Ultrasound Reactor Research Articles

Circulation process of methyl ester production from pretreated sludge palm oil using CaO/ABS catalytic static mixer coupled with an ultrasonic clamp

This study investigates the potential of fused deposition modeling (FDM) three-dimensional (3D) printing techniques for manufacturing catalytic static mixers during biodiesel synthesis. The printed catalytic mixing elements comprises acrylonitrile butadiene styrene (ABS) plastic with 15 wt% calcium oxide (CaO) as a solid catalyst. When the reactants flowed through the CaO/ABS mixing device, the blending and acceleration processes were both significantly impacted. Moreover, their characteristics, performance in biodiesel production, reusability, and economy were analyzed. The effects of methanol to oil (M:O) molar ratio, circulation time, and sonication time on methyl ester (ME) purity were also examined. The results showed that CaO crystals were distributed on the CaO/ABS mixer’s surface, which is crucial for catalytic purposes. During circulation process of ME from pretreated sludge palm oil (PSPO), catalytic static mixer (CSM) and CSM coupled with ultrasound (CSM/US) reactors were employed. The full ultrasonic power of CSM/US reactor of 16 × 400 W (total 6400 W) was operated at 20 kHz frequency. Moreover, the continuous and pulse ultrasonic modes of CSM/US reactor were compared to determine the ME purity and electricity consumption for ME production. For the CSM reactor, 12:1 M:O molar ratio and 8.5 h circulation time were recommended to realize 94.2 wt% ME purity. For the CSM/US reactor, 12:1 M:O molar ratio and 2.25 h circulation time were recommended to achieve 96.5 wt% ME purity. Under the pulsed mode operation, ME purity of 95.09 wt% was achieved, with a reduction in electricity consumption by approximately 37.6 % compared to continuous mode operation. Furthermore, the CaO/ABS catalytic static mixer was determined to be reusable for up to three cycles in both CSM and CSM/US reactors. Thus, CaO/ABS catalytic static mixers assure high purity ME production through FDM 3D printing technology with a CaO solid catalyst.

Cavitation-assisted synthesis and chracterization of a novel catalyst from waste coconut trunk biomass for biodiesel production

In the current study, a novel heterogeneous catalyst has been prepared from waste coconut trunk biomass using an ultrasound-assisted batch reactor. It is observed from the characterization studies that the raw coconut trunk biomass consists of the maximum amount of silicon dioxide (SiO2) present in it which is further converted to mullite (composition of 3Al2O3.2SiO2) with a composition of 94.18 % (analyzed through Energy Dispersive Spectroscopy (EDAX) studies) is formed through the reaction in an ultrasound reactor processed at a very mild reaction temperature and reaction time 80℃ and 90mins. Synthesis of catalyst at mild process conditions will help to enhance the formation of energy-intensive products at a low cost. It is also observed from the XRD studies of raw feedstock and synthesized catalyst a change in the crystalline structure from hexagonal silicon dioxide to orthorhombic mullite shape. In comparison with the surface area of the raw biomass and mullite, a large amount of surface area ∼ 32 m2/g is observed which is due to the process of reaction in a highly intense ultrasound reactor. A change in the morphological structure of raw feedstock and synthesized catalyst is also observed through scanning electron microscope (SEM) analysis. The activity of the synthesized catalyst has been analyzed through its application in the production of biodiesel from waste cooking oil is also studied., and a yield of 75 % with a conversion of 74 % is observed at process conditions of 1:3 (oil: ethanol) (volumetric ratio), 3 (wt%) of catalyst concentration and 3hrs of reaction time. A prospective aspect of the implication of the entire work to analyze the life cycle analysis (LCA) is also reported in terms of environmental friendliness and sustainability.

