Sonochemical oxidation activity in 20-kHz probe-type sonicator systems: The effects of probe positions and vessel sizes.

The 20-kHz probe-type sonicator systems were investigated for the enhancement of the cavitational oxidation activity under various geometric conditions including vertical and horizontal probe positions and vessel sizes/volumes as a following study to our previous study. The sonochemical oxidation activity (mass-based I3- ion generation rate) increased significantly for all vessel size conditions as the probe was placed close to the vessel bottom, owing to the expansion of the sonochemical active zone induced by the reflections of ultrasound at the bottom and the reactor wall. A concentric circular active zone is observed at positions close to the bottom. The highest sonochemical activity was obtained at 1 cm (vertical position) in the 20 cm vessels (input power: 50 %). At the vertical positions of 11 cm to 7 cm, no significant difference in the sonochemical activity was observed for all input power conditions (25, 50, and 75 %) because no meaningful reflections occurred. Higher sonochemical activities were obtained at an input power of 75 % owing to the increased power and strong reflection. The highest cavitational yield considering the energy efficiency was obtained at 6 cm (vertical position) for 75 % of all power and geometric conditions. Horizontal probe position tests showed that the asymmetric formation of the sonochemical active zone could significantly enhance the sonochemical activity. The highest activity was obtained at 1 cm (vertical position) and 2.5 cm (horizontal position) in the 20 cm vessel.

Utilizing machine learning for reactive material selection and width design in permeable reactive barrier (PRB).

Permeable reactive barrier (PRB) is an important groundwater treatment technology. However, selecting the optimal reactive material and estimating the width remain critical and challenging problems in PRB design. Machine learning (ML) has advantages in predicting evolution and tracing contaminants in temporal and spatial distribution. In this study, ML was developed to design PRB, and its feasibility was validated through experiments and a case study. ML algorithm showed a good prediction about the Freundlich equilibrium parameter (R2 0.94 for KF, R2 0.96 for n). After SHapley Additive exPlanation (SHAP) analysis, redefining the range of the significant impact factors (initial concentration and pH) can further improve the prediction accuracy (R2 0.99 for KF, R2 0.99 for n). To mitigate model bias and ensure comprehensiveness, evaluation index with expert opinions was used to determine the optimal material from candidate materials. Meanwhile, the ML algorithm was also applied to predict the width of the mass transport zone in the adsorption column. This procedure showed excellent accuracy with R2 and root-mean-square-error (RMSE) of 0.98 and 1.2, respectively. Compared with the traditional width design methodology, ML can enhance design efficiency and save experiment time. The novel approach is based on traditional design principles, and the limitations and challenges are highlighted. After further expanding the data set and optimizing the algorithm, the accuracy of ML can make up for the existing limitations and obtain wider applications.

UV/persulfate processes for the removal of total organic carbon from coagulation-treated industrial wastewaters.

Sulfate radical-based oxidation processes were investigated to understand the relationship between persulfate (PS) consumption and total organic carbon (TOC) removal from industrial wastewater under various PS concentrations. First, the degradation and mineralization of Bisphenol A (BPA) (initial concentration: 11 mg/L) were investigated in ultraviolet (UV)/PS systems. Complete degradation was achieved within 30 min of UV irradiation, and 41%-72% TOC removal was achieved at PS concentrations of 200 and 400 mg/L. The consumed concentration of S2O82- and generated concentration of SO42- increased gradually to similar levels. The ratio of the PS consumption to TOC removal based on the mass concentration (mg/L) was 14.5 and 23.2 at 180 min for 200 and 400 mg/L of S2O82-, respectively. Three types of coagulation-treated industrial wastewater from metal-processing, food-processing, and adhesive-producing plants were obtained, and TOC removal was analyzed using the same UV/PS systems (initial TOC concentration: 100 mg/L). The TOC removal rates ranged from 16.9% to 94.4% after 180 min of UV irradiation at PS concentrations of 1,000, 2,000, 4,000, and 8,000 mg S2O82-/L. Despite the higher TOC removal at higher PS concentrations, the PS activation efficiency decreased significantly as the PS concentration increased. Only approximately 30%-40% activation efficiency was achieved at a PS concentration of 8,000 mg/L. In this study, the ratio of PS consumption to TOC removal ranged from 20.6 to 43.9.

Effects of alcohols and dissolved gases on sonochemical generation of hydrogen in a 300 kHz sonoreactor.

