Search

• A broad overview of different aspects of ultrasonics and sonochemistry is presented in this article. • Among the applications covered are synthesis, emulsification, cleaning, and processing. • Food-related scale-up challenges are discussed. Ultrasonic waves can induce physical and chemical changes in liquid media via acoustic cavitation. Various applications have benefitted from utilizing these effects, including but not limited to the synthesis of functional materials, emulsification, cleaning, and processing. Several books and review articles in the public domain cover both fundamental and applied aspects of ultrasonics and sonochemistry. The Editors of the Ultrasonics Sonochemistry journal possess diverse expertise in this field, from theoretical and experimental aspects of acoustic cavitation to materials synthesis, environmental remediation, and sonoprocessing. This article provides Editors' perspectives on various aspects of ultrasonics and sonochemistry that may benefit students and early career researchers. [ABSTRACT FROM AUTHOR]

Highlights • Hydrodynamic cavitation is effective for the removal of Dicofol. • Highest rate of Dicofol degradation was observed at an inlet pressure of 7 bar. • HPLC and GC–MS analysis illustrated the presence of transformed products of Dicofol. • TOC removal of 85% was obtained within 60 min of treatment. Abstract Dicofol, a recommended Stockholm convention persistent organic pollutants (POPs) candidate is well known for its endocrine disruptive properties and has been extensively used as an organochlorine pesticide worldwide. The hydrodynamic cavitation (HC) treatment of Dicofol in aqueous media induced by a liquid whistle hydrodynamic cavitaion reactor (LWHCR) has been investigated while considering important parameters such as inlet pressure, initial concentration of Dicofol, solution temperature, pH, addition of H 2 O 2 and radical scavenger for the extent of degradation. The pseudo-first-order degradation rate constant (k) was determined to be 0.073 min−1 with a cavitational yield of 1.26 × 10−5 mg/J at optimum operating conditions and a complete removal of Dicofol was achieved within 1 h of treatment. Considering the removal rate and energy efficiency, the optimal inlet pressure was found to be 7 bar, resulting in a cavitation number of 0.17. High performance liquid chromatography (HPLC) and Gas chromatography mass spectroscopy (GC–MS) analyses indicated a sharp decline in the concentration of Dicofol with treatment time and indicated the presence of degraded products. An 85% total organic carbon (TOC) removal was achieved within 1 h of treatment time, demonstrating successful mineralization of Dicofol. The obtained results suggest that the degradation of Dicofol followed thermal decomposition and successive recombination reactions at bubble-vapor interface. Overall, the attempted hydrodynamic cavitation demonstrated successful and rapid removal of endocrine disruptive chemicals such as Dicofol and is expected to provide efficient solution for wastewater treatment. [ABSTRACT FROM AUTHOR]

With growing consumer demand for natural products, greener extraction techniques are found to be potential alternatives especially for pharmaceutical, nutraceutical, and cosmetic manufacturing industries. Cavitation-based technology has drawn immense attention as a greener extraction method, following its rapid and effective extraction of numerous natural products compared to conventional techniques. The advantages of cavitation-based extraction (CE) are to eliminate the application of toxic solvents, reduction of extraction time and to achieve better extraction yield, as well as purity. The cavitational phenomena enhance the extraction efficiency via increased mass transfer rate between the substrate and solvent, following the cell wall rupture, due to the intense implosion of bubbles. This review includes a detailed overview of the ultrasound-assisted extraction (UAE), negative pressure cavitation (NPC) extraction, hydrodynamic cavitation extraction (HCE) and combined extractions techniques which have been implemented for the extraction of high-value-added compounds. A list of essential parameters necessary for the maximum possible extraction yield has been discussed. The optimization of parameters, such as ultrasonic power density, frequency, inlet pressure of HC, extraction temperature and the reactor configuration denote their significance for better efficiency. Furthermore, the advantages and drawbacks associated with extraction and future research directions have also been pointed out. [ABSTRACT FROM AUTHOR]

Sonophotocatalysis (SPC) is considered to be one of the important wastewater treatment techniques and hence attracted the attention of researchers to eliminate recalcitrant hazardous organic pollutants from aqueous phase. In general, SPC refers to the integrated use of ultrasonic sound waves, ultraviolet radiation and the addition of a semiconductor material which functions as a photocatalyst. Current research has brought numerous improvements in the SPC based treatment by opting visible light irradiation, nanocomposite catalysts and numerous catalyst supports for better stability and performance. This review accomplishes a critical analysis with respect to the recent advancements. The efficiency of SPC based treatments has been analyzed by considering the individual methods i.e. sonolysis, photocatalysis, sonophotolysis, sono-ozone, photo-Fenton and sono-Fenton. Besides, the essential parameters such as solution temperature, concentrations of initial pollutant and catalyst, initial pH, dosages of Fenton’s reagent and hydrogen peroxide (H 2 O 2 ), ultrasonic power density, gas sparging, addition of radical scavenger, addition of carbon tetrachloride and methanol have been discussed with suggestions for the selection of optimum parameters. A higher synergistic pollutant removal rate has been reported during SPC treatment as compared to individual methods and the implementation of numerous doping materials and supports for the photocatalyst enhances the degradation rate of pollutants using DSPC under both visible and UV irradiation. Overall, SPC and DSPC based wastewater treatments are emerging as potential techniques as they provide effective solution in removing the recalcitrant organic pollutants and progressive research is expected to bring out superior treatment efficiency using these advanced technologies. Importance of this review The review has accomplished a thorough and a critical analysis of sonophotocatalysis (SPC) based on the recently published journals. Recent advancements in the doped sonophotocatalysis (DSPC) and the mechanisms behind synergistic enhancement in the pollutant degradation rate have been discussed with justifications. Besides, the possible future works are suggested for the advancements in sonophotocatalysis based treatment. This review will be beneficial for electing a SPC based method because of the accomplished sharp comparisons among the published results. The review includes current advancements of SPC based methods which aid for a low-cost and a large-scale wastewater treatment application. [ABSTRACT FROM AUTHOR]

