Using low intensity ultrasound to improve the efficiency of biological phosphorus removal

Low intensity ultrasound can produce various effects on biological materials, such as stimulating enzyme activity, cell growth, biosynthesis, etc., which may improve the efficiency of enhanced biological phosphorus removal (EBPR). We adopt total phosphorus (TP) and dehydrogenase activity (DHA) as indicators to confirm the feasibility of applying low intensity ultrasound in EBPR. Single-factor experiments and orthogonal test were conducted in batch anaerobic/oxic (A/O) process simulation to study the influence of ultrasonic intensity and exposure time in the EBPR process. The results showed that the optimal ultrasonic parameters were 0.2 W/cm² and 10 min under which condition the TP concentration in the effluent was 35–50% lower than that of the control (without ultrasonic irradiation). Changes of sludge activities after ultrasonic irradiation were examined. The improvement of sludge activity by ultrasound took 4 h after irradiation to reach the peak level, when an increase above 50% of DHA has been achieved by ultrasonic irradiation, and the enhancing effects induced by ultrasound disappeared in 16 h after irradiation. A tentative mechanism of biological phosphorus removal enhancement stimulated by ultrasound was discussed based on these phenomena.     

Study on degradation of dimethoate solution in ultrasonic airlift loop reactor

In this work, the degradation of dimethoate solution in ultrasonic airlift loop reactor (UALR) assisted with advanced oxidation processes was studied. The effects of O₃ flow rate, ultrasonic intensity, pH value and reaction temperature on the degradation rate were investigated. UALR imposed a synergistic effect combining sonochemical merit with high O₃ transfer rate. Under the optimal operation conditions: ultrasonic irradiation time was 4 h, O₃ flow rate was 0.41 m³ h⁻¹, ultrasonic intensity was 4.64 W cm⁻², pH value was 10.0, reaction temperature was 25 °C, and initial concentration of dimethoate was 20 mg L⁻¹, degradation rate of dimethoate increased to 90.8%. The experimental results indicated that the method of UALR degradation of organic pollutants in the presence of gas could reduce reaction time and improve degradation rate. UALR was an advisable choice for treating organic waste waters and this device could be easily scale up. Thus this process has wide application prospect in industry.     

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.     

Short-time sonolysis of chlorobenzene in the presence of Pd(II) salts and Pd(0)

The effect of PdSO₄, PdCl₂ and Pd(0) on the degradation of chlorobenzene in aqueous solution within 10 min under 200 kHz ultrasonic irradiation, was investigated. The reaction products remaining in the aqueous mixture were analyzed and quantified. The mechanism of chlorobenzene decomposition having benzene as key intermediate is discussed.     

Estimation of hydroxyl free radicals produced by ultrasound in Fricke solution used as a chemical dosimeter

Hydroxyl free radicals produced in Fricke solution exposed to 80 kV X-rays or 23 kHz ultrasound (intensity 3 W cm⁻²) or 20 kHz ultrasound (intensity 18.9 W cm⁻²) or 3.5 MHz clinical ultrasound (intensity 1.47 W cm⁻²), as estimated from the Fricke dosimetric data, exhibited a linear dose-response relationship. The dosimeter was found to be effective in the concentration range 1.0–8.0 mM of FeSO₄ solution. The hydroxyl radicals produced in Fricke solution were inhibited by the OH radical scavengers dimethyl sulfoxide (200 mM), -histidine (10 mM) and sodium benzoate (10 mM) in a manner proportional to the rate constants of their reaction with the OH radicals. The power threshold for OH radical formation, which is presumably the threshold for cavity formation, was estimated for 23 kHz ultrasound by this dosimeter as 1.28 W cm⁻² for a 4 cm³ sample volume.     

