Aqueous sonolytic decomposition of polycyclic aromatic hydrocarbons in the presence of additional dissolved species

Degradation studies of bisphenol S by ultrasound activated persulfate in aqueous medium

The degradation of recalcitrant organic pollutants by sulphate radical (SO4•-) represents one of the most recent developments in oxidation-based water treatment. In most cases, persulfate (PS) acts as a precursor of sulphate radicals. This study employed ultrasound-activated PS to generate reactive species, facilitating the degradation of bisphenol S (BPS), a well-known contaminant of emerging concern (CECs). An ultrasound with a frequency of 620 kHz and 80 W power was utilised for the degradation studies. The applied oxidation system successfully resulted in the complete degradation of BPS in both pure and real environmental water samples. Additionally, the Chemical oxygen demand (COD) was reduced to an acceptable limit in both matrices, with a reduction of 85 % in pure water and 73 % in river water. The degradation was monitored by varying chemical parameters such as pH, inorganic ions, and organics concentration. The results indicate that under specific pH conditions, the degradation efficiency followed the order of pH 3 > 4 > 7 > 11. The presence of coexisting matrices suppressed the efficiency by scavenging the reactive species. Utilizing high-resolution mass spectrometry (HRMS) analysis, this study identified seven intermediate products during identified during the degradation of BPS. Furthermore, a comprehensive mechanism has been deduced for the transformation and degradation process. All the results presented in this study underscore the applicability of the US/PS system in the removal of CECs.

Effect of single and multilayered Ti3C2TX MXene as a catalyst and adsorbent on enhanced sonodegradation of diclofenac and verapamil

Single and multilayered Ti₃C₂T_X MXene (referred to as SLM and MLM in this study, respectively) was applied as catalysts in the ultrasonic (US) process to treat selected pharmaceutical compounds including diclofenac and verapamil (VRP). Due to solid surface, elemental composition, and functional groups of Ti₃C₂T_X MXene, the free OH• production was increased by 48.8% for the US treatment with SLM and 59.8% for the US treatment with MLM compared with the US-only treatment. Additionally, adsorption affected the performance during the US treatment in the presence of the catalyst. Thus, the US treatment in the presence of Ti₃C₂T_X MXene had an enhanced performance not only because of increased oxidation but also because of adsorption, particularly between positively charged VRP and negatively charged Ti₃C₂T_X MXene. Moreover, although the degradation of the performance was higher for SLM (85.1%) than for MLM (81.8%), by improving the dispersion and reducing the size via sonication, the US treatment in the presence of MLM showed the highest synergy effect. In other words, the US treatment in the presence of MLM showed higher performance than the simple sum of oxidation and adsorption. These findings confirm that the US treatment in the presence of MLM may be a promising technology to treat various pharmaceuticals as a more degradable, strongly reusable, and less toxic process.

Synergistic, aqueous PAH degradation by ultrasonically-activated persulfate depends on bulk temperature and physicochemical parameters

Coupling ultrasound with other remediation technologies has potential to result in synergistic degradation of contaminants. In this work, we evaluated synergisms from adding high-power ultrasound (20 kHz; 250 W) to activated persulfate over a range of bulk temperatures (20-60 °C). We studied the aqueous degradation kinetics of three polycyclic aromatic hydrocarbons (PAHs: naphthalene, phenanthrene, and fluoranthene) treated by ultrasound-alone, heat-activated persulfate, and combined ultrasonically-activated persulfate (US-PS). At 20 °C, observed US-PS rate constants strongly correlated with Wilke-Chang diffusion coefficients. This correlation indicates PAH molecules diffuse to the bubble-water interface prior to reaction with sulfate radicals (SO₄^-) generated at the interface. At higher temperatures, observed US-PS rate constants appear to be a more complicated function of temperature and diffusion coefficients. Synergy indexes for PAHs with fast diffusion coefficients were greatest at 20 °C. Fluoranthene, the largest and most hydrophobic PAH, had a maximum synergy index at 30 °C; it benefited from additional thermal persulfate activation in bulk solution. Fluoranthene synergy indexes, however, decreased above 30 °C and became antagonistic at 60 °C. Electron paramagnetic resonance (EPR) spin trapping was used to quantify hydroxyl radical (OH) produced from acoustic cavitation in the absence of persulfate. These data showed consistent OH production from 20 to 60 °C, indicating PAH antagonisms at 60 °C were not due to lower bubble collapse temperatures. Instead, the results suggest that PAH antagonisms are caused by increased radical-radical recombination as bulk temperature increases. In effort to develop an efficient, combined remediation technology, this work suggests bulk temperatures between 20 and 40 °C maximize US-PS synergisms.