The ultrasonic-assisted extraction of polysaccharides (PS) from Ganoderma lucidum, was subjected to a scale-up study. 0.25 L extractor was used to optimize the extraction conditions toward maximum yield of PS. The extracted PS was observed to be reduced by increasing the scale from 1 to 6 L. To intensify the extraction, axial circulation at different stirring rates was induced and optimized in a 3 L U-tube extractor. Although circulation at 300 rpm improved the yield of PS for 3 L, introducing dispersion geometry (conical funnel) and adjusting the radiation distance in a 6 L U-tube extractor further intensified the extraction efficiency. A radiation distance of 4 cm and circulation induced using 600 rpm enhanced the PS as compared to the conventional 6 L extractor. Overall, the scale-up from 0.25 to 6 L was successful and introducing circulation and dispersion geometry intensified the extraction efficiency under similar dissipation of ultrasonic power. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1483-1491, 2015 [ABSTRACT FROM AUTHOR]

Highlights: [•] Ultrasound cavitation induced POME treatment. [•] Triple frequency ultrasound cavitation reactor was used to check the frequency effects. [•] Role of H2O2 in avoiding the fluctuating pattern of COD has been noted. [•] Promising and a fruitful green process engineering technique for POME treatment. [Copyright &y& Elsevier]

Abstract: The effect of acoustic cavitation on the carboxylation of carbon nanotubes (CNTs) at room temperature was studied and compared with the conventional reflux process. Due to the dispersion caused by the shockwave and jet damage from the collapse of microbubbles, and the energy imparted by intense local temperature and pressure, a positive correlation between the amount of attached functional groups and sonication time was observed. The use of ultrasonication for the carboxylation of CNTs demonstrated merits over the conventional reflux method in the form of significantly higher and easier recovery of reacted samples, improved carboxylation yield with simpler equipment setup. [Copyright &y& Elsevier]

Abstract: In the present study, response surface methodology (RSM) based on central composite design (CCD) was employed to investigate the influence of main emulsion composition variables, namely drug loading, oil content, emulsifier content as well as the effect of the ultrasonic operating parameters such as pre-mixing time, ultrasonic amplitude, and irradiation time on the properties of aspirin-loaded nanoemulsions. The two main emulsion properties studied as response variables were: mean droplet size and polydispersity index. The ultimate goal of the present work was to determine the optimum level of the six independent variables in which an optimal aspirin nanoemulsion with desirable properties could be produced. The response surface analysis results clearly showed that the variability of two responses could be depicted as a linear function of the content of main emulsion compositions and ultrasonic processing variables. In the present investigation, it is evidently shown that ultrasound cavitation is a powerful yet promising approach in the controlled production of aspirin nanoemulsions with smaller average droplet size in a range of 200–300nm and with a polydispersity index (PDI) of about 0.30. This study proved that the use of low frequency ultrasound is of considerable importance in the controlled production of pharmaceutical nanoemulsions in the drug delivery system. [Copyright &y& Elsevier]

Ultrasound and Microchannel coupling for the generation of nanoemulsions. • Nanoemulsion was generated by coupling ultrasound and microchannel. • The implemented process intensification strategy led to creating a smaller monodispersed nanoemulsion system. • Microchannels of multiple dimensions were used to realize their impact. • Further controlling parameters were tested, accompanying with the stability of nanoemulsion. O/W nanoemulsions are isotropic colloidal systems constituted of oil droplets dispersed in continuous aqueous media and stabilised by surfactant molecules. Nanoemulsions hold applications in more widespread technological domains, more crucially in the pharmaceutical industry. Innovative nanoemulsion-based drug delivery system has been suggested as a powerful alternative strategy through the useful means of encapsulating, protecting, and delivering the poorly water-soluble bioactive components. Consequently, there is a need to generate an emulsion with small and consistent droplets. Diverse studies acknowledged that ultrasonic cavitation is a feasible and energy-efficient method in making pharmaceutical-grade nanoemulsions. This method offers more notable improvements in terms of stability with a lower Ostwald ripening rate. Meanwhile, a microstructured reactor, for instance, microchannel, has further been realised as an innovative technology that facilitates combinatorial approaches with the acceleration of reaction, analysis, and measurement. The recent breakthrough that has been achieved is the controlled generation of fine and monodispersed multiple emulsions through microstructured reactors. The small inner dimensions of microchannel display properties such as short diffusion paths and high specific interfacial areas, which increase the mass and heat transfer rates. Hence, the combination of ultrasonic cavitation with microstructures (microchannel) provides process intensification of creating a smaller monodispersed nanoemulsion system. This investigation is vital as it will then facilitate the creation of new nanoemulsion based drug delivery system continuously. Following this, the fabrication of microchannel and setup of its combination with ultrasound was conducted in the generation of O/W nanoemulsion, as well as optimisation to analyse the effect of varied operating parameters on the mean droplet diameter and dispersity of the nanoemulsion generated, besides monitoring the stability of the nanoemulsion. Scanning transmission electron microscopy (STEM) images were also carried out for the droplet size measurements. In short, the outcomes of this study are encouraging, which necessitates further investigations to be carried out to advance a better understanding of coupling microchannel with ultrasound to produce pharmaceutical-grade nanoemulsions. [ABSTRACT FROM AUTHOR]

