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Endocrine disrupting compounds (EDCs) need to be removed by efficient treatment methods as they are a major concern for both human and environmental health. To reduce the impact of EDCs in water, this review examines the use of ultrasonic degradation processes. Following an overview of EDCs and their origins, the basic concepts of sonochemistry are examined, highlighting the potential of ultrasound in chemical reactions. An in-depth analysis of the variables that affect the ultrasonic degradation of EDCs, such as frequency, intensity/power, temperature and solution chemistry, prepares the reader for a case study investigation focusing on specific EDCs. The study also looks at synergistic methods, emphasizing how hybrid ultrasonic systems can improve removal efficiency. The study provides a comprehensive overview of the use of sonochemistry in the treatment of EDCs by addressing current issues and suggesting future research directions. The aim of this review paper is to provide insightful analysis and useful suggestions for scientists working on EDC remediation projects.

This study investigates the effectiveness of ultrasonic (US) treatment in removing and mineralizing surfactants in wastewater. It examines the complex mechanisms and variables (acoustic conditions, solution temperature, initial dose, etc.) that affect sonolytic processes. The effect of water matrix components (such as salts and the presence of secondary pollutants) on process performance is thoroughly investigated. Various treatments are analyzed through a detailed comparison of synergistic hybridization processes. The study also provides a comprehensive review of current environmental applications and explores potential directions for surfactant degradation using ultrasound. Insightful information is presented to advance sustainable wastewater treatment techniques. The literature review clearly reveals the promising future of sonotreatment for degrading various surfactants under different conditions. The use of multifrequency mechanisms and the integration of other advanced oxidation processes (AOPs) with the US process have significantly enhanced the energy efficiency of the sonochemical system. Additionally, the results highlight the need to focus on developing new sonoreactor designs, identifying degradation intermediates, and hybridizing the sonochemical system under innovative operating conditions.

The impact of hydrostatic pressure, commonly known as ambient or external pressure, on the phenomenon of sonochemistry and/or sonoluminescence has been extensively investigated through a multitude of experimental and computational studies, all of which have emphasized the crucial role played by this particular parameter. Numerous previous studies have successfully demonstrated the existence of an optimal static pressure for the occurrence of sonoluminescence and multi-bubble or single-bubble sonochemistry. However, despite these findings, a universally accepted value for this critical pressure has not yet been established. In addition, it has been found that the cavitation effect is completely inhibited when the static pressure is either too high or too low. This comprehensive review aims to delve into the primary experimental results and elucidate their significance in relation to hydrostatic pressure. We will then conduct an analysis of numerical calculations, focusing specifically on the influence of external pressure on single bubble sonochemistry. By delving into these calculations, we will be able to gain a deeper understanding of the experimental results and effectively interpret their implications.

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.

One of the likely methods for enhancing heat transfer in a latent thermal energy storage system is the conception of a thermal unit. In this study, the orientation of oval tubes (horizontal, vertical, and oblique) in phase change material (PCM, C19-C20)-based shell-tube heat exchanger was analyzed with respect to the metal foam (MF) type (graphite, copper, and nickel) in comparison to the case of pure PCM. For this purpose, a two-dimensional mathematical model was developed to investigate the thermal efficiency of the PCM-metal foam based composite energy storage unit. It was concluded that the orientation of the oval tubes (oblique, horizontal, and vertical) has a negligible impact on the performance of the thermal unit during the melting/solidification processes. Based on the liquid/solid fraction, total enthalpy and the average temperature in the annular space, the performance of a heat exchanger during fusion/solidification periods is in the order: copper-MF > graphite-MF > nickel-MF > pure PCM. Whatever the adopted MF or the geometry of tubes, the melting process is expedited compared to the solidification mechanism.

