Ultrasound/chlorine sono-hybrid-advanced oxidation process: Impact of dissolved organic matter and mineral constituents

Prediction of micropollutant degradation kinetic constant by ultrasonic using machine learning

A prediction model based on XGBoost is proposed for ultrasonic degradation of micropollutants' kinetic constants. After parameter optimization through iteration, the model achieves Evaluation metrics with R2 and SMAPE reaching 0.99 and 2.06%, respectively. The impact of design parameters on predicting kinetic constants for ultrasound degradation of trace pollutants was assessed using Shapley additive explanations (SHAP). Results indicate that power density and frequency significantly impact the predictive performance. The database was sorted based on power density and frequency values. Subsequently, 800 raw data were split into small databases of 200 each. After confirming that reducing the database size doesn't affect prediction accuracy, ultrasound degradation experiments were conducted for five pollutants, yielding experimental data. A small database with experimental conditions within the numerical range was selected. Data meeting both feature conditions were filtered, resulting in an optimized 60-data group. After incorporating experimental data, a model was trained for prediction. Degradation kinetic constants for experiments (kE) were compared with predicted constants (for 800 data-based model: kP-800 and for 60 data-based model: kP-60). Results showed ibuprofen, bisphenol A, carbamazepine, and 17β-Estradiol performed better on the 60-data group (kP-60/kE: 1.00, 0.99, 1.00, 1.00), while caffeine suited the model trained on the 800-data group (kP-800/kE: 1.02).

Sonochemical degradation of PFAS in ion exchange regeneration wastes

One of the primary technologies currently being deployed for the removal of per- and polyfluoroalkyl substances (PFAS) from water is ion exchange (IX). For regenerable IX resins, concentrated PFAS in the resulting spent brine and/or still bottoms requires further treatment. This research demonstrated that PFAS in spent brine and still bottoms can be effectively degraded sonochemically at 1000 kHz. Overall, PFAS degradation was negatively impacted by high total organic carbon (TOC) and residual methanol (MeOH) solvent (up to 50 g/kg; 5% w:w), but was enhanced by the high chloride. The addition of caustic (up to 1 N NaOH) partially mitigated the inhibition by TOC and MeOH. Sonochemical degradation of individual PFAS compounds resulted in significant mineralization to form inorganic fluoride, but small quantities of volatile organic fluorine species (VOF) were noted. This is believed to be the first report of sonochemical degradation of PFAS in ion exchange regeneration wastes, and indicates the possibility for the application of this technology as part of a complete PFAS capture and destruction treatment train.

One-pot hydrothermal synthesis of FeNbO4 microspheres for effective sonocatalysis

FeNbO4 sonocatalysts were successfully synthesized by a simple hydrothermal route at pH values of 3, 5, 7, 9 and 11. The catalysts were characterized by XRD, XPS, TEM, SEM, N2 adsorption and DRS to analyse the effect of pH parameters on the physicochemical properties of the materials during hydrothermal synthesis. The sonocatalytic activity of FeNbO4 microspheres was evaluated by using acid orange 7 (AO7) as the simulated contaminant. The experimental results showed that the best sonocatalytic degradation ratio (97.45%) of organic dyes could be obtained under the conditions of an initial AO7 concentration of 10 mg L-1, an ultrasonic power of 200 W, a catalyst dosage of 1.0 g L-1, and a pH of 3. Moreover, the sonocatalysts demonstrated consistent durability and stability across multiple test cycles. After active species capture experiments and calculation of the energy band, a possible mechanism was proposed based on the special Fenton-like mechanism and the dissociation of H2O2. This research shows that FeNbO4 microspheres can be used as sonocatalysts for the purification of organic wastewater, which has a promising application prospect.

The unveiling of a dynamic duo: hydrodynamic cavitation and cold plasma for the degradation of furosemide in wastewater

The degradation in water of furosemide (FUR), a widely used diuretic drug, was herein reported. The method entails an integrated approach based on the hybridisation of hydrodynamic cavitation (HC) with electrical discharge (ED) plasma technology. This dynamic duo could increase the production of oxidising compounds in water, in particular hydroxyl radicals (OH radicals), by triggering the rapid homolytic decomposition of water molecules and avoiding the addition of external oxidants. This study clearly emphasises the effectiveness of an integrated approach to improve the degradation of pollutants in wastewater originating from active pharmaceutical ingredients (APIs). The results of HC/ED-assisted FUR degradation in the presence of radical scavengers highlight the predominant role of the radical oxidation mechanism at the gas-liquid interface of the cavitation bubble during HC/ED treatment. A comparative analysis of the three technologies-HC alone, HC/ED and UV alone-emphasised the promising potential of hybrid HC/ED as a scalable industrial technology. This is demonstrated by the higher degradation rates (100%, 10 min) when treating large volumes (5L) of wastewater contaminated with FUR (50 mg/L), even in the presence of other APIs.

