Younggyu Son

Investigation of acoustic cavitation energy in a large-scale sonoreactor

Acoustic cavitation energy distributions were investigated for various frequencies such as 35, 72, 110 and 170 kHz in a large-scale sonoreactor. The energy analyses were conducted in three-dimensions and the highest and most stable cavitation energy distribution was obtained not in 35 kHz but in 72 kHz. However, the half-cavitation-energy distance was larger in the case of 35 kHz ultrasound than in the case of 72 kHz, demonstrating that cavitation energy for one cycle was higher for a lower frequency. This discrepancy was due to the large surface area of the cavitation-energy-meter probe. In addition, 110 and 170 kHz ultrasound showed a very low and poor cavitation energy distribution. Therefore larger input power was required to optimize the use of higher frequency ultrasound in the sonoreactor with long-irradiation distance. The relationship between cavitation energy and sonochemical efficiency using potassium iodide (KI) dosimetry was best fitted quadratically. From 7.77 x 10(-10) to 4.42 x 10(-9)mol/J of sonochemical efficiency was evaluated for the cavitation energy from 31.76 to 103. 67 W. In addition, the cavitation energy attenuation was estimated under the assumption that cavitation energy measured in this study would be equivalent to sound intensity, resulting in 0.10, 0.18 and 2.44 m(-1) of the attenuation coefficient (alpha) for 35, 72 and 110 kHz, respectively. Furthermore, alpha/(frequency)(2) was not constant, as some previous studies have suggested.

Frequency effects on the sonochemical degradation of chlorinated compounds

The effects of frequency in chlorobenzene, chloroform, and carbon tetrachloride have been experimentally investigated in this study. The irradiation frequencies were 35, 74, 170, 300 and 1000 kHz. The degradation rates of chlorobenzene, chloroform, and carbon tetrachloride were highest at 300 kHz. The results of between formation of hydrogen peroxide concentration and degradation of chlorinated compounds were not a coincidence. Methods of the sonochemical efficiency were needed to review. The concentration of total organic carbon was remained after 4 h of sonication. High power intensity, longer sonication time, addition of catalysts and combination of the AOP process, were needed for the degradation of TOC. The formation of chloride ion in aqueous solution was evident for the degradation of chlorinated compounds. However, the theoretical concentration of chloride ion was higher than the measured concentration. This means that the remaining chlorinated contaminants in each solution cannot complete dechlorination and some intermediated were produced.

Addition of Chlorinated Compounds in the Sonochemical Degradation of 2-Chlorophenol

This paper outlines the research carried out on the sonochemical degradation of 2-chlorophenol in the presence and absence of chlorinated compounds. The degree of enhancement varied according to the characteristics of chlorinated compounds. The higher oxidation states of carbon in chlorinated compounds increase the degradation rate of 2-chlorophenol. When tetrachloroethylene (PCE) and chloroform (CF) have the same oxidation number, PCE is in a fully oxidized state. Therefore, the degradation rate of 2-chlorophenol in PCE is higher than that in CF. Free chlorine was formed from the sonochemical decomposition of chlorinated compounds. This free chlorine was then used for degrading the 2-chlorophenol or chlorinated compound itself. The amount of free chlorine is ordered by oxidation states of carbon in chlorinated compounds. The degradation rates of chlorinated compounds decreased with the co-presence of 2-chlorophenol, which is a result of ultrasonic energy being distributed to both compounds. An increase in time corresponds to a higher concentration of chloride ion. However, the application of the full amount of chlorinated compounds cannot complete dechlorination.

Analysis of the Ultrasonic Cavitation Energy in a Pilot-Scale Sonoreactor

In this study, ultrasonic cavitation energy states were analyzed in a pilot-scale sonoreactor, using two- and three-dimensional mapping methods. The highest and most stable cavitation energy state, through the whole length, was obtained with an ultrasound application of 72 kHz. However, very poor energy distributions were obtained at ultrasound applications of 110 and 170 kHz. In the correlation between input acoustic power and average cavitation energy, proportional relationships were found in 35 and 72 kHz. It was anticipated that this method could be used for the optimization of large-scale sonoreactor designs. A three-dimensional cavitation energy analysis was also conducted in the application of 35 kHz and 160 W for the whole spots in the sonoreactor. The average energy in the pilot-sonoreactor was estimated to be 62.8 W, which accounts for approximately 40% energy conversion efficiency.