The 20th century has witnessed a remarkable enhancement in the demand for varieties of consumer products, ranging from food, pharmaceutical, cosmetics, to other industries. To enhance the quality of the product and to reduce the production cost, industries are gradually inclined towards greener processing technologies. Cavitation-based technologies are gaining interest among processing technologies due to their cost effectiveness in operation, minimization of toxic solvent usage, and ability to obtain superior processed products compared to conventional methods. Also, following the recent advancements, cavitation technology with large-scale processing applicability is only denoted to the hydrodynamic cavitation (HC)-based method. This review includes a general overview of hydrodynamic cavitation-based processing technologies and a detailed discussion regarding the process effectiveness. HC has demonstrated its usefulness in food processing, extraction of valuable products, biofuel synthesis, emulsification, and waste remediation, including broad-spectrum contaminants such as pharmaceuticals, bacteria, dyes, and organic pollutants of concern. Following the requirement of a specific process, HC has been implemented either alone or in combination with other process-intensifying steps, for example, catalyst, surfactant, ultraviolet (UV), hydrogen peroxide (H2O2), and ozone (O3), for better performance. The reactor set-up of HC includes orifice, slit venturi, rotor-stator, and sonolator type constrictions that initiate and control the formation of bubbles. Moreover, the future directions have also been pointed out with careful consideration of specific drawbacks. [ABSTRACT FROM AUTHOR]

• Evolution process of vortex and cavitation in an ARHCR was studied by CFD. • The "simplified flow field" strategy and the Q -criterion were utilized. • Flow instability caused by CGUs induces complex helical and vortex flows. • Stretching and dilatation terms dominate the vorticity transport process. • This work provides a reference value to understanding flow mechanism of ARHCRs. Hydrodynamic cavitation (HC), a promising technology for enhancing processes, has shown distinct effectiveness and versatility in various chemical and environmental applications. The recently developed advanced rotational hydrodynamic cavitation reactors (ARHCRs), employing cavitation generation units (CGUs) to induce cavitation, have demonstrated greater suitability for industrial-scale applications than conventional devices. However, the intricate interplay between vortex and cavitation, along with its spatial-temporal evolution in the complex flow field of ARHCRs, remains inadequately elucidated. This study investigated the interaction mechanism between cavitation and vortex in a representative interaction-type ARHCR for the first time using the "simplified flow field strategy" and the Q -criterion. The findings reveal that the flow instability caused by CGUs leads to intricate helical and vortex flows, subsequently giving rise to both sheet and vortex cavitation. Subsequently, utilizing the Q -criterion, the vortex structures are identified to be concentrated inside and at CGU edges with evolution process of mergence and separation. These vortex structures directly influence the shape and dimensions of cavities, establishing a complex interaction with cavitation. Lastly, the vorticity transport equation analysis uncovered that the stretching and dilatation terms dominate the vorticity transport process. Simultaneously, the baroclinic term focuses on the vapor-liquid interface, characterized by significant alterations in density and pressure gradients. These findings contribute to a better comprehension of the cavitation-vortex interaction in ARHCRs. [ABSTRACT FROM AUTHOR]

Highlights • Prospects of ultrasound in hydroxylating graphene. • Prospects of ultrasound in hydroxylating Buckminsterfullerene. • Design aspects for large-scale sonochemical hydroxylation. • Statistical approach to optimize sonochemical variables. Abstract The main objective of this review is to derive the salient features of previously developed ultrasound-assisted methods for hydroxylating graphene and Buckminsterfullerene (C 60). The pros and cons associated to ultrasound-assisted synthesis of hydroxy-carbon nanomaterials in designing the strategical methods for the industrial bulk production are also discussed. A guideline on the statistical methods has also been considered to further provide the scopes towards the application of the previously reported methods. Irrespective of many useful methods that have been developed in order to functionalize C 60 and graphene by diverse oxygenated functional groups e.g. epoxide, hydroxyl, carboxyl as well as metal/metal oxide via a combination of organic chemistry and sonochemistry, there is no report dealing exclusively on the application of ultrasonic cavitation particularly to synthesising polyhydroxylated carbon nanomaterials. On this context, this review emphasizes in investigating the critical aspects of sono-nanochemistry and the statistical approaches to optimize the variables in the sonochemical process towards a large-scale synthesis of polyhydroxylated graphene and C 60. [ABSTRACT FROM AUTHOR]

