Sonoelectrochemical degradation of triclosan in water

The sonoelectrochemical degradation of triclosan in aqueous solutions with high-frequency ultrasound (850 kHz) and various electrodes was investigated. Diamond coated niobium electrode showed the best results and was used as standard electrode, leading to effective degradation and positive synergistic effect. The influence of different parameters on the degradation degree and energy efficiency were evaluated and favorable reaction conditions were found. It could be shown that 92% of triclosan (1 mg L⁻¹ aqueous solution) was degraded within 15 min, following pseudo-first order kinetics.     

A critical review on the sonochemical degradation of organic pollutants in urine,seawater, and mineral water

Substances such as pharmaceuticals, pesticides, dyes, synthetic and natural hormones, plasticizers, and industrial chemicals enter the environment daily. Many of them are a matter of growing concern worldwide. The use of ultrasound to eliminate these compounds arises as an interesting alternative for treating mineral water, seawater, and urine. Thereby, this work presents a systematic and critical review of the literature on the elimination of organic contaminants in these particular matrices, using ultrasound-based processes. The degradation efficiency of the sonochemical systems, the influence of the nature of the pollutant (volatile, hydrophobic, or hydrophilic character), matrix effects (enhancement or detrimental ability compared to pure water), and the role of the contaminant concentration were considered. The combinations of ultrasound with other degradation processes, to overcome the intrinsic limitations of the sonochemical process, were considered. Also, energy consumptions and energy costs associated with pollutants degradation in the target matrices were estimated. Moreover, the gaps that should be developed in future works, on the sonodegradation of organic contaminants in mineral water, seawater, and urine, were discussed.     

Sonochemical degradation of trimethoprim in water matrices: Effect of operating conditions,identification of transformation products and toxicity assessment

The sonochemical degradation of trimethoprim (TMP), a widely used antibiotic, in various water matrices was investigated. The effect of several parameters, such as initial TMP concentration (0.5–3 mg/L), actual power density (20–60 W/L), initial solution pH (3–10), inorganic ions, humic acid and water matrix on degradation kinetics was examined. The pseudo-first order degradation rate of TMP was found to increase with increasing power density and decreasing pH, water complexity (ultrapure water > bottled water > secondary wastewater) and initial TMP concentration.TMP degradation is accompanied by the formation of several transformation products (TPs) as evidenced by LC-QToF-MS analysis. Nine such TPs were successfully identified and their time-trend profiles during degradation were followed. An in silico toxicity evaluation was performed showing that several TPs could potentially be more toxic than the parent compound towards Daphnia magna, Pimephales promelas and Pseudokirchneriella subcapitata.     

Sonochemical degradation of chlorophenols in water

Sonochemical degradation of dilute aqueous solutions of 2-, 3- and 4-chlorophenol and pentachlorophenol has been investigated under air or argon atmosphere. The degradation follows first-order kinetics in the initial state with rates in the range 4.5-6.6 microM min-1 under air and 6.0-7.2 microM min-1 under argon at a concentration of 100 microM of chlorophenols. The rate of OH radical formation from water is 19.8 microM min-1 under argon and 14.7 microM min-1 under air in the same sonolysis conditions. The sonolysis of chlorophenols is effectively inhibited, but not completely, by the addition of t-BuOH, which is known to be an efficient OH radical scavenger in aqueous sonolysis. This suggests that the main degradation of chlorophenols proceeds via reaction with OH radicals; a thermal reaction also occurs, although its contribution is small. The addition of appropriate amounts of Fe(II) ions accelerates the degradation. This is probably due to the regeneration of OH radicals from hydrogen peroxide, which would be formed from recombination of OH radicals and which may contribute a little to the degradation. The ability to inhibit bacterial multiplication of pentachlorophenol decreases with ultrasonic irradiation.     