Characterization of the acoustic cavitation in ionic liquids in a horn-type ultrasound reactor

Most ultrasound-based processes root in empirical approaches. Because nearly all advances have been conducted in aqueous systems, there exists a paucity of information on sonoprocessing in other solvents, particularly ionic liquids (ILs). In this work, we modelled an ultrasonic horn-type sonoreactor and investigated the effects of ultrasound power, sonotrode immersion depth, and solvent’s thermodynamic properties on acoustic cavitation in nine imidazolium-based and three pyrrolidinium-based ILs. The model accounts for bubbles, acoustic impedance mismatch at interfaces, and treats the ILs as incompressible, Newtonian, and saturated with argon. Following a statistical analysis of the simulation results, we determined that viscosity and ultrasound input power are the most significant variables affecting the intensity of the acoustic pressure field (P), the volume of cavitation zones (V), and the magnitude of the maximum acoustic streaming surface velocity (u). V and u increase with the increase of ultrasound input power and the decrease in viscosity, whereas the magnitude of negative P decreases as ultrasound power and viscosity increase. Probe immersion depth positively correlates with V, but its impact on P and u is insignificant. 1-alkyl-3-methylimidazolium-based ILs yielded the largest V and the fastest acoustic jets – 0.77 cm3 and 24.4 m s−1 for 1-ethyl-3-methylimidazolium chloride at 60 W. 1-methyl-3-(3-sulfopropyl)-imidazolium-based ILs generated the smallest V and lowest u – 0.17 cm3 and 1.7 m s−1 for 1-methyl-3-(3-sulfopropyl)-imidazolium p-toluene sulfonate at 20 W. Sonochemiluminescence experiments validated the model.

Pilot scale degradation of Sulfamerazine using different venturi based hydrodynamic cavitation and ultrasound reactors in combination with oxidation processes

In the present investigation, a sulfonamide drug named Sulfamerazine was degraded using the 5 L pilot scale hydrodynamic cavitation equipped with three different venturis namely circular (HCCV), slit (HCSV), and dual-slit venturi (HCDSV) operating at 4 bar inlet pressure. The novel HCDSV was successfully designed and applied for the first time to improve the cavitational activities and a subsequent increased ˙OH radical generation. The SMZ degradation achieved using individual HCDSV was 41.54% in comparison to 27.69% and 21.54% for HCSV and HCCV respectively, clearly showing the benefits for intensification. The resistance coefficient (convergent and divergent sections of the venturi), number of passes, and cavitation number significantly influence the cavitational activities, and HCDSV was observed to be the most efficient design based on these parameters. A pilot scale US reactor (USR) was likewise used for the degradation of SMZ at a similar capacity. The combination of hydrodynamic and acoustic cavitation with H2O2, PS, PMS, Fenton and Fenton-like processes were successfully demonstrated on a pilot scale investigation. The combined approach of Fenton (Fe2+ at 0.75 mM and H2O2 at 0.7 mM) coupled with hydrodynamic or acoustic cavitation was the most proficient approach, with maximum SMZ degradation of 96.92% and 97.25% achieved for HCDSV/Fe2+/H2O2 and USR/Fe2+/H2O2 (at 22 +44 kHz), respectively. The estimated cost of treatment for HCDSV/Fe2+/H2O2 and USR/Fe2+/H2O2 (at 22 +44 kHz) approaches were 0.1780 and 0.4583 ₹/L respectively, establishing HCDSV/Fe2+/H2O2 as the most effective method in terms of SMZ degradation as well as cost of degradation.

Treatment of Winery Wastewater by Combined Almond Skin Coagulant and Sulfate Radicals: Assessment of HSO5- Activators.

