Effect of intensifying additives on the degradation of thiamethoxam using ultrasound cavitation

The present study has investigated the degradation of thiamethoxam using ultrasound cavitation (US) operated at a frequency of 20 kHz and its combination with intensifying additives viz. hydrogen peroxide, Fenton and photo-Fenton reagent. At the outset, the performance of US (20 kHz) has been maximised by the optimization of process parameters. Highest rate of degradation of thiamethoxam was observed at the optimum ultrasonic power density of 0.22 W/mL, thiamethoxam concentration of 10 ppm and the pH of 2. The established optimum values of operating parameters were used further in case of combined treatment approaches. The effect of concentration of H₂O₂ on the rate of degradation of thiamethoxam in the case of US + H₂O₂ process has confirmed the existence of optimum concentration of H₂O₂ with the ratio of thiamethoxam: H₂O₂ as 1:10. US + Fenton process indicated the optimal molar ratio of FeSO₄·7H₂O:H₂O₂ as 1:15. The combined processes of US + H₂O_2, US + Fenton and US + photo-Fenton have resulted in the extent of degradation of 20.47 ± 0.61%, 34.41 ± 1.03% and 85.17 ± 2.56% respectively after 45 min. of operation. These combined processes lead to the synergistic index of 2.04 ± 0.06, 2.26 ± 0.07 and 2.42 ± 0.07 in case of US + H₂O₂, US + Fenton and US + photo-Fenton processes respectively over only US/stirring treatment with the additive. Additionally, the extent of mineralization and the energy efficiency of individual and combined processes have been compared. US + photo-Fenton process has been found to be the best strategy for effective degradation of thiamethoxam with a significant intensification benefit. The by-products formed during the ultrasonic degradation of thiamethoxam have been identified by using LC-MS/MS analysis.     

Effective removal of organics from Bayer liquor through combined sonolysis and ozonation: Kinetics and mechanism

The presence of organic compounds in the waste liquor is of serious environmental concern that has plagued the development of alumina industry (Bayer Process). The present work attempts to develop a green and efficient process for removal of organics utilizing combined effect of sonolysis and ozonation (US/O₃). The effects of reaction duration, ozone concentration and ultrasonic power are assessed for sonolysis (US), ozonation (O₃) and combination of sonolysis and ozonation (US/O₃). The optimal conditions for US/O₃ treatment system is identified to be a reaction duration of 7 h, ozone concentration of 7.65 g/h, and ultrasonic power of 600 W. The total organic carbon (TOC) removal and decolorization are 60.13% and 87.1%, respectively. The process can be scaled-up to industrial scale, which could potentially serve to be a convenient, safe and sustainable alternative to the exisiting treatment technologies. Additionally, the treated waste water can be reused contributing to an improvement in the overall economics.     

土壤中六种新烟碱类农药残留的分离及光谱研究

建立了一种可同时检测土壤中吡虫啉、啶虫脒、噻虫嗪、噻虫啉、噻虫胺、烯啶虫胺六种新烟碱类农药残留的方法,该方法操作简单、成本低廉且重现性好,符合环境研究过程中实验量大、样品量多的特点。土壤样品经乙腈：二氯甲烷(2∶1 φ)提取后,进一步用分散液液微萃取处理。分析方法采用Alltima TM C18 色谱柱(4.6 mm×250 mm,5 μm)分离,PDA检测器检测,外标法定量。六种农药在0.5～200 μg·L-1浓度范围内线性关系良好,相关系数为0.998 2～0.999 9,检测限为0.000 5～0.003 μg·mL-1 (S/N=3)。以五种土壤为代表,在0.05,0.1,1.0 mg·kg-1 三个添加水平的平均加标回收率为55.3%～95.6%,相对标准偏差为1.4～7.0%。同时应用紫外分光光度法对净化效果进行考察,证明本实验所建立的方法具有明显的净化作用,因此满足土壤中六种新烟碱类农药残留检测的要求。     

Degradation of imidacloprid containing wastewaters using ultrasound based treatment strategies

