Treatment of nano-sized rutile phase TiO2 powder under ultrasonic irradiation in hydrogen peroxide solution and investigation of its sonocatalytic activity

The treated mixed-crystal TiO(2) powder with high sonocatalytic activity was obtained through utilizing ultrasonic irradiation in hydrogen peroxide solution. At the same time, some influencing factors (including heat-treated temperature and heat-treated time) on the sonocatalytic activity of treated mixed-crystal TiO(2) powder were also considered through the degradation of methylene blue in aqueous solution. In this work, it was found that the sonocatalytic degradation ratio of methylene blue in the presence of treated mixed-crystal TiO(2) powder was much higher than ones in the presence of nano-sized rutile phase TiO(2) powder and with onefold ultrasonic irradiation. At last, the methylene blue in aqueous solution was completely degraded and became some simple inorganic anions such as NO(3)(-), SO(4)(2-) and Cl(-). All experiments indicated that the sonocatalytic method adopting treated mixed-crystal TiO(2) powder as sonocatalyst was an advisable choice for the treatments of non- or low-transparent wastewaters in future.     

Wastewater treatment using hybrid treatment schemes based on cavitation and Fenton chemistry: A review

Advanced oxidation processes such as cavitation and Fenton chemistry have shown considerable promise for wastewater treatment applications due to the ease of operation and simple reactor design. In this review, hybrid methods based on cavitation coupled with Fenton process for the treatment of wastewater have been discussed. The basics of individual processes (Acoustic cavitation, Hydrodynamic cavitation, Fenton chemistry) have been discussed initially highlighting the need for combined processes. The different types of reactors used for the combined processes have been discussed with some recommendations for large scale operation. The effects of important operating parameters such as solution temperature, initial pH, initial pollutant concentration and Fenton’s reagent dosage have been discussed with guidelines for selection of optimum parameters. The optimization of power density is necessary for ultrasonic processes (US) and combined processes (US/Fenton) whereas the inlet pressure needs to be optimized in the case of Hydrodynamic cavitation (HC) based processes. An overview of different pollutants degraded under optimized conditions using HC/Fenton and US/Fenton process with comparison with individual processes have been presented. It has been observed that the main mechanism for the synergy of the combined process depends on the generation of additional hydroxyl radicals and its proper utilization for the degradation of the pollutant, which is strongly dependent on the loading of hydrogen peroxide. Overall, efficient wastewater treatment with high degree of energy efficiency can be achieved using combined process operating under optimized conditions, as compared to the individual process.     

Sonochemical effectiveness factor (eUS) in the reactors for wastewater treatment by sono-Fenton oxidation: Novel considerations

A comprehensive algorithm was recently proposed for calculation of the sonochemical effectiveness factor and wastewater treatment modeling. The presented approach implies that ultrasound is an auxiliary source of free radicals in Fenton type reactions; introduction of ultrasound represents an enhancement of pollutant degradation rates. The sonochemical effectiveness factor was introduced in kinetic models as the e_US factor (Gr?i? et al., 2012 [1]). As a substantial follow-up, this study presents novel considerations. The e_US factor was modeled as a function of employed frequency, actual cavitation-related power intensity of ultrasound and a portion of the cavitationally active zone, i.e. dimensionless active volume. The effect of temperature was disregarded in the present model considerations. Cavitationally active zone in reactors was determined based on the erosion of aluminum foil, resulting in cone-shaped space arising from transducer.In the present study, sonochemical treatment of industrial wastewater containing HCOONa as organic pollutant was performed using different equipment: ultrasonic baths (UB1, UB2 and UB3), cylindrical reactor with homogenizer (HCR) and three-frequency hexagonal cell, i.e. ultrasonic pilot reactor prototype (PP). Explored frequency range was from 20 to 120 kHz. Homogeneous and heterogeneous Fenton-type sonochemical processes, US/Fe(II)(FeSO₄,aq.)/H₂O₂ and US/Fe(II)(steel-plate)/H₂O₂, respectively, applied to industrial wastewater were investigated in terms of mineralization kinetics. Newly modeled e_US factor was introduced in corresponding kinetic models and the overall model was validated. Kinetic parameters of Fenton process were treated as independent of ultrasound, since e_US factor consists of cavitation-related phenomena responsible for the mineralization rate enhancement. In average, a 21% increase of mineralization efficiency was achieved using a single frequency, while more than 70% increase can be achieved by combining 20, 68 and 120 kHz in PP.     

