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 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

Recent Advances In Ultrasonic Treatment: Challenges And Field Applications For Controlling Harmful Algal Blooms (Habs)

Algal blooms are a naturally occurring phenomenon which can occur in both freshwater and saltwater. However, due to excess nutrient loading in water bodies (e.g. agricultural runoff and industrial activities), harmful algal blooms (HABs) have become an increasing issue globally, and can even cause health effects in humans due to the release of cyanotoxins. Among currently available treatment methods, sonication has received increasing attention for algal control because of its low impact on ecosystems and the environment. The effects of ultrasound on algal cells are well understood and operating parameter such as frequency, intensity, and duration of exposure has been well studied. However, most studies have been limited to laboratory data interpretation due to complicated environmental conditions in the field. Only a few field and pilot tests in small reservoirs were reported and the applicability of ultrasound for HABs prevention and control is still under question. There is a lack of information on the upscaling of ultrasonication devices for HAB control on larger water bodies, considering field influencing factors such as rainfall, light intensity/duration, temperature, water flow, nutrients loading, and turbidity. In this review article, we address the challenges and field considerations of ultrasonic applications for controlling algal blooms. An extensive literature survey, from the fundamentals of ultrasound techniques to recent ultrasound laboratory and field studies, has been thoroughly conducted and summarized to identify future technical expectations for field applications. Case studies investigating spatial distribution of frequency and pressure during sonication are highlighted with future implications

Enhanced Electrochemical Detection Of Multi-Heavy Metal Ions Using A Biopolymer-Coated Planar Carbon Electrode

In this study, a chitosan biopolymer-coated planar carbon electrode was developed for in situ determination of heavy metals (Zn2+ and Pb2+) using square wave anodic stripping voltammetry (SWASV). The experimental conditions were optimized with respect to deposition time, amplitude and frequency. With 300 s deposition time, the heavy metal stripping was conducted at 0.05 V pulse amplitude, 20 Hz pulse frequency, and 0.004 V square wave step voltage in 0.1M acetate buffer at pH 4.6. Two distinguished peaks were observed at-0.86 and-0.37V, which are associated with the stripping of Zn2+ and Pb2+, respectively. Limit of detection (LOD) was 0.6 and 1 ppb for Zn2+ and Pb2+, respectively, and the relative standard deviations (RSD) for repetitive measurements of Zn2+ and Pb2+ were in the range of 4.8-5.4 % (n=30 with two identical electrodes). Overall, the developed biopolymer-coated carbon electrode exhibited excellent representativeness and reproductivity for in situ multi heavy metal ions detection in spiked samples, holding a great promise for on-site testing of heavy metals in drinking water

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