Biodiesel, with its nature of clean, biodegradability, and renewability, is an ideal substitute for fossil diesel. This critical review focuses on the advances in process intensification of biodiesel production by the emerging hydrodynamic cavitation (HC) technology. The recent progress in HC reactors and HC-assisted biodiesel production are summarized and discussed. Several key operating factors (i.e., reactor structure, cavitation intensity, temperature, molar ratio of alcohol to oil, catalyst, and duration) and the economic feasibility are analyzed. It is found that HC can effectively enhance acid- and alkali-catalyzed production processes by using various edible and non-edible oils (e.g., waste cooking oil) as feedstocks, and have economic practicability for industrialization. HC can achieve as high as over 99% yields in a short time, and the quality of the high-purity products meets EN 14214 and ASTM D6751 standards. Although the process simulation and life cycle cost analysis (LCCA) validated that the economics of HC process is far superior to that of conventional mechanical stirring at large scales, the experimental research at pilot or industrial scales is absent, and the amplification effect of both the reactor and process is unclear. Moreover, the investigations on the cavitation flow mechanism, structural optimization and design of HCRs, and feasibility (e.g., life cycle analysis (LCA), LCCA, and LCA-LCCA), have to be focused on in the future. At last, the strengths, weaknesses, opportunities, and threats (SWOT) of the HC process are evaluated by a SWOT matrix, which may hopefully provide some inspiration for the future development of this novel technology. [Display omitted] • High yield/conversion can be achieved by HC from edible and non-edible oils. • Rotational-type reactors demonstrate considerably high effectiveness and economics. • Continuous HC process is found to be available on laboratory scales. • LCCA indicates the cost of industrial-scale HC process is reasonable. • Feasibility of HC process is comprehensively assessed by a SWOT matrix. [ABSTRACT FROM AUTHOR]

• Emerging green technologies have increased interest in "Cavitation Processing" for protein extraction. • Cavitation is a non-invasive, non-ionizing and non-polluting technique. • Sustainable technology platform to produce high-quality protein products from renewable resources. • Limitations of the current investigations provide an integrated view for commercial product formulation. Increasing protein demands directly require additional resources to those presently and recurrently available. Emerging green technologies have witnessed an escalating interest in "Cavitation Processing" (CP) to ensure a non-invasive, non-ionizing and non-polluting extraction. The main intent of this review is to present an integrated summary of cavitation extraction methods specifically applied to food protein sources. Along with a comparative assessment carried out for each type of cavitation model, protein extraction yield and implications on the extracted protein's structural and functional properties. The basic principle of cavitation is due to the pressure shift in the liquid flow within milliseconds. Hence, cavitation emerges similar to boiling; however, unlike boiling (temperature change), cavitation occurs due to pressure change. Characterization and classification of sample type is also a prime candidate when considering the applications of cavitation models in food processing. Generally, acoustic and hydrodynamic cavitation is applied in food applications including extraction, brewing, microbial cell disruption, dairy processing, emulsification, fermentation, waste processing, crystallisation, mass transfer and production of bioactive peptides. Micro structural studies indicate that shear stress causes disintegration of hydrogen bonds and Van der Waals interactions result in the unfolding of the protein's secondary and/or tertiary structures. A change in the structure is not targeted but rather holistic and affects the physicochemical, functional, and nutritional properties. Cavitation assisted extraction of protein is typically studied at a laboratory scale. This highlights limitations against the application at an industrial scale to obtain potential commercial gains. [ABSTRACT FROM AUTHOR]

• Reducing decreasing JPCR's area ratio, HC intensity can be effectively enhanced. • A greater area ratio in JPCRs extends the operating range with a higher limit ratio. • In disinfection and algae control field, JPCR has a broad application prospect. Hydrodynamic cavitation (HC) has emerged as a promising technology for water disinfection. Interestingly, when subjected to specific cavitation pressures, jet pump cavitation reactors (JPCRs) exhibit effective water treatment capabilities. This study investigated the cavitation flow and vorticty transport in a JPCR with various area ratios by utilizing computational fluid dynamics. The results reveal that cavitation is more likely to occur within the JPCR as the area ratio becomes smaller. While as the area ratio decreases, the limit flow ratio also decreases, leading to a reduced operational range for the JPCR. During the cavitation inception stage, only a few bubbles with limited travel distances are generated at the throat inlet. A stable cavitation layer developed between the throat and downstream wall during the limited cavitation stage. In this phase, the primary flow carried the bubbles towards the outlet. In addition, it was found that the vortex stretching, compression expansion, and baroclinic torque terms primarily influence the vorticity transport equation in this context. This work may provide a reference value to the design of JPCRs for water treatment. [ABSTRACT FROM AUTHOR]

Theproduction of palm oil-based submicron emulsions in the presenceof Tween 80 has been studied in a liquid whistle hydrodynamic cavitationreactor (LWHCR). Preliminary investigations have been carried outusing two orifice plates with the hole diameters of 0.0010 and 0.0016cm with an aim of investigating the efficiency of LWHCR in the oxidationof aqueous solution of potassium iodide (KI). Based on the preliminarystudies, the orifice plate with the smallest hole diameter was chosenfor the generation of submicron emulsions. The effect of operatingparameters of LWHCR such as the distance between the orifice plateand blade (0.5, 0.6, and 0.8 cm) and the inlet operating pressures(400, 600, and 800 psi) has been successfully investigated and optimized.It has been observed that the minimum droplet size of 476 nm witha PDI of 0.5 was achieved using an orifice plate–blade distanceof 0.6 cm and at an inlet operating pressure of 800 psi. Furthermore,the influence of the addition of a co-surfactant, Span 80, has alsobeen investigated, and it has been observed that this co-surfactantdid not have any impact on the final droplet size attained. Besides,the encapsulation efficiency of curcumin was found to be 88% usingthe optimum operating conditions of submicron emulsion generation.The stability studies show that the final droplet size for curcumin-loadedsubmicron emulsions was found to be 532 nm. The present work provedthat LWHCR is an efficient yet feasible tool for the generation ofsubmicron emulsion encapsulating curcumin as an active ingredient. [ABSTRACT FROM AUTHOR]