Kinetics and mechanisms of ultrasonic degradation of volatile chlorinated aromatics in aqueous solutions

Ultrasonic decompositions of chlorobenzene (ClBz), 1,4-dichlorobenzene and 1-chloronaphthalene were investigated at 500 kHz in order to gain insight into the kinetics and mechanisms of the decomposition process. The disappearance of ClBz on sonication is almost simultaneously accompanied by the release of chloride ions as a result of the rapid cleavage of carbon–chlorine bonds with a concomitant release of CO, C₂H₂, CH₄ and CO₂. The intermediates resulting from attack of HO^√ radicals were detected but in a quite low yield (less than 2 μM). The generation of H₂O₂ on sonolysis is not significantly affected by the presence of aqueous ClBz while the generation of NO₂⁻ and NO₃⁻ is inhibited initially due to the presence of ClBz which diffuses into the gas–bubble interfaces and inhibits the interactions between free radicals and nitrogen. Moreover, brown carbonaceous particles are present throughout the ultrasonic irradiation process, which are consistent with soot formation under pyrolytic conditions. These important features suggest that, at the relatively high initial substrate concentrations used in this study, ultrasonic degradation of ClBz takes place predominantly both within the bubbles and within the liquid–gas interfaces of bubbles where it undergoes high-temperature combustion. Under these conditions, the oxidation of ClBz by free radical HO^√ outside of bubbles is a minor factor (though results of recent studies suggest that attack by HO^√ is more important at lower initial substrate concentrations). The sonochemical decomposition of volatiles follows pseudo-first-order reaction kinetics but the degradation rates are affected by operating conditions, particularly initial substrate concentration and ultrasonic intensity.     

Dosimetry in sonochemistry: the use of aqueous terephthalate ion as a fluorescence monitor

The generation of HO radicals by acoustic cavitation in water was monitored by their reaction with terephthalic acid (TA) anion to produce fluorescent hydroxyterephthalate ions using a cleaning bath (38kHz) and a probe system (20, 40 and 60 kHz) as different sources of ultrasound. When using the ultrasonic bath as a source of energy for sonochemical studies, the shape of the reaction vessel is important. In the case of HO production from water (50 cm³), reaction in a conical flask (100 cm³) produces 2.75 times more radicals than a round-bottomed flask of the same capacity. The fluorescence yield (fluorescence intensity/ultrasound dosage) obtained using the conical flask and ultrasonic bath was similar to that for a probe operating at 40 kHz on the same volume of solution. For a probe system operating at 20, 40 and 60 kHz the greatest sonochemical efficiency was attained at the highest of these frequencies (60 kHz). For the probe system the fluorescence yield is directly proportional to power input and the concentration of TA. The fluorescence yield decreases as the temperature is increased.     

Effect of various sono-oxidation parameters on the removal of aqueous 2,4-dinitrophenol

The influences of ultrasonic output intensity, solution pH, H₂O₂ concentration and the addition of Fenton reagent on the degradation of 2,4-dinitrophenol (DNP) under ultrasonic irradiation were investigated. It was observed that the degradation of DNP fitted pseudo-first-order dynamics under our experimental conditions. Increasing the ultrasonic output intensity increased the degradation efficiency of DNP and low pH favored the ultrasonic degradation of DNP. The addition of H₂O₂ enhanced the ultrasonic degradation efficiency of DNP. The further addition of Cu²⁺, however, hindered the degradation of DNP. In contrast, sono-oxidation treatment in combination with FeSO₄/H₂O₂ showed a synergistic effect for DNP degradation.     

A standard method to calibrate sonochemical efficiency of an individual reaction system

Fricke reaction, KI oxidation and decomposition of porphyrin derivatives by use of seven types of sonochemical apparatus in four different laboratories were examined in the range of frequency of 19.5 kHz to 1.2 MHz. The ultrasonic energy dissipated into an apparatus was determined also by calorimetry. Sonochemical efficiency of Fricke reaction and KI oxidation was defined as the number of reacted molecule per unit ultrasonic energy. The sonochemical efficiency is independent of experimental conditions such as the shape of sample cell and irradiation instruments, but depends on the ultrasonic frequency. We propose the KI oxidation dosimetry using 0.1 moldm(-3) KI solution as a standard method to calibrate the sonochemical efficiency of an individual reaction system.     