The sonochemical generation of hydrogen (H2) was investigated using various water/alcohol solutions under argon (Ar) 100 % in a 300 kHz sonoreactor. Five types of alcohols-methanol, ethanol, isopropanol, n-propanol, and n-butanol-were used at various concentrations (0 - 100 % v/v). The H2 generation rate in water was 0.31 µmol/min in the absence of alcohols. The H2 generation rate increased, peaked, and then decreased as the alcohol concentration increased. The concentrations used for the peak H2 generation were 5 %, 1 %, 0.5 %, 0.5 %, and 0.1 % for methanol, ethanol, isopropanol, n-propanol, and n-butanol, respectively. The highest generation rate (5.46 µmol/min) was obtained for methanol 5 % among all conditions in this study, and no H2 was detected for 100 % alcohol concentrations. The reason for the enhancement of the sonochemical H2 generation by the addition of alcohols might be due to strong scavenging effect of alcohols for sonochemically generated oxidizing radicals and vigorous reactions of alcohol molecules and their derivatives with H radicals. No significant correlations were found between the H2 generation rates and physicochemical properties of the alcohols in any of the data in this study. As alcohol concentration increased, the calorimetric power decreased. This indicates that the calorimetric power does not represent the degree of sonochemical reactions in the water/alcohol mixtures. The effect of oxygen (O2) content in the dissolved gases on the generation of H2O2 (representing sonochemical oxidation activity) and H2 (representing sonochemical reduction activity) was investigated using Ar/O2 mixtures for water, methanol 5 % and n-propanol 0.5 %. In water, the highest H2O2 generation was obtained for Ar/O2 (50:50), which is similar to previous research results. However, the H2O2 generation increased as the O2 content increased. In addition, H2 generation decreased as the O2 content increased under all liquid conditions (water, methanol, and n-propanol).

Developing an Improved Strategy for the Analysis of Polychlorinated Dibenzo-p-Dioxins/Furans and Dioxin-like Polychlorinated Biphenyls in Contaminated Soils Using a Combination of a One-Step Cleanup Method and Gas Chromatography with Triple Quadrupole Mass Spectrometry.

Soils contaminated with polychlorodibenzo-p-dioxins (PCDDs), polychlorodibenzofurans (PCDFs), and dioxin-like (dl) polychlorinated biphenyls (PCBs), known as persistent organic pollutants (POPs), have garnered global attention because of their toxicity and persistence in the environment. The standard method for target analytes has been used; however, it is an obstacle in large-scale sample analysis due to the comprehensive sample preparation and high-cost instrumental analysis. Thus, analytical development of inexpensive methods with lower barriers to determine PCDDs/Fs and dl-PCBs in soil is needed. In this study, a one-step cleanup method was developed and validated by combining a multilayer silica gel column and Florisil micro-column followed by gas chromatography with triple quadrupole mass spectrometry (GC-QqQ-MS/MS). To optimize the separation and quantification of 17 PCDDs/Fs and 12 dl-PCBs in soils, the sample cleanup and instrumental conditions were investigated. For quantification method validation, spiking experiments were conducted to determine the linearity of the calibration, recovery, and method detection limit of PCDDs/Fs and dl-PCBs using isotopic dilution GC-QqQ-MS/MS. The applicability of the simultaneous determination of PCDDs/Fs and dl-PCBs was confirmed by the recovery of native target congeners and labeled surrogate congeners spiked into the quality-control and actual soil samples. The results were in good agreement with the requirements imposed by standard methods. The findings in this work demonstrated the high accessibility of the sample cleanup and analysis methods for the efficient determination of PCDDs/Fs and dl-PCBs in contaminated soils.

Effects of gas saturation and sparging on sonochemical oxidation activity under different liquid level and volume conditions in 300-kHz sonoreactors: Zeroth- and first-order reaction comparison using KI dosimetry and BPA degradation.