• Effects of CGU arrangement on ARHCR performance are studied by CFD. • The "simplified flow field" strategy was utilized. • Lower intersection angle and number of rows are benefit to performance. • Proper radial and circumferential offsets and radial spacing are advisable. • This work may provide a reference value to the design of ARHCRs. Hydrodynamic cavitation (HC) is widely considered a promising process intensification technology. The novel advanced rotational hydrodynamic cavitation reactors (ARHCRs), with considerably higher performance compared with traditional devices, have gained increasing attention of academic and industrial communities. The cavitation generation unit (CGU), located on the rotor and/or stator of an ARHCR, is utilized to generate cavitation and consequently, its geometrical structure is vital for the performance. The present work studied, for the first time, the effect of the arrangement of CGU on the performance of a representative ARHCR by employing computational fluid dynamics based on the "simplified flow field" strategy. The effect of CGU arrangement, which was neglected in the past, was evaluated: radial offset distance (c), intersection angle (ω), number of rows (N), circumferential offset angle (γ), and radial spacing (r). The results indicate that the CGU, with an arrangement of a low ω and moderate c , N , γ , and r , performed the highest cavitation efficiency. The corresponding reasons were analyzed by combining the flow field and cavitation pattern. Moreover, the results also exposed a weakness of the "simplified flow field" strategy which may induce the unfavorable "sidewall effect" and cause false high-pressure region. The findings of this work may provide a reference value to the design of ARHCRs. [ABSTRACT FROM AUTHOR]

• Reclamation of surface water using Advanced Oxidation Processes. • Hybrid Hydrodynamic Cavitation(HC) technique for lake water treatment. • Optimized operating parameters i.e. pH, inlet pressure, H 2 O 2 loading. • Achieved ∼64% removal of COD and BOD and ∼95% removal of microbes using hybrid HC + H 2 O 2 Technique. Water reclamation from lakes needs to be accomplished efficiently and affordably to ensure the availability of clean, disinfected water for society. Previous treatment techniques, such as coagulation, adsorption, photolysis, ultraviolet light, and ozonation, are not economically feasible on a large scale. This study investigated the effectiveness of standalone HC and hybrid HC + H 2 O 2 treatment techniques for treating lake water. The effect of pH (3 to 9), inlet pressure (4 to 6 bar), and H 2 O 2 loading (1 to 5 g/L) were examined. At pH = 3, inlet pressure of 5 bar and H 2 O 2 loadings of 3 g/L, maximum COD and BOD removal were achieved·H 2 O 2 was observed to significantly improve the performance of the HC when used as a chemical oxidant. In an optimal operating condition, a COD removal of 54.5 % and a BOD removal of 51.5 % using HC alone for 1 h is observed. HC combined with H 2 O 2 removed 64 % of both COD and BOD. The hybrid HC + H 2 O 2 treatment technique resulted in a nearly 100% removal of pathogens. The results of this study indicate that the HC-based technique is an effective method for removing contaminants and disinfection of the lake water. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new Eulerian-Lagrangian model is developed for hydrodynamic cavitation. • Characteristics of multiscale cavitation features and noise are well revealed. • High-frequency noise induced by dispersed cavitation bubbles is identified. We have employed the large eddy simulation (LES) approach to investigate the cavitation noise characteristics of an unsteady cavitating flow around a NACA66 (National Advisory Committee for Aeronautics) hydrofoil by employing an Eulerian-Lagrangian based multiscale cavitation model. A volume of fluid (VOF) method simulates the large cavity, whereas a Lagrangian discrete bubble model (DBM) tracks the small bubbles. Meanwhile, noise is determined using the Ffowcs Williams-Hawkings equation (FW-H). Eulerian-Lagrangian analysis has shown that, in comparison to VOF, it is more effective in revealing microscopic characteristics of unsteady cavitating flows, including microscale bubbles, that are unresolvable around the cloud cavity, and their impact on the flow field. It is also evident that its evolution of cavitation features on the hydrofoil is more consistent with the experimental observations. The frequency of the maximum sound pressure level corresponds to the frequency of the main cavity shedding for the noise characteristics. Using the Eulerian-Lagrangian method to predict the noise signal, results show that the cavitation noise, generated by discrete bubbles due to their collapse, is mainly composed of high-frequency signals. In addition, the frequency of cavitation noise induced by discrete microbubbles is around 10 kHz. A typical characteristic of cavitation noise, including two intense pulses during the collapsing of the cloud cavity, is described, as well as the mechanisms that underlie these phenomena. The findings of this work provide for a fundamental understanding of cavitation and serve as a valuable reference for the design and intensification of hydrodynamic cavitation reactors. [ABSTRACT FROM AUTHOR]

In the present research, hydrodynamic cavitation (HC) and zero-valent iron (ZVI) were used to generate sulfate radicals through sulfite activation as a new source of sulfate for the efficient degradation of Direct Red 83 (DR83). A systematic analysis was carried out to examine the effects of operational parameters, including the pH of the solution, the doses of ZVI and sulfite salts, and the composition of the mixed media. Based on the results, the degradation efficiency of HC/ZVI/sulfite is highly dependent upon the pH of the solution and the dosage of both ZVI and sulfite. Degradation efficiency decreased significantly with increasing solution pH due to a lower corrosion rate for ZVI at high pH. The corrosion rate of ZVI can be accelerated by releasing Fe2+ ions in an acid medium, reducing the concentration of radicals generated even though ZVI is solid/originally non-soluble in water. The degradation efficiency of the HC/ZVI/sulfite process (95.54 % + 2.87%) was found to be significantly higher under optimal conditions than either of the individual processes (<6% for ZVI and sulfite and 68.21±3.41% for HC). Based on the first-order kinetic model, the HC/ZVI/sulfite process has the highest degradation constant of 0.035±0.002 min−1. The contribution of radicals to the degradation of DR83 by the HC/ZVI/sulfite process was 78.92%, while the contribution of SO 4 •− and •OH radicals was 51.57% and 48.43%, respectively. In the presence of HCO 3 − and CO 3 2− ions, DR83 degradation is retarded, whereas SO 4 2− and Cl− ions promote degradation. To summarise, the HC/ZVI/sulfite treatment can be viewed as an innovative and promising method of treating recalcitrant textile wastewater. [ABSTRACT FROM AUTHOR]

