Oualid Hamdaoui

Abstract:

Abstract: In this work, energy analysis of an oscillating isolated spherical bubble in water irradiated by an ultrasonic wave has been theoretically studied for various conditions of acoustic amplitude, ultrasound frequency, static pressure and liquid temperature in order to explain the effects of these key parameters on both sonochemistry and sonoluminescence. The Keller-Miksis equation for the temporal variation of the bubble radius in compressible and viscous medium has been employed as a dynamics model. The numerical calculations showed that the rate of energy accumulation, dE/dt, increased linearly with increasing acoustic amplitude in the range of 1.5-3.0 atm and decreased sharply with increasing frequency in the range 200-1000 kHz. There exists an optimal static pressure at which the power w is highest. This optimum shifts toward a higher value as the acoustic amplitude increases. The energy of the bubble slightly increases with the increase in liquid temperature from 10 to 60 C. The results of this study should be a helpful means to explain a variety of experimental observations conducted in the field of sonochemistry and sonoluminescence concerning the effects of operational parameters. © 2013 Elsevier B.V. All rights reserved.

Abstract: Formation of highly reactive species such as OH, H, HO2 and H2O2 due to transient collapse of cavitation bubbles is the primary mechanism of sonochemical reaction. The crucial parameters influencing the formation of radicals are the temperature and pressure achieved in the bubble during the strong collapse. Experimental determinations estimated a temperature of about 5000 K and pressure of several hundreds of MPa within the collapsing bubble. In this theoretical investigation, computer simulations of chemical reactions occurring in an O2-bubble oscillating in water irradiated by an ultrasonic wave have been performed for diverse combinations of various parameters such as ultrasound frequency (20-1000 kHz), acoustic amplitude (up to 0.3 MPa), static pressure (0.03-0.3 MPa) and liquid temperature (283-333 K). The aim of this series of computations is to correlate the production of OH radicals to the temperature and pressure achieved in the bubble during the strong collapse. The employed model combines the dynamic of bubble collapse in acoustical field with the chemical kinetics of single bubble. The results of the numerical simulations revealed that the main oxidant created in an O2 bubble is OH radical. The computer simulations clearly showed the existence of an optimum bubble temperature of about 5200 ± 200 K and pressure of about 250 ± 20 MPa. The predicted value of the bubble temperature for the production of OH radicals is in excellent agreement with that furnished by the experiments. The existence of an optimum bubble temperature and pressure in collapsing bubbles results from the competitions between the reactions of production and those of consumption of OH radicals at high temperatures. © 2013 Elsevier B.V. All rights reserved.

Abstract: The ability of cattail (Typha angustifolia) leaves (CL) for the biosorption of malachite green (MG), a cationic dye, from aqueous solutions was investigated. Biosorption isotherm and kinetics of MG by CL were studied through a number of batch sorption experiments. The influence of operating conditions such as initial dye concentration, biosorbent dose, initial pH, stirring speed, temperature, ionic strength and biosorbent particle size on the removal of MG was investigated. Equilibrium data were fitted to the Langmuir, Freundlich, Redlich-Peterson and Sips isotherm models using non-linear regression technique. Experimental equilibrium data were best represented by the Redlich-Peterson and Sips isotherms, but the Redlich-Peterson model was better. Biosorption kinetics obtained at different initial concentrations were analysed using pseudo-first-order, pseudo-second-order and pseudo-nth order equations. The pseudo-nth order model fit the kinetic data well and was best than the pseudo-first- and pseudo-second-order equations. The order of biosorption reaction n was found to be between 1.27 and 1.93. The results revealed that the CL has the potential to be used as a biosorbent for the removal of MG from aqueous solutions. © 2013 Copyright Balaban Desalination Publications.

Abstract: Numerical simulation of chemical reactions inside an isolated spherical bubble of oxygen has been performed for various ambient bubble radii at different frequencies and acoustic amplitudes to study the effects of these two parameters on the range of ambient radius for an active bubble in sonochemical reactions. The employed model combines the dynamic of bubble collapse with the chemical kinetics of single cavitation bubble. Results from this model were compared with some experimental results presented in the literature and good apparent trends between them were observed. The numerical calculations of this study showed that there always exists an optimal ambient bubble radius at which the production of oxidizing species at the end of the bubble collapse attained their upper limit. It was shown that the range of ambient radius for an active bubble increased with increasing acoustic amplitude and decreased with increasing ultrasound frequency. The optimal ambient radius decreased with increasing frequency. Analysis of curves showing optimal ambient radius versus acoustic amplitude for different ultrasonic frequencies indicated that for 200 and 300 kHz, the optimal ambient radius increased linearly with increasing acoustic amplitude up to 3 atm. However, slight minima of optimal radius were observed for the curves obtained at 500 and 1000 kHz. © 2012 Elsevier B.V. All rights reserved.

Abstract: Sonochemical oxidation has been investigated as a viable advanced oxidation process (AOP) for the destruction of various pollutants in water. Ultrasonic irradiation generates ·OH radicals that can recombine, react with other gaseous species present in the cavity, or diffuse out of the bubble into the bulk liquid medium where they are able to react with solute molecules. The extent of degradation of an organic dye such as malachite green (MG) is limited by the quantity of hydroxyl radicals diffused from cavitation bubbles. In this work, the effect of bromide ions on sonolytic degradation of MG was investigated. The obtained results clearly demonstrated the considerable enhancement of sonochemical destruction of MG in the presence of bromide. No significant differences were observed in the presence of chloride and sulfate, excluding the salting-out effect. Positive effect of bromide ions, which increases with increasing bromide level and decreasing MG concentration, is due to the generation of dibromine radical anion (Br 2 ·-) formed by reaction of Br - with ·OH radicals followed by rapid complexation with another anion. The generated Br 2 ·- radicals, reactive but less than ·OH, are likely able to migrate far from the cavitation bubbles towards the solution bulk and are suitable for degradation of an organic dye such as MG. Additionally, Br2- radicals undergo radical-radical recombination at a lesser extent than hydroxyl radicals and would be more available than ·OH for substrate degradation, both at the bubble surface and in the solution bulk. This effect compensates for the lower reactivity of Br 2 ·- compared to ·OH toward organic substrate. Addition of bromide to natural and sea waters induces a slight positive effect on MG degradation. In the absence of bromide, ultrasonic treatment for the removal of MG was promoted in complex matrices such as natural and sea waters. © 2011 Elsevier B.V. All rights reserved.

Abstract: In this study, removal of malachite green (MG), a cationic triphenylmethane dye, by 300. kHz ultrasound was investigated. The effects of operating parameters such as initial dye concentration, ultrasound power and initial pH on the sonochemical degradation were studied. The initial rate of MG degradation and hydrogen peroxide formation as a function of initial concentration were determined. The obtained results show that the degradation rate increases with increasing initial dye concentration up to a plateau. The rate of hydrogen peroxide formation decreases with increasing substrate concentration and reaches a minimum, followed by almost constant production rate for higher MG concentrations. The dominant degradation mechanism is the reaction of substrate with OH radicals both at the gas bubble-liquid interface and in the bulk solution. Sonochemical degradation of MG occurs via two competitive processes: N-demethylation and destruction of the conjugated structure. The degradation rate increased proportionally with increasing ultrasonic power, but decreased with the increase of initial pH value from 2 to 7. In the presence of 10. mg/L Fe(II), the initial degradation rate of MG became 2 times larger for initial dye concentration of 5. mg/L and 1.5 times larger for initial substrate concentration of 10. mg/L, respectively. © 2012 Elsevier B.V.

