Removal of dinitrotoluenes in wastewater by sono-activated persulfate

Oxidative degradation of dinitrotoluenes (DNTs) in wastewater was performed using persulfate anions combined with ultrasonic irradiation, wherein a synergistic effect is observed. The batch-wise experiments were carried out to elucidate the influence of various operating parameters on sono-activated persulfate oxidation, including ultrasonic power intensity, persulfate anion concentration, reaction temperature and acidity of wastewater. It is noteworthy that the nitrotoluene contaminants could be almost completely eliminated by virtue of sono-activated persulfate oxidation, wherein sulfate radicals serve as principal oxidants, of which amounts are significantly enhanced via addition of sodium sulfate. Based on the results given by gas chromatograph-mass spectrometer (GC-MS), it is postulated that the methyl group of DNTs preliminarily underwent oxidation pathway into dinitrobenzoic acid, followed by decarboxylation to form 1,3-dinitrobenzene (DNB). In sum, the sono-activated persulfate oxidation is a promising method for treatment of nitrotoluenes in wastewater.     

Degradation of amoxicillin in aqueous solution using sulphate radicals under ultrasound irradiation

Degradation of the antibiotics amoxicillin in aqueous solution using sulphate radicals under ultrasound irradiation was investigated. The preliminary studies of optimal degradation methodology were conducted with only oxone (2KHSO₅·KHSO₄·K₂SO₄), cobalt activated oxone (oxone/Co²⁺), oxone + ultrasonication (oxone/US) and cobalt activated oxone + ultrasonication (oxone/Co²⁺/US). The chemical oxygen demand (COD) removal efficiency were in the order of oxone < oxone/Co²⁺ < oxone/US < oxone/Co²⁺/US for the amoxicillin solution. The variables considered for the effect of degradation were the temperature, the power of ultrasound, the concentration of oxone, as well as catalyst and the initial amoxicillin concentration. More than 98% of COD removal was achieved within 60 min under optimum operational conditions. Comparative analysis revealed that the sulfate radicals had the high oxidation potential and the use of ultrasound irradiation reduced the energy barrier of the reaction and increased the COD removal efficiency of organic pollutants. The degradation of amoxicillin follows the first-order kinetics.     

Improving sono-activated persulfate oxidation using mechanical mixing in a 35-kHz ultrasonic reactor: Persulfate activation mechanism and its application

This study investigated the degradation of ibuprofen (IBP), an activated persulfate (PS), when subjected to ultrasonic (US) irradiation and mechanical mixing (M). The effects of several critical factors were evaluated, including the effect of rpm on M, PS concentration, and initial pH, and that of temperature on IBP degradation kinetics and the PS activation mechanism. The resulting IBP oxidation rate constant was significantly higher at 400 rpm. As the PS load increased, the IBP oxidation rate constant increased. The value of the IBP reaction rate increased with decreasing pH; below pH 4.9, there was no significant difference in the IBP oxidation rate constant. The IBP oxidation activation energy when using the US/M-PS system was 18.84 kJ mol⁻¹. In the US/M-PS system, PS activation was the primary effect of temperature at the interface during the explosion of cavitation bubbles. These encouraging results suggest that the US-PS/M process is a promising strategy for the treatment of IBP-based water pollutants.     

Intensification of sonochemical degradation of ammonium perfluorooctanoate by persulfate oxidant

Ammonium perfluorooctanoate (APFO) is an emerging environmental pollutant attracting significant attention due to its global distribution, high persistence, and bioaccumulation properties. The decomposition of APFO in aqueous solution with a combination of persulfate oxidant and ultrasonic irradiation was investigated. The effects of operating parameters, such as ultrasonic power, persulfate concentration, APFO concentration, and initial media pH on APFO degradation were discussed. In the absence of persulfate, 35.5% of initial APFO in 46.4 μmol/L solution under ultrasound irradiation, was decomposed rapidly after 120 min with the defluorination ratio reaching 6.73%. In contrast, when 10 mmol/L persulfate was used, 51.2% of initial APFO (46.4 μmol/L) was decomposed and the defluorination ratio reached 11.15% within 120 min reaction time. Enhancement of the decomposition of APFO can be explained by acceleration of substrate decarboxylation, induced by sulfate radical anions formed from the persulfate during ultrasonic irradiation. The SO₄^−•/APFO reactions at the bubble-water interface appear to be the primary pathway for the sonochemical degradation of the perfluorinated surfactants.     

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

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

Enrichment of surfactant from its aqueous solution using ultrasonic atomization

Dilute aqueous solutions of dodecyl-benzenesulfonic acid sodium salt (DBS-Na) and polyoxyethylenenonylphenyl ethers (PONPEs) were ultrasonically atomized. The surfactants were concentrated in collected mist droplets. The enrichment ratio increased with decreasing surfactant concentration. Depending on the surfactant’s molecular weight and affinity to water, different enrichment ratio was observed in the range of low feed concentrations. For anionic surfactant, DBS-Na, the enrichment ratio was significantly improved by KCl addition and a peak appeared on the plot of the ratio against KCl concentration. Addition of NaCl or CaCl₂ · 2H₂O to the surfactant solution also enhanced the enrichment ratio; however, the effect was relatively small. Such behaviors of the ratio were interpreted as enhanced interfacial adsorption of the surfactant and a lack of supply of surfactant monomers from liquid bulk because of slow breaking of surfactant micelles. Time required for collecting an amount of mist was also observed. Among the three salt systems, the time for KCl system was twice as long as others. This fact suggested that the formation of smaller droplets in KCl system.     