The sonochemical oxidation activity was investigated for gas saturation and gas sparging under various liquid levels and volumes in 300 kHz sonoreactors. The liquid levels and volumes ranged from 5λ (25 mm, 0.47 L) to 50λ (250 mm, 4.30 L) and two gas mixtures, Ar:O2 (75:25) and N2:O2 (75:25), were used. Two types of reaction kinetics were observed to quantitatively analyze the sonochemical oxidation reactions: zero-order (KI dosimetry: C0 = 60.2 mM) and first-order (Bisphenol A (BPA) degradation: C0 = 0.043 mM). The masses of the sonochemical oxidation reactions were calculated and compared rather than the concentrations to more accurately compare the sonochemical oxidation activity under different liquid volume conditions. First, as the liquid level or volume increased for the zero-order reactions, the concentration of I3- ions representing the volume-averaged activity decreased substantially for gas saturation owing to the increase in liquid volume. However, gas sparging substantially enhanced sonochemical oxidation activity, and the mass of I3- ions representing the total activity remained constant as the liquid level increased from 20λ because of the improved liquid mixing and a shift in the sonochemical active zone. Second, as evidenced by the zero-order reactions, the concentration of BPA decreased considerably as the liquid level or volume increased in the first-order reactions. When gas sparging was used, higher reaction constants were obtained for both gas mixtures, ranging from 40λ to 50λ. However, a comparison of the sonochemical oxidation activity in terms of the degraded mass of BPA was inapplicable as the concentration of BPA decreased substantially and a lack of reactants occurred for the lower liquid level and volume conditions as the irradiation time elapsed. Instead, using the first-order reaction constant, a comparison of the required reaction times for a specific removal efficiency (30%, 60%, and 90%) was proposed. Gas sparging can substantially reduce the reaction time required for a liquid level of 40λ or higher.

Effect of dissolved gases on sonochemical oxidation in a 20 kHz probe system: Continuous monitoring of dissolved oxygen concentration and sonochemical oxidation activity.

Dissolved gases have a substantial influence on acoustic cavitation and sonochemical oxidation reactions. Little research on the changes in dissolved gases and the resultant changes in sonochemical oxidation has been reported, and most studies have focused only on the initial dissolved gas conditions. In this study, the dissolved oxygen (DO) concentration was measured continuously during ultrasonic irradiation using an optical sensor in different gas modes (saturation/open, saturation/closed, and sparging/closed modes). Simultaneously, the resulting changes in sonochemical oxidation were quantified using KI dosimetry. In the saturation/open mode using five gas conditions of Ar and O2, the DO concentration decreased rapidly when O2 was present because of active gas exchange with the atmosphere, and the DO concentration increased when 100% Ar was used. As a result, the order of the zero-order reaction constant for the first 10 min (k0-10) decreased in the order Ar:O2 (75:25) > 100% Ar ≈ Ar:O2 (50:50) > Ar:O2 (25:75) > 100% O2, whereas that during the last 10 min (k20-30) when the DO concentration was relatively stable, decreased in the order 100% Ar > Ar:O2 (75:25) > Ar:O2 (50:50) ≈ Ar:O2 (20:75) > 100% O2. In the saturation/closed mode, the DO concentration decreased to approximately 70-80% of the initial level because of ultrasonic degassing, and there was no influence of gases other than Ar and O2. Consequently, k0-10 and k20-30 decreased in the order Ar:O2 (75:25) > Ar:O2 (50:50) > Ar:O2 (25:75) > 100% Ar > 100% O2. In the sparging/closed mode, the DO concentration was maintained at approximately 90% of the initial level because of the more active gas adsorption induced by gas sparging, and the values of k0-10 and k20-30 were almost the same as those in the saturation/closed mode. In the saturation/open and sparging/closed modes, the Ar:O2 (75:25) condition was most favorable for enhancing sonochemical oxidation. However, a comparison of k0-10 and k20-30 indicated that there would be an optimal dissolved gas condition that was different from the initial gas condition. In addition, the mass-transfer and ultrasonic-degassing coefficients were calculated using changes in the DO concentration in the three modes.

Effects of gas saturation and sparging on sonochemical oxidation activity in open and closed systems, part II: NO2-/NO3- generation and a brief critical review.

