Sonochemical and hydrodynamic cavitation reactors for laccase/hydrogen peroxide cotton bleaching

The main goal of this work is to develop a novel and environmental-friendly technology for cotton bleaching with reduced processing costs. This work exploits a combined laccase–hydrogen peroxide process assisted by ultrasound. For this purpose, specific reactors were studied, namely ultrasonic power generator type K8 (850 kHz) and ultrasonic bath equipment Ultrasonic cleaner USC600TH (45 kHz). The optimal operating conditions for bleaching were chosen considering the highest levels of hydroxyl radical production and the lowest energy input. The capacity to produce hydroxyl radicals by hydrodynamic cavitation was also assessed in two homogenizers, EmulsiFlex®-C3 and APV-2000. Laccase nanoemulsions were produced by high pressure homogenization using BSA (bovine serum albumin) as emulsifier. The bleaching efficiency of these formulations was tested and the results showed higher whiteness values when compared to free laccase. The combination of laccase–hydrogen peroxide process with ultrasound energy produced higher whiteness levels than those obtained by conventional methods. The amount of hydrogen peroxide was reduced 50% as well as the energy consumption in terms of temperature (reduction of 40 °C) and operating time (reduction of 90 min).     

Degradation of nitrobenzene in aqueous solution by dual-pulse ultrasound enhanced electrochemical process

The present work reports a novel dual-pulse ultrasound enhanced electrochemical degradation (US-ECD) process that synchronizes alternatively ultrasound pulses and potential pulses to degrade nitrobenzene in aqueous solution with a high percentage degradation and low energy consumption. In comparison to the test results generated from the conventional US-ECD and original electrochemical degradation (ECD) process, the dual-pulse US-ECD process increased degradation percentages to nitrobenzene by 2% and 17%, respectively, while energy used in the pulse process was only about 46.5% of that was used in the conventional US-ECD process. Test results demonstrated a superior performance of the dual-pulse US-ECD process over those of other conventional ones. Impacts of pulse mode, initial pH value, cell voltage, supporting electrolyte concentration and ultrasonic power on the process performances were investigated. With operation conditions optimized in the study at pH = 3.0, cell voltage = 10 V, ultrasonic power = 48.84 W, electrolyte concentration = 0.1 M and an experiment running time of 30 min, the percentage degradation of nitrobenzene could reach 80% (US pulse time = 50 ms and ECD pulse time = 50 ms). This process provided a reliable and effective technical approach to degrade nitrobenzene in aqueous solution and significantly reduced energy consumption in comparison to the conventional US-ECD or original ECD treatment.     

Degradation of chlortetracycline in wastewater sludge by ultrasonication,Fenton oxidation,and ferro-sonication

Residual emerging contaminants in wastewater sludge remain an obstacle for its wide and safe applications such as landfilling and bio-fertilizer. In this study, the feasibility of individual ultrasonication (UlS) and Fenton oxidation (FO) and combined, Ferro-sonication processes (FO) on the degradation of chlortetracycline (CTC) in wastewater sludge was investigated. UlS parameters such as amplitude and sonication time were optimized by response surface methodology (RSM) for further optimization of FS process. Generation of highly reactive hydroxyl radicals in FO and FS processes were compared to evaluate the degradation efficiency of CTC. Increasing in the ratio of hydrogen peroxide and iron concentration showed increased CTC degradation in FO process; whereas in FS, an increase in iron concentration did not show any significant effect (p > 0.05) on CTC degradation in sludge. The estimated iron concentration in sludge (115 mg/kg) was enough to degrade CTC without the addition of external iron. The only adjustment of sludge pH to 3 was enough to generate in-situ hydroxyl radicals by utilizing iron which is already present in the sludge. This observation was further supported by hydroxyl radical estimation with adjustment of water pH to 3 and with and without the addition of iron. The optimum operating UlS conditions were found to be 60% amplitude for 106 min by using RSM. Compared to standalone UlS and FO at 1:1 ratio, FS showed 15% and 8% increased CTC degradation respectively. In addition, UlS of sludge increased estrogenic activity 1.5 times higher compared to FO. FS treated samples did not show any estrogenic activity.     