一甲基硫脲与支持电解质的阴离子在银电极上共吸附的拉曼光谱研究

本文用电化学现场表面增强拉曼散射光谱（ＳＥＲＳ）技术研究了ＭＴＵ在ＨＣｌＯ４、Ｈ２ＳＯ４和ＨＮＯ３介质中分别与一种或两种无机阴离子的共吸附行为，发现ＣｌＯ－４、ＳＯ２－４和ＮＯ－３等弱吸附无机阴离子均能被ＭＴＵ诱导物理吸附在其质子化了的氨基（ＮＨ＋３）上，这三种无机阴离子被ＭＴＵ诱导物理吸附的强弱顺序是：在电极电位位于－０．２Ｖ～－０．７Ｖ区间时，ＳＯ２－４＞ＣｌＯ－４＞ＮＯ－３，在电位位于－０．８Ｖ～－１．２Ｖ区间时，ＣｌＯ－４＞ＳＯ２－４＞ＮＯ－３。     

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.     

Peroxydisulfate-assisted sonocatalytic degradation of metribuzin by La-doped ZnFe layered double hydroxide

Metribuzin is an herbicide that easily contaminates ground and surface water. Herein, La-doped ZnFe layered double hydroxide (LDH) was synthesized for the first time and used for the degradation of metribuzin via ultrasonic (US) assisted peroxydisulfate (PDS) activation. The synthesized LDH had a lamellar structure, an average thickness of 26 nm, and showed mesoporous characteristics, including specific surface area 110.93 m² g⁻¹, pore volume 0.27 cm³ g⁻¹, and pore diameter 9.67 nm. The degradation efficiency of the US/La-doped ZnFe LDH/PDS process (79.1 %) was much greater than those of the sole processes, and the synergy factor was calculated as 3.73. The impact of the reactive species on the sonocatalytic process was evaluated using different scavengers. After four consecutive cycles, 10.8 % loss occurred in the sonocatalytic activity of the La-doped LDH. Moreover, the efficiency of the US/La-doped LDH/PDS process was studied with respect to the degradation of metribuzin in a wastewater matrix. According to GC–MS analysis, six by-products were detected during the degradation of metribuzin. Our results indicate that the US/La-doped ZnFe LDH/PDS process has great potential for efficient degradation of metribuzin-contaminated water and wastewater.     

Intensification of oxidation capacity using chloroalkanes as additives in hydrodynamic and acoustic cavitation reactors

The effect of the presence and absence of the chloroalkanes, dichloromethane (CH(2)Cl(2)), chloroform (CHCl(3)) and carbon tetrachloride (CCl(4)) on the extent of oxidation of aqueous I(-) to I(3)(-) has been investigated in (a) a liquid whistle reactor (LWR) generating hydrodynamic cavitation and (b) an ultrasonic probe, which produces acoustic cavitation. The aim has been to examine the intensification achieved in the extent of oxidation due to the generation of additional free radicals/oxidants in the reactor as a result of the presence of chloroalkanes. It has been observed that the extent of increase in the oxidation reaction is strongly dependent on the applied pressure in the case of the LWR. Also, higher volumes of the chloroalkanes favour the intensification and the order of effectiveness is CCl(4)>CHCl(3)>CH(2)Cl(2). However, the results with the ultrasonic probe suggest that an optimum concentration of CH(2)Cl(2) or CHCl(3) exists beyond which there is little increase in the extent of observed intensification. For CCl(4), however, no such optimum concentration was observed and the extent of increase in the rates of oxidation reaction rose with the amount of CCl(4) added. Stage wise addition of the chloroalkanes was found to give marginally better results in the case of the ultrasonic probe as compared to bulk addition at the start of the run. Although CCl(4) is the most effective, its toxicity and carcinogenicity may mean that CH(2)Cl(2) and CHCl(3) offer a safer viable alternative and the present work should be useful in establishing the amount of chloroalkanes required for obtaining a suitable degree of intensification.     

