Mineralization enhancement of a recalcitrant pharmaceutical pollutant in water by advanced oxidation hybrid processes.

Degradation of the biorecalcitrant pharmaceutical micropollutant ibuprofen (IBP) was carried out by means of several advanced oxidation hybrid configurations. TiO(2) photocatalysis, photo-Fenton and sonolysis - all of them under solar simulated illumination - were tested in the hybrid systems: sonophoto-Fenton (FS), sonophotocatalysis (TS) and TiO(2)/Fe(2+)/sonolysis (TFS). In the case of the sonophoto-Fenton process, the IBP degradation (95%) and mineralization (60%) were attained with photo-Fenton (FH). The presence of ultrasonic irradiation slightly improves the iron catalytic activity. On the other hand, total removal of IBP and elimination of more than 50% of dissolved organic carbon (DOC) were observed by photocatalysis with TiO(2) in the presence of ultrasound irradiation (TS). In contrast only 26% of mineralization was observed by photocatalysis with H(2)O(2) (TH) in the absence of ultrasound irradiation. Additional results showed that, in the TFS system, 92% of DOC removal and complete degradation of IBP were obtained within 240 min of treatment. The advanced oxidation hybrid systems seems to be a promising alternative for full elimination/mineralization for the recalcitrant micro-contaminant IBP.

Ultrasonic treatment of water contaminated with ibuprofen.

The application of ultrasound (US) waves for remediation of wastewater is an area of increasing interest and promising results. The aim of this paper is to evaluate the influence of several parameters of the US process on the degradation of ibuprofen (IBP), a widely used non-steroidal anti-inflammatory recalcitrant drug found in water. Applied US power, dissolved gas, pH and initial concentration of IBP were the parameters investigated under sonication (300 kHz). Ultrasound increased the degradation of IBP from 30 to 98% in 30 min. Initial rate of IBP degradation was evaluated in the range of 1.35 and 6.1 micromolL(-1)min(-1) for initial concentrations of 2 to 21 mgL(-1) or 9.7 micromolL(-1) to 101 micromolL(-1), respectively. Under air and oxygen the degradation rate of IBP was 4 micromolL(-1)min(-1) being higher than that when argon was used. The most favorable degradation pH was acidic media. Complete removal of IBP was achieved but some dissolved organic carbon (DOC) remained in solution showing that long-lived intermediates were recalcitrant to the US irradiation. However, chemical and biological oxygen demands (COD and BOD(5)) indicated that the process oxidize the ibuprofen compound to biodegradable substances removable in a subsequent biological step.

A comparative study of ultrasonic cavitation and Fenton's reagent for bisphenol A degradation in deionised and natural waters.

Bisphenol A (BPA), a xenobiotic that exhibits endocrine disrupting action can be found in surface water. Its complete elimination can be obtained by advanced oxidation processes, notably upon the application of ultrasonic waves. In order to evaluate the feature of ultrasound relevance and the involvement of the hydroxyl radical in the BPA sonochemical degradation, ultrasound action was compared to Fenton's reaction in the cases of deionised acidic water (pH 3) and natural water (pH 7.6, main ions concentration: Ca(2+)=486mgL(-1), Na(+)=9.1mgL(-1), Cl(-)=10mg L(-1), SO(4)(2-)=1187mgL(-1), HCO(3)(-)=402mgL(-1)). Ultrasound was performed at 300kHz and 80W. Fenton's process was operated using ferrous sulphate (100micromolL(-1)) and continuous H(2)O(2) addition at the rate as it is produced when sonication is applied in water in absence of substrate. Experiments carried out in deionised water show that both processes exhibit identical BPA elimination rate and identical primary intermediates. Main chemical pathways involve reactions with OH radical. Chemical oxygen demand (COD) and total organic carbon (TOC) analyses show that the Fenton's process is slightly more efficient than ultrasonic treatment for the removal of BPA by-products in the case of deionised water. Experiments conducted in natural water evidenced the inhibition of the Fenton process while the ultrasound action was not hampered.

The use of pulsed ultrasound technology to improve environmental remediation: a comparative study.

Relatively little is known about the effects of pulsed ultrasound on the facilitation of chemical reactivity and remediation. Previous studies have indicated that sonochemistry using pulses may be either more or less effective than continuous wave (CW) ultrasonic irradiation. However, because of the time-modulated nature of the pulses used in these studies, less acoustic energy in general was transmitted to the solutions compared to CW sonication. The effectiveness of ultrasound when the pulse is adjusted so that the same amount of acoustic energy is input compared to continuous irradiation over a given time has not been previously explored. In this study we have embarked on a comparison of the efficacy of power-modulated pulsed (PMP) sonochemistry with more traditional time-modulated pulsing. As a prototypical reaction, we have explored the effects of pulse type on the degradation of acid orange, a common industrial colorant. An increase in the degradation rate by a factor of three was observed using PMP ultrasound compared with continuous irradiation under conditions of equivalent acoustic input power, while the use of time-modulated pulsed ultrasound from a commercially available direct-immersion (DI) horn-type sonicator exhibited a rate decrease compared to CW sonication. Possible mechanisms for the enhancement are discussed.