Intensification of degradation of methomyl (carbamate group pesticide) by using the combination of ultrasonic cavitation and process intensifying additives

In the present work, the degradation of methomyl has been carried out by using the ultrasound cavitation (US) and its combination with H₂O₂, Fenton and photo-Fenton process. The study of effect of operating pH and ultrasound power density has indicated that maximum extent of degradation of 28.57% could be obtained at the optimal pH of 2.5 and power density of 0.155 W/mL. Application of US in combination with H₂O₂, Fenton and photo-Fenton process has further accelerated the rate of degradation of methomyl with complete degradation of methomyl in 27 min, 18 min and 9 min respectively. Mineralization study has proved that a combination of US and photo-Fenton process is the most effective process with maximum extent of mineralization of 78.8%. Comparison of energy efficiency and cost effectiveness of various processes has indicated that the electrical cost of 79892.34 Rs./m³ for ultrasonic degradation of methomyl has drastically reduced to 2277.00 Rs./m³, 1518.00 Rs./m³ and 807.58 Rs./m³ by using US in combination with H₂O₂, Fenton and photo-Fenton process respectively. The cost analysis has also indicated that the combination of US and photo-Fenton process is the most energy efficient and cost effective process.     

Ultrasonically enhanced electrochemical oxidation of ibuprofen

A hybrid advanced oxidation process combining sonochemistry (US) and electrochemistry (EC) for the batch scale degradation of ibuprofen was developed. The performance of this hybrid reactor system was evaluated by quantifying on the degradation of ibuprofen under the variation in electrolytes, frequency, applied voltage, ultrasonic power density and temperature in aqueous solutions with a platinum electrode. Among the methods examined (US, EC and US/EC), the hybrid method US/EC resulted 89.32%, 81.85% and 88.7% degradations while using NaOH, H₂SO₄ and deionized water (DI), respectively, with a constant electrical voltages of 30 V, an ultrasound frequency of 1000 kHz, and a power density of 100 W L⁻¹ at 298 K in 1 h. The degradation was established to follow pseudo first order kinetics. In addition, energy consumption and energy efficiencies were also calculated. The probable mechanism for the anodic oxidation of ibuprofen at a platinum electrode was also postulated.     

Sonophotolytic diethyl phthalate (DEP) degradation with UVC or VUV irradiation

This study investigated the degradation of diethyl phthalate (DEP) by sonolytic, photolytic and sonophotolytic processes. Two types of UV lamps, UVC (254 nm) and VUV (185 nm + 254 nm), were combined with ultrasound (283 kHz). The pseudo-first order degradation rate constants were in the order of 10^?1–10^?3 min^?1 depending on the processes. The sonolytic DEP degradation rate increased with increasing applied power. Photolytic or sonophotolytic degradation of DEP when using a VUV lamp appeared to be effective because the photo ?? (UVC/VUV) resulted in a significantly faster degradation than the photo ? (UVC) processes due to the higher photon energy and higher hydroxyl radical generation by homolysis of water by VUV. Significant degradation and mineralization (TOC) of DEP were observed with the combined sonophotolytic processes. Moreover, synergistic effects of 1.68 and 1.23 were exhibited at DEP degradation of the sonophoto I and sonophoto II processes, respectively. This was attributed to the UV-induced dissociation of hydrogen peroxide (H₂O₂) generated by the application of US to hydroxyl radicals. Therefore, US in sonophotolytic processes can play an important role in enhancing DEP degradation. Moreover, the sonophoto ?? process is more effective on the mineralization and biodegradability of DEP.     