Investigation on the transition crystal of ordinary rutile TiO2 powder by microwave irradiation in hydrogen peroxide solution and its sonocatalytic activity

The transition crystal TiO(2) catalyst with high sonocatalytic activity was obtained utilizing the microwave irradiation in hydrogen peroxide solution. At the same time a series of affecting factors (microwave irradiation time, heat-treated time and heat-treated temperature) to prepare the TiO(2) catalyst on the sonocatalytic degradation of parathion were considered in this paper. The ultrasound of low power was used as an irradiation source to induce treated TiO(2) particles to perform catalytic activity. The results show that the sonocatalytic activity of the transition crystal TiO(2) powder is obviously higher than those of pure ordinary rutile and anatase TiO(2) powders. At last, the parathion in aqueous solution was degraded completely and became some simple inorganic ions such as NO(3)(-), PO(4)(3-), SO(4)(2-), etc. The degradation ratio of parathion in the presence of the transition crystal TiO(2) catalyst attains nearly 80% within 60 min ultrasonic irradiation, while corresponding ones are only 65.23% and 53.88%, respectively, for pure ordinary rutile and anatase TiO(2) powders.     

Sonozonation (sonication/ozonation) for the degradation of organic contaminants – A review

Ozonation (OZ) is an important advanced oxidation process to purify water and wastewater. Because of the lower solubility and instability of ozone (O₃), selective oxidation and dependence on pH value, the industrial applications of OZ have been hindered by the following disadvantages: incomplete removal of pollutants, lower mineralization efficiency and the formation of toxic by-products. Meanwhile, OZ seems to have higher processing costs than other technologies. To improve the treatment efficiency and O₃ utilization, several combined processes, such as H₂O₂/O₃, UV/O₃, and Cavitation/O₃, have been explored, while the combined method of ultrasonication (US) with OZ is a promising treatment technology with a complex physicochemical mechanism. In US alone, the sonolysis of water molecules can produce more powerful unselective oxidant hydroxyl radicals (OH), and directly cause the sonochemical pyrolysis of volatile pollutants. In US/OZ, US can promote the mass transfer of O₃, and also drive the chemical conversion of O₃ to enhance the formation of OH. Various layouts of US/OZ devices and the interactive effects of US/OZ (synergism or antagonism) on the degradation of various organics are illustrated in this review. The main factors, including US frequency, pH value, and radical scavengers, significantly affect the mass transfer and decomposition of O₃, the formation of OH and H₂O₂, the degradation rates of organics and the removal efficiencies of COD and TOC (mineralization). As a result, US can significantly increase the yield of OH, thereby improving the degradation efficiency and mineralization of refractory organics. However, US also enhances the decomposition of ozone, thereby reducing the concentration of O₃ in water and impairing the efficiency of selective oxidation with O₃ molecules.     

Strategies to improve biological oxidation of real wastewater using cavitation based pre-treatment approaches

The present work demonstrates the effective application of pretreatment based on cavitation to improve biological oxidation of real municipal and industrial wastewater. The optimum pretreatment conditions based on ultrasonic cavitation for treatment of municipal wastewater were observed as power dissipation of 90 W, a duty cycle of 70% and H₂O₂ dosage of 0.2 g/L resulting in about 24.9% COD reduction. The use of modified sludge and ultrasonic pretreatment for biological oxidation resulted in significant reduction in treatment time (36 h) than the treatment time (60 h) required for biological oxidation using untreated sludge as inoculum. Also, significantly enhanced biodegradability index (BI) from 0.33 to 0.6 was achieved using pretreatment for biological oxidation process. For the treatment of real industrial wastewater, different pretreatment approaches based on hydrodynamic cavitation (HC) in combination with H₂O₂, ozone or Fenton were investigated. The pretreatment using best approach of HC + Fenton resulted in 44.2% of COD reduction in total whereas only 28.1% of COD reduction was achieved for the untreated effluent being applied in the biological oxidation. Overall, the present work demonstrated the effectiveness of the pretreatment based on cavitation for the improved treatment of municipal and industrial wastewaters.