The sonochemical generation of NO2- and NO3- is considered to be one of the reasons for the low sonochemical oxidation activity in the presence of N2 in the liquid phase. In this study, the generation characteristics of NO2- and NO3- were investigated using the same 28 kHz sonoreactor and the 12 gas conditions used in Part I of this study. Three gas modes, saturation/closed, saturation/open, and sparging/closed, were applied. N2:Ar (25:75), N2:Ar (50:50), and O2:N2 (25:75) in the saturation/closed mode generated the three highest values of NO2- and NO3-. Ar and O2 were vital for generating relatively large concentrations of NO2- and NO3-. The absorption of N2 from the air resulted in high generation of NO2- and NO3- for Ar 100 % and Ar/O2 mixtures under the saturation/open mode. In addition, gas sparging enhanced the generation of NO2- and NO3- for N2:Ar (25:75), O2:N2 (25:75), and N2 significantly because of the change in the sonochemically active zone and the increase in the mixing intensity in the liquid phase, as discussed in Part I. The ratio of NO3- to NO2- was calculated using their final concentrations, and a ratio higher than 1 was obtained for the condition of Ar 100 %, Ar/O2 mixtures, and O2 100 %, wherein a relatively high oxidation activity was detected. From a summary of the results and findings of previous studies, it was revealed that the observations of NO2- + NO3- could be more appropriate for investigating the NO2- and NO3- generation characteristics. In addition, H2O2/NO2-/NO3- related activity rather than H2O2 activity was suggested to quantify the OH radical activity more appropriately in the presence of N2.

Effects of gas saturation and sparging on sonochemical oxidation activity in open and closed systems, Part I: H2O2 generation.

Cavitational/sonochemical activity can be significantly enhanced or reduced depending on the gases dissolved in the liquid. Although many researchers have suggested the order of importance of dissolved gas conditions that affect the degree of sonoluminescence (SL), sonochemiluminescence (SCL), and compound degradation, the most suitable gas condition for sonochemical oxidation reactions is currently unknown. In this study (Part I), the effects of gas saturation and sparging on the generation of H2O2 were investigated in a 28-kHz sonoreactor system. Four gas modes, saturation/closed, saturation/open, sparging/closed, and sparging/open, were applied to Ar, O2, N2, and binary gas mixtures. The change in dissolved oxygen (DO) concentration during ultrasonic irradiation was measured and was used as an indicator of whether the gaseous exchange between liquid and air altered the gas content of the liquid. Considerable difference in the DO concentration was observed for the gas saturation/open mode, ranging from -11.5 mg/L (O2 100 %) to +4.3 mg/L (N2 100 %), while no significant difference was observed in the other gas modes. The change in the gas content significantly reduced the linearity for H2O2 generation, which followed pseudo-zero-order kinetics, and either positively or negatively affected H2O2 generation. Ar:O2 (75:25) and Ar:O2 (50:50) resulted in the highest and second-highest H2O2 generation for both gas saturation and sparging, respectively. In addition, gas sparging resulted in much higher H2O2 generation for all gas conditions compared to gas saturation; this was because of the significant change in the cavitational active zone and concentrated ultrasonic energy, which formed a bulb-shaped active zone, especially for the Ar/O2 mixtures adjacent to the transducer at the bottom. The sparging flow rate and position also significantly affected H2O2 generation; the highest H2O2 generation was obtained when the sparger was placed at the bottom adjacent to the transducer, with a flow rate of 3 L/min. In Part II, the generation of nitrogen oxides, including nitrite (NO2-) and nitrate (NO3-), was investigated using the same ultrasonic system with three gas modes: saturation/open, saturation/closed, and sparging/closed.

Gas chromatography-triple quadrupole mass spectrometry as a cost-effective method for the determination of polychlorinated dibenzo-p-dioxins and furans in contaminated soils.

The aim of this study was to evaluate the performance of gas chromatography (GC)-triple quadrupole mass spectrometry (QqQ, MS/MS) as an alternative to the standard GC-high resolution mass spectrometry (GC-HR/MS) for soils contaminated with polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). GC-QqQ (MS/MS) using a dynamic multiple reaction monitoring (dMRM) mode was optimized for the quantitative analysis of 17 PCDD/Fs. A comparative study between GC-QqQ (MS/MS) and GC-HR/MS was carried out to validate the results of actual field soil samples. Although GC-HR/MS has excellent sensitivity and selectivity, the validation parameters obtained by GC-QqQ (MS/MS) also met the recommended criteria of the standard method. The results for total and I-TEQ (international toxic equivalent) value of the PCDD/F concentrations of over 86.0 pg/g and 4.3 pg I-TEQ/g, respectively, in actual field soil samples showed good agreement between the two methods, falling within ±25% relative difference. In consideration of the remediation goal (100 pg I-TEQ/g), GC-QqQ (MS/MS) can be an alternative cost-effective method for use in soil remediation research.