The present work deals with application of sonochemical reactors for the treatment of imidacloprid containing wastewaters either individually or in combination with other advanced oxidation processes. Experiments have been performed using two different configurations of sonochemical reactors viz. ultrasonic horn (20 kHz frequency and rated power of 240 W) and ultrasonic bath equipped with radially vibrating horn (25 kHz frequency and 1 kW rated power). The work also investigates the effect of addition of process intensifying agents such as H₂O₂ and CuO, which can enhance the production of free radicals in the system. The combination studies with advanced oxidation process involve the advanced Fenton process and combination of ultrasound with UV based oxidation. The extent of degradation obtained using combination of US and H₂O₂ at optimum loading of H₂O₂ was found to be 92.7% whereas 96.5% degradation of imidacloprid was achieved using the combination of US and advanced Fenton process. The process involving the combination of US, UV and H₂O₂ was found to be the best treatment approach where complete degradation of imidacloprid was obtained with 79% TOC removal. It has been established that the use of cavitation in combination with different oxidation processes can be effectively used for the treatment of imidacloprid containing wastewater.     

Degradation of diclofenac during sonolysis, ozonation and their simultaneous application

Diclofenac is a widely used anti-inflammatory non-steroidal drug that escapes conventional urban wastewater treatment trains because of its resistance to biodegradation. Therefore it is frequently found in treated effluents, lakes and rivers. It has been reported that diclofenac can exhibit adverse effects on aquatic organisms. Advanced oxidation processes like ozonation (O₃) and sonolysis (US) can be employed for the removal of such recalcitrant compounds from water matrices. This study included the investigation of the efficiency of O₃ and US and also of their combined application (US + O₃) for the degradation and potential mineralization of diclofenac in a water matrix. Under the conditions applied, all three systems proved to be effective in inducing diclofenac oxidation, leading to 22% of mineralization for O₃ and 36% for US after 40 min of treatment. The synergy observed in the combined schemes, mainly due to the effects of US in enhancing the O₃ decomposition, led to higher mineralization (about 40%) for 40 min treatment, and to a significantly higher mineralization level for shorter treatment duration.     

Removal of pesticide residues from fresh vegetables by the coupled free chlorine/ultrasound process

Pesticide residue in vegetables has been considered as a serious food safety problem across the whole world. This study investigates a novel advanced oxidation process (AOP), namely the coupled free chlorine/ultrasound (FC/US) process for the removal of three typical pesticides from lettuce. The removal efficiencies of dimethoate (DMT), trichlorfon (TCF) and carbofuran (CBF) from lettuce reached 86.7%, 79.8% and 71.3%, respectively by the FC/US process. There existed a synergistic effect in the coupled FC/US process for pesticide removal and the synergistic factors reached 22.3%, 19.0% and 36.4% for DMT, TCF and CBF, respectively. Based on the analysis of mass balance of pesticides, the synergistic effect was probably attributed to the efficient oxidation of pesticides both in vegetables and in water by the generated free radicals and FC. The surface area and surface structure of vegetables strongly affected the removal of pesticides by FC/US. The removal efficiency of DMT increased from 80.9% to 88.1% as solution pH increased from 5.0 to 8.0, and then decreased to 84.1% when solution pH further increased to 9.0. When the ultrasonic frequency changed from 20 to 40 kHz, a remarkable improvement in pesticide removal by FC/US was observed. As the FC concentration increased from 0 to 15 mg L^–l, the removal efficiencies of pesticides increased firstly, and then became stagnant when the FC concentration further increased to 25 mg L^–l. The pesticide degradation pathways based on the identified intermediates were proposed. The total chlorophyll content was reduced by less than 5% after the FC/US process, indicating a negligible damage to the quality of vegetables. It suggests that the FC/US process is a promising AOP for pesticides removal from vegetables.     

Sono-photo-degradation of carbamazepine in a thin falling film reactor: Operation costs in pilot plant

The photo-Fenton degradation of carbamazepine (CBZ) assisted with ultrasound radiation (US/UV/H₂O₂/Fe) was tested in a lab thin film reactor allowing high TOC removals (89% in 35 min). The synergism between the UV process and the sonolytic one was quantified as 55.2%.To test the applicability of this reactor for industrial purposes, the sono-photo-degradation of CBZ was also tested in a thin film pilot plant reactor and compared with a 28 L UV-C conventional pilot plant and with a solar Collector Parabolic Compound (CPC). At a pilot plant scale, a US/UV/H₂O₂/Fe process reaching 60% of mineralization would cost 2.1 and 3.8 €/m³ for the conventional and thin film plant respectively. The use of ultrasound (US) produces an extra generation of hydroxyl radicals, thus increasing the mineralization rate.In the solar process, electric consumption accounts for a maximum of 33% of total costs. Thus, for a TOC removal of 80%, the cost of this treatment is about 1.36 €/m³. However, the efficiency of the solar installation decreases in cloudy days and cannot be used during night, so that a limited flow rate can be treated.     