Abstract: Every year increasing amounts of industrial waste are generated worldwide. Depending on their characteristics, wastes can represent an important source of secondary raw materials in order to replace natural resources. The growing amount of carbide lime waste (CLW), a byproduct of acetylene production, has resulted in environmental problems. In the present study, the potential use of CLW for wastewater treatment was investigated. The main characteristics of the CLW were determined. Chemical and X-ray diffraction analyses indicated that CLW was similar in chemical and mineralogical compositions to industrial lime, except for the presence of carbon in the waste. Morphological and elemental chemical analyses by scanning electron microscopy and energy dispersive X-ray spectrometry revealed that CLW particles differ from industrial lime by the presence of carbon formations. The use of CLW was evaluated in the treatment of Annaba city wastewater effluent. CLW was found to be the suitable for the treatment of Annaba city wastewater for an optimal dose of 850mgL-1. Percentage removal efficiency for turbidity, total suspended solids (TSS), chemical oxygen demand (COD) and 5-day biochemical oxygen demand (BOD5) was found to be 96, 98.2, 90 and 84.5%, respectively. Residual turbidity in supernatant was 4.5 NTU and total residual bacteria was 68CFUmL-1. Algerian effluent quality standards for TSS and COD were met after treatment. However, BOD5, bacterial level and pH were high, emphasizing the need of pH adjustment and secondary treatment for the Annaba city effluent. The precipitation of heavy metals with CLW has been shown to be successful in reducing the level of soluble heavy metals in aqueous solution. The removal of heavy metals was enhanced at pH ranges 10-11 for zinc, 9.2-11.6 for lead, 4-11.8 for iron and 7-11.8 for copper. The results revealed that CLW can be effectively used in wastewater treatment. © 2012 Desalination Publications. All rights reserved.

Abstract: The feasibility of using loquat seeds (LS) for the sorption of Rhodamine B (RhB) from aqueous solutions has been investigated in the absence and presence of ultrasound and by combining concurrently ultrasonic irradiation and mechanical stirring. Batch sorption studies were conducted to study the effects of various parameters such as sorbent dose, initial dye concentration and ultrasonic power on RhB sorption. The obtained results show that both the rate and amount of RhB sorption were drastically improved in the presence of ultrasound. The dye sorption with the assistance of ultrasound was enhanced with the increase of sorbate initial concentration and ultrasonic power, and with the decrease of sorbent dosage. The simultaneous association of ultrasound and stirring leads to an intensification of the sorption. Equilibrium data were analyzed by the Langmuir, Freundlich and Redlich-Peterson models by using non-linear regression technique. The sorption equilibrium data were best represented by the Langmuir and Redlich-Peterson isotherms for the conventional and combined methods. In the presence of ultrasound alone, the Redlich-Peterson model yields a better fit than the Langmuir model. LS was shown to be an efficient sorbent for the removal of RhB from aqueous solutions. © 2010 Elsevier B.V.

Abstract: The sonolytic degradation of endocrine disrupting compound 4-cumylphenol (4-CyP) in aqueous solution was investigated. The influence of operating parameters for sonication process such as 4-CyP initial concentration, frequency, power, pH, temperature and saturating gas was examined. The extent of degradation was inversely proportional to the initial substrate concentration. The rate of 4-CyP degradation was frequency dependent. The degradation rate increased proportionally with increasing ultrasonic power from 20 to 100 W and temperature in the range of 20-50°C. The most favorable degradation pH was acidic media. Destruction in the presence of saturating gas follows the order: argon > air > nitrogen. The 4-CyP degradation was inhibited in the presence of nitrogen gas owing to the free radical scavenging effect in vapor phase within the bubbles of cavitation. The ultrasonic degradation of 4-CyP was clearly promoted in the presence of bromide anions and the promoting effect on degradation increased with increasing bromide concentration. At low 4-CyP concentration (0.05 mg L -1), bicarbonate ion drastically enhanced the rate of 4-CyP degradation. Experiments conducted using pure and natural water demonstrated that the sonolytic treatment was more efficient in the natural water compared to pure water. © 2010 Elsevier B.V. All rights reserved.

Abstract: In this work, the feasibility for the use of ultrasound as an innovative technique for the desorption of 4-chlorophenol (4-CP) from granular activated carbon (GAC) was investigated. Effects of operational parameters such as adsorbent dosage, adsorbent loading, ultrasonic power and temperature on the desorption kinetics were examined. The obtained results show that the amount of 4-CP desorbed decreased with the increase in adsorbent dose. The desorption gradually increased with increasing GAC loading, acoustic power and temperature. Better results were obtained with a multistage treatment process. The adsorbed molecules may be released into solution by breaking bonds and intensifying mass transfer phenomena through acoustic vortex microstreaming, shockwaves, microjets and thermal effects from cavitational collapse. For better understanding, desorption kinetic results were modeled using models with theoretical basis. Modeling of desorption kinetics shows that the second order surface kinetics seemed to play a more significant role than pore diffusion. © 2010 Elsevier Inc. All rights reserved.

Abstract: The influence of bicarbonate and carbonate ions on sonolytic degradation of cationic dye, Rhodamine B (RhB), in water was investigated. As a consequence of ultrasonic cavitation that generates {radical dot}OH radicals, carbonate radicals were secondary products of water sonochemistry when it contains dissolved bicarbonate or carbonate ions. The results clearly demonstrated the significant intensification of sonolytic destruction of RhB in the presence of bicarbonate and carbonate, especially at lower dye concentrations. Degradation intensification occurs because carbonate radicals sonochemically formed undergo radical-radical recombination at a lesser extent than hydroxyl radicals. The generated carbonate radicals are likely able to migrate far from the cavitation bubbles towards the solution bulk and are suitable for degradation of an organic dye such as RhB. Therefore, at low dye concentrations, carbonate radical presents a more selective reactivity towards RhB molecules than hydroxyl radical. In the presence of bicarbonate, degradation rate reached a maximum at 3 g L-1 bicarbonate, but subsequent addition retards the destruction process. In RhB solutions containing carbonate, the oxidation rate gradually increased with increasing carbonate concentration up to 10 g L-1 and slightly decreased afterward. Carbonate radicals sonochemically generated are suitable for total removal of COD of sonicated RhB solutions. © 2009 Elsevier B.V. All rights reserved.

Abstract: In this work, the extraction of bisphenol A (BPA), an endocrine disrupting compound, from aqueous solutions by emulsion liquid membrane (ELM) was studied. Liquid membrane consists of a diluent (hexane) and a surfactant (Span 80). 0.05N sodium hydroxide solution was used as internal aqueous phase. Effects of experimental conditions that affect the stability such as surfactant concentration, emulsification time, internal phase concentration and volume ratio of internal phase to membrane phase was investigated. The important variables governing the permeation of BPA were examined. These variables are sulfuric acid concentration in external phase, acid type in external phase, internal phase concentration, type of internal phase, surfactant concentration, stirring speed, volume ratio of internal phase to membrane phase, treatment ratio, BPA concentration, diluent type and presence of salt. This study also investigated the effect of NaOH concentration in the internal phase on the stripping of BPA. The results showed that by appropriate selection of the extraction and stability conditions, it was possible to extract nearly all of BPA molecules from the feed solution even in the presence of high concentration of salt. Under optimum conditions, very good stripping efficiency (98%) can be achieved. © 2009 Elsevier B.V. All rights reserved.

Abstract: The effects of various additives such as iron (elemental, bivalent and trivalent), carbon tetrachloride, hydrogen peroxide, tert-btyl alcohol, salt (Na2SO4), sucrose and glucose on the sonochemical destruction of cationic dye, Rhodamine B (RhB), in aqueous phase were studied. Additionally, sonolytic degradation of RhB was investigated at varying initial dye concentration, power, pH and temperature. RhB can be readily eliminated by the ultrasound process, but even after long ultrasound irradiation times (240 min), more than 40% of chemical oxygen demand (COD) remained in the solution. Sonochemical degradation of RhB was strongly affected by initial substrate concentration, ultrasonic power, temperature and pH. The ultrasonic degradation of dye was enhanced by iron addition. The acceleration effect of iron on the destruction rate displayed the following order: Fe(II) > Fe(III) > Fe0. It was found that the degradation of the dye was accelerated with increased concentrations of CCl4 via the formation of oxidant chlorine species. It was observed that there was an optimum concentration of H2O2 and Na2SO4 for enhancing the degradation degree of RhB. In the presence of tert-butyl alcohol at low concentration, unexpectedly, the rate of dye degradation was accelerated. Very slow RhB degradation occurs if the sonolysis is carried out in the presence of high tert-butyl alcohol concentration. The slight decrease in the degree of RhB removal in the presence of high concentrations of sucrose and glucose is a clear indication that ultrasonic irradiation is a promising process for the removal of RhB from alimentary liquids containing sucrose and glucose. © 2010 Elsevier B.V. All rights reserved.