Graphene is one of the highly explored nanomaterials due to its unique and extraordinary properties. In this study, by utilizing a hydrothermal reduction method, graphene oxide (GO) was successfully converted to reduced graphene oxide (RGO) without using any toxic reducing agents. Following this, with the use of ultrasonic cavitation, profoundly stable few layer thick RGO nanodispersion was generated without employing any stabilizers or surfactants. During ultrasonication, shockwaves from the collapse of bubbles cause a higher dispersing energy to the graphene nanosheets which surpass the forces of Van der Waal’s and π-π stacking and thus pave the way to form a stable aqueous nanodispersion of graphene. Ultrasonication systems with different power intensity have been employed to determine the optimum conditions for obtaining the most stable RGO dispersion. The optimised conditions of ultrasonic treatments led to the development of a very stable reduced graphene oxide (RGO) aqueous dispersion. The stability was observed for two years and was analyzed by using Zetasizer by measuring the particle size and zeta potential at regular intervals and found to have exceptional stability. The excellent stability at physiological pH promotes its utilization in nano drug delivery application as a carrier for Paclitaxel (Ptx), an anticancer drug. The in vitro cytotoxicity analysis of Ptx loaded RGO nanodispersion by MTT assay performed on the cell lines revealed the potential of the nanodispersion as a suitable drug carrier. Studies on normal lung cells, MRC-5 and nasopharyngeal cancer cells, HK-1 supported the biocompatibility of RGO-Ptx towards normal cell line. This investigation shows the potential of exceptionally stable RGO-Ptx nanodispersion in nano drug delivery applications. [ABSTRACT FROM AUTHOR]

Coupling multiple frequencies in ultrasonic systems is one of the highly desired area of research for sonochemists, as it is known for producing synergistic effects on various ultrasonic reactions. In this study, the characteristics of a hexagonal-shaped triple frequency ultrasonic reactor with the combination frequencies of 28, 40 and 70 kHz were studied. The results showed that uniform temperature increment was achieved throughout the reactor at all frequency combinations. On the other hand, sonochemiluminescence emission and degradation rate of Rhodamine B varies throughout different areas of the reactor, indicating the presence of acoustic ‘hot spots’ at certain areas of the reactor. Also, coupling dual and triple frequencies showed a decrease in the hydroxyl radical ( OH) production, suggesting probable wave cancelling effect in the system. The results can therefore be served as a guide to optimize the usage of a triple frequency ultrasonic reactor for future applications. [ABSTRACT FROM AUTHOR]

• Sonochemistry as an advanced oxidation process. • Mechanism of remediation/disinfection of microbial hazards in polluted water. • Types and comparison of sonochemical reactors for remediation. • Energy and economic aspects. • Challenges and recommendations for future studies. Water is one of the major sources that spread human diseases through contamination with bacteria and other pathogenic microorganisms. This review focuses on microbial hazards as they are often present in water and wastewater and cause various human diseases. Among the currently used disinfection methods, sonochemical reactors (SCRs) that produce free radicals combined with advanced oxidation processes (AOPs) have received significant attention from the scientific community. Also, this review discussed various types of cavitation reactors, such as acoustic cavitation reactors (ACRs) utilizing ultrasonic energy (UE), which had been widely employed, involving AOPs for treating contaminated waters. Besides ACRs, hydrodynamic cavitation reactors (HCRs) also effectively destroy and deactivate microorganisms to varying degrees. Cavitation is the fundamental phenomenon responsible for initiating many sonochemical reactions in liquids. Bacterial degradation occurs mainly due to the thinning of microbial membranes, local warming, and the generation of free radicals due to cavitation. Over the years, although extensive investigations have focused on the antimicrobial effects of UE (ultrasonic energy), the primary mechanism underlying the cavitation effects in the disinfection process, inactivation of microbes, and chemical reactions involved are still poorly understood. Therefore, studies under different conditions often lead to inconsistent results. This review investigates and compares other mechanisms and performances from greener and environmentally friendly sonochemical techniques to the remediation of microbial hazards associated with water and wastewater. Finally, the energy aspects, challenges, and recommendations for future perspectives have been provided. [ABSTRACT FROM AUTHOR]

