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

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.

Evaluation of Titanium Tetrachloride (TiCl4) as an Alternative Coagulant and Characterization of Recovered TiO2.

Titanium tetrachloride (TiCl4) as an alternative coagulant to remove organic matters and nutrients from the effluent of the secondary wastewater treatment was evaluated by comparison of removal efficiency of total phosphorous to Al- and Fe-based coagulants. Also, the surface characteristics, elemental contents, and crystallinity of the TiO2 produced from wastewater sludge flocculated with TiCl4 coagulant were investigated depending on the calcination temperatures. The more dosages of coagulants were injected, the greater concentrations of the cations (Al+3, Fe+3, Ti+4) and hydrogen ions (H+) resulted in the lower pH. Also, TiCl4 formed larger and heavier flocs than other coagulants and resulted in greater T-P removal efficiencies with reduced amounts of dosage. The phase change of anatase and rutile crystalline structures of TiO2 incinerated from wastewater sludges of TiCl4 coagulant was observed at relatively high calcination temperatures due to the existence of mixtures of organic matters, nutrients, and various impurities in the wastewater sludges of TiCl4 coagulant. Both C and P atoms were found to be mainly doped in/on TiO2 and the C and P atom originated from residual carbon of the settled organic matters and phosphorus nutrients present in effluents from sewage treatment plant, respectively. Therefore, 600-800 °C is the optimal calcination temperatures for TiO2 produced from TiCl4 coagulant flocculated with effluents from sewage treatment plant.