanobacterial removal efficiency.•pH and organic load concentration had no effect on the alga removal efficiency.

The need to improve on the use of modified soil/sand materials as safe and cost-effective protocol in mitigation of cyanobacterial harmful algal blooms (cyano-HAB) necessitated this study. Here we found that isolated extracts of Moringa oleifera seeds (MOSE), obtained via a simple precipitation procedure, turned local soils or sands into highly effective flocculants for cyano-HAB blooms removal. Removal efficiency greater than 95% of the initial concentration of 3.7×109 cells/L of the Microcystis aeruginosa cells, at an optimum loading, equivalent to 14.6 mg/L of MOSE+20 mg/L of soils/sand=34.6 mg/L, of flocculating mixture, was achieved when local soil/sand was modified with the MOSE. Within the pH range of 1 and 12, the negatively charged kaolin particles were turned into positively charged surfaces after the modification with the MOSE, which ascertained the role of electrical neutralization as a controlling mechanism. Within the cell concentration of 1.2×109 and 5.4×109 cells/L, the alga removal efficiency increased with the increase in the initial alga concentration and ionic strength. Variation in pH and organic load concentration had no significant effect on the alga removal efficiency. The materials from which the flocculants were derived have no competing economic interest and it could be used without any severe implications for man and the environment. This makes the material and the process to be sustainable.

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