Sonochemical and sonocatalytic degradation of monolinuron in water

The degradation of the phenylurea monolinuron (MLN) by ultrasound irradiation alone and in the presence of TiO(2) was investigated in aqueous solution. The experiments were carried out at low and high frequency (20 and 800 kHz) in complete darkness. The degradation of MLN by ultrasounds occurred mainly by a radical pathway, as shown the inhibitory effect of adding tert-butanol and bicarbonate ions to scavenge hydroxyl radicals. However, CO(3)(-) radicals were formed with bicarbonate and reacted in turn with MLN. In this study, the degradation rate of MLN and the rate constant of H(2)O(2) formation were used to evaluate the oxidative sonochemical efficiency. It was shown that ultrasound efficiency was improved in the presence of nanoparticles of TiO(2) and SiO(2) only at 20 kHz. These particles provide nucleation sites for cavitation bubbles at their surface, leading to an increase in the number of bubbles when the liquid is irradiated by ultrasound, thereby enhancing sonochemical reaction yield. In the case of TiO(2), sonochemical efficiency was found to be greater than with SiO(2) for the same mass introduced. In addition to the increase in the number of cavitation bubbles, activated species may be formed at the TiO(2) surface that promote the formation of H(2)O(2) and the decomposition of MLN.     

Investigations in sono-enzymatic degradation of ibuprofen

The drug ibuprofen (IBP) appears frequently in the wastewater discharge from pharmaceutical industries. This paper reports studies in degradation of IBP employing hybrid technique of sono-enzymatic treatment. This paper also establishes synergy between individual mechanisms of enzyme and sonolysis for IBP degradation by identification of degradation intermediates, and Arrhenius & thermodynamic analysis of the experimental data. Positive synergy between sonolysis and enzyme treatment is attributed to formation of hydrophilic intermediates during degradation. These intermediates form due to hydroxylation and oxidation reactions induced by radicals formed during transient cavitation. Activation energy and enthalpy change in sono-enzymatic treatment are lower as compared to enzyme treatment, while frequency factor and entropy change are higher as compared to sonolysis. Degradation of IBP in sono-enzymatic treatment is revealed to be comparable with other hybrid techniques like photo-Fenton, sono-photocatalysis, and sono-Fenton.     

Ultrasonic degradation, mineralization and detoxification of diclofenac in water: Optimization of operating parameters

The 20 kHz ultrasound-induced degradation of non-steroidal, anti-inflammatory drug diclofenac (DCF) was investigated. Several operating conditions, such as power density (25–100 W/L), substrate concentration (2.5–80 mg/L), initial solution pH (3.5–11), liquid bulk temperature and the type of sparging gas (air, oxygen, argon), were tested concerning their effect on DCF degradation (as assessed measuring absorbance at 276 nm) and hydroxyl radicals generation (as assessed measuring H₂O₂ concentration). Sample mineralization (in terms of TOC and COD removal), aerobic biodegradability (as assessed by the BOD₅/COD ratio) and ecotoxicity to Daphnia magna and Artemia salina were followed too.DCF conversion is enhanced at increased applied power densities and liquid bulk temperatures, acidic conditions and in the presence of dissolved air or oxygen. The reaction rate increases with increasing DCF concentration in the range 2.5–5 mg/L but it remains constant in the range 40–80 mg/L, indicating different kinetic regimes (i.e. first and zero order, respectively). H₂O₂ production rates in pure water are higher than those in DCF solutions, implying that decomposition basically proceeds through hydroxyl radical reactions. Mineralization is a slow process as reaction by-products are more stable than DCF to total oxidation; nonetheless, they are also more readily biodegradable. Toxicity to D. magna increases during the early stages of the reaction and then decreases progressively upon degradation of reaction by-products; nevertheless, complete toxicity elimination cannot be achieved at the conditions in question. Neither the original nor the treated DCF samples are toxic to A. salina.     

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.     

Effects and mechanism of diclofenac degradation in aqueous solution by US/Zn0

A system of ultrasound radiation coupled with Zn⁰ was applied to degrade diclofenac. The effects of initial pH, dosage of Zn⁰ and ultrasound density were investigated. To further explore the mechanism of the microcosmic reaction, the fresh and used Zn⁰ powders were characterized by SEM, XRD and XPS. Radical scavengers were used to determine the oxidation performance of strong oxidizing free radicals on diclofenac, including hydroxyl radicals and superoxide radicals. The results showed that the optimum removal of diclofenac reached to over 85% at pH of 2.0 in 15 min, with Zn⁰ dosage of 0.1 g/L and ultrasound density of 0.6 W/cm³. TOC removal of 72.6% in 15 min and dechlorination efficiency of diclofenac reached 70% in 30 min. Characterization results showed that a ZnO membrane was generated on the surface of Zn particles after use. According to the mass spectrometry results, several possible pathways of diclofenac degradation were proposed, and most diclofenac was turned into micro-molecules or CO₂ finally. The synergistic effect of US/Zn⁰ in the reactions led to a proposed degradation mechanism in which zinc could directly attack the target contaminant diclofenac because of its good reducibility with the auxiliary functions of ultrasonic irradiation, mechanical shearing and free radical oxidation.     

