Impact of water quality parameters on harmful algal bloom mitigation and phosphorus removal by lab-synthesized γFe2O3/TiO2 magnetic photocatalysts

Abstract

Harmful algal blooms (HABs) are a growing problem in freshwater systems, posing risks to human health and ecosystems. This study explores the use of γFe₂O₃/TiO₂ nanocomposites for HAB mitigation and phosphorus removal in lake water. The nanocomposite showed strong photocatalytic effects under simulated sunlight, having a Fe to Ti ratio of 2.2:1 and a specific surface area of 116.52 m²/g. It achieved 95 % inactivation of Microcystis aeruginosa and 90 % inactivation of Cylindrospermopsis raciborskii within 1 h at 100 mg/L concentration. In lake water, the inactivation of M. aeruginosa was reduced to 88 % due to the complex environment. Phosphorus adsorption was also effective, with 35 % removal in deionized water and 23 % in lake water. Environmental factors such as temperature, pH, natural organic matter (NOM), and alkalinity impact both processes. The inactivation of C. raciborskii increased at higher temperatures, while M. aeruginosa showed better inactivation at lower temperatures. The nanocomposite was most effective for M. aeruginosa inactivation at pH 7.5 and achieved the maximum phosphorus removal at 24 °C and pH 7.5. While NOM slightly inhibited performance, alkalinity significantly reduced both inactivation and adsorption. Phosphorus desorption tests demonstrated a 64 % recovery rate, indicating the potential for reusing the nanocomposite. Despite challenges in complex environments, the nanocomposite shows great potential for HAB mitigation and phosphorus removal in freshwater systems.