The direct synthesis of hydrogen peroxide using a combination of a hydrophobic solvent and water

The use of a hydrophobic solvent in combination with water leads to significant suppression of H₂O₂ degradation pathways over a AuPd/C catalyst.

Optimization of ciprofloxacin degradation in wastewater by homogeneous sono-Fenton process at high frequency

Emerging pollutants such as pharmaceuticals have been focusing international attention for a few decades. Ciprofloxacin (CIP) is a common drug that is widely found in hospital and wastewater treatment plants effluents, as well as in rivers. In this work, the feasibility of CIP degradation by ultrasound process at high frequency is discussed and sonolysis, sonolysis with hydrogen peroxide and sono-Fenton are evaluated. The amounts of hydrogen peroxide and ferrous ions (Fe²⁺) needed were optimized using response surface methodology. Best results were obtained with the sono-Fenton process resulting in a total pharmaceutical degradation within 15 min and a mineralization greater than 60% after 1 h. Optimal conditions were tested on a real matrix from a municipal wastewater treatment plant. Even if the degradation of the pollutants by sono-Fenton was hampered, the removal efficiency of both CIP and total organic carbon (TOC) is interesting as an increase in the biodegradability of the wastewater is found. These results show that sono-Fenton oxidation can be a promising pretreatment process for pharmaceutical-containing wastewaters.

Removal of polycyclic aromatic hydrocarbons (PAHs) from textile dyeing sludge by ultrasound combined zero-valent iron/EDTA/Air system

This paper proposes a combined ultrasound (US) and zero-valent iron/EDTA/Air (ZEA) system to remove polycyclic aromatic hydrocarbons (PAHs) from textile dyeing sludge. The removal efficiencies of 16 PAHs using ZEA, US/Air (air injected into the US process), and US/ZEA treatments were investigated, together with the effects of various operating parameters. The enhanced mechanisms of US and the role of reactive oxygen species (ROS) in removing PAHs in the US/ZEA system were explored. Results showed that only 42.5% and 32.9% of ∑16 PAHs were removed by ZEA and US/Air treatments respectively, whereas 70.1% were removed by US/ZEA treatment, (with favorable operating conditions of 2.0 mM EDTA, 15 g/L ZVI, and 1.08 w/cm³ ultrasonic density). The US/ZEA system could be used with a wide pH range. US led to synergistic improvement of PAHs removal in the ZEA system by enhancing sludge disintegration to release PAHs and promoting ZVI corrosion and oxygen activation. In the US/ZEA system, PAHs could be degraded by ROS (namely OH, O₂^-/HO₂, and Fe(IV)) and adsorbed by ZVI, during which the ROS made the predominant contribution. This study provides important insights into the application of a US/ZEA system to remove PAHs from sludge.

Ultrasonic Destruction of Acid Orange 7: Effect of Humic Acid, Surfactants and Complex Matrices

  The ultrasonic degradation at 600 kHz of an azo dye, acid orange 7 (AO7), in the presence of various dissolved natural organic matters (humic acid and surfactants) and in environmentally relevant matrices (natural water and seawater) was investigated. Additionally, the dependence of AO7 degradation on several operating parameters was clarified. The obtained results showed that ultrasound completely destroyed AO7 in 90 min of treatment but only 10% of TOC was removed after a long irradiation time. Investigations using the radical scavengers tert-butyl alcohol and KI revealed that AO7 degradation proceeds through radical reactions occurring at the bubble-liquid interface. AO7 conversion was strongly affected by the operating conditions. While the degradation of the dye was not affected by the presence of humic acid, it was impacted negatively by the presence of surfactants. Replacing deionized water by natural water and seawater as real environmental matrices did not affect the degradation of the dye.

