Efficient removal of harmful algae from eutrophic natural water by Mg(OH)₂ coated nanoscale zero-valent iron

Abstract

Iron-based nanoparticles have recently been developed to mitigate cyanobacterial blooms. In this study, a method utilizing Mg(OH)₂ coated nanoscale zero-valent iron (Fe⁰@Mg(OH)₂) was applied to treat cyanobacteria (Microcystis aeruginosa) in natural water. The influence of initial cell densities, Fe⁰@Mg(OH)₂ dosages, and water matrix on the removal efficiency of M. aeruginosa was systematically explored. Higher removal efficiencies of M. aeruginosa were achieved with increased initial cell densities, probably because larger amounts of cells and associated dissolved algal organic matters (AOM) promoted the formation and sedimentation of cell-Fe⁰@Mg(OH)₂-AOM complexes. About 98.7% of M. aeruginosa cells (initial cell density = 1.0 × 10⁶ cells/mL) were removed after treatment with 20 mg/L Fe⁰@Mg(OH)₂ for 10 h, despite anions (e.g., SO₄^2–) in natural water reduced the removal efficiency in the first 1.5 h. Most of the M. aeruginosa cells maintained intact during Fe⁰@Mg(OH)₂ treatment, as confirmed by the observation of their ultrastructure and the measurement of K⁺ and Chlorophyll a concentrations. As a result, the release of microcystins and AOM was negligible during the treatment. This study demonstrates that Fe⁰@Mg(OH)₂ is a promising approach for effective treatment of waters with high concentrations of cyanobacteria, without posing increased ecological risks.

Graphical abstract

Keywords

Algal removal / Influencing factors / Fe ⁰@Mg(OH) ₂ / Microcystin

Highlight

	● Fe0@Mg(OH)2 effectively removed cyanobacteria with high cell densities.
	● The impacts of various factors on the efficiency of Fe0@Mg(OH)2 were determined.
	● The in situ formed Fe(III) assisted the removal of cyanobacterial cells.
	● The release of MCs and AOM was negligible during Fe0@Mg(OH)2 treatment.

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