Abstract: The aim of this work was to evaluate the influence of mineral and organic matrices on the sonochemical degradation of 4-isopropyl-phenol (4-IPP), an endocrine disrupting chemical found in water. Bicarbonate ions as mineral matrix and sucrose as organic competitor were evaluated with respect to their effect on sonochemical degradation rates. At low 4-IPP concentration, the sonolytic degradation was clearly improved in the presence of bicarbonate involving the formation of the carbonate radical resulting from the reaction of bicarbonate with hydroxyl radical. In the presence of large excess of sucrose, the sonochemical degradation of 4-IPP at low concentration was not affected. © Taylor & Francis Group, LLC.

Abstract: The aim of this work was to study the emulsification assisted by ultrasonic probe (22.5 kHz) and investigate the removal of copper(II) ions from aqueous solution using water-in-oil-in-water (W/O/W) emulsion liquid membrane process (ELM). The membrane was prepared by dissolving the extractant bis(2-ethylhexyl)phosphoric acid (D2EHPA) and the hydrophobic surfactant sorbitan monooleate (Span 80) in hexane (diluent). The internal phase consisted of an aqueous solution of sulfuric acid. Effects of operating parameters such as emulsification time, ultrasonic power, probe position, stirring speed, carrier (D2EHPA) and surfactant (Span 80) concentrations volume ratios of organic phase to internal striping phase and of external aqueous phase to membrane (W/O) phase, internal phase concentration and choice of diluent on the membrane stability were studied. With ultrasound, the W/O emulsion lifetime were much higher than those reported previously by mechanical agitation. The effect of carrier and Cu(II) initial concentration on the extraction kinetics was also investigated. Nearly all of the Cu(II) ions present in the continuous phase was extracted within a few minutes. Additionally, the influence of H2SO4 concentration on the stripping efficiency was examined. © 2009 Elsevier B.V. All rights reserved.

Abstract: Sonochemical degradation of phenol (Ph), 4-isopropylphenol (4-IPP) and Rhodamine B (RhB) in aqueous solutions was investigated for a large range of initial concentrations in order to analyze the reaction kinetics. The initial rates of substrate degradation and H2O2 formation as a function of initial concentrations were determined. The obtained results show that the degradation rate increases with increasing initial substrate concentration up to a plateau and that the sonolytic destruction occurs mainly through reactions with hydroxyl radicals in the interfacial region of cavitation bubbles. The rate of H2O2 formation decreases with increasing substrate concentration and reaches a minimum, followed by almost constant production rate for higher substrate concentrations. Sonolytic degradation data were analyzed by the models of Okitsu et al. [K. Okitsu, K. Iwasaki, Y. Yobiko, H. Bandow, R. Nishimura, Y. Maeda, Sonochemical degradation of azo dyes in aqueous solution: a new heterogeneous kinetics model taking into account the local concentration OH radicals and azo dyes, Ultrason. Sonochem. 12 (2005) 255-262.] and Seprone et al. [N. Serpone, R. Terzian, H. Hidaka, E. Pelizzetti, Ultrasonic induced dehalogenation and oxidation of 2-, 3-, and 4-chlorophenol in air-equilibrated aqueous media. Similarities with irradiated semiconductor particulates, J. Phys. Chem. 98 (1994) 2634-2640.] developed on the basis of a Langmuir-type mechanism. The five linearized forms of the Okitsu et al.'s equation as well as the non-linear curve fitting analysis method were discussed. Results show that it is not appropriate to use the coefficient of determination of the linear regression method for comparing the best-fitting. Among the five linear expressions of the Okitsu et al.'s kinetic model, form-2 expression very well represent the degradation data for Ph and 4-IPP. Non-linear curve fitting analysis method was found to be the more appropriate method to determine the model parameters. An excellent representation of the experimental results of sonolytic destruction of RhB was obtained using the Serpone et al.'s model. The Serpone et al.'s model gives a worse fit for the sonolytic degradation data of Ph and 4-IPP. These results indicate that Ph and 4-IPP undergo degradation predominantly at the bubble/solution interface, whereas RhB undergoes degradation at both bubble/solution interface and in the bulk solution. © 2010 Elsevier B.V. All rights reserved.

Abstract: Melon (Cucumis melo L.) peel, an agricultural solid waste material, was utilized as a novel non-conventional sorbent for the removal of cadmium from aqueous phase. The effects of sorbent dose, pH, ionic strength, temperature, stirring speed, initial concentration and contact time on the sorption of cadmium were evaluated. Results indicate an increase in uptake by the sorbent with increasing initial cadmium concentration, solution pH and contact time. The amount of cadmium sorption decreases with increasing temperature, ionic strength and sorbent dose. Mixing rates up to 400 rpm increase uptake, however, higher mixing rates result in insignificant enhancement of uptake compared to the dissipated energy. The equilibrium sorption data of cadmium by melon peel were analyzed by Langmuir, Freundlich and Temkin isotherm models. The results indicate that the Langmuir model provides the best correlation of the experimental data, with maximum monolayer sorption capacity of 81.97 mg g-1. Pseudo-first-order, pseudo-second-order and intraparticle diffusion models were used to analyze the kinetic data obtained at different initial concentrations. Among the kinetic models studied, the pseudo-second-order model was the best applicable to describe the sorption of cadmium by melon peel. The results demonstrated that melon peel is very effective for the sorption of cadmium from aqueous solutions. © 2010 Desalination Publications.

Abstract: In this work, the decolorization of C.I. Acid Blue 25 (AB25), a commercially important anthraquinonic dye, by direct UV irradiation alone and UV/H2O2 and UV/Fe(II) processes was investigated. Experiments were conducted in batch mode using a low-pressure mercury lamp emitting mainly at 253.7 nm. For direct UV photolysis, the decolorization rate increased with decreasing pH and initial dye concentration. The decolorization of AB25 was investigated using UV irradiation in the presence of H2O2 as function of hydrogen peroxide concentration, dye concentration and pH. Additionally, the effect of salts on the bleaching of this dye was also studied. Decolorization rate was increased in the presence of UV/H2O2 compared to UV irradiation alone. The results showed that the bleaching increases as the initial H2O2 concentration increased up to a certain limit at which hydrogen peroxide reduced the bleaching by scavenging the OH radicals. The bleaching of AB25 decreased when the dye concentration increased. Decolorization rate by means of Fe(II) homogeneous photocatalysis under UV irradiation was increased compared to direct UV irradiation alone. The best working condition was found for an initial Fe(II) concentration of 30 mg L-1. The results revealed that the tested advanced oxidation processes are very effective for the decolorization of AB25 in aqueous solutions. © 2010 Elsevier B.V. All rights reserved.

Abstract:

Abstract: Central events of the ultrasonic action are the cavitation bubbles that can be considered as microreactors. Adiabatic collapse of cavitation bubbles leads to the formation of reactive species such as hydroxyl radicals (OH), hydrogen peroxide (H2O2) and hydroperoxyl radicals (HOO). Several chemical methods were used to detect the production of these reactive moieties in sonochemistry. In this work, the influence of several operational parameters on the sonochemistry dosimetries namely KI oxidation, Fricke reaction and H2O2 production using 300kHz ultrasound was investigated. The main experimental parameters showing significant effect in KI oxidation dosimetry were initial KI concentration, acoustic power and pH. The solution temperature showed restricted influence on KI oxidation. The acoustic power and liquid temperature highly affected Fricke reaction dosimetry. Operational conditions having important influence on H2O2 formation were acoustic power, solution temperature and pH. For the three tested dosimetries, the sonochemical efficiency was independent of liquid volume. © 2010 Elsevier B.V.