Application of persulfate with hydrodynamic cavitation and ferrous in the decomposition of pentachlorophenol

Hydrodynamic cavitation (HC) and Fe(II) are advanced oxidation processes, in which pentachlorophenol (PCP) is treated by the redox method of activating persulfate (PS). The kinetics and mechanism of the HC and Fe(II) activation of PS were examined in aqueous solution using an electron spin resonance (ESR) spin trapping technique and radical trapping with pure compounds. The optimum ratio of Fe(II)/PS was 1:2, and the hydroxyl radical (HO) and sulfate radical (SO₄⁻) generation rate were 5.56 mM h⁻¹ and 8.62 μM h⁻¹, respectively. The generation rate and R_ct of HO and SO₄⁻ at pH 3 and 50 °C in the Fe(II)/PS/HC system are 7584.6 μM h⁻¹, 0.013 and 24.02 μM h⁻¹, 3.95, respectively. The number of radicals was reduced as the pH increased, and it increased with increasing temperature. The PCP reaction rate constants was 4.39 × 10⁻² min⁻¹ at pH 3 and 50 °C. The activation energy was 10.68 kJ mol⁻¹. In addition, the mechanism of PCP treatment in the Fe(II)/PS/HC system was a redox reaction, and the HO⁻/SO₄⁻ contribution was 81.1 and 18.9%, respectively. In this study, we first examined PCP oxidation through HO and SO₄⁻ quantification using only the Fe(II)/PS/HC process. Furthermore, the results provide the foundation for activation of PS by HC and Fe(II), but also provide a data basis for similar organic treatments other than PCP.     

Removal and recovery of mercury from aqueous solution using magnetic silica nanocomposites

Thiol-functionalized magnetic silica nanocomposite was synthesized and tested for its mercury pick-up capability in aqueous solution. Magnetic property was to be utilized upon the collection of the adsorbents and the recovery adsorbed Hg by subsequent separation process. Cobalt ferrite nanoparticle, the core of magnetic silica nanocomposite, was synthesized using a thermal decomposition method and grown to a particle having an average size of 13 nm. The dispersed nanoparticles were then further arranged into spherical groups using a nanoemulsion method to enhance the reactivity toward magnets followed by tetraethyl orthosilicate coating using a modified Stöber method. The pore structure was modified by an additional coating of cetyltrimethylammonium bromide and tetraethyl orthosilicate. Finally, the surface of the magnetic silica nanocomposite was functionalized with thiol group. When tested for mercury adsorption capacity, a sufficiently high Hg adsorption capacity of 19.79 mg per g of adsorbent was obtained at room temperature and a pH of 5.5.     

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

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

Ultrasound and heat enhanced persulfate oxidation activated with Fe0 aggregate for the decolorization of C.I. Direct Red 23

Effluents from the paper printing and textile industries are often heavily contaminated with azo dyes. Azo dyes are difficult to oxidize biologically. This work investigated the decolorization of an azo dye, C.I. Direct Red 23 (DR23), by persulfate (PS) activated with Fe⁰ aggregates (PS/Fe⁰). Ultrasound (US) and heat were used as enhancement tools in the PS oxidation system. Neither US-activated PS nor thermally activated PS was effective in oxidizing DR23. However, the decolorization was significantly enhanced by PS/Fe⁰ combined with US (PS/Fe⁰/US) or heat (PS/Fe⁰/55 °C). Approximately 95% decolorization of 1 × 10⁻⁴ M DR23 was achieved within 15 min in the PS/Fe⁰/US system at an initial pH of 6.0, PS of 5 × 10⁻³ M, Fe⁰ of 0.5 g/L and US irradiation of 106 W/cm² (60 kHz). Complete decolorization was achieved within 10 min in the Fe⁰/PS/55 °C system. The rate of decolorization doubled when US was introduced in the PS/Fe⁰ system during the treatment of different initial dye concentrations. The dependence of dye and true color (ADMI) depletion on PS concentration has been discussed. DR23 was completely degraded based on the disappearance of aromatic groups of UV–vis spectra and the variation of TOC mineralization. The observed pseudo-first-order decolorization rate was substantially enhanced by increasing temperature. The Arrhenius activation energy for the PS activated with Fe⁰ was estimated as 8.98 kcal/mol, implying that higher temperature is beneficial for the DR23 decolorization. The addition of US into the PS/Fe⁰ system did not incur a substantial increase in electricity, whereas the mineralization of DR23 occurred quickly. Thus, both PS/Fe⁰/US and heated PS/Fe⁰ systems are practically feasible for the effective degradation of the direct azo dye in textile wastewater.     