Sonochemical degradation of Coomassie Brilliant Blue: effect of frequency, power density, pH and various additives

Coomassie Brilliant Blue (CBB), discharged mainly from textile industries, is an identified water pollutant. Ultrasound initiated degradation of organic pollutants is one among the promising techniques and forms part of the Advanced Oxidation Processes (AOPs). Ultrasonic degradation of CBB under different experimental conditions has been investigated in the present work. The effect of frequency (200 kHz, 350 kHz, 620 kHz and 1 MHz) and power density (3.5 W mL(-1), 9.8 W mL(-1) and 19.6 W mL(-1)) on the degradation profile was evaluated. The optimum performance was obtained at 350 kHz and 19.6 W mL(-1). Similar to other sonolytic degradation of organic pollutants, maximum degradation of CBB was observed under acidic pH. The degradation profile indicated a pseudo-first order kinetics. The addition of ferrous ion (1×10(-4) M), hydrogen peroxide (1×10(-4) M), and peroxodisulphate (1×10(-4) M) had a positive effect on the degradation efficiency. The influence of certain important NOM like SDS and humic acid on the sonolytic degradation of CBB was also investigated. Both the compounds suppress the degradation efficiency. LC-Q-TOF-MS was used to identify the stable intermediate products. Nearly 13 transformed products were identified during 10min of sonication using the optimized operational parameters. This product profile demonstrated that most of the products are formed mainly by the OH radical attack. On the basis of these results, a degradation mechanism is proposed.

Dephenolization, dearomatization and detoxification of olive mill wastewater with sonication combined with additives and radical scavengers

In this study, the effects of some additives [manganese (III) oxide (Mn3O4), Cu(+2), Fe(0) and potassium iodate (KIO3)] and some radical scavengers [sodium carbonate (Na2CO3), perfluorohexane (C6F14) and t-butyl alcohol (C4H10O)] on the sonication of olive mill effluent wastewater (OMW) were investigated since the wastewaters of this industry are removed with low efficiencies. The maximum total phenol and total aromatic amines (TAAs) removal efficiencies were 88% and 79%, respectively, at 60°C with only 150 min sonication. The maximum phenol removal was found as 98% with 19 mg L(-1) perfluorohexane and 5 mg L(-1) Fe(0) while the maximum TAAs removal was 99% with 16 mg L(-1) KIO3. Catechol, tyrosol, quercetin, caffeic acid, 4-methyl catechol, 2-phenylphenol (2-PHE) and 3-phenyl phenol (3-PHE) were detected as phenol intermediates while trimethlyaniline, aniline, o-toluidine, o-anisidine, dimethylaniline, ethylbenzene and durene were identified as TAAs in the OMW. The maximum acute toxicity removals were 96% and 99% in Vibrio fischeri and Daphnia magna, respectively. Total phenol, TAAs and the toxicity in an OMW were removed efficiently and cost-effectively through sonication.

Removal of polycyclic aromatic hydrocarbons in aqueous environment by chemical treatments: a review

Due to their carcinogenic, mutagenic and teratogenic potential, the removal of polycyclic aromatic hydrocarbons (PAHs) from aqueous environment using physical, biological and chemical processes has been studied by several researchers. This paper reviews the current state of knowledge concerning PAHs including their physico-chemical properties, input sources, occurrence, adverse effects and conventional and alternative chemical processes applied for their removal from water. The mechanisms and reactions involved in each treatment method are reported, and the effects of various variables on the PAH degradation rate as well as the extent of degradation are also discussed. Extensive literature analysis has shown that an effective way to perform the conversion and mineralization of this type of substances is the application of advanced oxidation processes (AOPs). Furthermore, combined processes, particularly AOPs coupled with biological treatments, seem to be one of the best solutions for the treatment of effluents containing PAHs.