Sonochemical and photosonochemical degradation of 4-chlorophenol in aqueous media

The degradation of 4-chlorophenol (4-CP) in aqueous media by 516 kHz ultrasonic irradiation was investigated in order to clarify the degradation mechanism. The degradation of concentrated 4-CP solution by means of ultrasound, UV irradiation and their combined application was also studied. The obtained results indicate that *OH radical are the primary reactive species responsible for 4-CP ultrasonic degradation. Very little 4-CP degradation occurs if the sonolysis is carried out in the presence of the *OH radical scavenger tert-butyl alcohol, also indicating that little or no pyrolysis of the compound occurs. The dominant degradation mechanism is the reaction of substrate with *OH radicals at the gas bubble-liquid interface rather than high temperature direct pyrolysis in ultrasonic cavities. This mechanism can explain the lower degradation rate of the ionic form of 4-CP that is partly due to the rapid dissociation of *OH radicals in alkaline solutions. The sonochemical destruction of concentrated 4-CP aqueous solution is obtained with low rate. Coupling photolysis with ultrasound irradiation results in increased efficiency compared to the individual processes operating at common conditions. Interestingly, the photosonochemical decomposition rate constant is greater than the additive rate constants of the two processes. This may be the result of three different oxidative processes direct photochemical action, high frequency sonochemistry and reaction with ozone produced by UV irradiation of air, dissolved in liquid phase because of the geyser effect of ultrasound streaming. Additionally, the photodecomposition, at 254 nm, of hydrogen peroxide produced by ultrasound generating *OH radical can partly explain the destruction enhancement.     

Effect of ultrasonic irradiation on production of fermented milk with Lactobacillus delbrueckii

Milk fermentation with Lactobacillus delbrueckii under ultrasonic irradiation was carried out in a 450 cm³ bioreactor with a polyethylene film bottom. Ultrasonic irradiation increased the hydrolysis of lactose in milk but decreased the cell viability. However, the viable cell count increased again when the ultrasound was stopped, because ultrasound did not destroy the ability for cell propagation. When the sonication power was 17.2 kW m^-2 and the sonication period was 3 h, 4.9 × 10⁸ cfu cm^-3 of the viable cell count and 55% lactose hydrolysis were attained. In contrast, the viable cell count was 2 × 10⁹ cfu cm^-3 and 35.6% lactose was hydrolysed in control fermentation.     

Improvement in sonochemical degradation of 4-chlorophenol by combined use of Fenton-like reagents

Studies on the sonolysis of a wide range of organic compounds have demonstrated that ultrasonic irradiation has potential for decomposition of organic pollutants in hazardous wastewater. However, the ultrasonic irradiation alone cannot provide high enough rate of decomposition to be used practically. One of the solutions to increase the degradation efficiency is to combine the ultrasound application with other advanced chemical oxidation processes (AOPs). In this study, in order to increase the efficiency of ultrasonically assisted degradation of organic pollutants in water, we examined effects of three kinds of solid Fe-containing catalysts, namely iron powder, basic oxygen furnace (BOF) slag and mill scale on the degradation rate of 4-CP (4-chlorophenol) in aqueous solutions containing hydrogen peroxide. In the experiments, 4-CP was considered as a model organic compound. All three Fe-containing matters when react with hydrogen peroxide are involved in the Fenton-like reaction system, which is one of the promising AOPs. The results showed that both the iron powder and mill scale additions can accelerate the degradation of 4-CP, although the effect is dependent on the solution pH. All 4-CP could be decomposed for 2 min at pH=3 and for 1h at pH=5.6. On the other hand, the BOF slag had no catalysis effect on the 4-CP degradation because of higher concentration of calcium and lower concentration of iron.     