OH/D A2sigma(+)-X2pi(i) rovibronic transitions in multibubble sonoluminescence.

Multibubble sonoluminescence spectra were recorded in the 300-350 nm wavelength range in the case of H(2)O/Ar, D(2)O/Ar and H(2)O/Kr solutions (acoustic frequency: 20 kHz; spectral resolution optimized to 0.34 nm). Three groups of rotational components (R(1)/R(2), Q(1)/Q(2) and P(1)/P(2)) were identified in the OH/D A2sigma(+)-X2pi(i) (0,0) transitions via the substitution of H(2)O for D(2)O. The congestion of bands and the origin of a red shading extending up to 350 nm are broached.

Reduction of chloroform formation potential of humic acid by sonolysis and ultraviolet irradiation.

This study is concerned with the changes of chloroform formation potential during the reaction of humic acid (HA) and sodium hypochlorite caused by different oxidative pretreatments: ultraviolet (UV) irradiation, ultrasonic (US) irradiation or combined UV-US irradiations. The UV and US decomposition of a reagent HA in water was investigated. The characterization of the oxidized HA sample by UV absorptiometry, synchronous fluorescence spectroscopy and size exclusion chromatography points a synergetic effect of the combined process. The values of the chlorine demand and chloroform formation potential were conventionally determined after a 96 h reaction at neutral pH. It was found that all applied processes decreased the concentration of chloroform but the highest decrease was observed for the UV-US treatment.

Effects of ultrasound on adsorption-desorption of p-chlorophenol on granular activated carbon.

The aim of this work is the evaluation of the effects of ultrasound on p-chlorophenol adsorption-desorption on granular activated carbon. Adsorption equilibrium experiments and batch kinetics studies were carried out in the presence and the absence of ultrasound at 21 kHz. Results indicate that the adsorption of p-chlorophenol determined in the presence of ultrasound is lower than the adsorption observed in the absence of ultrasound. Desorption of p-chlorophenol from activated carbon with and without the application of ultrasound was studied. The desorption rates were favoured by increased ultrasound intensity. This rise is more noticeable as temperature increases. The addition of ethanol or NaOH to the system causes an enhancement of the amount of p-chlorophenol desorbed, especially in the presence of ultrasound. A synergetic enhancement of the desorption rate was observed when ultrasonic irradiation was coupled with ethanol chemical regeneration.

Evaluation of 1-octanol degradation by photocatalysis and ultrasound using SPME.

Solid-phase micro-extraction has been used for identifying, quantifying and following the evolution of intermediate products of octanol degradation by two advanced oxidation treatments (AOTs), photocatalytic and ultrasound processes, inducing mainly the same active species. Headspace extraction enabled direct extraction of the organic compounds in a heterogeneous process like photocatalysis. The presence of a solid does not affect the extraction percentage of alkanes, alkenes and aldehydes while alcohols and carboxylic acids are not completely extracted if the extraction time is too short. To extract C3-C8 alkanes, alkenes and aldehydes a Carboxen/PDMS fiber and an extraction time of 25 min are used. The presence of alcohol and carboxylic acids requires the use of the presence of salt under acidic conditions, a longer extraction time and a polyacrylate fiber (PA), having a polar fiber. The in situ derivatization--pyrenyldiazomethane on a PA fiber--increases the carboxylic acid extraction containing smaller hydrocarboned chain while diazomethane derivatization is not as efficient due to its volatility. Whatever be the treatment, photocatalysis or ultrasound processes, aldehydes are the main intermediate products, which is not surprising since the same oxidation species (HO2(o), O2(o-), OH(o)) are formed. Alkanes and alkenes are also detected in both processes; however, alkane formation is more important in photocatalysis while alkenes are formed in higher amounts by ultrasound. Moreover, the presence of carboxylic acids in more important amounts by ultrasound than by photocatalysis is attributed to the presence of holes (h+) in photocatalysis which induces photo-Kolbe degradation. The sonochemical formation of small-chained dienes and alkynes is probably due to pyrolysis of hydrophobic compounds in cavitation bubbles.

Water treatment by TiO2 photocatalysis and/or ultrasound: degradations of phenyltrifluoromethylketone, a trifluoroacetic-acid-forming pollutant, and octan-1 -ol, a very hydrophobic pollutant.