The large production of wine and almonds leads to the generation of sub-products, such as winery wastewater (WW) and almond skin. WW is characterized by its high content of recalcitrant organic matter (biodegradability index < 0.30). Therefore, the aim of this work was to (1) apply the coagulation-flocculation-decantation (CFD) process with an organic coagulant based on almond skin extract (ASE), (2) treat the organic recalcitrant matter through sulfate radical advanced oxidation processes (SR-AOPs) and (3) evaluate the efficiency of combined CFD with UV-A, UV-C and ultrasound (US) reactors. The CFD process was applied with variation in the ASE concentration vs. pH, with results showing a chemical oxygen demand (COD) removal of 61.2% (0.5 g/L ASE, pH = 3.0). After CFD, the germination index (GI) of cucumber and corn seeds was ≥80%; thus, the sludge can be recycled as fertilizer. The SR-AOP initial conditions were achieved by the application of a Box-Behnken response surface methodology, which described the relationship between three independent variables (peroxymonosulfate (PMS) concentration, cobalt (Co2+) concentration and UV-A radiation intensity). Afterwards, the SR-AOPs were optimized by varying the pH, temperature, catalyst type and reagent addition manner. With the application of CFD as a pre-treatment followed by SR-AOP under optimal conditions (pH = 6.0, [PMS] = 5.88 mM, [Co2+] = 5 mM, T = 343 K, reaction time 240 min), the COD removal increased to 85.9, 82.6 and 80.2%, respectively, for UV-A, UV-C and US reactors. All treated wastewater met the Portuguese legislation for discharge in a municipal sewage network (COD ≤ 1000 mg O2/L). As a final remark, the combination of CFD with SR-AOPs is a sustainable, safe and clean strategy for WW treatment and subproduct valorization.

Dual frequency ultrasonic cavitation in various liquids: High-speed imaging and acoustic pressure measurements

Ultrasonic cavitation is used in various processes and applications, utilizing powerful shock waves and high-speed liquid jets generated by the collapsing bubbles. Typically, a single frequency source is used to produce the desired effects. However, optimization of the efficiency of ultrasound reactors is necessary to improve cavitation activity in specific applications such as for the exfoliation of two dimensional materials. This research takes the next step to investigate the effect of a dual frequency transducer system on the bubble dynamics, cavitation zone, pressure fields, acoustic spectra, and induced shock waves for four liquids with a range of physical properties. Using ultra-high-speed imaging and synchronized acoustic pressure measurements, the effect of ultrasonic dual frequencies on bubble dynamics was investigated. The addition of a high frequency transducer (1174 kHz) showed that the bubble fragments and satellite bubbles induced from a low frequency transducer (24 kHz) were able to extend their lifecycle and increase spatial distribution, thus, extending the boundaries of the cavitation zone. Furthermore, this combination of ultrasonic frequencies generated higher acoustic pressures (up to 180%) and enhanced the characteristic shock wave peak, indicating more bubble collapses and the generation of additional shock waves. The dual frequency system also enlarged the cavitation cloud size under the sonotrode. These observations specifically delineated the enhancement of cavitation activity using a dual frequency system pivotal for optimization of existing cavitation-based processing technologies.

Scaling up continuous ultrasound-assisted extractor for plant extracts by using spinach leaves as a test material

The ultrasound-assisted extraction (UAE) process of chlorophylls (a, b) and carotenoids in aqueous ethanol solutions from spinach leaves was upscaled from a batch laboratory reactor to a continuous modular flow-cell of pilot scale. The extraction in the laboratory scale was organized in a loop reactor, where pulp was circulated between a stirred vessel and the ultrasound reactor. The pilot scale extraction was made in a novel continuous tubular flow-cell reactor. The analysis of the experimental data proved that the ultrasound application provided a better extraction yield. In the laboratory scale, the application of ultrasound (24 kHz and 2500 W/L) showed the 2.6-fold higher maximum extraction yield compared to non-sonicated conventional solvent extraction. In the pilot scale, the effect was less significant (1.9-fold), due to smaller ultrasound power density (25 kHz and 1500 W/L). The scale-up of the UAE was based on equal extraction yield at both scales. The scale-up revealed that 2.5-fold higher volume-specific ultrasound power is required in the pilot scale to reach the yield obtained in the laboratory scale reactor.