Simple quantification of ultrasonic intensity using aqueous solution of phenolphthalein

Aqueous phenolphthalein solution under sonication was investigated for use as a chemical dosimeter. The fading time of aqueous phenolphthalein solution under sonication depended on the concentration of phenolphthalein and the pH values of solutions. The fading time was correlated to the ultrasonic intensity in a reaction vessel that is estimated on the basis of decomposition of porphyrin. The relation between the fading time and the ultrasonic intensity for different frequencies is expressed by a single curve. From these results, it is indicated that aqueous solutions of phenolphthalein is useful for simple quantification of ultrasonic intensity for practical use, and one can regard it as one of the ultrasonic intensity indicators.     

超声波和紫外光协同降解酸性橙Ⅱ水溶液的机理研究

以含有多个苯环的典型偶氮染料-酸性橙Ⅱ为研究对象,研究了超声波和紫外光分别辐照及共同辐照下的降解现象。酸性橙Ⅱ水溶液在超声波及紫外光分别辐照下均发生显著降解,反应过程符合准一级反应动力学规律。在超声波和紫外光共同辐照下,反应过程也符合准一级反应动力学规律,同时酸性橙Ⅱ水溶液降解呈现显著的声光协同效应,即同一辐照时间内超声波和紫外光共同辐照下酸性橙Ⅱ的降解率大于超声波和紫外光单独辐照下各自降解率之和。动力学分析结果表明,该协同效应可归因于紫外光对超声空化过程中产生的过氧化氢的裂解作用。      

Kinetics of hydrazinium nitrate decomposition in nitric acid solutions under the effect of power ultrasound

The effect of ultrasound (f = 20 kHz) on the decomposition of hydrazinium nitrate was investigated in a nitric acid medium. The kinetics of N2H5+ decomposition and initial HN3 formation increase in a linear manner with the HNO3 concentration (from 1 to 6 M) and with the ultrasonic intensity (from 0.5 to 3.1 W cm-2). Both rates were equal to that of HNO2 formation in the absence of N2H5+, indicating that the N2H5+ decomposition mechanism is the same as observed without ultrasound between HNO2 and N2H5+. The variation of the steady-state HN3 concentration with the HNO3 concentration and the ultrasonic intensity suggests the existence of a nonexplosive HN3 thermal decomposition mechanism in the cavitation bubble under the effect of ultrasound. It was also observed at ultrasonic intensities exceeding 3.5 W cm-2 that the decomposition of HN3 led to the accumulation of NH4+ in solution.     

Fragmentation of chitosan by ultrasonic irradiation

Kinetics of chitosan fragmentation by ultrasonic irradiation at frequency of 20 kHz, and the effects of experimental variables (power of ultrasound, chitosan concentration and solution temperature) on fragmentation were investigated. The kinetics studies were followed by measuring solution viscosity of the original and its fragments, and determining average number of chain scission of the fragments. The effects of ultrasonic power, chitosan concentration and solution temperature on fragmentation process were followed by viscometry and size exclusion chromatography. The chemical structure of the original chitosan and its fragments were examined by (1)H NMR spectroscopy and elemental analysis. The experimental results showed that the rate of fragmentation increased with an increase in power of ultrasound. Chain scission increased with an increase in power of ultrasound; and solution temperature, but a decrease in chitosan concentration. The chemical structure and polydispersity of the original and the fragments were nearly identical. A model based on experimental data to describe the relationship between chain scission and experimental variables (power of ultrasound; irradiation time; reduced concentration, c[eta]; and solution temperature) was proposed. It was concluded that ultrasonic irradiation is a suitable method to perform partial depolymerization and to obtain moderate macromolecules from large ones.     