Abstract: In this work, the extraction of Congo red (CR), an anionic disazo direct dye, from aqueous solutions by emulsion liquid membrane (ELM) was investigated. The important operational parameters governing emulsion stability and extraction behavior of dye were studied. The extraction of CR was influenced by a number of variables such as surfactant concentration, stirring speed, acid concentration in the feed solution and volume ratios of internal phase to organic phase and of emulsion to feed solution. Under most favorable conditions, practically all the CR molecules present in the feed phase were extracted even in the presence of salt (NaCl). At the optimum experimental conditions, total removal of antharaquinonic dye Acid Blue 25 was attained after only 10. min. Influence of sodium carbonate concentration as internal receiving phase on the stripping efficiency of CR was examined. The best sodium carbonate concentration in the internal phase that conducted to excellent stripping efficiency (>99%) and emulsion stability was 0.1N. The membrane recovery was total and the permeation of CR was not decreased up to seven runs. ELM process is a promising alternative to conventional methods and should increase awareness of the potential for recovery of anionic dyes. © 2010 Elsevier B.V.

Abstract: The dynamic removal of copper by Purolite C100-MB cation exchange resin was studied in packed bed columns. The values of column parameters are predicted as a function of flow rate and bed height. Batch experiments were performed using the Na-form resin to determine equilibrium and kinetics of copper removal. The uptake of Cu(II) by this resin follows first-order kinetics. The effect of stirring speed and temperature on the removal kinetics was studied. The activation energy for the exchange reaction is 13.58 kJ mol-1. The equilibrium data obtained in this study have been found to fit both the Langmuir and Freundlich isotherm equations. A series of column tests were performed to determine the breakthrough curves with varying bed heights and flow rates. To predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design, four kinetic models; Bohart-Adams, Bed Depth Service Time (BDST), Clark and Wolborska models are applied to experimental data. All models are found suitable for describing the whole or a definite part of the dynamic behavior of the column with respect to flow rate and bed height. The simulation of the whole breakthrough curve is effective with the Bohart-Adams and the Clark models, but the Bohart-Adams model is better. The breakthrough is best predicted by the Wolborska model. The breakthrough data gave a good fit to the BDST model, resulting in a bed exchange capacity very close to the value determined in the batch process. © 2008 Elsevier B.V. All rights reserved.

Abstract: This work describes the results of investigations carried out to examine the adsorption kinetics of 4-chlorophenol (4-CP) from aqueous solution containing tert-butyl alcohol (10%, v/v) onto granular activated carbon (GAC) in the presence of ultrasound of different high frequencies (516, 800 and 1660 kHz) and acoustic powers (15.2, 21.5, 31.1 and 38.3 W). The main objective of this study is to describe the mechanism of ultrasound-assisted adsorption rather than the enhancement of adsorption capacity. Sonochemical degradation of 4-CP was studied in the absence and presence of tert-butyl alcohol. The sonolysis of 4-CP is effectively inhibited by the addition of tert-butyl alcohol (10%, v/v) and very little 4-CP degradation occurs, indicating that little or no pyrolysis of the compound occurs. Without addition of tert-butyl alcohol, after 300 min and at 1660 kHz, the removal of 4-CP in the presence of ultrasound for an acoustic power of 38.3 W was nearly total (99%), but in the conventional method only 60% was eliminated. In this case, the removal of 4-CP by GAC in the ultrasound-assisted technique is due to both adsorption and ultrasonic degradation, but the removal by simple stirring is only due to adsorption, which makes a direct comparison unacceptable. In order to distinguish sonochemical degradation and adsorption of 4-CP onto GAC and to make an exact and practical comparison of the adsorption in the absence and presence of ultrasound, kinetic adsorption experiments were conducted using aqueous solution containing 10% (v/v) tert-butyl alcohol. The obtained results show that both adsorption rate and adsorbed amount were significantly enhanced and improved in the presence of ultrasound for all the studied frequencies and powers. The enhancement of adsorption is favored by increasing ultrasonic power. Adsorption kinetic data were modeled using the liquid-film mass transfer equation and intraparticle diffusion model. The values of the intraparticle diffusion coefficient obtained in the presence of ultrasound are greater than that obtained in the absence of ultrasound. In the initial period of adsorption, where external mass transfer is assumed to predominate, liquid-film mass transfer coefficients significantly increased by the assistance of ultrasound. These results indicate that ultrasound enhances the mass transport in the pores as well as across the boundary layer. This effect increased with increasing ultrasonic power for the three studied frequencies. The average order for the studied ultrasonic waves according to the initial adsorption rate, the intraparticle diffusion coefficient and the liquid-film mass transfer coefficient is 516 kHz > 800 kHz > 1660 kHz. © 2008 Elsevier B.V. All rights reserved.

Abstract: In this work, the influence of CCl4 on the sonochemical decolorization of anthraquinonic dye Acid Blue 25 (AB25) in aqueous medium was investigated using high frequency ultrasound (1700 kHz). This frequency, reputed ineffective, was tested in order to introduce the ultrasound waves with high frequency in the field of degradation or removal of dyes from wastewater, due to its limited use in this field, and to increase the application of high frequency ultrasound wave in the field of environmental protection. The effects of various parameters such as the concentration of CCl4, frequency (22.5 and 1700 kHz), solution pH, temperature and tert-butyl alcohol adding on the decolorization rate of AB25 was studied. The obtained results clearly demonstrated the significant intensification of AB25 decolorization in the presence of CCl4. The enhancement effect of CCl4 increased by decreasing temperature and by increasing the CCl4 concentration. The pH has a significant influence on the bleaching of dye both in the absence and presence of CCl4. The three investigated dosimeter methods (KI oxidation, Fricke reaction and H2O2 production) well corroborate the improvement of the sonochemical effects in the presence of CCl4. The best sonochemical decolorization rate of AB25 in aqueous solution both in the absence and presence of CCl4 is observed to occur at 1700 kHz compared to 22.5 kHz. The sonochemical oxidation of CCl4 generates oxidizing species in the liquid phase that are highly beneficial for oxidation of hydrophilic and non-volatile pollutant, such as dyes, because they are less susceptible to free radical attack due to lower stability of the generated free radicals. © 2008 Elsevier B.V. All rights reserved.

Abstract: In this work, eucalyptus bark, a forest waste, was evaluated for its ability to remove malachite green (MG) from aqueous solutions. Sorption kinetic experiments were studied in a batch mode operation at various initial dye concentrations, sorbent dosages, and temperatures. The equilibrium sorption data of MG by eucalyptus bark were analyzed by Langmuir and Freundlich iso- therm models. The results indicate that both the Langmuir and Freundlich equations provide good correlation of the experimental data, but the Langmuir expression fits the equilibrium data better. The maximum sorption capacity of eucalyptus bark was found to be 59.88 mg g 1 at 20 C. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to analyze the kinetic data obtained at different concentrations. Among the kinetic models studied, the pseudo-second-order was the best applicable model to describe the sorption of MG by eucalyptus bark. The overall rate of dye uptake was found to be controlled by external mass transfer at the beginning of sorption, while intraparticle diffusion controlled the overall rate of sorption at a later stage. The results indicate the potential of eucalyptus bark as biosorbent for the removal of basic dye from aqueous solution. © 2009 Desalination Publications.

Abstract: In this work, the sonolytic degradation of an anthraquinonic dye, C.I. Acid Blue 25 (AB25), in aqueous phase using high frequency ultrasound waves (1700 kHz) for an acoustic power of 14 W was investigated. The sonochemical efficiency of the reactor was evaluated by potassium iodide dosimeter, Fricke reaction and hydrogen peroxide production yield. The three investigated methods clearly show the production of oxidizing species during sonication and well reflect the sonochemical effects of high frequency ultrasonic irradiation. The effect of operational conditions such as the initial AB25 concentration, solution temperature and pH on the degradation of AB25 was studied. Additionally, the influence of addition of salts on the degradation of dye was examined. The rate of AB25 degradation was dependent on initial dye concentration, pH and temperature. Addition of salts increased the degradation of dye. Experiments conducted using distilled and natural waters demonstrated that the degradation was more efficient in the natural water compared to distilled water. To increase the efficiency of AB25 degradation, experiments combining ultrasound with Fe(II) or H2O2 were conducted. Fe(II) induced the dissociation of ultrasonically produced hydrogen peroxide, leading to additional OH radicals which enhance the degradation of dye. The combination of ultrasound with hydrogen peroxide looks to be a promising option to increase the generation of free radicals. The concentration of hydrogen peroxide plays a crucial role in deciding the extent of enhancement obtained for the combined process. The results of the present work indicate that ultrasound/H2O2 and ultrasound/Fe(II) processes are efficient for the degradation of AB25 in aqueous solutions by high frequency ultrasonic irradiation. © 2008 Elsevier B.V. All rights reserved.