Degradation of imidacloprid using combined advanced oxidation processes based on hydrodynamic cavitation

The harmful effects of wastewaters containing pesticides or insecticides on human and aquatic life impart the need of effectively treating the wastewater streams containing these contaminants. In the present work, hydrodynamic cavitation reactors have been applied for the degradation of imidacloprid with process intensification studies based on different additives and combination with other similar processes. Effect of different operating parameters viz. concentration (20–60 ppm), pressure (1–8 bar), temperature (34 °C, 39 °C and 42 °C) and initial pH (2.5–8.3) has been investigated initially using orifice plate as cavitating device. It has been observed that 23.85% degradation of imidacloprid is obtained at optimized set of operating parameters. The efficacy of different process intensifying approaches based on the use of hydrogen peroxide (20–80 ppm), Fenton’s reagent (H₂O₂:FeSO₄ ratio as 1:1, 1:2, 2:1, 2:2, 4:1 and 4:2), advanced Fenton process (H₂O₂:Iron Powder ratio as 1:1, 2:1 and 4:1) and combination of Na₂S₂O₈ and FeSO₄ (FeSO₄:Na₂S₂O₈ ratio as 1:1, 1:2, 1:3 and 1:4) on the extent of degradation has been investigated. It was observed that near complete degradation of imidacloprid was achieved in all the cases at optimized values of process intensifying parameters. The time required for complete degradation of imidacloprid for approach based on hydrogen peroxide was 120 min where as for the Fenton and advance Fenton process, the required time was only 60 min. To check the effectiveness of hydrodynamic cavitation with different cavitating devices, few experiments were also performed with the help of slit venturi as a cavitating device at already optimized values of parameters. The present work has conclusively established that combined processes based on hydrodynamic cavitation can be effectively used for complete degradation of imidacloprid.     

Enhancement of biogas production from individually or co-digested green algae Cheatomorpha linum using ultrasound and ozonation treated biochar

This paper proposes the use of modified biochar, derived from Sawdust (SD) biomass using sonication (SSDB) and Ozonation (OSDB) processes, as an additive for biogas production from green algae Cheatomorpha linum (C. linum) either individually or co-digested with natural diet for rotifer culture (S. parkel). Brunauer-Emmett-Teller (BET), Fourier-Transform Infrared (FTIR), thermal-gravimetric (TGA), and X-ray diffraction (XRD) analyses were used to characterize the generated biochar. Ultrasound (US) specific energy, dose, intensity and dissolved ozone (O₃) concentration were also calculated. FTIR analyses proved the capability of US and ozonation treatment of biochar to enhance the biogas production process. The kinetic model proposed fits successfully with the data of the experimental work and the modified Gompertz models that had the maximum R² value of 0.993 for 150 mg/L of OSDB. The results of this work confirmed the significant impact of US and ozonation processes on the use of biochar as an additive in biogas production. The highest biogas outputs 1059 mL/g VS and 1054 mL/g VS) were achieved when 50 mg of SSDB and 150 mg of OSDB were added to C. linum co-digested with S. parkle.     

Analysis of ultrasonic pre-treatment for the ozonation of humic acids

This paper presents an intensification study of an ozonation process through an ultrasonic pre-treatment for the elimination of humic substances in water and thus, improve the quality of water treatment systems for human consumption. Humic acids were used as representative of natural organic matter in real waters which present low biodegradability and a high potential for trihalomethane formation. Ultrasonic frequency (98 kHz, 300 kHz and 1 MHz), power (10–40 W) and sonicated volume (150–400 mL) was varied to assess the efficiency of the ultrasonic pre-treatment in the subsequent ozonation process. A direct link between hydroxyl radical (HO) formation and fluorescence reduction was observed during sonication pre-treatment, peaking at 300 kHz and maximum power density. Ultrasound, however, did not reduce total organic carbon (TOC). Injected ozone (O₃) dose and reaction time were also evaluated during the ozonation treatment. With 300 kHz and 40 W ultrasonic pre-treatment and the subsequent ozonation step (7.4 mg O₃/L_gas), TOC was reduced from 21 mg/L to 13.5 mg/L (36% reduction). HO attack seems to be the main degradation mechanism during ozonation. A strong reduction in colour (85%) and SUVA₂₅₄ (70%) was also measured. Moreover, changes in the chemical structure of the macromolecule were observed that led to the formation of oxidation by-products of lower molecular weight.     

