Magnetic-assisted micro-ozone applied to oxidize reactive blue dye simulated wastewater

Lu Xiuguo, Zhai Jian, Zhao Chunxia, Li Hui
(College of Chemistry and Environmental Science, HeBei University, Baoding 071002,  China)

Abstract The treatment of reactive blue dye simulated wastewater by magnetic-assisted micro-ozone oxidation system has been studied. The optimum conditions were investigated and the mechanism of degradation was briefly discussed. The results showed that the removal rate of chromaticity achieved 97.8% after oxidizing 30min without magnetic field. Comparatively, the removal rate of chromaticity achieved 97.8% after oxidizing 24min under the action of magnetic field. The result showed that the presence of magnetic field quickened the velocity of producing·OH from O₃ and improved the efficiency of oxidation.
Keywords magnetic field, micro-ozone, oxidation, reactive blue dye

1 INTRODUCTION
The aromatic hydrocarbon and the heterocyclic compound are mainly taken as a matrix in the dying and printing wastewater. It has the colored groups and bases (for example -N=N-, -N=O) and the polar groups and bases (for example -SO₃Na, -OH, -NH₂). If the dye molecules contain many groups and bases (-SO₃H, -COOH, –OH) which can form the hydrogen bond with water molecule like reactive dyes and the neutral dyes and so on, then dye molecules can absolutely dissolve in the wastewater; If the dye molecules contain no or little hydrophilic groups and bases (-SO₃H, -COOH, –OH), then dye molecules exist in the wastewater in the form of suspended particulate. If dye molecules contain few hydrophilic groups and bases but the molecular weight is very large or does not contain the hydrophilic groups and bases, the dye molecules usually exist in water as colloid form. Presently, the hydrophobic or water-fast dye wastewater decoloration has basically been solved, but many hydrophilic or water-soluble dye wastewater is difficultly decolored^[1].
    At present, the chroma and COD_Cr of dyeing wastewater is usually removed by physical method, chemical method, or physical chemical method, and biological method, but above methods have their insurmountable shortcomings. This article takes reactive blue dye solution which is commonly used but difficultly biodegraded as the breakdown products, micro-ozone is the oxidant and magnetic field is the sur-field. The effect and efficiency which magnetic-assisted micro-ozone oxidation system degrades reactive blue dye is explored, the coordinated oxidizing mechanism is preliminary researched.

2 EXPERIMENTAL
2.1 Instruments and Reagent
Micro-ozone generator (Shanghai,China), KC-70C permanent magnetizer (Shanghai,China), SXG-1B teslameter (Shanghai,China), UV-265 spectrophotometer (Japan).
    Active blue dye solution, the soluble starch is the analytical purity, the other are chemical purity.
2.2 Experimental procedures
2.2.1 Ascertain the dosage of ozone production
Appropriate amount of O₃ was aerated into 500mL KI solution in a graduated cylinder under normal temperature, for a certain time, the ration of oxidized solution (V_KI) was taken to titrate with the Na₂S₂O₃, then the productive quantity of ozone was calculated ^[2]

    In the formula: Q and t respectively expresses the ozone current capacity (L·min^-1) and reaction time (min).
2.2.2 Ascertain the factors of the removal rate chroma of reactive blue dye simulative wastewater
500mL simulative wastewater, regulates solution pH value, aerates the ration O₃ under the normal temperature, reacts for a certain time, the absorbency of simulative wastewater is determined, computes the decolorization rate.

    In the formula: A₀，A respectively expressed absorbency of reactive blue dye simulative wastewater in the highest absorption peak place before and after treatment. Magnetic-assisted micro-ozone oxidation experiment as the same to normal oxidation experiment, the difference lies in which the reactive blue dye simulative wastewater in the graduated cylinder is put in the magnetic field in the magnetic-assisted micro-ozone oxidation experiment.
    The factors which affect the removal rate of chroma are studied. These factors include the time of aerating O₃, pH value, intensity of magnetic field, magnetization time.
2.2.3 The quality of raw wastewater and chromophore of reactive blue dye
    The chromophore of reactive blue dye is ﹥C=N- group.