An advanced ANSYS FLUENT-based model was developed for hydrogen recovery from a multi-tubular fixed-bed metal hydride (MH) reactor of large-scale design. The model was firstly validated by comparing its results to specific experimental data. Mass and heat transfer processes inside the fixed bed were investigated for various pressures and thermochemical characteristics of the MH (thermal conductivity, porosity and reaction parameters). The findings were reported as average, local and spatial changes in the metal’s bed temperature and hydrogen content. During the initial stage of the endothermic desorption (t

Abstract Acoustic cavitation-induced sonochemistry is employed for a variety of industrial and laboratory-scale physical and chemical applications, including cleaning, nanomaterial synthesis, and destruction of water contaminants. In acoustic bubbles, CCl4 pyrolysis can totally alter the bubble sonochemistry as well as the active bubble-size population. The present theoretical work provides the unique study on the effect of liquid temperature on the size distribution of acoustically active bubbles in the presence of CCl4 (i.e., precursor of reactive chlorine species, RCS, and scavenger of hydrogen atom in pyrolytic reactions) in the bulk liquid. An updated reaction scheme for CCl4 sonopyrolysis is used. It was found that the sonopyrolysis of CCl4 within the bubble reduces its maximal temperature, but it notably increases its maximal molar yield. For lower CCl4 concentrations (≤ 0.1 mM), the broadness of active bubbles range for the total oxidants yield increased proportionally with the rise of liquid temperature from 20 to 50 °C. Nevertheless, the increase of CCl4 concentration amortizes this width increase over the same range of liquid temperature (20–50 °C). At higher concentrations of CCl4 (> 0.1 mM), the broadness of the active bubbles range becomes approximately constant and independent of the liquid temperature and CCl4 concentration.

As an alternative to a water-based cooling system for a sonoreactor, the present work presents for the first time the use of a phase change material for the management and storage of the dissipated heat within the sonicated water. The performance of the PCM is analyzed as a function of liquid height (LH = 5.1, 10.2, 15.3, and 20.4 cm) at a frequency of 300 kHz and two electric powers (PE = 20 and 60 W). The effective powers dissipated in the irradiated water were determined by the calorimetric technique. A computational fluid dynamics (CFD) model (implemented in ANSYS Fluent® software), was used for the analysis of the combined system (sonoreactor + PCM-thermal unit) at different operating conditions (liquid height and electric power). By analyzing the different outputs (variation of temperature, velocity, enthalpy, liquid fraction of PCM) of the used CFD model, more clarifications are provided about the behaviour of the combined system (sonoreactor + PCM-thermal unit) as function of the liquid height (5.1–20.4 cm) and electric power (20 and 60 W). In terms of temperature, velocity, enthalpy and liquid fraction of the PCM, promising results were obtained in spite of the low thermal conductivity of the employed PCM. The best performance of the combined system (sonoreactor and thermal unit) was obtained at the liquid height of 15.3 cm (corresponding to a water volume of 300 mL) with a similar behaviour (evolution of temperature, velocity, enthalpy, and liquid fraction of the PCM) at both electric powers (i.e., 20 and 60 W) with an intensified response at the PE = 60 W.

This study aims principally to assess numerically the impact of methanol mass transport (i.e., evaporation/condensation across the acoustic bubble wall) on the thermodynamics and chemical effects (methanol conversion, hydrogen and oxygenated reactive species production) of acoustic cavitation in sono-irradiated aqueous solution. This effect was revealed at various ultrasound frequencies (from 213 to 1000 kHz) and acoustic intensities (1 and 2 W/cm2) over a range of methanol concentrations (from 0 to 100%, v/v). It was found that the impact of methanol concentration on the expansion and compression ratios, bubble temperature, CH3OH conversion and the molar productions inside the bubble is frequency dependent (either with or without consideration of methanol mass transport), where this effect is more pronounced when the ultrasound frequency is decreased. Alternatively, the decrease in acoustic intensity decreases clearly the effect of methanol mass transport on the bubble sono-activity. When methanol mass transfer is eliminated, the decrease of the bubble temperature, CH3OH conversion and the molar yield of the bubble with the rise of methanol concentration was found to be more amortized as the wave frequency is reduced from 1 MHz to 213 kHz, compared to the case when the mass transport of methanol is taken into account. Our findings indicate clearly the importance of incorporating the evaporation and condensation mechanisms of methanol throughout the numerical simulations of a single bubble dynamics and chemical activity.