Sonocatalytic degradation of amoxicillin from aquaculture effluent by zinc oxide nanoparticles

In this study, zinc oxide nanoparticles (nano-ZnO) was effectively synthesised by precipitation method to catalyse the ultrasound degradation of amoxicillin aquaculture effluent. The nanoparticles at different calcination temperatures were characterised by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, x-ray diffraction, and Brunauer, Emmett and Teller (BET) surface area determination. Characterisation results indicated that Zn existed as different compounds at different temperature, besides, pure zincite (ZnO) was obtained at 500 °C having a BET surface area of 8.39 m2/g. The degradation experiments indicated that the ultrasound/H2O2 system with nano-ZnO was more effective for amoxicillin degradation than they were independently. The ultrasound/H2O2 system with nano-ZnO could be described by the Langmuir-Hinshelwood kinetic model. The addition of H2O2 and nano-ZnO to the ultrasound reactor enhanced the degradation of amoxicillin from 46.87% up to 98.9%. The recyclability and stability of nano-ZnO also showed that the catalytic activity of nano-ZnO during ultrasound degradation of amoxicillin was not lost up to five cycles. Thus, the application of ultrasound in the presence of H2O2 and nano-ZnO is favorable and effective for the remediation of aquaculture effluent.

Acoustic Optimization of a Flow Through Ultrasonic Cavitation Reactor for Treatment of Cellulose Fibers

In pulp and paper manufacturing cellulose fibers are modified in various process steps to obtain an end product with certain specifications. In this chain of interlinked processes, the mechanical refining stage has a significant impact on modifying the properties of the fiber wall. However, refining is identified as the most energy intensive process in paper manufacturing and in order to reduce the energy use for a more sustainable process, the development of alternative refining methods are of increasing interest. Ultrasound cavitation has proved to be a efficient refining process but so far it is limited to small volumes and batch process’s. The developed ultrasonic reactor is capable of handling larger fiber volumes in a continuous, scalable, flow process. The proposed method could therefore be an alternative and efficient way of processing fibers to minimize energy usage and waste. In this study, both numerical simulations and experiments are combined and analysed to establish a design of a scalable, flow-through ultrasound reactor. The implemented model is based on the linearized wave equation in the frequency domain with appropriate addition of nonlinear attenuation by cavitation bubbles. The influence of ultrasound cavitation was experimentally verified by characterization of the modification of CTMP softwood cellulose fiber properties. Results shows that the proposed method using ultrasound cavitation can modify the fiber’s mechanical properties at energy levels of 804 kWh/bdt. However, there was no significant change in paper strength properties as per ISO 1924-3.

Full-Scale Assessment of Ultrasonic Sewage Sludge Pretreatment Using a Novel Double-Tube Reactor

The performance of a novel double-tube ultrasound (US) reactor for waste activated sludge (WAS) pretreatment was assessed at a full-scale wastewater treatment plant (WWTP). For high transferability...

Understanding the role of different operating modes and ultrasonic reactor configurations for improved sonocrystallization of lactose

The current work focuses on understanding the effect of different ultrasonic reactors on the recovery of lactose using crystallization. Three different scales of operations selected in the work include laboratory scale, medium scale and pilot scale based on the different reactor configurations. Ultrasonic bath (25 kHz) showed higher recovery of 90.3 ± 0.3 % for 20 min of sonication as compared to ultrasonic horn (20 kHz) with recovery of 88.8 ± 0.6 % with a standing time of 24 h in both the cases. Analysis of variance (ANOVA) demonstrated the significant dominance of all the factors studied on the response (recovery). The dual frequency ultrasound reactor (22 + 44 kHz) proved to be more efficient in delivering higher recovery values as compared to ultrasonic bath in the case of large scale systems with maximum recovery of 91.3 ± 0.9 %. The recovery of ethanol used as antisolvent was performed using distillation and the reusability of ethanol was studied. It was demonstrated that ethanol could be very well recycled, which is an important aspect at large scale operation. Overall, a systematic study helped in elucidating the role of ultrasonic parameters and reactor configuration in deciding an energy efficient and economical approach for maximum lactose recovery.