Abstract: In this work, the leaves of olive tree (Olea europaea) are proposed as a novel low-cost non-conventional sorbent for the removal of cadmium from aqueous solutions with and without the assistance of ultrasound and by associating simultaneously ultrasonic irradiation and stirring. Sorption kinetics and isotherms were investigated. The operating variables studied were initial cadmium concentration, sorbent dosage, temperature and ultrasonic power. The sorption was significantly increased in the presence of ultrasound. The amount of cadmium sorption with the assistance of ultrasound was improved with the increase of sorbate initial concentration and temperature, and with the decrease of sorbent dosage. The acoustic power was an important factor for the enhancement of the removal of cadmium. The combination of stirring and ultrasound leads to an intensification of the removal of cadmium. Sorption isothermal data could be well simulated by Freundlich model, and then Temkin and Langmuir models. Langmuir simulation showed that the monolayer sorption capacities of olive leaves were 42.19, 55.87 and 64.94 mg g-1 for the conventional method, the ultrasound-assisted method and the combined method, respectively. The kinetic data fitted very well the pseudo-second-order kinetic model. © 2009 Elsevier B.V. All rights reserved.

Abstract: The dead needles of Aleppo pine (Pinus halepensis) were tested as a possible sorbent for the removal of malachite green from aqueous solutions in the absence and presence of ultrasound. Batch process was employed for sorption kinetic and equilibrium studies. Sorption experiments indicated that the sorption capacity was dependent of operating variables. Both the rate and the amount of malachite green sorption are markedly increased in the presence of the ultrasonic field. The dye removal with the assistance of ultrasound was enhanced with the increase of sorbate initial concentration and temperature, and with the decrease of sorbent dosage and ionic strength. The combination of stirring and ultrasound leads to an improvement of the removal of dye. The sorption kinetics was controlled by the intraparticle diffusion. The intraparticle diffusion coefficient increased 1.7 times in the presence of ultrasound and up to 3.6 times in the combined process. The sorption capacity, estimated according to the Freundlich model, indicates that ultrasound enhanced the sorption properties of the sorbent. The effect of ultrasound on the improvement of dye sorption is due to a variety of physical and mechanical effects as well as to thermal properties. The combination of ultrasound and stirring for the sorption process was shown to be of interest for the treatment of wastewaters contaminated with malachite green. © 2008 Elsevier B.V. All rights reserved.

Abstract: In the present study, the aptitudes of cedar (Cedrus atlantica Manatti) sawdust and crushed brick to remove copper(II) ions from aqueous solutions were investigated. Kinetic results and equilibrium removal isotherms were determined. The influence of pH and ionic strength on the sorption of copper was also studied. The removal of copper by both sorbents increased with an increase in contact time and pH (from 1 to 6) and decreased with an increase in ionic strength. Various kinetic models such as the pseudo-first and pseudo-second order rate equations, Boyd model, and external mass-transfer expression were tested. It was concluded that, for both sorbents, copper sorption occurs through a film diffusion mechanism and the kinetic results were best described by the pseudo-second order kinetic model. The equilibrium data has been correlated with both Langmuir and Freundlich isotherms. The results indicate that the Langmuir model fits the data better. The Freundlich model does not lead to a correct determination of the maximum sorption capacity. Thermodynamic parameters such as the changes in free energy, enthalpy, and entropy of sorption of the copper-sorbent systems were also evaluated. The negative values of the change in free energy indicate the feasibility and spontaneous nature of the process, and the negative heats of the change in enthalpy suggest the exothermic nature of the process. Additionally, different types of chemical treatments were applied: alkaline treatments (NaOH, KOH), acidic treatments (H2SO4, H3PO4, CH3COOH), treatments with mineral salts (NaCl, KCl, Na2HPO4, NaHCO3), treatment with urea, and phosphorylation treatment (urea + H3PO4) in order to enhance the sorption aptitudes of the both sorbents. Among the studied chemical treatments applied, treatments with mineral salts (Na2HPO4, KCl, NaCl, and NaHCO3) for crushed brick and alkaline treatments by NaOH and KOH for cedar sawdust were the most effective. © 2008 Elsevier B.V. All rights reserved.

Abstract: The efficiency of eucalyptus bark as a low cost sorbent for removing cadmium ions from aqueous solution has been investigated in batch mode. The equilibrium data could be well described by the Langmuir isotherm but a worse fit was obtained by the Freundlich model. The five linearized forms of the Langmuir equation as well as the non-linear curve fitting analysis method were discussed. Results show that the non-linear method may be a better way to obtain the Langmuir parameters. Maximum cadmium uptake obtained at a temperature of 20 °C was 14.53 mg g-1. The influence of temperature on the sorption isotherms of cadmium has been also studied. The monolayer sorption capacity increased from 14.53 to 16.47 when the temperature was raised from 20 to 50 °C. The ΔG° values were negative, which indicates that the sorption was spontaneous in nature. The effect of experimental parameters such as contact time, cadmium initial concentration, sorbent dose, temperature, solution initial pH, agitation speed, and ionic strength on the sorption kinetics of cadmium was investigated. Pseudo-second-order model was evaluated using the six linear forms as well as the non-linear curve fitting analysis method. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model using the non-linear method. The pseudo-second-order model parameters were function of the initial concentration, the sorbent dose, the solution pH, the agitation speed, the temperature, and the ionic strength. © 2007 Elsevier B.V. All rights reserved.

Abstract: The degradation of 4-chlorophenol (4-CP) in aqueous media by 516 kHz ultrasonic irradiation was investigated in order to clarify the degradation mechanism. The degradation of concentrated 4-CP solution by means of ultrasound, UV irradiation and their combined application was also studied. The obtained results indicate that {radical dot}OH radical are the primary reactive species responsible for 4-CP ultrasonic degradation. Very little 4-CP degradation occurs if the sonolysis is carried out in the presence of the {radical dot}OH radical scavenger tert-butyl alcohol, also indicating that little or no pyrolysis of the compound occurs. The dominant degradation mechanism is the reaction of substrate with {radical dot}OH radicals at the gas bubble-liquid interface rather than high temperature direct pyrolysis in ultrasonic cavities. This mechanism can explain the lower degradation rate of the ionic form of 4-CP that is partly due to the rapid dissociation of {radical dot}OH radicals in alkaline solutions. The sonochemical destruction of concentrated 4-CP aqueous solution is obtained with low rate. Coupling photolysis with ultrasound irradiation results in increased efficiency compared to the individual processes operating at common conditions. Interestingly, the photosonochemical decomposition rate constant is greater than the additive rate constants of the two processes. This 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, dissolved in liquid phase because of the geyser effect of ultrasound streaming. Additionally, the photodecomposition, at 254 nm, of hydrogen peroxide produced by ultrasound generating {radical dot}OH radical can partly explain the destruction enhancement. © 2008 Elsevier B.V. All rights reserved.

Abstract: In the present study, the dead leaves of plane tree (Platanus vulgaris) were investigated as a novel biosorbent of dyes taking aqueous malachite green solutions as a model system. Kinetic data and sorption equilibrium isotherms were carried out in batch process. The effect of different experimental conditions such as contact time, sorbent dose, initial concentration of dye, agitation speed, ionic strength, and temperature on the kinetics of malachite green removal was studied. Modeling of kinetic results shows that sorption process is best described by the type 1 expression of the pseudo-second order model. The sorption rate constant, the sorption equilibrium capacity, and the initial sorption rate were functions of the sorbent dose, the initial concentration, the temperature, and the ionic strength. The agitation speed showed a limited influence on the removal kinetics. The activation energy of the sorption process was also calculated. The malachite green uptake process was found to be controlled by pore diffusion. The average intraparticle diffusion coefficient (D/d2) was calculated and found to be 6.03 × 10-4 min-1. Equilibrium isotherm data could be well described by both the Langmuir and Freundlich models, but the Langmuir expression fits the equilibrium data better. The five Langmuir linear equations were discussed. The effect of temperature on the sorption isotherms of dye has been also studied and the thermodynamic parameters ΔG°, ΔH°, and ΔS° were determined. © 2007 Elsevier B.V. All rights reserved.