In this work, after exploring the first report on the synergism of combining ultrasound (US: 600 kHz) and chlorine toward the degradation of Allura Red AC (ARAC) textile dye, as a contaminant model, the impact of various mineral water constituents (Cl−, SO42−, NO3−, HCO3− and NO2−) and natural organic matter, i.e., humic acid (HA), on the performance of the US/chlorine sono-hybrid process was assessed for the first time. Additionally, the process effectiveness was evaluated in a real natural mineral water (NMW) of a known composition. Firstly, it was found that the combination of ultrasound and chlorine (0.25 mM) at pH 5.5 in cylindrical standing wave ultrasonic reactor (f = 600 kHz and Pe = 120 W, equivalent to PA ∼ 2.3 atm) enhanced in a drastic manner the degradation rate of ARAC; the removal rate being 320% much higher than the arithmetic sum of the two separated processes. The source of the synergistic effect was attributed to the effective implication of reactive chlorine species (RCS: Cl·, ClO· and Cl2·−) in the degradation process. Radical probe technique using nitrobenzene (NB) as a specific quencher of the acoustically generated hydroxyl radical confirmed the dominant implication of RCS in the overall degradation rate of ARAC by US/chlorine system. Overall, the presence of humic acid and mineral anions decreased the efficiency of the sono-hybrid process; however, the inhibition degrees depend on the type and the concentration of the selected additives. The reaction of these additives with the generated RCS is presumably the reason for the finding results. The inhibiting effect of Cl−, SO42−, NO3− and NO2− was more pronounced in US/chlorine process as compared to US alone, whereas the inverse scenario was remarked for the effect of HA. These outcomes were associated to the difference in the reactivity of HA and mineral anions toward RCS and ·OH oxidizing species, in addition to the more selective character of RCS than hydroxyl radical. The displacement of the reaction zone with increasing the additive concentration may also be another influencing factor that favors competition reactions, which subsequently reduce the available reactive species in the reacting medium. The NMW exerted reductions of 43% and 10% in the process efficiency at pH 5.5 and 8, respectively, thereby confirming the RCS-quenching mechanism by the water matrix constituents. Hence, this work provided a precise understanding of the overall mechanism of chlorine activation by ultrasound to promote organic compounds degradation in water.

The present paper introduces a novel semi-empirical technique for the determination of active bubbles’ number in sonicated solutions. This method links the chemistry of a single bubble to that taking place over the whole sonochemical reactor (solution). The probe compound is CCl4, where its eliminated amount within a single bubble (though pyrolysis) is determined via a cavitation model which takes into account the non-equilibrium condensation/evaporation of water vapor and heat exchange across the bubble wall, reactions heats and liquid compressibility and viscosity, all along the bubble oscillation under the temporal perturbation of the ultrasonic wave. The CCl4 degradation data in aqueous solution (available in literature) are used to determine the number density through dividing the degradation yield of CCl4 to that predicted by a single bubble model (at the same experimental condition of the aqueous data). The impact of ultrasonic frequency on the number density of bubbles is shown and compared with data from the literature, where a high level of consistency is found.

