Eunju Cho

Occurrence of micropollutants in four major rivers in Korea

There has been an increasing concern in recent years over the presence of numerous micropollutants in river water. Simultaneously, risk assessment of micropollutants has become increasingly important due to their high toxicity. Therefore, the aims of this study were to characterize the levels of micropollutants in rivers, to identify the sources of these pollutants, and to evaluate their risk quotients (RQ) to the ecological system. Monitoring data from 159 sites distributed across four major rivers in Korea were collected from the Ministry of the Environment (KME) reports. Tests were performed to check for the presence of 35 pollutants in river waters, from which 29 pollutants were detected. Organochlorine pesticides (OCPs) occurred most frequently, at low concentrations, whereas volatile organic compounds (VOCs) and phthalates were detected at higher concentrations. Based on this study, it was suggested that the factories near the sampling sites where pollutants were found represent one of the main sources of chemicals. After comparing the industrial activities with the measured pollutants, although the released amounts were not reported, representative intermediate chemicals were found in the river water. The RQs of most VOCs were below one, despite their concentration range being higher, compared with other pollutants. Methyl bromide and di-n-octyl phthalate occurred frequently in the Han River Basin and the Nakdong River Basin, respectively, and their RQs were consistently high, so further studies should focus on their exact emission source in order to reduce ecological risk. The results suggest that it will be necessary to develop methods of risk assessment that are more tailored to the various micropollutants present in river water, in addition to the implementation of water treatment systems to reduce ecological risk.

Effect of ultrasonic frequency and power density for degradation of dichloroacetonitrile by sonolytic ozonation

The degradation of dichloroacetonitrile (DCAN) by means of the processes of sonolysis, ozonolysis and sonolytic ozonolysis was studied, and degradation rate constants were evaluated at various frequencies and power densities of ultrasound. The ultrasonic frequencies used were 35, 170, 283, 450, and 935 kHz. The power densities were in the range of 9.5 to 20 W/L. The degradation rate constants for the sonolytic ozonolysis were (3.1–4.4)×10-3 min-1 with the power density of 9.5 W/L and the ozone dose of 3.7 g/h. And the synergistic effect in sonolytic ozonolysis was significant at 35 and 283 kHz among the five frequencies. The sonolytic ozonolysis provided an extra oxidation mechanism by generating additional hydroxyl radicals, giving significant enhancement on the process. The calculated values of synergistic effect were 2.56 and 2.15 at 35 and 283 kHz, respectively.

Sonophotocatalytic Destruction of Chloroform: Comparison of Processes and Synergistic Effects

This study compared ultrasound, ultraviolet, and catalyst processes and evaluated their respective synergistic effects. The ultrasonic frequencies in this study used 35, 283, 450, and 935 kHz, whereas short wavelength ultraviolet lamp (UVC) was used. The dose of TiO2 was 0.3 g/L. The degradation rate constants for the sonophotolytic processes were (4.2–8.7)×10-3 min-1, nearly the same for the sonolytic processes. The value of the synergistic effect was 1.07. The main mechanism of this process was pyrolysis by ultrasound. The ultraviolet provided another mechanism as using oxidation by hydroxyl radicals, but the enhancement was not significant. The rate constants of sonophotocatalytic processes were (48.1–64.6)×10-3 min-1. The calculated value of synergistic effect was 1.54. In this process, the main mechanism for degradation was oxidation by hydroxyl radicals on the surface of TiO2. The roles of the ultrasound were the dispersion of catalyst and mass transport of pollutant to the surface of the catalyst.

Synergistic sonoelectrochemical removal of substituted phenols: implications of ultrasonic parameters and physicochemical properties.

The effects of ultrasonic conditions and physicochemical properties on the synergistic degradation in synthetic solution were investigated. A wide range of ultrasound frequencies, including 35, 170, 300, 500 and 700 kHz, and ultrasonic power densities, including 11.3, 22.5 and 31.5 W/L were used. It was revealed that the physical effect of ultrasound plays a major role in synergistic mechanism and 35 kHz was found to be the most effective frequency due to its more vigorous physical effect induced by high implosive energy released from collapse of cavitation bubbles. The highest ultrasonic power density (31.5 W/L) showed the highest synergy index as it increases the number of cavitation bubbles and the energy released when they collapse. The synergy indexes of various substituted phenols under identical condition were investigated. These results were correlated with physicochemical properties, namely octanol-water partition coefficient (Log K OW), water solubility (SW), Henrys law constant (KH) and water diffusivity (DW). Among these parameters, Log K OW and DW were found to have substantial effects on synergy indexes.

Effects of salt and pH on sonophotocatalytic degradation of azo dye reactive black 5

The effects of salt and pH on the sonophotocatalytic degradation of azo dye Reactive Black 5 (RB5) were investigated. The applied frequency was 35 kHz, and 254 nm UVC lamps and TiO2 were used. At salt concentrations of 0, 50, 500, and 5000 mg/L, salt acted as an inhibitor or a OH radical scavenger under neutral pH condition and there was no significant difference in the removal trends for salt-added conditions. Under acidic condition, adsorption of RB5 on the surface of TiO2 was observed before the start of the sonophotocatalytic process and it was revealed that adsorption of RB5, negatively charged dye anions, could be enhanced under acidic condition because the charge of the TiO2 surface was changed from negative to positive at a pH of 6.6. This enhancement under acidic condition was observed during the entire operation time. In the comparison of the pH and salt effects, the enhancement by acidic pH control was larger than the inhibition by the effect of salt as a radical scavenger.