超声功率对电化学沉积铜过程速率的影响

测定了H2SO4-CuSO4溶液中，超声频率为24kHz时，超声功率对铜电化学阴极沉积过程速率的影响。实验结果表明，在超声作用下铜电化学阴极沉积过程的电流密度明显提高，即超声作用能提高过程的沉积速率。超声对铜电化学沉积过程速率强化程度随超声功率的增加而增大；在相同温度和超声功率下，超声强化速率的效果从反应控制区域（低操作过电位）向传质控制区（高操作过电位）过渡时而更加显著；在其它条件相同的情况下，超声对铜电化学沉积过程速率的强化程度随温度的升高而减小：超声强化速率的效果与溶液中铜离子的浓度基本无关。     

CdTe量子点功能化玻片的制备及其对Pb2+浓度的检测

通过羟基化和氨基硅烷化处理,得到表面接枝氨基的玻片载体。水相合成巯基乙酸修饰的CdTe量子点(CdTe-TGA),采用EDC/NHS活化反应,将量子点偶联到氨基化玻片表面,制备出具有荧光性能的功能化玻片。考察了量子点与EDC的量比、活化时间、偶联温度以及偶联时间对偶联效果的影响。结果表明,在量子点与EDC的量比为1:30、活化时间1 h、偶联温度30 ℃、偶联时间4 h条件下获得的功能化玻片具有最佳的荧光性能。将该条件下制备的功能化玻片用于水溶液中Pb²⁺的浓度检测,得到玻片相对荧光猝灭强度随Pb²⁺浓度变化的线性曲线,线性范围为1.0×10^-9~4.0×10^-8mol·L^-1,检出限为3.8×10^-9mol·L^-1,且具有良好的选择性。该方法可以灵敏而准确地检测Pb²⁺浓度。     

Ultrasonic pretreatment for lipase-catalyed synthesis of phytosterol esters with different acyl donors

This study is focused on the enzymatic esterification of phytosterols with different acyl donors to produce the corresponding phytosterol esters catalyzed by Canadia sp. 99-125 lipase under ultrasound irradiation. An ultrasonic frequency of 35 kHz, power of 200 W and time of 1h was determined to guarantee satisfactory degree of esterification and lipase activity. The influence of temperature, substrates concentration and molar ratio was investigated subsequently. The optimum production was achieved in isooctane system at 60°C with phytosterol concentration of 150 μmol/mL and phytosterol to fatty acid molar ratio of 1:1.5, resulting in a phytosterol esters conversion of above 85.7% in short reaction time (8h). Phytosterols esters could also be converted in high yields to the corresponding long-chain acyl esters via transesterification with triacylglycerols (above 90.3%) under ultrasound irradiation. In optimum conditions, the overall esterification reaction rate using the ultrasonic pretreatment process was above 2-fold than that of mechanical stirring process without damage the lipase activity.     

Precipitation of calcium carbonate by ultrasonic irradiation

Supersaturated solution of calcium carbonate ([Ca²⁺]=1.2 mmol/L, [HCO₃⁻]=3.2 mmol/L, pH=8.8, T=30±0.5 °C), a scale forming component, was irradiated by an ultrasonic homogenizer (24 kHz, 15–250 W/cm²) to study the factors that affect its precipitation rate. The factors of (1) depth of horn immersion, (2) ultrasonic intensity and horn tip size and (3) cavitation, which can affect the precipitation rate were investigated in this study. Ultrasonic irradiation was observed to accelerate the precipitation of calcium carbonate and it was found that there exists an optimum range of horn immersion depth for maximizing the precipitation rate. The experimental data also established that the precipitation rate was proportional to ultrasonic intensity and diameter of horn tip. These findings were correlated to the effects of physical mixing, that arises due to ultrasonic irradiation. However, the effect of cavitation in accelerating the precipitation rate was found to be small. Thus it is forwarded that the physical mixing effect, especially macrostreaming is the main factor that accelerates the precipitation rate of calcium carbonate during ultrasonic treatment. Further, neither the morphology nor the size of the calcium carbonate crystals formed were found to be affected by the ultrasonic irradiation.