Effect of nitrate ions on the efficiency of sonophotochemical phenol degradation

A sonophotochemical oxidation process has been used for the treatment of an aqueous solution of phenol. The aim of this work is to evaluate the effect of nitrate ions on hydroxyl radical production and on phenol oxidation. It has been demonstrated that ultrasound can produce NOx (nitrate and nitrite), with a production rate of 2.2 μM min⁻¹. The photolysis of nitrate can significantly improve the hydroxyl radical production. The apparent rate constant for hydroxyl radical production increased from 0.0015 min⁻¹ to 0.0073 min⁻¹ while increasing initial nitrate concentration from 0 to 0.5 mM. The concentration of hydroxyl radical was directly proportional to the initial nitrate concentration. Using US/UV process, the apparent reaction rate constant of phenol degradation in the presence of nitrate reached 0.020 min⁻¹, which was relatively lower than the value obtained (0.027 min⁻¹) in the absence of nitrate. It appeared that, nitrate ions can inhibit the sonochemical degradation of organic compounds such as phenol.     

Degradation of imidacloprid using combined advanced oxidation processes based on hydrodynamic cavitation

The harmful effects of wastewaters containing pesticides or insecticides on human and aquatic life impart the need of effectively treating the wastewater streams containing these contaminants. In the present work, hydrodynamic cavitation reactors have been applied for the degradation of imidacloprid with process intensification studies based on different additives and combination with other similar processes. Effect of different operating parameters viz. concentration (20–60 ppm), pressure (1–8 bar), temperature (34 °C, 39 °C and 42 °C) and initial pH (2.5–8.3) has been investigated initially using orifice plate as cavitating device. It has been observed that 23.85% degradation of imidacloprid is obtained at optimized set of operating parameters. The efficacy of different process intensifying approaches based on the use of hydrogen peroxide (20–80 ppm), Fenton’s reagent (H₂O₂:FeSO₄ ratio as 1:1, 1:2, 2:1, 2:2, 4:1 and 4:2), advanced Fenton process (H₂O₂:Iron Powder ratio as 1:1, 2:1 and 4:1) and combination of Na₂S₂O₈ and FeSO₄ (FeSO₄:Na₂S₂O₈ ratio as 1:1, 1:2, 1:3 and 1:4) on the extent of degradation has been investigated. It was observed that near complete degradation of imidacloprid was achieved in all the cases at optimized values of process intensifying parameters. The time required for complete degradation of imidacloprid for approach based on hydrogen peroxide was 120 min where as for the Fenton and advance Fenton process, the required time was only 60 min. To check the effectiveness of hydrodynamic cavitation with different cavitating devices, few experiments were also performed with the help of slit venturi as a cavitating device at already optimized values of parameters. The present work has conclusively established that combined processes based on hydrodynamic cavitation can be effectively used for complete degradation of imidacloprid.     

Synergistic effects of combining ultrasound with the Fenton process in the degradation of Reactive Blue 19

The decoloration of reactive dye C.I. Reactive Blue 19 (RB 19) using combined ultrasound with the Fenton process has been investigated. The effect of varying the concentrations of hydrogen peroxide and iron sulfate, initial pH, ultrasonic power, initial dye concentration and dissolved gas on the decoloration and degradation efficiencies was measured. Calibration of the ultrasound systems was performed using calorimetric measurements and oxidative species monitoring using the Fricke dosimeter and degradations were carried out with a 20 kHz probe type transducer at 2, 4, 6 and 8 W cm⁻² of acoustic intensity at 15, 25, 50 and 75 mg L⁻¹ initial dye concentrations. First order rate kinetics was observed. It was found that while the degradation rate due to ultrasound alone was slow, sonication significantly accelerated the Fenton reaction. While the results were similar to those reported for other dyes, the effects occurred at lower concentrations. The rate and extent of decoloration of RB 19 increased with rising hydrogen peroxide concentration, ultrasonic powers and iron sulfate concentration but decreased with increasing dye concentration. An optimum pH value of pH = 3.5 was found. The rate of decoloration was higher when dissolved oxygen was present as compared with nitrogen and argon confirming the solution phase mechanism of the degradation.     