Power ultrasonic (>100 ​kHz) splits water into free radicals and hydrogen. As a result, water sonochemistry is considered as an alternative clean and fossil-fuel-free hydrogen production technique. In this research work, the impact of rare gases (Xe, Ar, and He) on the sonochemical production of hydrogen as well as the population of active bubbles has been investigated computationally for various sonicated frequencies (213–515 ​kHz) and intensities (1–2 ​W/cm2). It has been found that both the H2 yielding and the bubble population size for H2 yielding are in the order Xe ​> ​Ar ​> ​He, whatever the imposed sonolytic parameters (i.e., frequency and power). These findings were principally ascribed to the thermal conductivity of the saturating gases, which is in the reverse order (He ​> ​Ar ​> ​Xe). Besides, the difference between Ar and Xe is condensed in comparison with the He gas. For wave frequencies larger than 213 ​kHz, however, all saturating gases (Xe, Ar, and He) behave identically, with the influence of thermal conductivity of these gases on the optimal radius muted. At 213 ​kHz, however, this impact is plainly visible (Ropt (Ar and Xe)>Ropt (He)). As per the results obtained, helium's inefficiency as a saturating gas for hydrogen production is verified, but xenon's maximal efficacy is reached when water is saturated with it. These results support the fewer experimental data reported in this emerging branch of sonochemistry, while the discussed results in the present paper (i.e., noble gases effect on sono-hydrogen production) are treated for the first time. Consequently, our work is considered as a guideline for increasing the efficacy of hydrogen production in a sonochemical reactor.

The sonolysis of certain substrates in water has proved its effectiveness for the enhancement of the sonochemical production of hydrogen. In this study, the sonolysis of methane has been investigated for the first time in a single acoustic bubble (microreactor) over a frequency from 140 to 515 kHz. The obtained findings have been compared to those available in the literature. Independently of the methane dose (inside the bubble), the yield of H2 was improved especially with the decrease in wave frequency (from 515 to 140 kHz). For the driving frequencies 140, 213, 355, and 515 kHz, the production of hydrogen was maximized at 20, 15, 10, and 10% CH4, respectively. For 213 kHz, and the presence of 10% methane, the yield of hydrogen goes up by 111 fold compared to the case where the gas atmosphere is saturated only by argon. On the other hand, the highest methane conversions (~100% for 2, 5 and 7% CH4) were retrieved at 140 and 213 kHz. In terms of hydrogen formation and methane decay, the use of 140 kHz was found to be the best choice, whereas for a multi-bubble system, the number of acoustic bubbles should be taken into account for an optimal choice of frequency. Interestingly, it was observed that at 140 and 213 kHz and for methane mole fractions lower than or equal to 30 and 10%, respectively, a maximal formation of H2 and a relatively important production of •OH could result simultaneously.

Numerical simulations have been performed on a range of ambient bubble radii, in order to reveal the effect of mass transport, heat exchange and chemical reactions heat on the chemical bubble yield of single acoustic bubble. The results of each of these energy mechanisms were compared to the normal model in which all these processes (mass transport, thermal conduction, and reactions heat) are taken into account. This theoretical work was carried out for various frequencies (f: 200, 355, 515 and 1000 kHz) and different acoustic amplitudes (PA: 1.5, 2 and 3 atm). The effect of thermal conduction was found to be of a great importance within the bubble internal energy balance, where the higher rates of production (for all acoustic amplitudes and wave frequencies) are observed for this model (without heat exchange). Similarly, the ignorance of the chemical reactions heat (model without reactions heat) shows the weight of this process into the bubble internal energy, where the yield of the main species (·OH, H·, O and H2) for this model was accelerated notably compared to the complete model for the acoustic amplitudes greater than 1.5 atm (for f = 500 kHz). However, the lowest production rates were registered for the model without mass transport compared to the normal model, for the acoustic amplitudes greater than 1.5 atm (f = 500 kHz). This is observed even when the temperature inside bubble for this model is greater than those retrieved for the other models. On the other hand, it has been shown that, at the acoustic amplitude of 1.5 atm, the maximal production rates of the main species (·OH, H·, O and H2) for all the adopted models appear at the same optimum ambient-bubble size (R0 ~ 3, 2.5 and 2 µm for, respectively, 355, 500 and 1000 kHz). For PA = 2 and 3 atm (f = 500 kHz), the range of the maximal yield of ·OH radicals is observed at the range of R0 where the production of ·OH, O and H2 is the lowest, which corresponds to the bubble temperature at around 5500 K. The maximal production rate of H·, O and H2 is shifted toward the range of ambient bubble radii corresponding to the bubble temperatures greater than 5500 K. The ambient bubble radius of the maximal response (maximal production rate) is shifted toward the smaller bubble sizes when the acoustic amplitude (wave frequency is fixed) or the ultrasound frequency (acoustic power is fixed) is increased. In addition, it is observed that the increase of wave frequency or the acoustic amplitude decrease cause the range of active bubbles to be narrowed (scenario observation for the four investigated models).