[Display omitted] • The suitability of high-intensity ultrasound for the inactivation of enzymes in amla juice was investigated. • Inactivation rates as high as 90.72% and 73.18% for PPO and POD respectively were observed. • Optimized process included energy density of 1610 W cm−2 pulsed at 5 s on and 5 s off for 7 min 30 s. • The goodness of fit for approximation of responses was adequate (R2 > 0.90) The enzymatic browning induced in amla juice due to the high activity of polyphenol oxidase (PPO) and peroxidase (POD) is one of the critical issues faced by the industry. The present study assessed the suitability of non-thermal, high-intensity ultrasound (US) on the inactivation of PPO and POD in fresh Indian Gooseberry juice. Ultrasonic waves, using a 6 mm titanium alloy probe were irradiated in the juice at a maximum power of 455 W and frequency of 20 kHz. The subsequent effects on biochemical attributes were studied using response surface methodology. Inactivation rates of 90.72 % and 73.18 %, respectively, for PPO and POD enzymes, were observed at the highest US intensity and exposure time. Numerical optimisation using the three-factor, three-level Box-Behnken design suggested that an optimum process at 70 % (energy density: 1610 Wcm−2) pulsed at 5 s on and 5 s off for 7 min 30 s resulted in PPO and POD inactivation of the order of 76.42 % and 64.57 % respectively. At these experimental conditions, the optimized levels of biochemical attributes i.e., ascorbic acid (738.50 mg/100 mL), total phenols (17.10 mg/mL), DPPH antioxidant activity (58.47 %), tannins (7.11 µg/mL), colour change (Δ E = 9.04) and flavonoids (6.14 mg/mL) were achieved. The overall statistical models were significant for all the responses except for reducing sugars. Furthermore, the approximation equations for individual responses indicated that the goodness of fit was adequate (R 2 > 0.90). The results suggested that ultrasound is a suitable processing technique for amla juice stabilisation compared to thermal treatments that result in the loss of quality. [ABSTRACT FROM AUTHOR]

[Display omitted] • Acoustic wave induces microstreaming, bubble oscillation, microjetting, and shockwave. • Ultrasound assists in improving nanocellulose properties and production efficiency. • Effects of ultrasonic parameters on nanocellulose extraction and surface modification. • Barriers to ultrasound application and avenues for future developments. With rising consumer demand for natural products, a greener and cleaner technology, i.e., ultrasound-assisted extraction, has received immense attention given its effective and rapid isolation for nanocellulose compared to conventional methods. Nevertheless, the application of ultrasound on a commercial scale is limited due to the challenges associated with process optimization, high energy requirement, difficulty in equipment design and process scale-up, safety and regulatory issues. This review aims to narrow the research gap by placing the current research activities into perspectives and highlighting the diversified applications, significant roles, and potentials of ultrasound to ease future developments. In recent years, enhancements have been reported with ultrasound assistance, including a reduction in extraction duration, minimization of the reliance on harmful chemicals, and, most importantly, improved yield and properties of nanocellulose. An extensive review of the strengths and weaknesses of ultrasound-assisted treatments has also been considered. Essentially, the cavitation phenomena enhance the extraction efficiency through an increased mass transfer rate between the substrate and solvent due to the implosion of microbubbles. Optimization of process parameters such as ultrasonic intensity, duration, and frequency have indicated their significance for improved efficiency. [ABSTRACT FROM AUTHOR]

This investigation focuses on activated carbon (AC) adsorption and ultrasound (US) cavitation for polishing the palm oil mill effluent (POME). Both AC adsorption and US cavitation were investigated individually, in series and operating them in a combined way. The efficiency of above processes has been evaluated in terms of removal of chemical oxygen demand (COD) and total suspended solids (TSS). For the individual operation, the optimisation studies were carried out by using the following conditions: AC dosage (50–200 g/L); contact time (2, 4, 6 h); US power amplitude (50% and 80%) and US cavitation time (30–180 min). The optimisation studies utilising US power amplitude (50%) and cavitation time (15 min) followed by AC adsorption using minimum AC dosage (50 g/L) and contact time (30 min) resulted in ∼100% COD and 83.33% TSS removals which meets the discharge limits set by the Department of Environment (DoE), Malaysia. The hybrid operation was also studied by simultaneously employing AC adsorption and US cavitation and it was observed that an adsorption dosage of 50 g/L resulted into achieving 73.08% COD and 98.33% TSS removals within 15 min of US irradiation. With the possibility of continuous and feasible sonochemical reactors, this hybrid approach of US cavitation followed by AC adsorption could be an alternative processing technique for POME polishing. [ABSTRACT FROM AUTHOR]