Effects of single- and tri-frequency ultrasound on self-assembly and characterizations of bionic dynamic rat stomach digestion of pepsin-soluble collagen from chicken leg skin

Chicken feet, aplenty by-products in the chicken industry, are rich in collagen and contain abundant amino acids so that it can be used as an important source for the collagen market. Pepsin-soluble collagen (PSC) was extracted from chicken leg skin and explored the effects of single- and tri-frequency ultrasound on the self-assembly and vitro digestion characteristics. By the diverging and tri-frequency ultrasound reactor, PSC was treated with 20 kHz/270w (C20H5m), 40 kHz/270w (C40H5m), 60 kHz/270w (C60H5m), 20/40/60 kHz/90w × 3 (CtH5m) for 5 min. Results showed that ultrasound could accelerate the process of collagen self-assembly, and 60 kHz/270w was the fastest. Microfiber diameters of C60H5m were 65–89 nm, which was significantly lower than the control without ultrasound (80–161 nm). The digestion results indicated polypeptides with relative molecular weights founded in the range 200–5000 Da were exceeded 85%. The final digested product had the highest content of oligopeptide, consistent rheological properties, and elastic behavior. The cavitation and mechanical of ultrasound have effects on the self-assembly process and collagen gel structure and digestion characteristics, which is of great significance for the development of the chicken industry and collagen market.

An Investigation on Improvements to Ultrasound Reactor Configuration for Extraction of Phytochemicals in Industrial Scale

Industrial attentiveness and demand for natural bioactive compounds are rising continuously, regarding their growing commercial values in nutrition, pharmaceuticals, cosmetics and many other industries. The progress in ultrasound technology has spread the use of ultrasonication on a broad field of application areas, including extraction of bio-materials from plant sources. Ultrasound-assisted extraction is a powerful alternative to conventional techniques, in terms of extracting bio-compounds from variable kinds of matrices, higher efficiency, reduced extraction time, toxic-free operation, lower energy demand, lesser water consumption and better extract quality. Existing research pointed out that the reactor configuration is vital for maximizing the efficacy of extraction process, however basic reactor configurations that were mainly used in the literature may not be feasibly adapted to full-scale industrial applications. In this study, an investigation on possible improvements and modifications to existing reactor designs are discussed, such as detecting the optimum frequency range of ultrasound transmission depending on the material rheology and composition, possible modifications in beam-forming by means of frequency modulation and finally transmitting the waves in combination of different frequencies.

Effects of ultrasonic reactor design on sewage sludge disintegration

The impact of ultrasound (US) reactor design on cavitation intensity distribution and disintegration efficiency was studied for sewage sludge pre-treatment, using a US flatbed reactor of variable reaction chamber height (RCH, 20–100 mm). Mapping of cavitation intensity and treatment effects was conducted using (i) hydrophone measurements, (ii) aluminum foil tests, and (iii) soluble chemical oxygen demand (COD) analyses. The overall disintegration efficiency was evaluated based on average COD solubilization. The impact of flow on treatment (in)homogeneity was additionally examined using computational fluid dynamics (CFD). Results of all measurement techniques suggest that small RCHs (20 mm, for instance) enable uniform and intense treatments, while large RCHs, which are subjected to strong sound wave attenuation, entail inhomogeneous treatments where large fractions of substrate are no longer exposed to notable cavitation activity. For instance, COD solubilization (relative to alkaline hydrolysis) measured in the channel center dropped from 6.4% to zero as RCH widened from 20 mm to 100 mm. Flow-through sonication further aggravates treatment inhomogeneity due to the high flow rates in the low-cavitation channel centers. Overall disintegration efficiency declined with increasing RCH, showing a drop in average COD solubilization by 73% from RCH = 20 mm to RCH = 100 mm. The drop correlated with average cavitation noise levels (R2 = 0.82), indicating that hydrophone measurements may be a suitable tool for US reactor design optimization. Overall, results suggest that reactor geometry has a critical impact on both treatment (in)homogeneity and treatment efficiency and that equal specific energy inputs do not imply equal US treatments.

Low-frequency Ultrasound with Short Application Time Improves Cellulase Activity and Reducing Sugars Release.