Effect of liquid recirculation flow on sonochemical oxidation activity in a 28 kHz sonoreactor.

Sonochemical oxidation activity may be significantly enhanced by optimizing the geometric factors of a sonoreactor and implementing additional physical actions, such as mechanical mixing and gas sparging. This study investigates the effects of liquid recirculation flow on sonochemical oxidation reactions. This was carried out through experimental testing with a 28 kHz bath-type sonoreactor under various liquid heights and flow rates, ranging from 1λ to 4.0λ and 1.5-6.0 L/min, respectively. The potassium iodide (KI) dosimetry and sonochemiluminescence methods were used in the experiment. With an increase in the liquid height/volume, the pseudo zero-order kinetic constant and the mass of triiodide (I3-) ions fluctuated. The optimal liquid height was 2.0λ, 2.5λ, and 3.0λ, based on the appropriate formation of a cavitation active zone in the reactor. The introduction of a liquid recirculation flow led to a large reduction in sonochemical activity due to the shrinkage of the cavitation active zone. However, the sonochemical activity increased at higher flow rates through the capture of ultrasonic energy at the bottom zone. This increase was attributed to the formation of a strong and expanded active zone limited to the reactor bottom to the height of the recirculation flow. The results demonstrate that applying a high rate liquid flow adjacent to the transducer module may be beneficial for enhanced sonochemical activity.

Quantification of sonochemical and sonophysical effects in a 20 kHz probe-type sonoreactor: Enhancing sonophysical effects in heterogeneous systems with milli-sized particles.

Even though acoustic cavitation has been widely investigated, only few researchers focused on the relationship between sonochemical and sonophysical activities and on the enhancement of sonophysical activity. In this study, sonochemical and sonophysical activities were investigated in a heterogeneous system to understand the relationship between these two activities and to suggest optimal conditions for ultrasonic desorption/extraction processes comprising milli-sized glass beads. The sonochemical activity was quantitatively analyzed using potassium iodide dosimetry in homogeneous and heterogeneous systems. Sonophysical activity was quantitatively and qualitatively analyzed using paint-coated bead desorption tests and aluminum foil erosion tests under three probe positions of "T" (1 cm below the liquid surface), "B" (1 cm above the vessel bottom), and "M" (midpoint between "T" and "B"). Three different sizes of glass beads (diameter: 0.2, 1.0, and 4.0 mm) were used in this study. The highest sonochemical activity was obtained at "B" in both homogeneous and heterogeneous systems. However, three times lower sonochemical activity was observed in the heterogeneous system than in the homogeneous system because significant attenuation and unstable reflection of ultrasound occurred in the bead layer and suspension. Higher sonophysical activity was observed, when the bead size decreased and the probe approached the bottom. However, no significant sonophysical activity was detected when the beads were attached to the bottom. Therefore, the sonophysically active region was the zone around the probe body, opposite to the ultrasound irradiation tip, and only suspended beads could undergo severe cavitational actions. This was confirmed via aluminum foil tests. Several erosion marks on the foil were observed in the area around the probe body, whereas no severe damage was observed at the bottom. Moreover, the degree of sonophysical activity did not change for various saturating gases. This might be due to the different thresholds of sonochemical and sonophysical activities.

Ultrasound-assisted soil washing processes using organic solvents for the remediation of PCBs-contaminated soils.

Ultrasonic soil washing processes using organic solvents were investigated for the development of novel remediation technologies for persistent organic pollutants (POPs)- contaminated soils. Aluminum foil erosion was first tested to understand sonophysical activity in water, methanol (polar) and n-hexane (nonpolar) in a 28 kHz double-bath-type sonoreactor. Significant sonophysical damage on the aluminum foil was observed at the antinodes for all solvents, and the order of degree of sonophysical damage was as follows: water > methanol > n-hexane. Subsequently, conventional (mechanical mixing only) and ultrasonic soil washing (mechanical mixing and ultrasound) techniques were compared for the removal of polychlorinated biphenyls (PCBs) from soil. Two types of contaminated soils, fresh (Soil A, C0 = 2.5 mg/kg) and weathered (Soil B, C0 = 0.5 mg/kg), were used and the applied soil-to-liquid (S:L) ratio was 1:5 and 1:10 for methanol and n-hexane, respectively. The polar solvent significantly increased washing efficiencies compared to the nonpolar solvent, despite the nonpolar nature of the PCBs. Washing efficiency was significantly enhanced in ultrasonic soil washing compared to conventional washing, owing to macro- and micro-scale sonophysical actions. The highest washing efficiencies of 90% for Soil A and 70% for Soil B were observed in the ultrasonic washing processes using methanol. Additionally, a single operation of the ultrasonic washing process was superior to two sequential processes with conventional mixing in terms of washing efficiency, consumption of washing agents, treatment of washing leachate, and operation time. Finally, the removal of PCBs in an organic solvent (methanol) was investigated in photolytic and sonolytic processes for the post-treatment of soil washing leachate. A photolysis efficiency of 80% was obtained within 60 min of UV exposure for intensities of 1.0, 2.0, and 4.0 W/cm2. The primary mechanism of PCBs degradation is photolytic dechlorination. In contrast, no degradation was detected in the sonolytic process, as the excess organic solvent acted as a strong radical scavenger.