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

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

磁性碳纳米管吸附去除水中甲基橙的研究

采用高温催化裂解法制备碳纳米管,对其用浓硝酸氧化法进行纯化处理,并用化学共沉淀方法制备了磁性碳纳米管(简称磁性管)。利用场发射扫描电子显微镜对磁性管进行了表征。将磁分离技术应用于碳纳米管吸附性能研究,探索碳纳米管负载磁性颗粒后对甲基橙的吸附性能,寻找最佳实验条件,对吸附质溶液进行紫外-可见吸收光谱分析。同时,进行了磁性管的脱附和再吸附性能研究。     

Ultrasound-assisted removal of malachite green from aqueous solution by dead pine needles

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.     

Ultrasound assisted enzymatic depolymerization of aqueous guar gum solution

The present work investigates the effectiveness of application of low intensity ultrasonic irradiation for the intensification of enzymatic depolymerization of aqueous guar gum solution. The extent of depolymerization of guar gum has been analyzed in terms of intrinsic viscosity reduction. The effect of ultrasonic irradiation on the kinetic and thermodynamic parameters related to the enzyme activity as well as the intrinsic viscosity reduction of guar gum using enzymatic approach has been evaluated. The kinetic rate constant has been found to increase with an increase in the temperature and cellulase loading. It has been observed that application of ultrasound not only enhances the extent of depolymerization but also reduces the time of depolymerization as compared to conventional enzymatic degradation technique. In the presence of cellulase enzyme, the maximum extent of depolymerization of guar gum has been observed at 60 W of ultrasonic rated power and ultrasonic treatment time of 30 min. The effect of ultrasound on the kinetic and thermodynamic parameters as well as the molecular structure of cellulase enzyme was evaluated with the help of the chemical reaction kinetics model and fluorescence spectroscopy. Application of ultrasound resulted in a reduction in the thermodynamic parameters of activation energy (E_a), enthalpy (ΔH), entropy (ΔS) and free energy (ΔG) by 47%, 50%, 65% and 1.97%, respectively. The changes in the chemical structure of guar gum treated using ultrasound assisted enzymatic approach in comparison to the native guar gum were also characterized by FTIR. The results revealed that enzymatic depolymerization of guar gum resulted in a polysaccharide with low degree of polymerization, viscosity and consistency index without any change in the core chemical structure which could make it useful for incorporation in food products.     

Sonolytic degradation of hazardous organic compounds in aqueous solution

Benzene, chlorobenzene, 1,2-, 1,3-, 1,4-dichlorobenzene, biphenyl, and polychlorinated biphenyls such as 2-, 4-chlorobiphenyl and 2,2′-dichlorobiphenyl in aqueous solutions have been subjected to sonolysis with 200 kHz ultrasound at an intensity of 6 W cm⁻² under an argon atmosphere. 80–90% of initial amount of these compounds were degraded by 30–60 min of sonication when the initial concentrations were 10–100 μmol l⁻¹. The degradation rate of these compounds increased with increase in their vapor pressures. In all cases of sonolysis of chlorinated organic compounds, an appreciable amount of liberated chloride ion was observed.     

Removal of disperse blue 2BLN from aqueous solution by combination of ultrasound and exfoliated graphite

This paper reports an efficient and convenient removal of disperse blue 2BLN from aqueous solution by the combination of ultrasound and exfoliated graphite. The various affecting factors were studied. The removal ratio of disperse blue 2BLN is 96.9% for the initial concentration of 200 mg/L using 600 mg/L exfoliated graphite (exfoliation volume of 300 mL/g) at 45 degrees C within 120 min under ultrasound. The combination method was more effective than sonolysis or exfoliated graphite treatment individually.     

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

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

Ultrasound-assisted mineralization of organic contaminants using a recyclable LaFeO3 and Fe3+/persulfate Fenton-like system

A recyclable heterogeneous catalyst has been successfully developed for application in a Fenton-type advanced oxidation process without adding external H₂O₂. LaFeO₃ was prepared from Fe(NO₃)₃·9H₂O and La(NO₃)·6H₂O by a simple sol-gel method and its catalytic efficiency was evaluated for mineralization of 4-chlorophenol using a Fenton-like process. The mineralization process was carried out under ultrasonication in presence of heterogeneous LaFeO₃ catalyst with H₂O₂ that was produced during ultrasonication. The mineralization process was monitored through total organic carbon (TOC) analysis. Very importantly, utmost 5-fold synergism was evidenced by the ultrasound mediated LaFeO₃-catalyzed system. Besides, more than twofold synergism was observed by combining the ultrasound assisted LaFeO₃ catalytic process and potassium persulfate (KPS) assisted advanced oxidation process. It is worth to mention that complete mineralization (∼96%) of 4-chlorophenol (initial concentration of 1.25 × 10⁻⁴ M) was observed within 1 h in the presence of LaFeO₃ (0.5 g L⁻¹) and KPS (1.0 mmol) under ultrasonication (40 kHz). Even after four cycles, the activity of LaFeO₃ remained intact which proved its recyclability. Extremely reusable heterogeneous LaFeO₃ catalyst makes the system more interesting from both economic and environmental points of view.