Sonochemical degradation of a pharmaceutical waste, atenolol, in aqueous medium

Atenolol is a β-blocker drug and an identified emerging pollutant. Advanced oxidation processes (AOPs) utilise the reaction of a highly oxidising species (hydroxyl radicals, (•)OH) for the mineralisation of emerging pollutants since conventional treatment methodologies generally fail to degrade these compounds. In the present work, degradation of atenolol was carried out using ultrasound with frequencies ranging from 200 kHz to 1 MHz as a source of hydroxyl radical. The degradation was monitored by HPLC, total organic carbon (TOC) and chemical oxygen demand (COD) reduction and ion chromatography (IC). Nearly 90 % of degradation of atenolol was observed with ultrasound having 350 kHz. Both frequency and power of ultrasound affect the efficiency of degradation. Nearly 100 % degradation was obtained at a pH of 4. Presence of various additives such as sodium dodecyl sulphate, chloride, sulphate, nitrate, phosphate and bicarbonate was found to reduce the efficiency of degradation. Although nearly 100 % degradation of atenolol was observed under various experimental conditions, only about 62 % mineralisation (from TOC and COD measurements) was obtained. Nearly eight intermediate products were identified using high-resolution mass spectrometry (LC-Q-TOF). These products were understood as the results of hydroxyl radical addition to atenolol. The degradation studies were also carried out in river water which also showed a similar degradation profile. A mechanism of degradation and mineralisation is presented.

Aqueous phenanthrene toxicity after high-frequency ultrasound degradation

Given that polycyclic aromatic hydrocarbons (PAHs), such as phenanthrene (PH), possess a potent risk for aquatic biota, a great attempt to develop and apply advanced oxidation processes, such as ultrasound (US), is of great concern nowadays. However, because US PAH-derived toxic intermediates are difficult to detect, the present study investigates aqueous PH toxicity before and after high-frequency US degradation, in hemocytes of mussel Mytilus galloprovincialis. Specifically, cell viability (with the use of neutral red uptake/NRU method), and oxidative-stress indices in terms of superoxide anions, (O2(-)), nitric oxides (NO, in terms of nitrites), lipid peroxidation products (in terms of malondialdehyde/MDA content) and DNA damage (with the use of Comet assay method) were investigated in mussel hemocytes exposed to environmentally relevant concentrations of PH (0.01, 0.1, 1 and 10 μg L(-1)), before and after US treatment for 120 min (at a frequency of 582 kHz). According to the results, the NRU method showed a significant attenuation of PH-induced mortality in US PH-treated hemocytes in all cases. Moreover, the increased levels of O2(-) and NO generation, as well as MDA content measured in PH-treated hemocytes, were drastically decreased after US degradation in any case. Similarly, the disturbance of DNA integrity (in terms of % DNA in tail, OM and TM), was negligible in case of US PH-treated hemocytes. Although further in vitro and in vivo studies are needed, the present study showed for the first time that high frequency US could be applied as a highly efficient and "environmentally friendly" process for degrading low molecular weight PAH, such as PH.

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.

Degradation of PAHs by high frequency ultrasound

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic compounds, which have been reported in the literature to efficiently degrade at low (e.g. 20 kHz) and moderate (e.g. 506 kHz) ultrasound frequencies. The present study focuses on degradation of naphthalene, phenanthrene, and pyrene by ultrasound at three different relatively high frequencies (i.e. 582, 862, and 1142 kHz). The experimental results indicate that for all three frequencies and power inputs ≥ 133 W phenanthrene degrades to concentrations lower than our experimental detection limit (<1 μg/L). Phenanthrene degrades significantly faster at 582 kHz than at 862 and 1142 kHz. For all three frequencies, the degradation rates per unit mass are similar for naphthalene and phenanthrene and lower for pyrene. Furthermore, naphthalene degradation requires less energy than phenanthrene, which requires less energy than pyrene under the same conditions. No hexane-extractable metabolites were identified in the solutions.