Modeling metal-sediment interaction processes

Sensitivity and uncertainty analysis of contaminant fate and transport modeling have received considerable attention in the literature. In this study, our objective is to elucidate the uncertainty pertaining to micropollutant modeling in the sediment-water column interface. Our sensitivity analysis suggests that not only partitioning coefficients of metals but also critical stress values for cohesive sediment affect greatly the predictions of suspended sediment and metal concentrations. Bayesian Monte Carlo is used to quantify the propagation of parameter uncertainty through the model and obtain the posterior parameter probabilities. The delineation of periods related to different river flow regimes allowed optimizing the characterization of cohesive sediment parameters and effectively reducing the overall model uncertainty. We conclude by offering prescriptive guidelines about how Bayesian inference techniques can be integrated with contaminant modeling and improve the methodological foundation of uncertainty analysis. Sensitivity and uncertainty analysis was performed for sediment-metal modeling.Suspended sediment predictions are sensitive to critical erosion stress.Sediment bed-water partitioning coefficient is critical for metal predictions.River flow dynamics affect contaminant fate and model parameter sensitivity.Strategies to improve uncertainty analysis of sediment-metal modeling are discussed.

Distribution of electrical energy consumption for the efficient degradation control of THMs mixture in sonophotolytic process

Sonophotolytic degradation of THMs mixture with different electrical energy ratio was carried out for efficient design of process. The total consumed electrical energy was fixed around 50W, and five different energy conditions were applied. The maximum degradation rate showed in conditions of US:UV=1:3 and US:UV=0:4. This is because the photolytic degradation of bromate compounds is dominant degradation mechanism for THMs removal. However, the fastest degradation of total organic carbon was observed in a condition of US:UV=1:3. Because hydrogen peroxide generated by sonication was effectively dissociated to hydroxyl radicals by ultraviolet, the concentration of hydroxyl radical was maintained high. This mechanism provided additional degradation of organics. This result was supported by comparison between the concentration of hydrogen peroxide sole and combined process. Consequently, the optimal energy ratio was US:UV=1:3 for degradation of THMs in sonophotolytic process.

Arsenite removal using a pilot system of ultrasound and ultraviolet followed by microfiltration.

Batch and continuous-flow pilot tests using ultrasound (US), ultraviolet (UV) and a combination of US and UV were conducted to determine the oxidation rates of arsenite [As(III)]. Compared to the single processes of US or UV, the combined US/UV system was more effective for As(III) oxidation with a synergy index of more than 1.5. A high rate constant of As(III) removal was obtained as ferrous [Fe(II)] ions existed. Like the pseudo-Fenton reaction, Fe(II) species can participate in the production of additional ·OH by reacting with H2O2 produced by US, before being oxidized to Fe(III). From the results of batch tests, the optimum molar ratio of Fe(II)/As(III) and pH were found to be 83 and 6-9.5, respectively. Similarly, the continuous-flow pilot tests showed that US/UV system could remove As(III) below the regulation [10 μg L(-1) as total As (Astot)] at 91 of molar ratio [Fe(II)/As(III)] and 3-h HRT. The continuous-stirred-tank-reactor (CSTR) modeling showed that the scavenging effect of anionic species (Cl(-) and CO3(2-)) for ·OH might prevail in the single processes, whereas it is insignificant in the combined process. Without using chemicals, microfiltration (MF) was adopted to treat sludge produced in oxidation step. In terms of an engineering aspect, the operational critical flux (CF) and cycle time were also optimized through the continuous-flow tests of MF system. As an energy-utilizing oxidation technique that does not require a catalyst, the combined energy system employing US/UV followed by MF could be a promising alternative for treating As(III) and Fe(II) simultaneously.

Effects of Power Density and TiO2 Dose in the Sonocatalytic Degradation of Diethyl Phthalate Using High Frequency

Few studies using high frequencies have been carried out on the sono-TiO2 process, and consistent results based on the specific experimental conditions have not been reported thus far. Therefore, in the present work the effects of power density and dose on the kinetic constant of diethyl phthalate at 500 and 35 kHz using TiO2 have been evaluated. The slopes of kinetic constants depending on the power density regardless of TiO2 were increased and they were shown to be linear. However, the enhancement percentage according to the frequencies at 500 kHz was lower than that at 35 kHz, though clear discussions on the enhancement in the presence of TiO2 have not yet been produced. Also, the optimal dose was 1 g/L, which was not changed according to the frequency.

Sonophotolytic Degradation of Estriol at Various Ultraviolet Wavelength in Aqueous Solution

This study investigated degradation of the hormone estriol by sonolysis, photolysis and sonophotolysis at various UV wavelengths. Degradation was determined with UVA (365 nm), UVC (254 nm), or VUV (185 nm) irradiation and/or ultrasound exposure (283 kHz). The pseudo-first order degradation rate constants were in the order of 10-1 to 10-4 min-1 depending on the processes. The dominant reaction mechanism of estriol in sonolysis was estimated as hydroxyl radical reaction by the addition of tert-butanol (t-BuOH), which is a common hydroxyl radical scavenger. Photolytic and sonophotolytic estriol degradation rate also were high at shortest UV wavelength (VUV) due to the higher energy of photons, higher molar absorption coefficient of estriol and increased hydroxyl radical generation from the homolysis of water. Small synergistic effects were observed for sonophotolytic degradation with UVA and UVC irradiation. No synergy was observed for sonophotolysis with VUV irradiation.