Ethanol separation from binary ethanol–water mixture by utilizing “ultrasonic atomization” or ‘ultrasonic distillation’ has been investigated and inferred as a case of evaporation. It was assumed that the operation of ultrasonic transducer reveals itself as mechanical agitation where the ultrasonic energy is ultimately regarded as heat input into the separation unit. Thus the local deviations from non-equilibrium owing to the propagation of ultrasonic waves through the bulk liquid were excluded from consideration. The process is accompanied by an enlargement of total vapor–liquid interfacial area due to the generation of atomized mist droplets that are supposed to have the same composition as that of bulk liquid. It contradicts with the previous concept of ‘ultrasonic distillation’ where the mist droplets were characterized by a higher percentage of volatile (ethanol) fraction. Consequently, this study demonstrates that ethanol enrichment process reported earlier might still be assessed by assuming that initial mist droplets have the same composition as that of the bulk liquid mixture. Thus, either by ultrasonic distillation or by bubbling carrier gas through the bulk liquid or even blowing it over the surface of the liquid, the conversion of liquid into vapour phase occurs and could be interpreted as equivalent to evaporation phenomena. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrasound disrupted macroporous resins can be recycled for adsorption. • Mild sonication during adsorption strengthened the influence of surface diffusion. • Intensive ultrasound pretreatment weakened the contribution of surface diffusion. • Bubble dynamics and sonochemical reactions under sonication were calculated. • Relationships between mass transfer behavior and bubble properties were established. Ultrasound is efficient to enhance various mass transfer processes. This study demonstrates that both ultrasound pretreatment and ultrasonication during adsorption promote the physisorption of polyphenols. The time to reach the adsorption equilibrium was shortened by more than 90 % when the resin diameter deceased from 592 μm to 60.23 μm in the intensive ultrasound pretreatment. The mass transfer mechanism of adsorption under mild sonication differs from that of adoption with intensive ultrasound pretreatment. Mild sonication during adsorption strengthens the influence of surface diffusion of polyphenols on intraparticle diffusion. In contrast, severe disruption of resin particles due to intensive ultrasound pretreatment weakens the surface diffusivity of polyphenols and reduces the contribution of surface diffusion. Also, the physics and sonochemistry of cavitation under sonication environments were explored. Under intensive and mild ultrasound treatments, the calculated bubble numbers were approximately 18789 L-1 and 6312 L-1, respectively. Moreover, a relationship was established between adsorption capacity from mass transfer modeling and bubble properties including the bubble collapse pressure, bubble number, processing time, and processing scale. This bridge between mass transfer behavior and properties of bubbles provides guidance and new insight for the design and scale-up of the ultrasound-assisted adsorption. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrasound (US) is a powerful synthesis method for a multitude of nanobiomaterials. • US-synthesised nanobiomaterials display better properties and performance. • Top-down and bottom-up nanobiomaterials synthesis are evaluated. • Mechanisms involved in the synthesis process are discussed. • Main challenges of US-synthesised nanobiomaterials are addressed. Ultrasound (US) demonstrates remarkable potential in synthesising nanomaterials, particularly nanobiomaterials targeted towards biomedical applications. This review briefly introduces existing top-down and bottom-up approaches for nanomaterials synthesis and their corresponding synthesis mechanisms, followed by the expounding of US-driven nanomaterials synthesis. Subsequently, the pros and cons of sono-nanotechnology and its advances in the synthesis of nanobiomaterials are drawn based on recent works. US-synthesised nanobiomaterials have improved properties and performance over conventional synthesis methods and most essentially eliminate the need for harsh and expensive chemicals. The sonoproduction of different classes and types of nanobiomaterials such as metal and superparamagnetic nanoparticles (NPs), lipid- and carbohydrate-based NPs, protein microspheres, microgels and other nanocomposites are broadly categorised based on the physical and/or chemical effects induced by US. This review ends on a good note and recognises US-driven synthesis as a pragmatic solution to satisfy the growing demand for nanobiomaterials, nonetheless some technical challenges are highlighted. [ABSTRACT FROM AUTHOR]

This investigation explores the efficacy of employing ultrasonic cavitation and coupling it with advanced oxidation processes (hydrogen peroxide and Fenton's reagent) for reducing the levels of total ammonia nitrogen in fish pond water containing Tilapia fishes. Ultrasonic cavitation is a phenomenon where the formation, growth and collapse of vaporous bubbles occur in a liquid medium producing highly reactive free radicals. Ultrasonic probe system (20 kHz with 750 W and 1000 W) was used to induce cavitation. Besides, to intensify the process, ultrasonic cavitation was coupled with hydrogen peroxide and Fenton's reagent. Using SERA colour indicator test kits, the levels of ammonium, nitrite and carbonate hardness were measured. The results obtained from this study clearly show that the advanced oxidation processes are more efficient in reducing the ammonium and nitrite levels in fish pond water than using ultrasound alone. The pH and carbonate hardness levels were not affected significantly by ultrasonic cavitation. The optimal treatment time and ultrasound power to treat the water samples were also established. Energy efficiency and cost analysis of this treatment have also been presented, indicating that ultrasonic cavitation coupled with hydrogen peroxide appears to be a promising technique for reducing total ammonia nitrogen levels in the fish pond water. [Display omitted] • Ultrasonic cavitation with AOP efficiently treats fishpond wastewater. • Ultrasonic cavitation is highly energy-efficient and reduces operational cost. • Labour cost and operation downtime can be reduced as maintenance is not needed. • Ultrasonic probes can be switched on and off instantaneously to save time. • Does not use hazardous chemicals and thus safe for aquatic life and humans. [ABSTRACT FROM AUTHOR]

• Integration of ultrasound and liquid biphasic flotation for astaxanthin extraction. • Single-step cell disruptive extraction approach was carried out. • Optimization of various parameters for ultrasound-assisted liquid biphasic flotation. • Astaxanthin recovery of 83.73 ± 0.70% and partition coefficient of 157.83 ± 7.47. The purpose of this investigation is to evaluate the implementation of ultrasound-assisted liquid biphasic flotation (LBF) system for the recovery of natural astaxanthin from Haematococcus pluvialis microalgae. Various operating conditions of ultrasound-assisted LBF systems such as the position of ultrasound horn, mode of ultrasonication (pulse and continuous), amplitude of ultrasonication, air flowrate, duration of air flotation, and mass of H. pluvialis microalgae were evaluated. The effect of ultrasonication on the cellular morphology of microalgae was also assessed using microscopic analysis. Under the optimized operating conditions of UALBF, the maximum recovery yield, extraction efficiency, and partition coefficient of astaxanthin were 95.08 ± 3.02%, 99.74 ± 0.05%, and 185.09 ± 4.78, respectively. In addition, the successful scale-up operation of ultrasound-assisted LBF system verified the practicability of this integrated approach for an effective extraction of natural astaxanthin. [ABSTRACT FROM AUTHOR]