Degradation of bisphenol-A using ultrasonic irradiation assisted by low-concentration hydrogen peroxide

This study investigated the degradation of bisphenol-A (BPA) by ultrasonic irradiation in the presence of different additives (H2O2, air bubbles and humic acid) under various operating conditions, i.e., ultrasonic frequency, power intensity and power density. The results demonstrated that the BPA degradation followed pseudo first-order kinetics under different experimental conditions. The optimum power intensities were 0.9, 1.8, and 3.0 W/cm2 at the frequencies of 400, 670, and 800 kHz, respectively. At the fixed frequency (800 kHz), the degradation rate of BPA was shown proportional to the increase of power density applied. With this manner, the BPA sonolysis could be facilitated at H2O2 dosage being lower than 0.1 mmol/L; while BPA degradation was hindered at H2O2 concentration in excess of 1 mmol/L. Additionally, BPA removal was shown to be inhibited by the presence of aeration and humic acid during ultrasonic irradiation. The present study suggested that the degradation rate of BPA assisted by ultrasonic irradiation was influenced by a variety of factors, and high BPA removal rate could be achieved under appropriate conditions.

Complexation of anthracene with folic acid studied by FTIR and UV spectroscopies

Toxicity and transformation process of polycyclic aromatic hydrocarbons (PAHs) is strongly depended on the interaction between PAHs and the coexisting compounds. Complexation between folic acid (FA) and a typical PAH, anthracene, was investigated using FTIR and UV spectra. Appearance of a new IR band at 2362cm(-1) demonstrates that NH(2)-CN(1)- moiety on pterin (PT) ring in FA is protonated when anthracene is introduced. The shift of the characteristic IR band of the PT ring and the emergence of two charge transfer bands at 254nm and 246nm in UV difference spectra show the presence of pi-pi complexation between folic acid and anthracene. These experiments confirm that anthracene could combine with the pterin ring of folic acid through pi-pi donor-acceptor interaction (EDA) and induce the protonation process in FA upon strengthening electron accepting ability of PT ring.

Sonochemical degradation of PAH in aqueous solution. Part I: monocomponent PAH solution

The sonolysis of selected monocomponent PAH aqueous solution is studied at 20 and 506 kHz in the microg l(-1) range. The highest activity observed at 506 kHz, compared to 20 kHz, is tentatively explained by examination of the physical characteristics of bubbles (size and life-time) as well as by the calculation of the number of bubble at both frequency (5 x 10(3)bubbles l(-1) at 20 kHz and 4.5 x 10(9)bubbles l(-1) at 506 kHz). It is demonstrated that the main mechanism of sonodegradation is the pyrolysis of PAHs in the heart of the cavitation bubbles, and that a possible PAH oxidation by means of HO degrees appears as a minor way, since gaseous byproducts such as CO, CO2, C2H2 and CH4 have been detected. Correlations have been found by examination of kinetic variations in terms of the physical-chemical properties of PAHs. The rate constants of PAH degradation increase when the water solubility, the vapour pressure and the Henry's law constant increase.

Removal of organic matter and ammonia nitrogen from landfill leachate by ultrasound

Experiments on the removal of organic matters and ammonia nitrogen from landfill leachate by ultrasound irradiation were carried out. The effects of COD reduction and ammonia removal of power input, initial concentration, initial pH and aeration were studied. It was found that the sonolysis of organic matters proceeds via reaction with ()OH radicals; a thermal reaction also occurs with a small contribution. The rise of COD at some intervals could be explained by the complexity of organic pollutant sonolysis in landfill leachate. Ultrasonic irradiation was shown to be an effective method for the removal of ammonia nitrogen from landfill leachate. After 180 min ultrasound irradiation, up to 96% ammonia nitrogen removal efficiency can be obtained. It was found that the mechanism of ammonia nitrogen removal by ultrasound irradiation is largely that the free ammonia molecules in leachate enter into the cavitation bubbles and transform into nitrogen molecules and hydrogen molecules via pyrolysis under instant high temperature and high pressure in the cavitation bubbles.

Degradation of naturally contaminated polycyclic aromatic hydrocarbons in municipal sewage sludge by electron beam irradiation

This study was to evaluate the degradation efficiency of naturally contaminated polycyclic aromatic hydrocarbons in sewage sludge by using electron beam irradiation as a function of the absorbed dose. Degradation efficiency of PAHs was near to 90% at the absorbed doses 5 kGy. The degradation of PAHs was "first order" reaction rates with respect to absorbed dose. The electron beam irradiation was found effective in means of removing PAHs in domestic wastewater.