TiO2 photocatalysis and ultrasound are advanced oxidation processes for water treatment. Our study aimed at showing, via the purposely chosen title compounds, that these techniques can be complementary. For C6H5COCF3 (PTMK), the photocatalytic removal rate was higher than the ultrasonic (515 kHz) removal rate in the presence of TiO2 in the dark, whereas it was the opposite for octan-1-ol under the conditions employed. Simultaneous UV and ultrasound irradiation of the TiO2 suspension led, for PTMK, to a removal rate about equal to the sum of the removal rates observed for separate irradiations, and decreased by a factor of approximately 20% for octan- 1 -ol as if the photocatalytic degradation was suppressed by the dominant distribution of octan-1-ol to the cavitation bubbles. This distribution was substantiated by the large detrimental effect of octan- 1-ol on the PTMK ultrasonic removal rate. The concurrent use of both techniques allowed a faster removal of both pollutants in binary mixtures. The amount of CF3COOH from PTMK was approximately eight times lower in sonicated, than in UV-irradiated, TiO2 suspensions. Several intermediate products showed the occurrence of chemical transformations occurring in and/or on the cavitation bubbles. COD decline and CO2 formation were initially higher for ultrasonic than for photocatalytic treatment. However, complete mineralization (except for CF3COOH) was achieved more rapidly by photocatalysis and even more rapidly by simultaneous use of both techniques.

Sonochemical and photochemical oxidation of organic matter.

Recent developments in sonochemistry have led us to study its use to treat water and wastewater. The effects of ultrasound wave in hydrophilic chemical oxidations are mainly due to hydroxyl radical production during the cavitation-induced water decomposition. Currently, the sonochemical destruction of aromatic compounds in water solution is obtained with low rates. The aim of this work is to evaluate the efficiency of the sonochemical effect in conjunction with a photochemical irradiation. Taking phenol as an example, the combined action of sonochemistry and photochemistry has been considered in a 'sonuv' reactor. An important enhancement of the degradation rate of phenol has been observed. It may be the result of three different oxidative processes: direct photochemical action, high frequency sonochemistry and reaction with ozone (produced by UV irradiation of air). The process has been successfully tested to lower the chemical oxygen demand of a municipal wastewater.

Ultrasound-enhanced reactivity of calcium in the reduction of aromatic hydrocarbons

Reductions of aromatic hydrocarbons by calcium in ethylenediamine-n-alkylamine mixture were investigated under ultrasonic conditions. Using an ultrasonic probe, with naphthalene as test molecule, it has been demonstrated that under ultrasonic action the reactions proceed faster (x10) and require a lower metal quantity (0.5) than the reactions conducted with an efficient mechanical stirrer. In addition, at ambient temperature and depending on the specific alcohol addition, selective naphthalene reduction can be performed using ultrasound. 1,2-Dihydronaphthalene (88% yield) results from the reaction in the presence of 2-propanol, and 1,4,5,8-tetrahydronaphthalene (88% yield) is obtained with tert-butanol. Investigation of the metal surface points out the characteristics of the calcium ultrasonic activation. The procedure was efficiently tested with several aromatic hydrocarbons.

Degradation of pentachlorophenol aqueous solutions using a continuous flow ultrasonic reactor: experimental performance and modelling.

The degradation of aqueous solutions of pentachlorophenol (PCP) in a three-stage sonochemical reactor operating in the continuous flow mode has been investigated. The experimental reactor may be considered as a series of three high-frequency ultrasonic units. The influence of several parameters such as ultrasonic power, reactor volume and volumetric feed flow rate on the reactor performance is reported. Application of classical basic chemical engineering principles leads to a model that enables us to predict the PCP concentration within the reactor. In steady state, experimental conversion rates are shown to be in good agreement with model predictions.

Experimental study of the hydrodynamic behaviour of a high frequency ultrasonic reactor.

In relation to design and modeling of sonochemical reactors, the hydrodynamic behaviour of a high-frequency ultrasonic reactor has been investigated. Residence time distribution (RTD) measurements have been performed by means of a tracer method. The influence of ultrasound on the response to an inlet pulse was evidenced. It was shown that the reactor behaves like a completely stirred tank reactor (CSTR) as soon as ultrasonic irradiation operates. Preliminary observations on acoustic streaming occurring within the reactor will also be presented.

Ultrasonic waste-water treatment: incidence of ultrasonic frequency on the rate of phenol and carbon tetrachloride degradation.

Organic compounds in aqueous solution submitted to an ultrasonic irradiation behave differently according to their physical and chemical properties. In this work, hydrogen peroxide formation and the degradation rate of phenol and carbon tetrachloride have been studied at different frequencies: 20, 200, 500 and 800 kHz. Whatever the frequency, it is easier to decompose CCl4 than phenol by means of ultrasonic wave. It is shown that the rates of reactions involving hydroxyl radicals (hydrogen peroxide formation and phenol degradation) have a maximum value at 200 kHz. The best yield observed at 200 kHz for the phenol degradation may be the result of better HO radicals availability outside of the bubble of cavitation. The degradation rate for carbon tetrachloride which decomposes into the bubble of cavitation increases with frequency. Calculating the reaction rate for one ultrasonic period shows that the efficiency of one ultrasonic cycle decreases as frequency increases.