Degradation of ibuprofen by hydrodynamic cavitation: Reaction pathways and effect of operational parameters

Ibuprofen (IBP) is an anti-inflammatory drug whose residues can be found worldwide in natural water bodies resulting in harmful effects to aquatic species even at low concentrations. This paper deals with the degradation of IBP in water by hydrodynamic cavitation in a convergent–divergent nozzle. Over 60% of ibuprofen was degraded in 60 min with an electrical energy per order (E_EO) of 10.77 kWh m⁻³ at an initial concentration of 200 μg L⁻¹ and a relative inlet pressure p_in = 0.35 MPa. Five intermediates generated from different hydroxylation reactions were identified; the potential mechanisms of degradation were sketched and discussed. The reaction pathways recognized are in line with the relevant literature, both experimental and theoretical. By varying the pressure upstream the constriction, different degradation rates were observed. This effect was discussed according to a numerical simulation of the hydroxyl radical production identifying a clear correspondence between the maximum kinetic constant k_OH and the maximum calculated OH production. Furthermore, in the investigated experimental conditions, the pH parameter was found not to affect the extent of degradation; this peculiar feature agrees with a recently published kinetic insight and has been explained in the light of the intermediates of the different reaction pathways.     

SonoFenton degradation of an azo dye,Direct Red

The degradation of a reactive azo dye, Direct Red 81 (DR81), by Fenton process and in conjunction with sonolysis (SonoFenton) was studied. The synergistic effect of Fenton process and sonolysis enhanced the degradation of Direct Red 81 in aqueous solutions and the reaction followed the mechanism of hydroxyl radical (HO) oxidation. The influence of the initial substrate concentration, pH and catalyst loading on the rate of decolorisation were studied. The dye decolorisation followed apparent first order kinetics. The optimum conditions for decolorisation were pH = 3.0, [Fe²⁺] = 0.2 g/l, [H₂O₂] = 5.1 × 10⁻³ mol/l and ultrasonic frequency = 120 kHz, 60 W. These conditions yielded 99% decolorisation of DR81 within 75 min. The sonolytic degradation products of DR81 were identified using Electrospray Ionization-Mass Spectrometry (ESI-MS). The presence of CO₃²⁻, HCO₃⁻, Cl⁻, NO₃⁻, and SO₄²⁻ ions in the dye solution did not have a considerable effect on the decolorisation efficiency. This study demonstrates that Fenton and SonoFenton methods can effectively decolorize DR81 dye in waste water. The dye concentration used in this study is higher compared to earlier studies illustrating the effective mineralization by the SonoFenton process. The mechanism of dye degradation is also proposed.     

Novel approaches based on ultrasound for treatment of wastewater containing potassium ferrocyanide

Industrial wastewaters containing biorefractory compounds like cyanide offer significant environmental problems attributed to the fact that the conventional methods have limited effectiveness and hence developing efficient treatment approaches is an important requirement. The present work investigates the use of novel treatment approach of ultrasound (US) combined with advanced oxidation techniques for the degradation of potassium ferrocyanide (KFC) for the first time. An ultrasonic bath equipped with longitudinal horn (1 kW rated power and 25 kHz frequency) has been used. The effect of initial pH (2–9) on the progress of degradation has been investigated initially and subsequently using the optimized pH, effect of addition of hydrogen peroxide (ratio of KFC:H₂O₂ varied over the range of 1:0.5–1:5) and TiO₂ in the presence of H₂O₂ (1:1 ratio by weight of TiO₂) as process intensifying approach has been studied. Combination of ultrasonic irradiation with ozone (O₃) (100–400 mg/h) and ultraviolet irradiation (UV) has also been investigated. Use of combination of US with H₂O_2, H₂O₂ + TiO₂ and ozone resulted in extent of KFC degradation as 54.2%, 74.82% and 82.41% respectively. Combination of US with both UV and ozone was established to be the best approach yielding 92.47% degradation. The study also focused on establishing kinetic rate constants for all the treatment approaches which revealed that all the approaches followed first order kinetic mechanism with higher rate constants for the combination approaches. Overall, it has been conclusively established that ultrasound based combined treatment schemes are very effective for the treatment of KFC containing wastewaters.     