Sonochemical degradation of ciprofloxacin and ibuprofen in the presence of matrix organic compounds

Ciprofloxacin (CIPRO) and ibuprofen (IBU), a hydrophilic and a hydrophobic compound, respectively, were degraded by ultrasound at the frequencies of 20 and 620 kHz in aqueous solution containing matrix organic compounds. Compared to in its absence, in the presence of terephthalate (TA), a commonly used OH scavenger, CIPRO degradation was inhibited by a factor of 40–1500 depending on the frequency and initial concentration. However, the degradation rates of IBU were only reduced between 30% and 80% with TA present compared to in its absence. Similar to TA, the presence of Suwannee River Fulvic Acid (SRFA) inhibited CIPRO degradation to a greater extent than that of IBU but overall inhibition by SRFA was dramatically less than by TA. Although both TA and SRFA inhibited the degradation of CIPRO and IBU, the mechanisms of inhibition are different. TA reacts with OH in bulk solution and our evidence also indicates that it accumulates on or interacts with cavitation bubbles. On the other hand, SRFA stays in bulk solution, quenching OH and/or associating with the target compounds.     

Ultrasound-assisted heterogeneous activation of persulfate by nano zero-valent iron (nZVI) for the propranolol degradation in water

This study investigated the degradation of propranolol (PRO), a beta (β)-blockers, by nano zero-valent iron (nZVI) activated persulfate (PS) under ultrasonic irradiation. Effects of several critical factors were evaluated, inclusive of PS concentration, nZVI dosage, ultrasound power, initial pH, common anions, and chelating agent on PRO degradation kinetics. Higher PS concentration, nZVI dosage and ultrasound power as well as acidic pH favored the PRO degradation. Conversely, anions and chelating agent took on the inhibitory effect towards PRO degradation to different extents. Furthermore, the variations of morphology and surface composition of nZVI before and after the reaction were characterized by TEM, XRD and XPS. Finally, on the basis of identified degradation intermediates by LC/MS/MS analysis, this work tentatively proposed the degradation pathways. These encouraging results suggest that US/nZVI/PS process is a promising strategy for the treatment of PRO-induced water pollutant.     

Sonochemical effect of flat sweep frequency and pulsed ultrasound (FSFP) treatment on stability of phenolic acids in a model system

To obtain greater knowledge on the stability of phenolic acids for the application of FSFP ultrasound technique in the extraction, the sonochemical effects of ultrasonic factors were investigated. The kinetic model and mechanism of degradation reaction were developed and identified by FT-IR and HPLC-ESIMS. The results showed that caffeic and sinapic acids were degraded under FSFP ultrasound treatment. The ultrasonic temperature, frequency, sweep range, sweep cycle, and pulse ratio were proved to be important factors in affecting the degradation rates of caffeic and sinapic acids. Relatively high temperature, frequency away from the resonance frequency, narrow sweep range, moderate sweep cycle, and relatively low or high pulse ratio were recommended to maintain high stability of caffeic and sinapic acids. The degradation kinetics of these two phenolic acids under FSFP ultrasound treatment were conformed to zeroth-order reaction at 10–50 °C. Moreover, FSFP ultrasound had a stronger sonochemical effect on sinapic acid than caffeic acid. The FT-IR and HPLC-ESIMS proved that decomposition and polymerization reactions occurred when caffeic and sinapic acids were subjected to FSFP ultrasound. Degradation products, such as the corresponding decarboxylation products and their dimers, were tentatively identified.     

Enhanced ultrasound-assisted degradation of methyl orange and metronidazole by rectorite-supported nanoscale zero-valent iron

In this study, the rectorite-supported nanoscale zero-valent iron (nZVI/R) was synthesized through a reduction method. X-ray diffraction analysis showed the existence of the nZVI in the nZVI/R composite and X-ray photoelectron spectroscopy analysis indicated that the nZVI particles were partly oxidized into iron oxide. Scanning electron microscopy analysis revealed that the nZVI particles were highly dispersed on the surface of the rectorite. The specific surface area of the nZVI/R composite is 21.43 m²/g, which was higher than that of rectorite (4.30 m²/g) and nZVI (17.97 m²/g). In the presence of ultrasound (US), the degradation of methyl orange and metronidazole by the nZVI/R composite was over 93% and 97% within 20 min, respectively, which is much higher than that by the rectorite and the nZVI. The degradation ratio of methyl orange and metronidazole by the nZVI/R composite under US was 1.7 and 1.8 times as high as that by the nZVI/R composite without US, respectively. The mechanism of the enhanced degradation of methyl orange and metronidazole under US irradiation was studied. These results indicate that the US/nZVI/R process has great potential application value for treatment of dye wastewater and medicine wastewater.     

