Sonochemical oxidation activity in 20-kHz probe-type sonicator systems: The effects of probe positions and vessel sizes.

The 20-kHz probe-type sonicator systems were investigated for the enhancement of the cavitational oxidation activity under various geometric conditions including vertical and horizontal probe positions and vessel sizes/volumes as a following study to our previous study. The sonochemical oxidation activity (mass-based I3- ion generation rate) increased significantly for all vessel size conditions as the probe was placed close to the vessel bottom, owing to the expansion of the sonochemical active zone induced by the reflections of ultrasound at the bottom and the reactor wall. A concentric circular active zone is observed at positions close to the bottom. The highest sonochemical activity was obtained at 1 cm (vertical position) in the 20 cm vessels (input power: 50 %). At the vertical positions of 11 cm to 7 cm, no significant difference in the sonochemical activity was observed for all input power conditions (25, 50, and 75 %) because no meaningful reflections occurred. Higher sonochemical activities were obtained at an input power of 75 % owing to the increased power and strong reflection. The highest cavitational yield considering the energy efficiency was obtained at 6 cm (vertical position) for 75 % of all power and geometric conditions. Horizontal probe position tests showed that the asymmetric formation of the sonochemical active zone could significantly enhance the sonochemical activity. The highest activity was obtained at 1 cm (vertical position) and 2.5 cm (horizontal position) in the 20 cm vessel.

Machine learning model to predict rate constants for sonochemical degradation of organic pollutants.

In this study, machine learning (ML) algorithms were employed to predict the pseudo-1st-order reaction rate constants for the sonochemical degradation of aqueous organic pollutants under various conditions. A total of 618 sets of data, including ultrasonic, solution, and pollutant characteristics, were collected from 89 previous studies. Considering the difference between the electrical power (Pele) and calorimetric power (Pcal), the collected data were divided into two groups: data with Pele and data with Pcal. Eight input variables, including frequency, power density, pH, temperature, initial concentration, solubility, vapor pressure, and octanol-water partition coefficient (Kow), and one target variable of the degradation rate constant, were selected for ML. Statistical analysis was conducted, and outliers were determined separately for the two groups. ML models, including random forest (RF), extreme gradient boosting (XGB), and light gradient boosting machine (LGB), were used to predict the pseudo-1st-order reaction rate constants for the removal of aqueous pollutants. The prediction performance of the ML models was evaluated using different metrics, including the root mean squared error (RMSE), mean absolute error (MAE), and R squared (R2). A significantly higher prediction performance was obtained using data without outliers and augmented data. Consequently, all the applied ML models could be used to predict the sonochemical degradation of aqueous pollutants, and the XGB model showed the highest accuracy in predicting the rate constants. In addition, the power density and frequency were the most influential factors among the eight input variables in prediction with the Shapley additive explanation (SHAP) values method. The degradation rate constants of the two pollutants over a wide frequency range (20-1,000 kHz) were predicted using the trained ML model (XGB) and the prediction results were analyzed.

Effect of liquid recirculation flow on sonochemical oxidation activity in a 28 kHz sonoreactor.

Sonochemical oxidation activity may be significantly enhanced by optimizing the geometric factors of a sonoreactor and implementing additional physical actions, such as mechanical mixing and gas sparging. This study investigates the effects of liquid recirculation flow on sonochemical oxidation reactions. This was carried out through experimental testing with a 28 kHz bath-type sonoreactor under various liquid heights and flow rates, ranging from 1λ to 4.0λ and 1.5-6.0 L/min, respectively. The potassium iodide (KI) dosimetry and sonochemiluminescence methods were used in the experiment. With an increase in the liquid height/volume, the pseudo zero-order kinetic constant and the mass of triiodide (I3-) ions fluctuated. The optimal liquid height was 2.0λ, 2.5λ, and 3.0λ, based on the appropriate formation of a cavitation active zone in the reactor. The introduction of a liquid recirculation flow led to a large reduction in sonochemical activity due to the shrinkage of the cavitation active zone. However, the sonochemical activity increased at higher flow rates through the capture of ultrasonic energy at the bottom zone. This increase was attributed to the formation of a strong and expanded active zone limited to the reactor bottom to the height of the recirculation flow. The results demonstrate that applying a high rate liquid flow adjacent to the transducer module may be beneficial for enhanced sonochemical activity.