Sonocatalytic rapid degradation of Congo red dye from aqueous solution using magnetic Fe0/polyaniline nanofibers

Nano-sized magnetic Fe⁰/polyaniline (Fe⁰/PANI) nanofibers were used as an effective material for sonocatalytic degradation of organic anionic Congo red (CR) dye. Fe⁰/PANI_, was synthesized via reductive deposition of nano-Fe⁰ onto the PANI nanofibers at room temperature. Prepared catalyst was characterized using HR-TEM, FE-SEM, XRD, FTIR instruments. The efficacy of catalyst in removing CR was assessed colorimetrically using UV–visible spectroscopy under different experimental conditions such as % of Fe⁰ loading into the composite material, solution pH, initial concentration of dye, catalyst dosage, temperature and ultrasonic power. The optimum conditions for sonocatalytic degradation of CR were obtained at catalyst concentrations = 500 mg.L⁻¹, concentration of CR = 200 ppm, solution pH = neutral (7.0), temperature = 30 °C, % of Fe⁰ loading = 30% and 500 W ultrasonic power. The experimental results showed that ultrasonic process could remove 98% of Congo red within 30 min with higher Q_max value (Q_max = 446.4 at 25 °C). The rate of degradation of CR dye was much faster in this ultrasonic technique rather than conventional adsorption process. The degradation efficiency declined with the addition of common inorganic salts (NaCl, Na₂CO₃, Na₂SO₄ and Na₃PO₄). The rate of degradation suppressed more with increasing salt concentration. Kinetic and isotherm studies indicated that the degradation of CR provides pseudo-second order rate kinetic and Langmuir isotherm model compared to all other models tested. The excellent high degradation capacity of Fe⁰/PANI under ultrasonic irradiation can be explained on the basis of the formation of active hydroxyl radicals (OH) and subsequently a series of free radical reactions.     

Ultrasonic pilot-scale reactor for enzymatic bleaching of cotton fabrics

The potential of ultrasound-assisted technology has been demonstrated by several laboratory scale studies. However, their successful industrial scaling-up is still a challenge due to the limited pilot and commercial sonochemical reactors. In this work, a pilot reactor for laccase-hydrogen peroxide cotton bleaching assisted by ultrasound was scaled-up. For this purpose, an existing dyeing machine was transformed and adapted by including piezoelectric ultrasonic devices. Laboratory experiments demonstrated that both low frequency, high power (22 kHz, 2100 W) and high frequency, low power ultrasounds (850 kHz, 400 W) were required to achieve satisfactory results. Standard half (4 g/L H₂O₂ at 90 °C for 60 min) and optical (8 g/L H₂O₂ at 103 °C for 40 min) cotton bleaching processes were used as references. Two sequential stages were established for cotton bleaching: (1) laccase pretreatment assisted by high frequency ultrasound (850 kHz, 400 W) and (2) bleaching using high power ultrasound (22 kHz, 2100 W). When compared with conventional methods, combined laccase-hydrogen peroxide cotton bleaching with ultrasound energy improved the whitening effectiveness. Subsequently, less energy (temperature) and chemicals (hydrogen peroxide) were needed for cotton bleaching thus resulting in costs reduction. This technology allowed the combination of enzyme and hydrogen peroxide treatment in a continuous process. The developed pilot-scale reactor offers an enhancement of the cotton bleaching process with lower environmental impact as well as a better performance of further finishing operations.     