Analysis of pesticide multi-residues in leafy vegetables by ultrasonic solvent extraction and liquid chromatography-tandem mass spectrometry

Ultrasonic solvent extraction (USE) of pesticide multi-residues including monocrotophos, dimethoate, imidacloprid, carbendazim, carbaryl and simazine from leafy vegetables is presented. The extraction procedure was optimized with regard to the solvent type and amount, sonication time and number of extraction steps. The extract did not need clean-up before injected into liquid chromatography-tandem mass spectrometry (LC-MS-MS) which was employed together with electron microscope to verify the effect of USE method. The proposed procedure allows the extraction of six pesticide residues in a single step with 40 ml of ethyl acetate for 35 min sonication, providing recovery over 83% and LOQ less than 1.4 microg/kg. The optimized USE method is a simple, low cost and an effective preparation method for determination of pesticide multi-residues at trace levels in leafy vegetables in comparison with homogenized extraction method.     

Treatment of complex sulfur-containing solutions in ammonia desulfurization ammonium sulfate production by ultrasonic-assisted ozone technology

In this work, the cause of abnormal color in ammonium sulfate products formed by flue gas desulfurization is revealed by investigating the conversion relationship between different sulfur-containing ions and their behavior in a sulfuric acid medium. Both thiosulfate (S₂O₃²⁻) and sulfite (SO₃²⁻ ＆ HSO₃⁻) impurities affect the quality of ammonium sulfate. The S₂O₃²⁻ is the main reason for the yellowing of the product due to the formation of sulfur impurities in concentrated sulfuric acid. To address the yellowing of ammonium sulfate products, a unified technology (US/O₃), using ozone (O₃) and ultrasonic waves (US) simultaneously, is exploited to remove both thiosulfate and sulfite impurities from the mother liquor. The effect of different reaction parameters on the degree of removal of thiosulfate and sulfite is investigated. The synergistic effect of ultrasound and ozone on ion oxidation is further explored and demonstrated by the comparative experiments with O₃ and US/O₃. Under the optimized conditions, the thiosulfate and sulfite concentration in the solution is 2.07 and 5.93 g/L, respectively, and the degree of removal is 91.39 and 90.83%, respectively. The product obtained after evaporation and crystallization is pure white and meets the national standard requirements for ammonium sulfate products. Under the same conditions, the US/O₃ process has apparent advantages, such as saving reaction time compared with the O₃ process alone. Introducing an ultrasonically intensified field improves the generation of oxidation radicals ·OH, ¹O₂, and ·O₂^– in the solution. Furthermore, the effectiveness of different oxidation components in the decolorization process is studied by adding other radical shielding agents using the US/O₃ process supplemented with EPR analysis. The order of the different oxidation components is O₃(86.04%) > ¹O₂(6.53%) > •OH(4.45%) > •O₂^–(2.97%) for the oxidation of thiosulfate, and it is O₃(86.28%) > •OH(7.49%) > ¹O₂(4.99%) > •O₂^–(1.25%) for the oxidation of sulfite.     

Fabrication of Au nanorod‐coated Fe3O4 microspheres as SERS substrate for pesticide analysis by near‐infrared excitation

Au nanorods coated Fe3O4 (Fe₃O₄@NRs) microspheres were designed as functional surface‐enhanced Raman scattering substrate with a feature of magnetic property and used for detection of pesticide residues that are annually used in agriculture by near‐infrared (NIR) excitation. With this strategy, the Fe₃O₄ microspheres were synthesized by hydrothermal method and surface functionalized with polyethylenimine, and then coated with Au nanorods densely. The Raman spectra were carried out by NIR excitation and 4‐ATP was chosen as the probe molecule. The results showed a good SERS activity of the Fe₃O₄@NRs microspheres. Moreover, this substrate could be used for pesticide analysis by portable Raman spectrometer with NIR excitation. Especially, the microspheres could be transferred from pesticides contaminated fruits peel to specially cleaned glass slide with the aid of the external magnetic field, by which the strong fluorescence of the apple components can be avoided while performing the pesticide analysis of fruits peel. Copyright © 2015 John Wiley & Sons, Ltd.     