Abstract: In this study, eucalyptus camaldulensis bark, a forest solid waste, is proposed as a novel material for the removal of mercury(II) from aqueous phase. The operating variables studied were sorbent dosage, ionic strength, stirring speed, temperature, solution pH, contact time, and initial metal concentration. Sorption experiments indicated that the sorption capacity was dependent on operating variables and the process was strongly pH-dependent. Kinetic measurements showed that the process was uniform and rapid. In order to investigate the mechanism of sorption, kinetic data were modeled using the pseudo-first-order and pseudo-second-order kinetic equations, and intraparticle diffusion model. Among the kinetic models studied, the pseudo-second-order equation was the best applicable model to describe the sorption process. Equilibrium isotherm data were analyzed using the Langmuir and the Freundlich isotherms. The Langmuir model yields a much better fit than the Freundlich model. Isotherms have also been used to obtain the thermodynamic parameters such as free energy, enthalpy, and entropy of sorption. The maximum sorption capacity was 33.11 mg g-1 at 20 °C and the negative value of free energy change indicated the spontaneous nature of sorption. These results demonstrate that eucalyptus bark is very effective in the removal of Hg(II) from aqueous solutions. © 2008 Elsevier B.V. All rights reserved.

Abstract: The main objective of this work is the utilization of W/O emulsions prepared by low-frequency ultrasonic irradiation (22.5 kHz) for the removal and recovery of cationic dyes from aqueous solution by emulsion liquid membrane containing di(2-ethylhexyl) phosphoric acid (D2EHPA) as carrier. The important parameters governing the extraction behavior of dyes have been investigated. These parameters were contact time of the external phase with W/O emulsions, external phase concentration, feed phase pH, stirring speed, extractant concentration, presence of salts, and type of diluent. The extraction of a mixture of four cationic dyes (methylene blue, rhodamine B, malachite green, and basacryl red GL) is also investigated in the absence and presence of salt in the external phase. The possibility of stripping the dyes is evaluated and the influence of sulfuric acid concentration on the stripping efficiency is also examined. The obtained results show that, under most favorable conditions, practically all the dye cations present in the feed phase were extracted. The removal percentage of the mixed dye was found to be higher than 98% even in the presence of salt in the continuous phase. The transport mechanism of cationic dyes for the present system was determined and divided into six stages. The best sulfuric acid concentration in the internal phase that conducted to very good stripping efficiency (≥97%) and excellent emulsion stability was 0.5 M. In all cases, the recovery of the membrane phase was total and the extraction of dyes was not decreased up to seven runs. © 2008 Elsevier B.V. All rights reserved.

Abstract: In this work, the efficiency of emulsification by ultrasound was investigated for the preparation of water-in-oil (W/O) emulsions. The produced W/O emulsions will be employed for the recovery and separation of cationic dyes by emulsion liquid membrane (ELM), a novel and effective method. The study highlights the importance of emulsion stability that is the major problem associated with ELMs. The membrane phase contained hexane as diluent, di(2-ethylhexyl)phosphoric acid (D2EHPA) as extractant, and Span 80 as emulsifying agent. The internal aqueous phase consisted of a solution of sulfuric acid. The influence of operating parameters that affect the stability such as ultrasonic power, emulsification time, carrier, surfactant, and internal phase concentrations, volume ratios of internal phase to organic phase and of external phase to W/O emulsions, stirring speed, diluent, and contact time was studied. The results showed that the production of W/O emulsions by using ultrasound is a very attractive and effective technique and an excellent stability was obtained. © 2008 Elsevier B.V. All rights reserved.

Abstract: In this work, a fundamental investigation on the removal of methylene blue from aqueous solutions by wheat bran is conducted in batch conditions. Removal kinetic data are determined, and the effects of different experimental parameters, such as wheat bran mass, initial concentration of methylene blue, agitation speed, solution pH, particle size, temperature, and ionic strength on the kinetics of methylene blue removal are investigated. The cationic dye recovery increases with an increase of sorbent mass, solution pH, and temperature. Methylene blue removal decreases with an increase of initial concentration, particle size, and ionic strength. The agitation speed showed a limited influence on the removal kinetics. Modeling of kinetic results shows that sorption process is best described by the pseudo-second order model, with determination coefficients higher than 0.996 under all experimental conditions. The applicability of both internal and external diffusion models shows that liquid-film and particle diffusion are effective sorption mechanisms. The activation energy of sorption calculated using the pseudo-second order rate constants is found to be 13.41 kJ mol-1 from an Arrhenius plot. The low value of the activation energy indicates that sorption is an activated and physical process. Thus, wheat bran, a low cost and easily available biomaterial, can be efficiently used as an excellent sorbent for the removal of dyes from wastewater. It can be safely concluded that wheat bran is much economical, effectual, viable, and can be an alternative to more costly adsorbents.

Abstract: In this work, the mechanisms underlying ultrasonic desorption of 4-chlorophenol from granular activated carbon have been explored. Desorption experiments are investigated in the absence and presence of 516 kHz ultrasound of different intensities. Using three regenerating solutions and two temperatures, it has been shown that ultrasonic irradiation considerably improves both the amount and the rate of desorption. Desorption increases with increasing temperature and ultrasound intensity. The addition of sodium hydroxide or a mixture of sodium hydroxide and ethanol to the regenerating medium leads to an enhancement of the desorption, especially in the presence of ultrasound. The mechanisms of ultrasonically enhanced desorption is due both to the thermal and non-thermal (hydrodynamical) effects of ultrasound. Hydrodynamical phenomena are principally produced by the acoustic vortex microstreaming within porous solids as well as at the solid-liquid interface and by the high-speed micro-jets and high-pressure shock waves produced by acoustic cavitation. The thermal effects are evaluated as localized hot spots formed when bubbles cavitated as well as by global heating of the medium and piezoelectric transducer heating-up. Additionally, the non-thermal effect of ultrasound is greater than the thermal effect, and it is more noticeable when the ultrasonic irradiation is carried out in a high temperature regenerating medium. © 2007 American Institute of Chemical Engineers.

Abstract: The adsorption equilibrium isotherms of five phenolic compounds from aqueous solutions onto granular activated carbon (GAC) were studied and modeled. Phenol (Ph), 2-chlorophenol (2-CP), 4-chlorophenol (4-CP), 2,4-dichlorophenol (DCP), and 2,4,6-trichlorophenol (TCP) were chosen for the adsorption tests. To predict the adsorption isotherms and to determine the characteristic parameters for process design, seven isotherm models: Langmuir (five linear forms), Freundlich, Elovich, Temkin, Fowler-Guggenheim, Kiselev, and Hill-de Boer models were applied to experimental data. The results reveal that the adsorption isotherm models fitted the data in the order: Fowler-Guggenheim > Hill-de Boer > Temkin > Freundlich > Kiselev > Langmuir isotherms. Adsorption isotherms modeling shows that the interaction of phenolic compounds with activated carbon surface is localized monolayer adsorption, that is adsorbed molecules are adsorbed at definite, localized sites. Each site can accommodate only one molecule. The interaction among adsorbed molecules is repulsive and there is no association between them, adsorption is carried out on energetically different sites and is an exothermic process. Uptake of phenols increases in the order Ph < 2-CP < 4-CP < DCP < TCP, which correlates well with respective increase in molecular weight, cross-sectional area, and hydrophobicity and decrease in solubility and pKa. Additionally, for the four tested chlorophenols, it seems that the magnitude of adsorption is directly proportional to their degree of chlorination. © 2007 Elsevier B.V. All rights reserved.

