Growth inhibition of harmful algae using TiO2-embedded expanded polystyrene balls in the hypereutrophic stream

Abstract

TiO2-embedded expanded polystyrene (TiO2EPS) balls were produced in large quantities using continuous manufacturing plants and four processes (i.e., fixing-coating-freeze drying-air drying). Two mesocosms [i.e., a photocatalytic zone (PZ) vs. a control zone (CZ)] and in-situ real-time monitoring device were installed to monitor the water quality within the hypereutrophic stream and to elucidate the long-term effect of TiO2EPS balls on the growth inhibition of harmful algae for two years (i.e., 2016–2017). The difference in the concentrations of both Chl-a and phycocyanin between CZ and PZ was temporally variable and was significant from August to October with higher solar irradiation levels. Although the effective depth of TiO2EPS balls varied as a complex function of the photocatalytic reactions of TiO2EPS balls and various environmental factors, the photooxidation effect of TiO2EPS balls decreased with the increase in water depth and the effective water depth for growth inhibition was less than 0.5 m. Compare to bimodal distributions in concentrations of both Chl-a and phycocyanin in CZ, both shifted and lowered peaks were mainly due to the photocatalytic degradation and irradiation shading under natural solar irradiation by applying TiO2EPS balls in hypereutrophic water body. Consequently, the TiO2EPS balls developed in this study can prevent both growth and reproduction of harmful algae in hypereutrophic water body, regardless of the environmental factors.