基于拉曼光谱的苹果中农药残留种类识别及浓度预测的研究

应用拉曼光谱技术结合化学计量学方法能有效的实现果蔬中农药残留的定性定量分析。本研究借助实验室自主研发的拉曼光谱检测系统,对苹果中溴氰菊酯和啶虫脒的快速无损识别和检测进行了探索。定性分析时将拉曼峰574 和843 cm-1分别作为识别溴氰菊酯和啶虫脒的拉曼指纹,当苹果中的溴氰菊酯和啶虫脒残留的含量分别为0.78和0.15 mg·kg-1时,两种农药的特征峰仍清晰可见。定量分析首先对光谱进行多种预处理（Savitzky-Golay平滑、一阶导、二阶导、基线校准、标准正态变量变换）,结合偏最小二乘法分别建立苹果中溴氰菊酯和啶虫脒含量的定量模型。结果表明,采用8次多项式拟合进行基线校准的预处理方法效果最好,对于溴氰菊酯,偏最小二乘模型预测值与气相色谱法测定值的相关系数和预测均方根误差分别为0.94和0.55 mg·kg-1,对于啶虫脒,其偏最小二乘模型的相关系数与预测均方根误差分别为0.85和0.12 mg·kg-1。本研究证实了利用拉曼技术对苹果农残进行无损检测的可行性,使用该方法进行检测时,在光谱测定前不需要进行前处理,光谱测定后样品无任何损伤,该技术实现了果蔬农残的现场检测,可在检测部门、果蔬加工企业、超市、市场等场所得到推广使用,为果蔬品质安全提供了一种无损、快速和环保的检测方法。     

Hybrid hydrodynamic cavitation (HC) technique for the treatment and disinfection of lake water

Water reclamation from lakes needs to be accomplished efficiently and affordably to ensure the availability of clean, disinfected water for society. Previous treatment techniques, such as coagulation, adsorption, photolysis, ultraviolet light, and ozonation, are not economically feasible on a large scale. This study investigated the effectiveness of standalone HC and hybrid HC + H₂O₂ treatment techniques for treating lake water. The effect of pH (3 to 9), inlet pressure (4 to 6 bar), and H₂O₂ loading (1 to 5 g/L) were examined. At pH = 3, inlet pressure of 5 bar and H₂O₂ loadings of 3 g/L, maximum COD and BOD removal were achieved·H₂O₂ was observed to significantly improve the performance of the HC when used as a chemical oxidant. In an optimal operating condition, a COD removal of 54.5 % and a BOD removal of 51.5 % using HC alone for 1 h is observed. HC combined with H₂O₂ removed 64 % of both COD and BOD. The hybrid HC + H₂O₂ treatment technique resulted in a nearly 100% removal of pathogens. The results of this study indicate that the HC-based technique is an effective method for removing contaminants and disinfection of the lake water.     

Ultrasonic-assisted ozone degradation of organic pollutants in industrial sulfuric acid

In this work, a combination of ozone (O₃) and ultrasound (US) has been firstly used to decolorize black concentrated sulfuric acid with high organic content. The effect of different reaction factors on the transparency, extent of decolorization, H₂SO₄ mass fraction, and organic pollutants removal is studied. In addition, the systematic interaction between ultrasound and ozone on the decolorization process is reviewed through comparative experiments of O₃, US and US/O₃. A sulfuric acid product that meets the requirements for first-class products in national standards, with an extent of decolorization of 74.07%, transparency of 70 mm, and a mass fraction of 98.04%, is obtained under the optimized conditions. Under the same conditions, it has been established that the treatment time can be saved by 25% using the US/O₃ process compared to using O₃. Further, the production of oxidative free radicals (•OH) in a concentrated sulfuric acid system is enhanced using the US/O₃ process compared with O₃. In addition, the degree of effectiveness of different oxidizing components on the decolorization process is revealed by adding different free radical shielding agents when the US/O₃ process is used.     