Sonochemical degradation of triclosan in water and wastewater

The sonochemical degradation of 5 microg l(-1) triclosan, a priority micro-pollutant, in various environmental samples (seawater, urban runoff and influent domestic wastewater) as well as in model solutions (pure and saline water) was investigated. Experiments were conducted with a horn-type sonicator operating at 80 kHz frequency and a nominal applied power of 135 W, while solid-phase microextraction coupled with gas chromatography-electron capture detector (SPME/GC-ECD) was employed to monitor triclosan degradation. The latter followed pseudo-first order kinetics with the rate constant being (min(-1)): 0.2284 for seawater>0.1051 for 3.5% NaCl in deionised water>0.0597 for centrifuged urban runoff approximately 0.0523 for untreated urban runoff >0.0272 for deionised water >0.0063 for wastewater influent. SPME/GC-ECD and SPME coupled with gas chromatography-mass spectrometry (SPME/GC-MS) were also used to check for the formation of chlorinated and other toxic by-products; at the conditions in question, the presence of such compounds was not confirmed.

Enhancement of ultrasonically initiated emulsion polymerization rate using aliphatic alcohols as hydroxyl radical scavengers

Ultrasonically initiated emulsion polymerization of styrene was carried out in the presence of aliphatic alcohols, e.g. methanol, ethanol, n-pronanol and n-butanol, as volatile hydroxyl radical scavengers. With the addition of methanol, the polymerization rate of styrene increased, while the molecular weight and the average particle size of the produced polystyrene decreased because more radicals were produced in the presence of methanol. This is true also for the other polymerization system using other aliphatic alcohols, such as ethanol, n-pronanol and n-butanol, suggesting that the alcohols enter into cavitation bubbles and further react with hydroxyl radicals (*OH) from the sonolysis of water to produce hydroxyalkyl radicals, so as to reduce the recombination of *H and *OH radicals, therefore more radicals will be present in the systems for initiating polymerization. Obviously, it is an effective way to enhance ultrasonically initiated emulsion polymerization rate of styrene by adding volatile hydroxyl radical scavenger.

Soil remediation by an advanced oxidative method assisted with ultrasonic energy

A new process for the remediation of soil contaminated with hydrocarbons is proposed. The innovation consists on coupling an advanced oxidative method, using a Fenton-type catalyst, with the application of ultrasonic energy. The use of ultrasonic energy not only assists the desorption of the contaminants from the soil, but also promotes the formation of OH radicals, which are the oxidant agents involved in the oxidation process. Different Fenton-like catalysts were employed in the present study; however, the highest removal of toluene and xylenes were obtained with iron sulfate and copper sulfate, respectively. Also, hydrogen peroxide was tested at different concentrations, and it was found that increasing its concentration enhanced the removal of all the contaminants. Finally, it was demonstrated that applying ultrasonic energy to the reacting system process noticeably enhanced the global efficiency of the process due to a synergistic effect in conjunction with the hydrogen peroxide concentration and type of catalyst.

Kinetics of low frequency sonodegradation of linear alkylbenzene sulfonate solutions

The decomposition of sodium dodecylbenzene sulfonate (SDBS) in water by means of ultrasound irradiation at 20kHz was investigated. Experiments were conducted at surfactant concentrations of 175, 260 and 350 mg l(-1), liquid volumes of 120, 170 and 220 ml, temperatures of 20, 30 and 45 degrees C and applied power of 40, 80 and 125 W. The extent of degradation was followed monitoring substrate and organic carbon concentrations, while hydrogen peroxide concentration was also measured; the latter is a product of water sonolysis due to hydroxyl radical recombination. 80% SDBS conversion was achieved after 120 min of sonication at 125 W and 30 degrees C; nonetheless, SDBS and its degradation intermediates proved difficult to oxidise as only about 20-25% of the initial carbon content was transformed to carbon dioxide. At the initial stages of the reaction, degradation rate appears to be only weakly dependent on the substrate concentration with the rate increasing from 3.1 to 4 mg l(-1)min(-1) with increasing concentration from 175 to 350 mg l(-1). Degradation appears to occur at the bubble-liquid interface through hydroxyl radical-mediated reactions whose role was established by performing experiments in the presence of radical scavengers, namely potassium bromide and sodium benzoate. Degradation rates increased with increasing power and decreasing temperature and volume.