Degradation of phenol using a combination of ultrasonic and UV irradiations at pilot scale operation

In the present work, combination of ultraviolet (UV) irradiations (using 8 W UV tube) with ultrasonic (US) irradiations (rated power 1 kW and frequency of 25 kHz) has been investigated for the degradation of phenol at pilot scale of operation. Different modes of operation viz. UV alone, US alone, UV/US, UV/TiO₂ (photocatalysis), UV/H₂O₂, UV/NaCl, UV/US/TiO₂ (sonophotocatalysis) and H₂O₂ assisted sonophotocatalysis have been investigated with an objective of maximizing the extent of phenol degradation. Effect of presence of hydrogen peroxide and sodium chloride at a concentration of 10 g/l and TiO₂ over a range of 0.5–2.5 g/l has been investigated. It has been observed that 2.0 g/l of TiO₂ is the optimum concentration, beyond which a decrease in the extent of degradation is observed. Maximum extent of degradation of phenol was 37.75% for H₂O₂ assisted photosonocatalysis at pH of 2. The present work is first of its kind to report the use of combined ultrasonic and UV irradiations at pilot scale operation and obtained results should induce some degree of certainty in proposed industrial applications of sonochemical reactors for wastewater treatment.     

Alternate pulses of ultrasound and electricity enhanced electrochemical process for p-nitrophenol degradation

A novel alternated ultrasonic and electric pulse enhanced electrochemical process was developed and used for investigating its effectiveness on the degradation of p-nitrophenol (PNP) in an aqueous solution. The impacts of pulse mode, pH, cell voltage, supporting electrolyte concentration, ultrasonic power and the initial concentration of PNP on the performance of PNP degradation were evaluated. Possible pathway of PNP degradation in this system was proposed based on the intermediates identified by GC–MS. Experimental results showed that 94.1% of PNP could be removed at 2 h in the dual-pulse ultrasound enhanced electrochemical (dual-pulse US-EC) process at mild operating conditions (i.e., pulse mode of electrochemical pulse time (T_EC) = 50 ms and ultrasonic pulse time (T_US) = 100 ms, initial pH of 3.0, cell voltage of 10 V, Na₂SO₄ concentration of 0.05 M, ultrasonic powder of 48.8 W and initial concentration of PNP of 100 mg/L), compared with 89.0%, 58.9%, 2.4% in simultaneous ultrasound enhanced electrochemical (US-EC) process, pulsed electrochemical (EC) process and pulsed ultrasound (US), respectively. Moreover, energy used in the dual-pulse US-EC process was reduced by 50.4% as compared to the US-EC process. The degradation of PNP in the pulsed EC process, US-EC process and dual-pulse process followed pseudo-first-order kinetics. Therefore, the dual-pulse US-EC process was found to be a more effective technique for the degradation of PNP and would have a promising application in wastewater treatment.     

Removal of pharmaceuticals from wastewater by biological processes,hydrodynamic cavitation and UV treatment

To augment the removal of pharmaceuticals different conventional and alternative wastewater treatment processes and their combinations were investigated. We tested the efficiency of (1) two distinct laboratory scale biological processes: suspended activated sludge and attached-growth biomass, (2) a combined hydrodynamic cavitation–hydrogen peroxide process and (3) UV treatment. Five pharmaceuticals were chosen including ibuprofen, naproxen, ketoprofen, carbamazepine and diclofenac, and an active metabolite of the lipid regulating agent clofibric acid.Biological treatment efficiency was evaluated using lab-scale suspended activated sludge and moving bed biofilm flow-through reactors, which were operated under identical conditions in respect to hydraulic retention time, working volume, concentration of added pharmaceuticals and synthetic wastewater composition. The suspended activated sludge process showed poor and inconsistent removal of clofibric acid, carbamazepine and diclofenac, while ibuprofen, naproxen and ketoprofen yielded over 74% removal. Moving bed biofilm reactors were filled with two different types of carriers i.e. Kaldnes K1 and Mutag BioChip? and resulted in higher removal efficiencies for ibuprofen and diclofenac. Augmentation and consistency in the removal of diclofenac were observed in reactors using Mutag BioChip? carriers (85% ± 10%) compared to reactors using Kaldnes carriers and suspended activated sludge (74% ± 22% and 48% ± 19%, respectively). To enhance the removal of pharmaceuticals hydrodynamic cavitation with hydrogen peroxide process was evaluated and optimal conditions for removal were established regarding the duration of cavitation, amount of added hydrogen peroxide and initial pressure, all of which influence the efficiency of the process. Optimal parameters resulted in removal efficiencies between 3–70%. Coupling the attached-growth biomass biological treatment, hydrodynamic cavitation/hydrogen peroxide process and UV treatment resulted in removal efficiencies of >90% for clofibric acid and >98% for carbamazepine and diclofenac, while the remaining compounds were reduced to levels below the LOD. For ibuprofen, naproxen, ketoprofen and diclofenac the highest contribution to overall removal was attributed to biological treatment, for clofibric acid UV treatment was the most efficient, while for carbamazepine hydrodynamic cavitation/hydrogen peroxide process and UV treatment were equally efficient.     