In this study, we investigated the effect of ultrasound (US) on the activity of commercial cellulase (Celluclast® 1.5 L) in the absence and in the presence of a cellulosic substrate (Avicel®, 2% w.v-1) using a central composite rotatable design. Sonication time (10 to 330 s), US intensity (120.6 to 263.7 W cm-2), and reaction temperature (25 to 50 °C) were varied using a horn-type ultrasound reactor, and endoglucanase (CMCase) and total cellulase (FPase) activities were determined. US intensity had a positive effect on enzyme activity. Under optimal conditions (170 s, 180.8 W cm-2, and 25 °C), CMCase activity was 13% higher than that of the control. In the presence of substrate, CMCase activity increased by 33.87% and KM reduced by 23% in relation to that of the control. The theoretical yield of cellulose was 42.08%. Cellulase activity can be improved by US treatment to maximize productivity gains and reduce costs in second-generation ethanol production, by the action of a low-frequency ultrasound with a short ultrasonication time of application.

Comparison of two different ultrasound reactors for the treatment of cellulose fibers.

The pulp and paper industry is in continuous need for energy-efficient production processes. In the refining process of mechanical pulp, fibrillation is one of the essential unit operations that count for up to 80% of the total energy use. This initial study explores the potential and development of new type of scalable ultrasound reactor for energy efficient mechanical pulping. The developed reactor is of continuous flow type and based on both hydrodynamic and acoustic cavitation in order to modify the mechanical properties of cellulose fibers. A comparison of the prototype tube reactor is made with a batch reactor type where the ultrasonic horn is inserted in the fluid. The pulp samples were sonicated by high-intensity ultrasound, using tuned sonotrodes enhancing the sound pressure and cavitation intensity by a controlled resonance in the contained fluid. The resonant frequency of the batch reactor is 20.8 kHz and for the tube reactor it is 22.8 kHz. The power conversion efficiency for the beaker setup is 25% and 36% in case of the tube reactor in stationary mode. The objective is to verify the benefit of resonance enhanced cavitation intensity when avoiding the effect of Bjerkenes forces. The setup used enables to keep the fibers in the pressure antinodes of the contained fluid. In case of the continuous flow reactor the effect of hydrodynamic cavitation is also induced. The intensity of the ultrasound in both reactors was found to be high enough to produce cavitation in the fluid suspension to enhance the fiber wall treatment. Results show that the mechanical properties of the fibers were changed by the sonification in all tests. The continuous flow type was approximately 50% more efficient than the beaker. The effect of keeping fibers in the antinode of the resonant mode shape of the irradiation frequency was also significant. The effect on fiber properties for the tested mass fraction was determined by a low-intensity ultrasound pulse-echo based measurement method, and by a standard pulp analyzer.

Impact of ultrasound-induced cavitation on the fluid dynamics of water and sewage sludge in ultrasonic flatbed reactors

The fluid dynamics of water, thickened waste activated sludge (WAS, total solids concentration 4.4%) and digested sludge (DS, total solids concentration 2.5%) within a lab-scale ultrasonic flatbed reactor were experimentally investigated. For a visual observation of the opaque sludge flow, sewage sludges were approximated by transparent xanthan solutions with identical flow behavior. The visualization of the flow was realized by use of an ultrasonic reactor with a transparent panel and dye streams injected into the flow. Without ultrasonic treatment, xanthan solutions showed distinct laminar flow behavior (generalized Reynolds numbers < 1), at a flow rate of 100 L/h. In water, dye streams remained coherent as well, but with slightly unsteady features (Reynolds number ∼ 350). Activation of the ultrasound reactor caused strong fluid dynamic disturbance in the water flow and dye streams were dissolved instantly, thus indicating turbulent mixing. For the xanthan solutions, however, mixing was considerably less pronounced. The dye streams in the DS substitute (0.5% xanthan solution) remained overall in laminar shape, but exhibited an eruption-like branching and an increase in diameter with advancing treatment duration. For the solution resembling WAS (2.0% xanthan solution), only weak dye stream disruption was observed, thus indicating that WAS flow in flatbed reactors is nearly laminar during ultrasonic treatment.