Abstract: In the present study, the sorption of cadmium from aqueous phase by wheat bran was investigated with and without the assistance of ultrasound. Kinetic data and sorption equilibrium isotherms were carried out in batch conditions. The influence of different operating parameters such as ultrasonic power, cadmium initial concentration, sorbent mass, temperature, and the combination of ultrasound and mechanical stirring on the kinetics of cadmium removal was studied. The obtained results show that the ultrasonic irradiation significantly enhances and improves the efficiency of the removal of cadmium, especially in the combined method. The sorption kinetic data were found to be well-represented by the pseudo-second-order rate equation, both in the absence and presence of ultrasound as well as in the combined process (stirring and ultrasonication). Ultrasonic power played a key role in the removal of cadmium. Equilibrium isotherm results could be well described by the Langmuir model both with and without the assistance of ultrasound. The effect of temperature on the sorption isotherms of cadmium in the absence and presence of ultrasound has been also studied and the thermodynamic parameters △G°, △H°, and △S° were determined. The monolayer, sorption capacities were 51.81, 35.09, and 22.78 mg g-1 for experiments conducted by the combined process, in the presence of ultrasound, and in passive conditions, respectively. The combination ultrasound-stirring for the sorption process was shown to be of interest for the treatment of wastewaters contaminated with cadmium. © 2007 American Chemical Society.

Abstract: The adsorption equilibrium isotherms of five phenolic compounds, phenol, 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, and 2,4,6-trichlorophenol, from aqueous solutions onto granular activated carbon were studied and modeled. In order to determine the best-fit isotherm, the experimental equilibrium data were analyzed using thirteen adsorption isotherm models with more than two-parameter; nine three-parameter equations - the Redlich-Peterson, Sips, Langmuir-Freundlich, Fritz-Schlunder, Radke-Prasnitz (three models), Tóth, and Jossens isotherms - three four-parameter equation - the Weber-van Vliet, Fritz-Schlunder, and Baudu isotherms - and one five-parameter equation - the Fritz-Schlunder isotherm. The results reveal that the adsorption isotherm models fitted the experimental data in the order: Baudu (four-parameter) > Langmuir-Freundlich (three-parameter) > Sips (three-parameter) > Fritz-Schlunder (five-parameter) > Tóth (three-parameter) > Fritz-Schlunder (four-parameter) > Redlich-Peterson (three-parameter). The influence of solution pH on the adsorption isotherms of 4-CP was investigated. It was shown that the solution pH has not an effect on the adsorption isotherms for pH < pKa. The pH at which the uptake decreased was found to be dependent on the adsorptive pKa and the pHPZC. © 2007 Elsevier B.V. All rights reserved.

Abstract: Studies on a batch sorption process using wheat bran as a low cost sorbent was investigated to remove cadmium ions from aqueous solution. The influence of operational conditions such as contact time, cadmium initial concentration, sorbent mass, temperature, solution initial pH, agitation speed and ionic strength on the sorption kinetics of cadmium was studied. Pseudo-second-order model was evaluated using the six linear forms as well as the non-linear curve fitting analysis method. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model using the non-linear method. The sorption of cadmium was found to be dependent on initial concentration, sorbent mass, solution pH, agitation speed, temperature, ionic strength and contact time. The value of activation energy (12.38 kJ mol-1) indicates that sorption has a low potential barrier corresponding to a physical process. Sorption equilibrium isotherms at different temperatures was determined and correlated with common isotherm equations such as Langmuir and Freundlich models. It was found that the Langmuir model appears to well fit the isotherm data but a worse correlation was obtained by the Freundlich model. The five Langmuir linear equations as well as the non-linear curve fitting analysis method were discussed. Results show that the non-linear method may be a better way to obtain the Langmuir parameters. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were calculated. These parameters indicate that the sorption of cadmium by wheat bran is a spontaneous process and physical in nature involving weak forces of attraction and is also endothermic. © 2007 Elsevier B.V. All rights reserved.

Abstract: This paper presents a study on the batch adsorption of basic dye, methylene blue, from aqueous solution (40 mg L-1) onto cedar sawdust and crushed brick in order to explore their potential use as low-cost adsorbents for wastewater dye removal. Adsorption isotherms were determined at 20 °C and the experimental data obtained were modelled with the Langmuir, Freundlich, Elovich and Temkin isotherm equations. Adsorption kinetic data determined at a temperature of 20 °C were modelled using the pseudo-first and pseudo-second-order kinetic equations, liquid-film mass transfer and intra-particle diffusion models. By considering the experimental results and adsorption models applied in this study, it can be concluded that equilibrium data were represented well by a Langmuir isotherm equation with maximum adsorption capacities of 142.36 and 96.61 mg g-1 for cedar sawdust and crushed brick, respectively. The second-order model best describes adsorption kinetic data. Analysis of adsorption kinetic results indicated that both film- and particle-diffusion are effective adsorption mechanisms. The Influence of temperature and pH of the solution on adsorption process were also studied. The extent of the dye removal decreased with increasing the solution temperature and optimum pH value for dye adsorption was observed at pH 7 for both adsorbents. The results indicate that cedar sawdust and crushed brick can be attractive options for dye removal from dilute industrial effluents. © 2005 Elsevier B.V. All rights reserved.

Abstract: Experimental results for the batch extraction of chromium (VI) from sulphuric acid aqueous solutions using a liquid surfactant membrane (LSM) are presented. Effects of various parameters such as time and speed of emulsification, internal phase concentration, extractant concentration, choice and concentration of surfactant, contact time, stirring speed, choice of diluent, and volume ratios of the membrane phase to internal stripping phase and that of the water-in-oil emulsions to the aqueous external phase on the membrane stability were studied. The membrane phase consists of hexane as diluent, tributyl phosphate, as extractant, and sorbiton monooleate (Span 80) as surfactant. A NaOH solution is the internal aqueous phase. Results show that with proper adjustment of experimental conditions the stability of the membrane can be enhanced to a great extent. This study also examined the effects of the concentrations of feed phase acid, metal ions, and carrier on the extraction of Cr(VI) ions. Further, the extraction kinetics of the metal ions by LSMs was examined. The results also showed that by appropriate selection of the extraction and stability conditions, nearly all of the Cr(VI) ions present in the continuous phase were extracted within a few minutes. The influence of the NaOH concentration on stripping efficiency was investigated. © 2006 Elsevier B.V. All rights reserved.

Abstract: The dynamic removal of methylene blue by cedar sawdust and crushed brick was studied in packed bed columns. The values of column parameters were predicted as a function of flow rate and bed height. On evaluating the breakthrough curves, the sorption isotherms of methylene blue onto cedar sawdust and crushed brick in 20 °C aqueous solution were experimentally determined in batch conditions. Both the Freundlich and the Langmuir models were found to fit the sorption isotherm data well, but the Langmuir model was better. A series of column tests using cedar sawdust and crushed brick as low-cost sorbents were performed to determine the breakthrough curves with varying bed heights and flow rates. To predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design, five kinetic models; Bohart and Adams, bed depth service time (BDST), Clark, Wolborska, and Yoon and Nelson models were applied to experimental data. All models were found suitable for describing the whole or a definite part of the dynamic behavior of the column with respect to flow rate and bed height, with the exception of Bohart and Adams model. The simulation of the whole breakthrough curve was effective with the Yoon and Nelson and the Clark models, but the breakthrough was best predicted by the Wolborska model. © 2006 Elsevier B.V. All rights reserved.

Abstract: In this study ultrasound was used as an alternative method to regenerate granular activated carbon saturated with p-chlorophenol. Desorption experiments of exhausted activated carbon have been conducted in the presence of ultrasound of different frequencies (21, 800 and 1660 kHz) and in silent conditions with stirring. The desorption rates were significantly increased by ultrasound. The ultrasonic effects increase with increasing acoustic intensity at frequencies of 21 and 800 kHz. The rates of desorption of p-chlorophenol from activated carbon appreciably increase by increasing temperature. In all cases, this rise is more noticeable as ultrasonic power increases. The stability of activated carbon was not affected until an ultrasonic power of 38.3 W showing the adsorbent stiffness towards ultrasonic application. The addition of NaOH to the desorption system causes an enhancement in the amount of p-chlorophenol desorbed, especially in the presence of ultrasound. The rate of desorption was significantly increased by the addition of ethanol to the regenerating solution. This behaviour was higher in the presence of ultrasonic irradiation, with the exception of that at 1660 kHz. In general, a synergetic enhancement of the desorption rate was observed when ultrasonic irradiation was coupled with chemical regeneration. © 2004 Elsevier B.V. All rights reserved.

