Comparison of Immobilization Methods for TiO₂-Embedded Expanded Polystyrene Balls and Growth Inhibition of Microcystis aeruginosa

Abstract

Two immobilization methods (i.e., ice water-soaked using a digital temperature controller vs. freeze-dried using liquid nitrogen) were applied for mass production techniques of TiO2-embedded expanded polystyrene (TiEPS) balls with nanoscale TiO2 particles embedded on EPS balls. No significant changes in crystalline structure of TiO2 nanoparticles embedded on the TiEPS balls were observed during the mass production of TiEPS balls. Greater residuals of freeze-dried TiEPS balls suggested the improved immobilization methods for mass production procedures of TiEPS balls. Although similar growth inhibition between TiEPS balls using two immobilization methods was observed within 10 hrs, both growth and reproduction of M. aeruginosa can be more significantly inhibited by applying the freeze-dried TiEPS balls after 10 hrs. These results were mainly attributed to the difference in exposed surface area of embedded TiO2 nanoparticles which generated various reactive oxygen species peroxidizing and leading to the inactivation and degradation of M. aeruginosa. Relatively greater k value (0.207 day-1) was estimated from freeze-dried TiEPS balls than that (0.089 day-1) from ice water-soaked TiEPS balls, suggesting that both growth and reproduction of M. aeruginosa were effectively inhibited with greater amounts of reactive oxygen species generated from freeze-dried TiEPS balls. Consequently, self-floating freeze-dried TiEPS balls can be readily applied to inhibit the excessive growth of harmful algae in the stagnant water body without the recovery process for long time.