Ultrasound-assisted soil washing processes for the remediation of heavy metals contaminated soils: The mechanism of the ultrasonic desorption.

Ultrasound-assisted soil washing processes were investigated for the removal of heavy metals (Cu, Pb, and Zn) in real contaminated soils using HCl and EDTA. The ultrasound-assisted soil washing (US/Mixing) process was compared with the conventional soil washing (Mixing) process based on the mechanical mixing. High removal efficiency (44.8% for HCl and 43.2% for EDTA) for the metals was obtained for the most extreme conditions (HCl 1.0 M or EDTA 0.1 M and L:S = 10:1) in the Mixing process. With the aide of ultrasound, higher removal efficiency (57.9% for HCl and 50.0% for EDTA) was obtained in the same extreme conditions and similar or higher removal efficiency (e.g., 54.7% for HCl 0.5 M and L:S = 10:1 and 50.5% for EDTA 0.05 M and L:S = 5:1) was achieved even in less extreme conditions (lower HCl or EDTA concentration and L:S ratio). Therefore, it was revealed that the US/Mixing was advantageous over the conventional Mixing processes in terms of metal removal efficiency, consumption of chemicals, amount of generated washing leachate, and volume/size of washing reactor. In addition, the heavy metals removal was enhanced for the smaller soil particles in the US/Mixing process. It was due to more violent movement of smaller particles in slurry phase and more violent sonophysical effects. In order to understand the mechanism of ultrasonic desorption, the desorption test was conducted using the paint-coated beads with three sizes (1, 2, and 4 mm) for the free and attached conditions. It was found that no significant desorption/removal of paint from the beads was observed without the movement of beads in the water including floatation, collision, and scrubbing. Thus, it was suggested that the simultaneous application of the ultrasound and mechanical mixing could enhance the physical movement of the particles significantly and the very high removal/desorption could be attained.

Evaluation of stabilizing material and stabilization efficiency through comparative study of toxic heavy metal transfer between corn and peanut grown in stabilized field soil.

Soil contaminated with toxic heavy metals (THMs) was stabilized by adding a combination of waste resources in 7.0 wt%, including coal-mine drainage sludge, waste cow bone, and steelmaking slag, in the ratio of 5:35:60. Subsequently, corn and peanut were cultivated in treated soil to investigate the effects of the waste resources on THM mobility in soil and translocation to plants. Sequential extraction procedures (SEP) was used to analyze mobile phase THMs which could be accumulated in the plants. SEP shows that mobile Pb, Cd, Cu, Zn, Ni, Cr, and As were reduced by 8.48%, 29.22%, 18.85%, 21.66%, 4.58%, 62.78%, and 20.01%, respectively. The bioaccumulation of THMs was clearly hindered by stabilization; however, the increment in the amount of immobile-phase THMs and change in the amount of translocated THMs was not proportional. The corn grains grown above the soil surface were compared with the peanut grains grown beneath the soil surface, and the results indicating that the efficiency of stabilization on THM translocation may not depend on the contact of grain to soil but the nature of plant. Interestingly, the results of bioaccumulation with and without stabilization showed that the movement of some THMs inside the plants was affected by stabilization.

Effects of gas sparging and mechanical mixing on sonochemical oxidation activity.