Combined hydrodynamic cavitation based processes as an efficient treatment option for real industrial effluent

In the present work, hydrodynamic cavitation (HC) operated alone and in combination with chemical oxidants has been applied for the treatment of real industrial effluent obtained from a local industry. Initially, the analysis of literature related to the hybrid methods involving hydrodynamic cavitation has been presented along with recommendations for the selection of important operating conditions for the HC operated individually and in combination with oxidation processes based on hydrogen peroxide (H2O2), ozone (O3) and persulphate (KPS). Subsequently, the treatment of real industrial effluent has also been investigated in details using HC alone and in combined mode with other oxidation processes focusing on the main objective of COD reduction. The reduction in the COD achieved using individual treatment of HC under the optimized conditions of inlet pressure as 4 bar and pH as 4 was only 7.9%. The application of different hybrid approaches based on HC such as HC + H2O2, HC + O3, HC + KPS and HC + H2O2 + O3 established higher COD reduction as compared to only HC. The maximum extent of COD reduction as 60.8% was achieved using HC + H2O2 + O3 combination whereas, relatively lower extent of COD was achieved for operations of HC + H2O2, HC + O3 and HC + KPS with the actual COD reduction being 40.3%, 38.7% and 8.5% respectively. It was also observed that 30.4%, 28.2%, 15.6%, and 4.7% of TOC reduction was obtained for the combined process of HC + H2O2 + O3, HC + H2O2, HC + O3, and HC + KPS respectively. Based on the kinetic study, it was established that the degradation fitted the first order kinetics for all the approaches. The combined processes of HC with oxidants were also compared with ultrasound reactors (both individual and combined operation) in terms of COD reduction, cavitational yield calculations, and treatment cost. HC reactors were established to be more energy efficient and also yielded treatment costs significantly lower than ultrasonic reactors.

Impact of sound attenuation on ultrasound-driven yield improvements during olive oil extraction

High frequency ultrasound can enhance olive oil extractability industrially. However, the ultrasound attenuation phenomena and their implications on extractability, are not well understood. This work aims at evaluating the ultrasound attenuation effects on the oil extraction efficiency, while providing deeper insights into the physics behind the ultrasound extraction in a heterogeneous medium. Olives were collected and processed both in Italy and Uruguay during their respective harvest seasons. Sound pressure distribution was characterized in a high frequency ultrasound reactor, carrying 3 kg of water or paste, by using an indirect contact hydrophone device at 0.4 MHz or 2 MHz. A through-transmission ultrasonic technique was applied to determine attenuation profiles and coefficients in paste at the central frequency of each transducer, with various paste to water ratios and reactor sizes. Other ultrasound improvements on extractability were evaluated including reduction of malaxation time (10, 30 min), sonication time (2.5, 5 min) and power level (174, 280 W) without water addition and in a reactor with a 14.5 cm transducer to wall distance. However, no sound pressure levels in paste were detectable beyond 9 cm from the transducer at both frequencies. Among the various effects evaluated, an emission frequency of 0.4 MHz better improved extractability compared to 2 MHz. The attenuation profiles corroborated these findings with attenuation coefficients of 3.9 and 5.3 dB/cm measured near the respective frequencies. Improvements in oil extractability due to increasing sonication time and power level were significant (p < 0.05) also when sonicating beyond 14.5 cm and without water addition. Oil extractability improvements were observed even when sound pressure was undetectable beyond 9 cm from the transducer, suggesting that the standing wave oil trapping effect is not the governing mechanism for separation in high attenuation media for large scale systems.

Benzophenone-3 ultrasound degradation in a multifrequency reactor: Response surface methodology approach

Response Surface Methodology was used for optimizing operating variables for a multi-frequency ultrasound reactor using BP-3 as a model compound. The response variable was the Triclosan degradation percent after 10 sonication min. Frequency at levels from 574, 856 and 1134 kHz were used. Power density, pulse time (PT), silent time (ST) and PT/ST ratio effects were also analyzed. 22 and 23 experimental designs were used for screening purposes and a central composite design was used for optimization. An optimum value of 79.2% was obtained for a frequency of 574 kHz, a power density of 200 W/L, and a PT/ST ratio of 10. Significant variables were frequency and power level, the first having an optimum value after which degradation decreases while power density level had a strong positive effect on the whole operational range. PT, ST, and PT/ST ratio were not significant variables although it was shown that pulsed mode ultrasound has better degradation rates than continuous mode ultrasound; the effect less significant at higher power levels.