Abstract: The aim of the present work is to explore the effects of ultrasound on desorption of metal ions from activated carbon. The desorption of Cu(II), Mn(II), Hg(II), and Cr(VI) from activated carbon in the absence and the presence of ultrasound is investigated. Desorption studies are performed under various conditions of temperature and intensity. Results indicate that ultrasonic irradiation considerably improves the desorbed amount and the rate of desorption. The amount of desorbed metal ions increases with increasing temperature and ultrasound intensity. The addition of ethanol to the desorption system leads to an enhancement of the desorption rates, especially in the presence of ultrasound. Acidification of the regenerating solution to pH l leads to an enhancement of the desorption of Cu(II). This improvement is more obvious in the presence of ultrasound. Modeling of desorption kinetics shows that ultrasound enhances surface diffusivity. This can be attributed to the phenomena induced by acoustic cavitation: acoustic vortex microstreaming, high-speed microjets, high-pressure shock waves, and intense localized heating. © 2005 American Chemical Society.

Abstract: 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. © 2002 Elsevier Science B.V. All rights reserved.

Abstract: The general objective of this work was to compare the performance of conventional coagulants (aluminum sulfate, ferric chloride) with that of polymeric coagulants (PASS, PAC, SPIC) for the removal of organic matter. There were carried out entirely in the laboratory using conventional Jar test apparatus. The coagulated effluents were filtered on a laboratory sand filter. Coagulation tests were carried out under different conditions of pH, temperature and coagulant concentration. The effect of activated silica used as a coagulant aid and the influence of flocculation time were also studied. This study was conducted using two types of surface raw water: Seybouse river water and Bounamoussa dam water (Annaba - Algeria). The obtained results show that the optimal removal of organic matter accurse at low pH conditions for all coagulants used. Low temperature and activated silica used as a coagulant aid, were found to slightly impair organic matter removal. Considering the industrial application of coagulation with PASS and activated silica, organic matter removal should be improved as the time between the injection points in the plant of the two reagents increases. Results also showed that a signifiant amount of organic matter is removed during the first minutes of the flocculation process. This observation was more pronounced in the case of polymeric coagulants. A slight improvement in organic matter removal was observed with polymeric coagulants under low pH conditions. In normal conditions of treatment i.e.: pH7, aluminum sulfate and ferric chloride remain the best choices for the removal of organic matter considering the higher cost of polymeric coagulants.

Abstract: In this study, electrochemical measurements were carried out to characterize the inhibition efficiency of the commercial product Kemazur 1620, employed for water treatment in cooling circuits. The influence of parameters such as the concentration of the compound and the effect of the temperature on the behavior of the carbon steel / corrosion medium interface was studied. Polarization curves have been obtained by a three-electrode device. In the first part of this study, only the evolution of the corrosion rate as a function of concentration was examined. It has been shown from the polarization curves that the Kemazur 1620 presents a very good efficiency for a concentration of 2.000 ppm. Between 1.000 and 2.000 ppm, the inhibition efficiency increases from 56 to 91%. In a second part, the inhibition efficiency of the compound has been compared to an inhibitor used for similar uses. In this study, electrochemical measurements were carried out to characterize the inhibition efficiency of the commercial product Kemazur 1620, employed for water treatment in cooling circuits. The influence of parameters such as the concentration of the compound and the effect of the temperature on the behavior of the carbon steel/corrosion medium interface was studied. Polarization curves have been obtained by a three-electrode device. In the first part of this study, only the evolution of the corrosion rate as a function of concentration was examined. It has been shown from the polarization curves that the Kemazur 1620 presents a very good efficiency for a concentration of 2.000 ppm. Between 1.000 and 2.000 ppm, the inhibition efficiency increases from 56 to 91%. In a second part, the inhibition efficiency of the compound has been compared to an inhibitor used for similar uses.

Abstract: Acoustic cavitation is responsible for both sonochemistry and sonoluminescence. In this theoretical investigation, computer simulation of chemical reactions occurring in an isolated cavitation bubble oscillating in water irradiated by an ultrasonic wave has been performed for various acoustic amplitudes, different static pressures and diverse liquid temperatures to study the relationship between these three key parameters in sonochemistry and the oxidants created in the bubble. The results of the numerical simulations indicated that the main oxidants created in an O2 bubble are •OH radical and O atom. The amount of the oxidants formed in the bubble at the end of the bubble collapse increases as the acoustic amplitude increases from 1.5 to 3 atm. For each acoustic amplitude, there exists an optimal static pressure for the production of the oxidants, which shifts toward a higher value as the acoustic amplitude increases. Correspondingly, for each acoustic amplitude, an optimum of liquid temperature was observed at 20 °C for •OH, HO2 • and H2O2. The simple model adopted in this work, after comparisons with the trends obtained with the literature experimental observations, seems to satisfactorily explain the experimental observations and should practically aid in optimization of operating conditions for sonochemical reactions. Results from this study were discussed and some recommendations were given. © 2013 Springer Science+Business Media Dordrecht.

Abstract: The ability of melon peel (Cucumis melo L.) (MP) for the biosorption of methylene blue (MB), a cationic dye, from aqueous solutions was investigated. Biosorption isotherm and kinetics of MB by MP were studied through a number of batch sorption experiments. The influence of operating conditions such as initial dye concentration, biosorbent dose, initial pH, stirring speed, temperature, and ionic strength on the removal of MB was examined. Equilibrium data were fitted to the Langmuir, Freundlich, and Temkin isotherm models. Experimental equilibrium data were best represented by the Langmuir isotherm with maximum monolayer sorption capacity of 333 mg g-1. Biosorption kinetic obtained at different initial concentrations were analyzed using pseudo-first-order and pseudo-second-order equations. The pseudo-second-order model fit the kinetic data well and was better than the pseudo-first-order equation. The results revealed that the MP has the potential to be used as a biosorbent for the removal of MB from aqueous solutions. © 2013 Copyright Balaban Desalination Publications.

Abstract: In this work, the removal of the worldwide non-steroidal anti-inflammatory drugs ibuprofen (IBP) and ketoprofen (KTP) by emulsion liquid membrane (ELM) was carried out. An ELM system is made up of hexane as diluent, Span 80 as the surfactant and sodium carbonate as the inner aqueous solution. Effect of experimental conditions that affect the extraction of IBP such as surfactant concentration, emulsification time, sulfuric acid concentration in external phase, acid type in external phase, internal phase concentration, type of internal phase, stirring speed, volume ratio of internal phase to membrane phase, treatment ratio, IBP initial concentration, diluent type and salt was investigated. The obtained results showed that by appropriate selection of the operational parameters, it was possible to extract nearly all of IBP molecules from the feed solution even in the presence of high concentration of salt. Under optimum operating conditions, the efficiencies of IBP removal from distilled water (99.3 %), natural mineral water (97.3 %) and sea water (94.0 %) were comparable, which shows that the ELM treatment process represents a very interesting advanced separation process for the removal of IBP from complex matrices such as natural and sea waters. Under the optimized experimental conditions, approximately 97.4 % KTP was removed in less than 20 min of contact time. © 2013 Springer-Verlag Berlin Heidelberg.

Abstract: Potato peel (PP) was used as a biosorbent to remove malachite green (MG) from aqueous solution under various operating conditions. The effect of the experimental parameters such as initial dye concentration, biosorbent dose, initial pH, stirring speed, temperature, ionic strength and biosorbent particle size was investigated through a number of batch sorption experiments. The sorption kinetic uptake for MG by PP at various initial dye concentrations was analyzed by non-linear method using pseudo-first, pseudo-second and pseudo-nth order models. It was found that the pseudo-nth order kinetic model was the best applicable model to describe the sorption kinetic data and the order n of sorption reaction was calculated in the range from 0.71 to 2.71. Three sorption isotherms namely the Langmuir, Freundlich and Redlich-Peterson isotherms in their non-linear forms were applied to the biosorption equilibrium data. Both the Langmuir and Redlich-Peterson models were found to fit the sorption isotherm data well, but the Redlich-Peterson model was better. Thermodynamic parameters show that the sorption process of MG is endothermic and more effective process at high temperatures. The results revealed that PP is very effective for the biosorption of MG from aqueous solutions. © 2011.