Development of Titanium Dioxide (TiO2)-Embedded Buoyant Photocatalyst Balls Using Expanded Polystyrene.

A new immobilization technique of nanoscale TiO2 powders to expanded polystryrene (EPS) balls with temperature-controlled melting method was developed for mass production, and the characterization of TiO2 powder-embedded EPS (TiEPS) balls was evaluated. Based on the scanning electron microscope (SEM) images and associated energy-dispersive X-ray spectroscopy (EDX) analysis, the components of intact EPS balls are carbon and oxygen whereas those of TiEPS balls are carbon, oxygen, and titanium, indicating that TiO2 powders were embedded on the surface of EPS balls. As also evident by the X-ray diffraction (XRD) and FTIR analyses, no significant changes in crystalline structure of TiO2 powders embedded on the EPS balls were found during the preparation and application processes of TiEPS balls. These characterization results indicated that the patches of TiO2 powders were soundly impregnated over the surface of EPS balls without the significant changes in crystalline structure of TiO2 powders and both structural changes and deformation of EPS polymer.

Application of Titanium Dioxide (TiO2)-Embedded Buoyant Photocatalyst Balls Using Expanded Polystyrene.

A new immobilization technique of nanoscale TiO2 powders to expanded polystryrene (EPS) balls with temperature-controlled melting method was validated for mass production, and the photocatalytic activity of TiO2 powder-embedded EPS (TiEPS) balls using methylene blue (MB) solution with different concentrations under ultraviolet irradiation and under the natural solar light irradiation. Whereas MB molecules were weakly adsorbed onto the surface of both TiO2 powders and supporting polymers without any specific interactions, the photocatalytic efficiency of TiEPS balls with UV (Kapp =0.016~0.043 min-1) was greater through coupled reaction processes (adsorption, photolysis, and photocatalysis). After 5-min sonication, more TiO2 powders on the TiEPS balls can be involved into the both adsorption and photocatalytic reactions of MB, and can increase the MB removal efficiencies. TiEPS balls can be reused for several consecutive runs without any significant decrease in photocatalytic activity until the recalcitrant contaminants were completely coated on the surface of TiEPS balls and loss of TiO2 powders embedded on the surface of TiEPS balls was significant. Based on the aforementioned results, self-floating TiEPS balls manufactured from this simple and cost-effective melting method can be used to remove the organic contaminants and to inhibit the excessive growth of harmful algae in the stagnant water body.

Application of WQIEUT and TSIKO for comprehensive water quality assessment immediately after the construction of the Yeongju Multipurpose Dam in the Naeseong Stream Basin, Republic of Korea.

This study evaluated changes in the aquatic environment and river water quality due to the construction of the Yeongju Multipurpose Dam (YMD) in the Naeseong Stream Basin, Republic of Korea, over eight years. This study evaluated water quality characteristics immediately after dam construction in the target area with aquatic environmental values and important water quality parameters using classification schemes. The drastic formation of new lentic systems in the upstream dammed pool presented exponential algal growth and high potential availability of nitrogenous compounds depending on seasonally. The results of the river system analyzed with the water quality index focused on eutrophication (WQIEUT) and trophic state index of the Republic of Korea (TSIKO) provided adequate complementary information for specific water quality background within the extensive basin for future management. From the results, inflow and accumulation of anthropogenic organic matter as potential eutrophic factors in the upstream dammed pool were significant in the short-term period. However, the downstream lotic systems adjacent to the dam presented the temporary disturbance by physical factors. Furthermore, potential microbial factors were significant in the outlet in the basin depending on seasonally. These results using classification schemes can aid accessible decision-making for water quality management to prevent eutrophication in the dammed pool of upstream or best management practices (BMP) with microbial source tracking (MST) approaches in the downstream area.

Physicochemical and fertility characteristics of microalgal soil ameliorants using harvested cyanobacterial microalgal sludge from a freshwater ecosystem, Republic of Korea.

The recovery and reuse strategy of cyanobacterial microalgal sludge (CyanoMS) is a novel sustainable platform that can mitigate cyanobacterial harmful algal blooms (CyanoHABs) in the freshwater system. This study aimed to assess the nutritional feasibility of harvested CyanoMS for microalgal soil ameliorants (MSAs) as efficient biofertilizers by the composting process. Most MSAs exhibited stable nutrient levels during the sequential metabolic phases for the entire period. The qualitative value of all MSAs using CyanoMS as a biofertilizer was verified by the excellent Fertility Index (FI), Clean Index (CI), and plant growth values. Also, successfully matured MSAs provided long-term support for retarded release of nutrients along the microbial transitional pathway. However, suitable CyanoMS contents of 11.7-37.6% (w/w) in MSAs were critical for efficient microbial activation and substrate inhibition. Since these results were fundamentally based on microbial transition on the CyanoMS content, optimum weight content and composting period were required. Nevertheless, MSAs were commercially applicable to high value-added crops due to their high fertilization potential and recyclable value.

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

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.

Growth Inhibition of Microcystis aeruginosa Using TiO2-Embedded Expanded Polystyrene Balls.

Mass production technique of nanoscale TiO2 particle-embedded expanded polystyrene (EPS) balls with temperature-controlled melting method was developed, and the photocatalytic activity of TiO2-embedded EPS (TiEPS) balls to suppress the excessive growth of Microcystis aeruginosa (M. aeruginosa) cultured from both indoor and outdoor experiments was verified under ultraviolet and solar light irradiation, respectively. According to the experimental results, the growth inhibition of M. aeruginosa was evidently observed by applying TiEPS balls, and increased proportionally with the surface area coverage of TiEPS balls. Based on the comparison of both specific growth rate (µ) and first-order degradation rate (k), the experimental cases using TiEPS balls with surface area coverage of 100% suppressed more significantly the growth of M. aeruginosa cultured from both indoor and outdoor experiments during the initial period of the experiment. However, through the whole experiment, both µ and k values between experimental cases using TiEPS balls and EPS balls with surface area coverage of 100% were not statistically different (p > 0.05). These results indicated that the photocatalytic degradation effect was dominant during the initial period of application, and the irradiation shading became dominant with the elapsed time. Therefore, the growth of M. aeruginosa can be suppressed due to both synergistic and combinational effects of photocatalytic degradation and irradiation shading under natural solar light. Based on the aforementioned results, self-floating TiEPS balls produced from this simple and cost-effective mass production technique can be readily applied to inhibit the excessive growth of harmful algae in the stagnant water body.