Sonochemistry dosimetries in seawater

Due to the complex physical and chemical interactions taking place in the sonicated medium, various methods have been proposed in the literature for a better understanding of the sonochemical system. In the present paper, the performance of calorimetry, iodometry, Fricke, 4-nitrophenol, H2O2, and ascorbic acid dosimetry techniques have been evaluated over the electric power range from 20 to 80 W (f = 300 kHz). These methods have been analyzed for distilled and seawater in light of the literature findings. It has been found that the lowest temperatures and calorimetric energies were obtained for seawater in comparison to distilled water. However, the discrepancy between both mediums disappears with the increase in the electric power up to 80 W. Compared to the calorimetry results, a similar trend was obtained for the KI dosimetry, where the discrepancy between both solutions (seawater and distilled water) increased with the reduction in the electric power down to 20 W. In contrast, over the whole range of the electric power (20-80 W), the H2O2 dosimetry was drastically influenced by the salt composition of seawater, where, I3- formation was clearly reduced in comparison to the case of the distilled water. On the other hand, a fluctuated behavior was observed for the Fricke and 4-nitrophenol dosimetry methods, especially at the low electric powers (20 and 40 W). It has been found that dosimetry techniques based on ascorbic acid or potassium iodide are the best means for accurate quantification of the sonochemical activity in the irradiated liquid. As a result, it has been concluded, in terms of the dosimetry process's performance, that the dosimetry methods are in the following order: Ascorbic acid ≈ KI > Fricke > 4-nitrophenol > H2O2.

Sonochemical formation of peroxynitrite in water: Impact of ultrasonic frequency and power

There is a lack of literature on peroxynitrite formation due to sonolysis of aerated water. In this work, the impact of sonication parameters, frequency and power, on ultrasonic peroxynitrite production in aerated alkaline water was investigated. Peroxynitrite formation was clearly established with undeniable evidence at all the tested frequencies in the range of 516-1140 kHz with a typical G-value (energy-specific yield) of 0.777 × 10-10, 0.627 × 10-10, 0.425 × 10-10 and 0.194 × 10-10 mol/J at 516, 558, 860 and 1140 kHz, respectively. The ultrasonication frequency has a direct impact on the sonochemical peroxynitrite production. Increasing the ultrasonication frequency in the interval 321-1140 kHz reduces peroxynitrite formation. The most practical sonochemistry dosimetries, including hydrogen peroxide production, triiodide dosimetry, Fricke dosimetry, and 4-nitrocatechol formation, were compared with the sonochemical efficiency of the reactors used to produce peroxynitrite. The G-value, energy specific yield, for the tested dosimetries was higher than that for peroxynitrite formation, regardless of frequency. For all chemical dosimetries investigated, the same trend of frequency dependence was found as for peroxynitrite generation. The influence of ultrasonication power on peroxynitrite formation by sonication at diverse frequencies in the interval 585-1140 kHz was studied. No peroxynitrite was formed at lower acoustic power levels, regardless of frequency. As the frequency increases, more power is required for peroxynitrite formation. The production of peroxynitrite increased as the acoustic power increased, despite the frequency of ultrasonic waves. Ultrasonic power is a key factor in the production of peroxynitrite by sonolysis. Since peroxynitrite is uniformly distributed in the bulk solution, peroxynitrite-sensitive solutes can be transformed both in the bulk of the solution and in the surfacial region (shell) of the cavitation bubble. The formation of peroxynitrite should be taken into account in sonochemistry, especially at higher pH values. Ultrasonic peroxynitrite formation in alkaline solution (pH 12) can be considered as a kind of chemical dosimetry in sonochemistry.

Comparison of effects of multiple oxidants with an ultrasonic system under unified system conditions for bisphenol A degradation

Bisphenol A (BPA) as a trace contaminant has been reported, due to widespread use in the plastics industry. This study applied the 35 kHz ultrasound (US) to activate four different common oxidants (H₂O₂, HSO₅^-, S₂O₈^2-, and IO₄^-) for BPA degradation. With increasing initial concentration of oxidants, the degradation rate of BPA increased. The synergy index confirmed that a synergistic relationship between US and oxidants. This study also examined the impact of pH and temperature. The results showed that the kinetic constants of US, US-H₂O₂, US-HSO₅^- and US-IO₄^-decreased when the pH increased from 6 to 11. The optimal pH for US-S₂O₈^2- was 8. Notably, increasing temperature decreased the performance of US, US-H₂O₂, and US-IO₄^- systems, while it could increase the degradation of BPA in US-S₂O₈^2- and US-HSO₅^-. The activation energy for BPA decomposition using the US-IO₄^- system was the lowest, at 0.453nullkJnullmol^-1, and the synergy index was the highest at 2.22. Additionally, the ΔG# value was found to be 2.11 + 0.29T when the temperature ranged from 25 °C to 45 °C. The main oxidation contribution is achieved by hydroxyl radicals in scavenger test. The mechanism of activation of US-oxidant is heat and electron transfer. In the case of the US-IO₄^- system, the economic analysis yielded 271 kwh m^-3, which was approximately 2.4 times lower than that of the US process.