Ultrasound assisted catalytic wet peroxide oxidation of phenol: kinetics and intraparticle diffusion effects

The combination of ultrasound irradiation and catalytic wet peroxide oxidation was used as a means to degrade phenol. Direct and indirect irradiation were employed, while experiments in the absence of ultrasound were used as reference. A mixed (Al-Fe) pillared clay named FAZA, was used as a catalyst in the form of powder, extrudates and crushed extrudates. Ultrasound was found to clearly enhance the extrudates performance, increasing the conversion at 4h by more than 6 times under direct and almost 11 times under indirect irradiation. This observation is attributed to the reduction of diffusion resistance within the catalyst pores. The overall sonication-catalytic wet peroxide oxidation process appears very promising for environmental purposes.

Enhancement of sonochemical degradation of phenol using hydrogen atom scavengers

Sonochemical degradation of phenol was found to be enhanced in the presence of the volatile hydrogen atom scavengers CCl4 and perfluorohexane. The non-volatile hydrogen atom scavenger iodate did not enhance phenol degradation. The first order rate constant for aqueous phenol degradation in separate experiments using different sonochemical probes increased in the presence of 150 microM CCl4 from 0.014 to 0.031 min(-1) (probe 1) and from 0.022 to 0.061 min(-1) (probe 2). In the presence of <1.5 microM C6H14, the first order rate constant increased from 0.014 to 0.032 min(-1) (probe 1). Hydroquinone was the major observed reaction intermediate both in the presence and absence of hydrogen atom scavengers. Hydroquinone yields were substantially higher in the presence of hydrogen atom scavengers, suggesting that hydroxyl radical pathways for phenol degradation were enhanced by the hydrogen atom scavengers. These additives may be useful in improving pollutant degradation efficiency or improving synthetic processes that rely on hydroxyl radical as a key intermediate.

The effect of heterogeneous solvent systems on sonochemical reactions: accelerated degradation of alkyl thiols in emulsion

Sonochemical reactions of alkyl and aryl thiols in water-organic mixed solvent systems were kinetically investigated. The reaction in the liquid-liquid interface apparently depends on the polarities, surface activities, vapor pressures and hydrophobicities of organic solvents and thiols. Interestingly, the rate jump in sonochemical disappearance of alkyl thiols was observed under emulsified conditions.

Permanganate oxidation of sorbed polycyclic aromatic hydrocarbons

The polycyclic aromatic hydrocarbons (PAH) that contaminate soils at many industrial and government sites are resistant to natural biotic and abiotic degradation processes. The recalcitrant nature of these compounds may require aggressive chemical treatment to effectively remediate these sites. This study was conducted to assess the viability of permanganate oxidative treatment as a method to reduce PAH concentration in contaminated soils. Study results demonstrated a reduction in soil sorbed concentration for a mixture of six PAHs that included anthracene, benzo(a)pyrene, chrysene, fluoranthene, phenanthrene, and pyrene by potassium permanganate (KMnO4) oxidative treatment. The greatest reduction in soil concentration was observed for benzo(a)pyrene, pyrene, phenanthrene, and anthracene at 72.1, 64.2, 56.2, and 53.8%, respectively, in 30 min at a KMnO4 concentration of 160 mM. Minimal reductions in fluoranthene and chrysene concentration were observed at 13.4 and 7.8%, respectively, under the same conditions. A relative chemical reactivity order of benzo(a)pyrene>pyrene>phenanthrene>anthracene>fluoranthene>chrysene towards permanganate ion was observed. Aromatic sextet theory was applied to the degradation results to explain the highly variable and compound-specific chemical reactivity order.