The effects of air sparging (0-16 L min-1) and mechanical mixing (0-400 rpm) on enhancing the sonochemical degradation of rhodamine B (RhB) was investigated using a 28 kHz sonoreactor. The degradation of RhB followed pseudo first-order kinetics, where sparging or mixing induced a large sonochemical enhancement. The kinetic constant varied in three stages (gradually increased â†’ increased exponentially â†’ decreased slightly) as the rate of sparging or mixing increased, where the stages were similar for both processes. The highest sonochemical activity was obtained with sparging at 8 L min-1 or mixing at 200 rpm, where the standing wave field was significantly deformed by sparging and mixing, respectively. The cavitational oxidation activity was concentrated at the bottom of the sonicator when higher sparging or mixing rates were employed. Therefore, the large enhancement in the sonochemical oxidation was attributed mainly to the direct disturbance of the ultrasound transmission and the resulting change in the cavitation-active zone in this study. The effect of the position of air sparging and mixing was investigated. The indirect inhibition of the ultrasound transmission resulted in less enhancement of the sonochemical activity. Moreover, the effect of various sparging gases including air, N2, O2, Ar, CO2, and an Ar/O2 (8:2) mixture was compared, where all gases except CO2 induced an enhancement in the sonochemical activity, irrespective of the concentration of dissolved oxygen. The highest activity was obtained with the Ar/O2 (8:2) mixture. Therefore, it was revealed that the sonochemical oxidation activity could be further enhanced by applying gas sparging using the optimal gas.

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 Rct 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.

Geometric and operational optimization of 20-kHz probe-type sonoreactor for enhancing sonochemical activity.

The use of a 20-kHz probe-type sonicator irradiating downward in a 500 mL vessel was optimized for the enhancement of the sonochemical activity in terms of the geometric and operational factors. These factors included the probe immersion depth (the vertical position of the probe), input power, height of the liquid from the bottom, horizontal position of the probe, and thickness of bottom plate The sonochemical oxidation reactions were investigated both quantitatively and qualitatively using calorimetry, KI dosimetry, and luminol (Sonochemiluminescence, SCL) techniques. The sonochemical activity was very positively affected by the vertical boundaries. The highest sonochemical activity was obtained when the probe was placed close to the bottom of the vessel (immersion depth of 60 mm), with a high input power (input power of 75%), and optimal liquid height condition (liquid height of 70 mm). The SCL image analysis showed that the cavitational activity zone gradually expanded around the probe body and changed into a circular shape as the experimental conditions were optimized, and consequently the sonochemical activity increased. The formation of a large bright circular-shaped activity zone could be attributed to the strong reflections of the ultrasound firstly, at the vessel bottom and secondly, at the liquid surface. On the other hand, the cavitational activity zone and the sonochemical activity were negatively affected by the horizontal boundaries when the probe was placed close to the side wall of the vessel. In addition, it was found that the sonochemical activity was also significantly affected by the thickness of the support plate owing to the reflection and transmission of the ultrasound at the boundary between the liquid and the solid media.

Development of modified mesoporous carbon (CMK-3) for improved adsorption of bisphenol-A.

The adsorption of bisphenol-A (BPA) on ordered mesoporous carbon (CMK-3) and modified CMK-3 (MCMK-3) for decontamination of aqueous medium was investigated. The CMK-3 and MCMK-3 materials had uniform pore sizes of 3.60 and 3.70 nm and high Brunauer-Emmett-Teller (BET) surface areas of 751 and 564 m2 g-1, respectively. The maximum adsorption capacities of CMK-3 and MCMK-3 were 178.57 (0.24 mg m-2) and 238.01 (0.42 mg m-2) mg g-1, respectively at 298 K (pH 6.4). The difference in the adsorption capacities is attributed to the specific surface area and hydrophobicity of the adsorbents. The adsorption of BPA on CMK-3 and MCMK-3 may be influenced by π-π bonding and hydrophobic and electrostatic interactions, and the excellent adsorption capacity of MCMK-3 is attributed to its unique sp2-hybridized single-atom-layer structure. The kinetics and isotherm data were described by the pseudo-second order kinetic model and the Langmuir isotherm, respectively. This difference in the adsorption kinetics of CMK-3 and MCMK-3 is caused by the increase in the pore diameter of the latter. Further, CMK-3 and MCMK-3, with an open geometry consisting of interlinked nanorods, allow for faster intraparticle diffusion. Overall, CMK-3 and MCMK-3 could be promising adsorbents for the removal of chemicals containing benzene rings from wastewater.