Liquid Height Effect on Sonochemical Reactions in a 35 kHz Sonoreactor

In order to investigate the effect of liquid height based on the wavelength of ultrasound for sonochemical reactions, various liquid heights and input powers were applied in a large-scale 35 kHz sonoreactor. For the liquid height of 1 λ to 6 λ, 5 λ was determined as the optimum level for all applied input powers of 30, 60, and 90 W. The results revealed that liquid height should be above a certain level in order to optimize both sonochemical efficiency and conversion efficiency. Moreover, the enhancement of applying a higher input power was reducing as the liquid height increased and there was no significant difference of conversion efficiency at optimal liquid height due to a larger attenuation for a higher input power. To understand further the effect of the water level, the liquid height was adjusted by quarter of a wavelength from the liquid height of 1 L. Consequently, a small change of liquid height resulted in a significant difference for both sonochemical efficiency and conversion efficiency. A peak value for each change of the liquid height by half a wavelength was also observed.

Effects of Hydrogen Peroxide and Frequency for the Sonochemical Degradation of Aqueous Phenol

The effect of hydrogen peroxide and frequency on the degradation of phenol was investigated in this study. The concentrations of phenol and hydrogen peroxide were 0.05 and 0.0018 mM, respectively. When a high frequency of sonication (1 MHz) was irradiated to a phenol solution, the efficiency of decomposition of phenol was about 95% within 120 min. At a low frequency, the phenol degradation was slower than at a high frequency, while the degradation of the total organic carbon at a low frequency was nearly the same as that at a high frequency. Hydrogen peroxide was formed due to the dissipation of water. Through a comparison, it can be seen that the order of degradation rates of phenol and the formation rate of hydrogen peroxide were not the same. The relationship between the degradation rate of compounds and the formation rate of hydrogen peroxide was not clear. With the addition of hydrogen peroxide in phenol solution, the phenol concentration was almost completely degradable within 30 min. In the case of total organic carbon (TOC), the concentration was degraded by 50%. Therefore, for the decomposition of total organic carbon, the addition of hydrogen peroxide or other catalysts was required.

Remediation of Diesel-Contaminated Soil Using Supercritical Carbon Dioxide and Ultrasound

The purpose of this study was to identify and evaluate the efficiency of the supercritical fluid extraction (SFE) method for removing diesel from an artificially contaminated soil using a supercritical carbon dioxide and an ultrasound. Compared with SFE, ultrasound-enhanced/assisted SFE (USFE) was able to provide a 14.8% increase in the diesel removal rate from diesel-contaminated soil at the SFE conditions of 40 °C, 16 MPa, 2 mL/min CO2 flow rate and 40 min dynamic extraction time, and the ultrasound conditions of 316 W/cm2 and 20 kHz. These results showed that an ultrasound reduce the extraction time, the extraction pressure, the CO2 flow rate and the extraction temperature during the SFE process by enhancing the mass transfer from the soil to the supercritical CO2.

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.

Estimation of Sonochemical Reactions under Single and Dual Frequencies Based on Energy Analysis

Sonochemical reactions were quantified using KI dosimetry and analyzed based on calorimetry and electric energy consumption under single (35, 72, 170, 300, 500, and 1000 kHz) and dual (35/35, 35/72, 35/170, 35/300, 35/500, and 35/1000 kHz) frequency conditions. For single-frequency conditions, ultrasonic energy under calorimetry decreased as the applied frequency increased, while there was no significant change with the applied frequency for dual-frequency conditions. A synergistic effect was observed in the dual-frequency mode not considering the energy consumption; however, double the electric energy consumption in the dual mode was considered as the main reason for high performance. It seemed that calorimetry was not adequate for determining the optimal condition even though it was based on the direct measurement of the temperature in the solution. For electric energy analysis, there was no significant synergistic effect for dual-frequency applications and some single-frequency applications were superior to their dual-frequency counterparts.

Elimination of two hormones by ultrasonic and ozone combined processes

A direct ultrasonic (US) and ozone (O3) combination (US/O3) process for the removal of two hormones, estrone (E1) and estriol (E3), in aqueous solutions was investigated. These two hormones were detected in a wastewater treatment plant effluent in Korea. It was found that the ultrasonic/ozone process showed a higher removal performance than the US and O3 process even though the O3 process also showed approximately the same removal efficiency after 60 min. Chemical oxygen demand/total organic carbon (CODcr/TOC) ratios for E1 and E3 decreased, indicating that biodegradability could be increased significantly in the US/O3 process. The optimal pH condition was determined above the neutral pH condition.