超声波与电化学协同作用降解硝基苯溶液的实验研究

本文以硝基苯模拟废水为研究对象，探讨了超声波与电化学协同作用降解硝基苯的实验情况。考察了处理时间、处理温度、硝基苯初始浓度、pH值、电解电压等因素对硝基苯降解率的影响。实验结果表明：随着作用时间增加，硝基苯的降解率升高；温度高于40℃时，硝基苯的降解率随温度的升高而降低，低于40℃时，硝基苯的降解率随温度的升高而增大；硝基苯的降解率随电压的升高而增大；酸性条件有利于硝基苯的降解；硝基苯初始浓度越大降解率越高。     

Ultrasound-assisted electrochemical treatment for phenolic wastewater

With the rapid development of industry, especially the rapid rise of the chemical industry, the problem of water pollution is becoming more and more serious. Among them, the discharge of organic pollutants represented by phenolic substances has always been at the forefront. In this paper, ultrasound-assisted electrochemical treatment for phenolic wastewater is investigated. The effects of ultrasonic frequency, current, pH value and the amount of fly ash-loaded titanium TiO₂-Fe³⁺ particles on phenol removal from phenol-containing wastewater are investigated. The experimental results demonstrate that the removal rate of phenol in phenol-containing wastewater is the best when ultrasonic frequency is 45 kHz, power is 200 W, the current is 1.2 A, pH is 5 and the dosage of fly ash-loaded titanium TiO₂-Fe³⁺ particles is 3 g. In addition, microwave-assisted-Fenton reagent treatment for phenol wastewater is investigated. The effects of Fenton reagent dosage, initial pH value, microwave power density and radiation time on phenol degradation rate are investigated. The results show that microwave can accelerate the reaction rate, reduce the number of metal ions, save the process cost and reduce the difficulty of post-treatment. Finally, the research status of phenol wastewater treatment technology at the present stage is reviewed, and the future development direction is discussed.     

Sonochemical water splitting in the presence of powdered metal oxides

Kinetics of hydrogen formation was explored as a new chemical dosimeter allowing probing the sonochemical activity of argon-saturated water in the presence of micro- and nano-sized metal oxide particles exhibiting catalytic properties (ThO₂, ZrO₂, and TiO₂). It was shown that the conventional sonochemical dosimeter based on H₂O₂ formation is hardly applicable in such systems due to catalytic degradation of H₂O₂ at oxide surface. The study of H₂ generation revealed that at low-frequency ultrasound (20 kHz) the sonochemical water splitting is greatly improved for all studied metal oxides. The highest efficiency is observed for relatively large micrometric particles of ThO₂ which is assigned to ultrasonically-driven particle fragmentation accompanied by mechanochemical water molecule splitting. The nanosized metal oxides do not exhibit particle size reduction under ultrasonic treatment but nevertheless yield higher quantities of H₂. The enhancement of sonochemical water splitting in this case is most probably resulting from better bubble nucleation in heterogeneous systems. At high-frequency ultrasound (362 kHz), the effect of metal oxide particles results in a combination of nucleation and ultrasound attenuation. In contrast to 20 kHz, micrometric particles slowdown the sonolysis of water at 362 kHz due to stronger attenuation of ultrasonic waves while smaller particles show a relatively weak and various directional effects.     