The present study treats the effects of mass transport, heat transfer and chemical reactions heat on the bubble dynamics by spanning a range of ambient bubble radii. The thermodynamic behavior of the acoustic bubble was shown for three wave frequencies, 355, 515 and 1000 kHz. The used acoustic amplitude ranges from 1 to 3 atm. It has been demonstrated that the ambient bubble radius, R0, of the maximal response (i.e., maximal bubble temperature and pressure, Tmax and Pmax) is shifted toward lower values if the acoustic amplitude (at fixed frequency) or the ultrasonic frequency (at fixed amplitude) are increased. The range of the ambient bubble radius narrows as the ultrasonic frequency increases. Heat exchange at the bubble interface was found to be the most important mechanism within the bubble internal energy balance for acoustic amplitudes lower than 2.5 and 3 atm for ultrasonic frequencies of 355 and 515 kHz, respectively. For acoustic amplitudes greater or equal to 2.5 and 3 atm, corresponding to 355 and 515 kHz, respectively, mass transport mechanism (i.e., evaporation and condensation of water vapor) becomes dominant compared to the other mechanisms. At 1000 kHz, the mechanism of heat transfer persists to be dominant for all the used acoustic amplitudes (from 1 to 3 atm). Practically, all the above observations were maintained for bubbles at and around the optimum bubble radius, whereas no significant impact of the three energetic mechanisms was observed for bubbles of too lower and too higher values of R0 (limits of the investigated ranges of R0).

Although most of researchers agree on the elementary reactions behind the sonolytic formation of molecular hydrogen (H2) from water, namely the radical attack of H2O and H2O2 and the free radicals recombination, several recent papers ignore the intervention of the dissolved gas molecules in the kinetic pathways of free radicals, and hence may wrongly assess the effect of dissolved gases on the sonochemical production of hydrogen. One may fairly ask to which extent is it acceptable to ignore the role of the dissolved gas and its eventual decomposition inside the acoustic cavitation bubble? The present opinion paper discusses numerically the ways in which the nature of dissolved gas, i.e., N2, O2, Ar and air, may influence the kinetics of sonochemical hydrogen formation. The model evaluates the extent of direct physical effects, i.e., dynamics of bubble oscillation and collapse events if any, against indirect chemical effects, i.e., the chemical reactions of free radicals formation and consequently hydrogen emergence, it demonstrates the improvement in the sonochemical hydrogen production under argon and sheds light on several misinterpretations reported in earlier works, due to wrong assumptions mainly related to initial conditions. The paper also highlights the role of dissolved gases in the nature of created cavitation and hence the eventual bubble population phenomena that may prevent the achievement of the sonochemical activity. This is particularly demonstrated experimentally using a 20 kHz Sinaptec transducer and a Photron SA 5 high speed camera, in the case of CO2-saturated water where degassing bubbles are formed instead of transient cavitation.

Abstract This work aimed at the characterization and application of a cavitation field induced in water by an ultrasonic reactor operating at 1700 kHz and 15 W. It was found that the size of active bubbles varied from 0.23 to 3 µm. The number of active bubbles increased from 6.1142 × 108 s−1 L−1 at 25 °C to 4.4684 × 109 s−1 L−1 at 55 °C. The most active bubbles were those achieving temperature of 4000 K and pressure of 1000 atm at the collapse. The characterized cavitation field removed efficiently toluidine blue (TB), an emerging organic contaminant, through reaction with hydroxyl radical. The best TB-removal rate was obtained under argon saturation, but CO2 completely suppressed the process. TB degradation rate sensitively enhanced with increasing initial substrate concentration and solution pH, whereas the liquid temperature did not affect the degradation rate. Formic acid, as an organic competitor, reduced considerably the degradation of the pollutant.