Catalytic activity of copper (II) oxide prepared via ultrasound assisted Fenton-like reaction

Copper (II) oxide nanoparticles were synthesized in an ultrasound assisted Fenton-like aqueous reaction between copper (II) cations and hydrogen peroxide. The reactions were initiated with the degradation of hydrogen peroxide by ultrasound induced cavitations at 0 °C or 5 °C and subsequent generation of the OH radical. The radical was converted into hydroxide anion in Fenton-like reactions and copper hydroxides were readily converted to oxides without the need of post annealing or aging of the samples. The products were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer–Emmett–Teller (BET) surface area analysis. Catalytic activity of the nanoparticles for the hydrogen peroxide assisted degradation of polycyclic aromatic hydrocarbons in the dark was tested by UV–visible spectroscopy with methylene blue as the model compound. The rate of the reaction was first order, however the rate constants changed after the initial hour. Initial rate constants as high as 0.030 min⁻¹ were associated with the high values of surface area, i.e. 70 m²/g. Annealing of the products at 150 °C under vacuum resulted in the decrease of the catalytic activity, underlying the significance of the cavitation induced surface defects in the catalytic process.     

Ultrasonic assisted-Fenton-like degradation of nitrobenzene at neutral pH using nanosized oxides of Fe and Cu

Ultrasonic-assisted heterogeneous Fenton reaction was used for degradation of nitrobenzene (NB) at neutral pH conditions. Nano-sized oxides of α-Fe₂O₃ and CuO were prepared, characterized and tested in degradation of NB (10 mg L⁻¹) under sonication of 20 kHz at 25 °C. Complete degradation of NB was effected at pH 7 in presence of 10 mM H₂O₂ after 10 min of sonication in presence of α-Fe₂O₃ (1.0 g L⁻¹), (k = 0.58 min⁻¹) and after 25 min in case of CuO (k = 0.126 min⁻¹). α-Fe₂O₃ showed also effective degradation under the conditions of 0.1 g L⁻¹ oxide and 5.0 mM of H₂O₂, even though with a lower rate constant (0.346 min⁻¹). Sonication plays a major role in enhancing the production of hydroxyl radicals in presence of solid oxides. Hydroxyl radicals-degradation pathway is suggested and adopted to explain the differences noted in rate constants recorded on using different oxides.     

Sonoelectrochemical degradation of phenol in aqueous solutions

The sonoelectrochemical degradation of phenol in aqueous solutions with stainless steel electrodes and high-frequency ultrasound (850 kHz) was investigated. A 60% synergetic effect was obtained in the combined reaction system. High concentration of electrolyte (sodium sulfate) and a high electrical voltage are favorable conditions for the degradation of phenol. A nearly complete degradation of phenol was achieved with 4.26 g/L Na₂SO₄ and 30 V electrical voltages at 25 °C in 1 h. The degradation of phenol follows pseudo-first order kinetics. Considering costs and application, the energy efficiency of the reaction system with different reaction conditions was evaluated.