Simultaneous hydrodynamic cavitation and glow plasma discharge for the degradation of metronidazole in drinking water

In this study, a novel hydrodynamic cavitation unit combined with a glow plasma discharge system (HC-GPD) was proposed for the degradation of pharmaceutical compounds in drinking water. Metronidazole (MNZ), a commonly used broad-spectrum antibiotic, was selected to demonstrate the potential of the proposed system. Cavitation bubbles generated by hydrodynamic cavitation (HC) can provide a pathway for charge conduction during glow plasma discharge (GPD). The synergistic effect between HC and GPD promotes the production of hydroxyl radicals, emission of UV light, and shock waves for MNZ degradation. Sonochemical dosimetry provided information on the enhanced formation of hydroxyl radicals during glow plasma discharge compared to hydrodynamic cavitation alone. Experimental results showed a MNZ degradation of 14% in 15 min for the HC alone (solution initially containing 300 × 10⁻⁶ mol L⁻¹ MNZ). In experiments with the HC-GPD system, MNZ degradation of 90% in 15 min was detected. No significant differences were observed in MNZ degradation in acidic and alkaline solutions. MNZ degradation was also studied in the presence of inorganic anions. Experimental results showed that the system is suitable for the treatment of solutions with conductivity up to 1500 × 10⁻⁶ S cm⁻¹. The results of sonochemical dosimetry showed the formation of oxidant species of 0.15 × 10⁻³ mol H₂O₂ L⁻¹ in the HC system after 15 min. For the HC-GPD system, the concentration of oxidant species after 15 min reached 13 × 10⁻³ mol H₂O₂ L⁻¹. Based on these results, the potential of combining HC and GPD systems for water treatment was demonstrated. The present work provided useful information on the synergistic effect between hydrodynamic cavitation and glow plasma discharge and their application for the degradation of antibiotics in drinking water.     

Effects of ultrasound on the beef structure and water distribution during curing through protein degradation and modification

The objective of this study was to explore the mechanisms of power ultrasound (PUS, 150 and 300 W) and treatment time (30 and 120 min) on the water-holding capacity (WHC) and tenderness of beef during curing. Beef muscle at 48 h post mortem was subjected to PUS treatment at a frequency of 20 kHz. Analysis of compression loss and shear force showed that PUS-assisted curing significantly increased the WHC and the tenderness of beef compared to static brining (p < 0.05). According to the analysis of LF-NMR, PUS treatment could increase the P₂₁ values which indicated an improvement in water-binding ability of beef muscle. SDS-PAGE and LC-ESI-MS/MS analysis suggested that PUS induced moderate oxidation of myosin causing polymerization, which may contribute to increased water retention. On the other hand, an increased tenderness of beef is suggested by the increased MFI values and proteolysis of desmin and troponin-T. Transmission electron microscopy (TEM) further supported the effects of PUS on WHC and tenderness changes due to the swelling and disruption of myofibrils. Thus, these results provide knowledge about the mechanism for improving WHC and tenderness of beef by PUS curing, which could be employed as an emerging technology for various meat curing processes.     

Mechanistic investigations in sono-hybrid (ultrasound/Fe2+/UVC) techniques of persulfate activation for degradation of Azorubine

Persulfate-based oxidation of recalcitrant pollutants has been investigated as an alternative to OH radical based advanced oxidation processes due to distinct merits such as greater stability and non-selective persistent reactivity of ${\text{SO}}_4^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}-}$ oxidant species. The present study has attempted to highlight mechanistic features of persulfate-based decolorization of textile dye (Azorubine) using sono-hybrid techniques of activation. Three activation techniques, viz. sonolysis, Fe²⁺ ions and UVC light and combinations thereof, have been examined. UVC is revealed to be the most efficient decolorization technique. The mechanism of sonolysis (i.e. thermal activation of persulfate in the bubble-bulk interfacial region) is revealed to be almost independent of the mechanism of UVC. Fe²⁺ activation is revealed to have an adverse interaction with UVC due to scavenging of sulfate radicals by Fe²⁺ ions. The best hybrid activation technique for persulfate-based degradation and mineralization of Azorubine is UVC + ultrasound. Due to independent mechanisms, degradation and mineralization of the dye obtained with simultaneous application of UVC and ultrasound is nearly equal to the sum of degradation and mineralization obtained using individual techniques.     

Potential uses of ultrasound in the biological decontamination of water

In the past there was a prevailing feeling in industry that power ultrasound would be too expensive to use for water treatment on an industrial scale. This was based on calculations involving the direct scale up of power consumption in small-scale (generally batch) laboratory experiments. In recent times this attitude has changed somewhat as a result of the installation of a number of ultrasonic devices in operational water or sewage treatment plants. In our laboratories we have investigated the decontamination of water under the influence of ultrasound alone and in conjunction with other treatments. The results, particularly when applied to flowing systems, indicate a real future for sonochemistry in water treatment.