Cactus polysaccharides enhance preservative effects of ultrasound treatment on fresh-cut potatoes

The shelf life of fresh-cut fruits and vegetables is affected by microbial growth, enzymatic browning, and loss of flavor. Although ultrasound (US) treatment is often used in the preservation of fresh-cut fruits and vegetables, it has limited antibacterial and preservative effects. Here, we used cactus polysaccharides (CP) to enhance the preservative effect of ultrasound treatment and extended the shelf life of fresh-cut potatoes. The results showed that combined treatment (CP + US) exerted better antimicrobial and anti-browning effects than individual treatments (either US or CP alone). In addition, CP + US has no adverse effect on texture and quality properties, as well as reduced the mobility of internal water. Combination treatment not only significantly decreased the activities of polyphenol oxidase and peroxidase (P < 0.05), but also maintained a high level of phenylalanine ammonia lyase activity and total phenol content during storage. It also maintained the integrity of cell membrane and reduced its permeability by inhibiting the peroxidation of membrane lipids. In addition, CP + US treatment significantly inhibited the activity of antioxidant enzymes and maintained a high DPPH scavenging ability. GC-IMS technology was used to evaluate the flavor of fresh-cut potatoes. The results showed that CP + US treatment reduced the production of a peculiar smell during storage and maintained a good flavor by inhibiting the production of aldehydes. Taken together, these results indicate that the effective preservation method of CP + US treatment can be utilized to increase the shelf life of fresh-cut potatoes.     

Improved direct synthesis of TiO2 catalyst using sonication and its application for the desulfurization of thiophene

TiO₂ catalyst was synthesized in the presence of ultrasound (ultrasonic horn at 20 kHz frequency and 70% duty cycle) at different power (80 W to 120 W) and durations as well as surfactant concentration with an objective of establishing best conditions for achieving lowest particle size of the photocatalyst. Detailed characterization in terms of crystal phase, crystallinity, functional groups and morphology of the photocatalyst has been performed using SEM, XRD and FTIR analysis. It was demonstrated that sonication significantly reduced the particle size with high degree of sphericity and homogeneity as compared to conventionally synthesized TiO₂ with similar crystallinity in both cases. The catalytic performance was subsequently evaluated for the deep desulfurization of thiophene. Different desulfurization approaches including individual US (ultrasonic horn at 20 kHz frequency, 110 W power and 70% duty cycle) and UV irradiations, US/UV, US/UV/H₂O₂, US/UV/TiO₂ and US/UV/H₂O₂/TiO₂ were applied to evaluate the catalytic activity. The best approach was demonstrated as US/UV/H₂O₂/TiO₂ and also activity of catalyst synthesized using ultrasound was much better compared to conventionally synthesized catalyst. The studies related to different model solvents demonstrated lowest reactivity for toluene whereas n-hexane and n-octane resulted in complete desulfurization in 60 min and 50 min treatment respectively. The desulfurization followed pseudo first order reaction kinetics irrespective of the solvent used. Overall the work clearly demonstrated the efficacy of ultrasound in improving the catalyst synthesis as well as desulfurization of thiophene.     

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.     

Intensification of depolymerization of polyacrylic acid solution using different approaches based on ultrasound and solar irradiation with intensification studies

Depolymerization of polyacrylic acid (PAA) as sodium salt has been investigated using ultrasonic and solar irradiations with process intensification studies based on combination with hydrogen peroxide (H₂O₂) and ozone (O₃). Effect of solar intensity, ozone flow and ultrasonic power dissipation on the extent of viscosity reduction has been investigated for individual treatment approaches. The combined approaches such as US + solar, solar + O₃, solar + H₂O₂, US + H₂O₂ and US + O₃ have been subsequently investigated under optimum conditions and established to be more efficient as compared to individual approaches. Approach based on US (60 W) + solar + H₂O₂ (0.01%) resulted in the maximum extent of viscosity reduction as 98.97% in 35 min whereas operation of solar + H₂O₂ (0.01%), US (60 W), H₂O₂ (0.3%) and solar irradiation resulted in about 98.08%, 90.13%, 8.91% and 90.77% intrinsic viscosity reduction in 60 min respectively. Approach of US (60 W) + solar + ozone (400 mg/h flow rate) resulted in extent of viscosity reduction as 99.47% in 35 min whereas only ozone (400 mg/h flow rate), ozone (400 mg/h flow rate) + US (60 W) and ozone (400 mg/h flow rate) + solar resulted in 69.04%, 98.97% and 98.51% reduction in 60 min, 55 min and 55 min respectively. The chemical identity of the treated polymer using combined approaches was also characterized using FTIR (Fourier transform infrared) spectra and it was established that no significant structural changes were obtained during the treatment. Overall, it can be said that the combination technique based on US and solar irradiations in the presence of hydrogen peroxide is the best approach for the depolymerization of PAA solution.