Natural Pyrite as a Sustainable Mineral Reagent for Rapid Removal and Detoxification of <i>Microcystis aeruginosa</i> Blooms: Aggregation by Iron Oxyhydroxides and Oxidation with In Situ Fenton-Like ^• OH

Abstract Microcystis aeruginosa (M. aeruginosa) , a prevalent cyanobacterial species in eutrophic waters, threatens aquatic ecosystems and public health through bloom formation and toxin release. This study investigates the use of natural pyrite for controlling M. aeruginosa , examining both removal efficiency and underlying mechanisms. Within 240 min of pyrite treatment, turbidity, cell density, and chlorophyll a (Chl-a) decreased significantly to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="0.94 plus or minus 0.06" display="inline" overflow="scroll"> <mml:mn>0.94</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.06</mml:mn> </mml:math> NTU, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="0.08 plus or minus 0.01 times 10 Superscript 6 Baseline c e l l s divided by m upper L" display="inline" overflow="scroll"> <mml:mn>0.08</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.01</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mn>6</mml:mn> </mml:msup> <mml:mtext> </mml:mtext> <mml:mi>cells</mml:mi> <mml:mo stretchy="false">/</mml:mo> <mml:mi>mL</mml:mi> </mml:math> , and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="8.2 plus or minus 0.6 normal mu normal g divided by normal upper L" display="inline" overflow="scroll"> <mml:mn>8.2</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.6</mml:mn> <mml:mtext> </mml:mtext> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">g</mml:mi> <mml:mo stretchy="false">/</mml:mo> <mml:mi mathvariant="normal">L</mml:mi> </mml:math> , corresponding to removal rates of 93.8%, 97.9%, and 98.2%, respectively, effectively ending eutrophic conditions. Mechanistic analyses indicated that FeOOH and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="upper F e 2 normal upper O 3" display="inline" overflow="scroll"> <mml:msub> <mml:mi>Fe</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>3</mml:mn> </mml:msub> </mml:math> , formed during pyrite oxidation, serve as binding sites that promote M. aeruginosa aggregation and sedimentation. Meanwhile, hydroxyl radicals ( • OH) generated via Fenton-like reactions disrupted cellular integrity and facilitated the degradation of dissolved extracellular organic matters and microcystin-LR (MC-LR). By Day 7, the MC-LR concentration was reduced to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="0.37 plus or minus 0.02 normal mu normal g divided by normal upper L" display="inline" overflow="scroll"> <mml:mn>0.37</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.02</mml:mn> <mml:mtext> </mml:mtext> <mml:mi mathvariant="normal">μ</mml:mi> <mml:mi mathvariant="normal">g</mml:mi> <mml:mo stretchy="false">/</mml:mo> <mml:mi mathvariant="normal">L</mml:mi> </mml:math> , below the regulatory limit, thus avoiding secondary pollution. This study demonstrates the potential of pyrite as a sustainable, mineral-based strategy for mitigating M. aeruginosa blooms, offering both theoretical and practical insights for environmentally friendly water remediation.