Table 1 The quality of raw wastewater

3 RESULTS AND DISCUSSION
3.1 The factors of the removal rate of chroma of reactive blue dye
3.1.1 The aeration time of ozone choice The pH value is 10, 500mL simulative wastewater, the density of aerated ozone is 1.167mg·L^-1·h^-1, at room temperature. The effect of ozone aeration time on the removal rate about chroma of the simulative dyeing wastewater has been investigated.
    From Figure1, it can be seen that the chroma of simulative reactive blue dye is removed in a certain degree when ozone is aerated into this reaction system, and the removal rate of chroma increase with the aeration time of ozone increasing. The removal rate of chroma reached 97.8% when the aeration time of ozone is 30min. The removal rate of chroma reached 99% when the aeration time of ozone is 35min. According to the practical application, the best aeration time of ozone is 30min.
3.1.2 Reaction pH value choice 500mL simulative wastewater, the density of aerated ozone is 1.167mg·L^-1·h^-1, the aeration time of ozone is 30min, at room temperature. The effect of pH value of the solution (use thin vitriol or sodium hydroxide to regulate) on the removal rate of chroma of the simulative dye wastewater has been investigated.
    From Figure2, it can be seen that the oxidization effect is best under the alkalinity condition (namely pH 10). The reactive blue dye wastewater is a kind of industrial wastewater which is difficultly degraded by biochemistry method. The general chemistry method very difficultly oxidized it. Ozone directly attacks organic matter by molecular form under acidity or neutral condition, moreover the molecular ozone response has the greatly strengthened selectivity. It only reacts with the unsaturated aromatic compound either the aliphatic compound or certain special groups and bases response. But the reason which the removal rate of chroma enhanced under the alkalinity condition is that ozone produces ·OH. It has stronger oxidation ability and is only inferior in fluorin . Thus those difficultly biodegraded organic matter can be effectively degraded. First, the passive groups（  -NO₂,-SO₃^-）of dye molecules were substituted by ·OH, it made aromatic rings active. Then the aromatic rings were decomposed and generated low fatty acid compounds. At last they were turned into CO₂ and H₂O.

Fig1 Effect of the aeration time of O₃ on colority removal

Fig2 Effect of pH value on colority removal

3.1.3 Sur-magnetic fields magnetizations time choice pH value is 10, 500mL simulative wastewater, the density of aerated ozone is 1.167mg·L^-1·h^-1, at room temperature. The effect of aeration time of ozone on the removal rate of chroma under 374.1mT magnetic intensity is investigated.
    The removal rate of chroma reached 97.8% needs 24min when the intensity of sur-magnetic field is 374.1mT. It is 6min shorter than without magnetic field. But with the magnetizations reaction time increasing, removal rate of chroma in intensity of magnetic field being 374.1mT was close to which without magnetic field. The result showed that the productive rate of hydroxyl radical was improved, but the productivity of hydroxyl radical was not improved.
3.1.4 Intensity of sur-magnetic field choice The pH value is 10, 500mL simulative wastewater, the density of aerated ozone is 1.167mg·L^-1·h^-1, at room temperature, with the aeration time of ozone 30min. The effect of intensity of sur-magnetic field on the removal rate of chroma is investigated.
    From Figure 4, it also can be seen that the removal rate of chroma by different intensity of sur-magnetic field at the same reaction time was different. The greater intensity of sur-magnetic field was, the more removal rate of chroma was. But with the magnetizations reaction time increasing, the removal rates of chroma in different intensity of magnetic field were close to each other. The result showed that the sur-magnetic field enhanced productive rate of ·OH from micro-O₃/OH^- system truly, but has not enhanced its productivity.

Fig3 Effect of magnetic-assisted reaction time on colority removal

Table2 The relation between A and reaction velocity

Fig4 Effect of intensity of magnetic field on colority removal

3.2 In magnetic field ozone oxidize active blue dye response dynamics When pH value is 10, 500mL simulative wastewater, the density of aerated ozone is 1.167mg·L^-1·h^-1, at room temperature, every two minutes take a sample until 40 minutes. Determine absorbency in the 600nm, the results are listed on Table 2.
   According to data in the table, the relation between g and A is simulated in first-order kinetics equation under the magnetic field condition, the obtained correlation coefficient of linear equation above 0.99. It shows that the decolority response which micro-ozone oxidizes reactive blue dye simulative wastewater conforms to first-order reaction kinetics in the magnetic field ^[3].
3.3 Preliminarily reaction mechanisms research
It has been very early discovered that the magnetic field has the obvious response to the free radical, free radical response is main response in the micro-O₃/OH^- oxidation system, therefore extrapolates the magnetic field/micro-O₃/OH^- oxidation system associated technology enhance the oxidation decomposed velocity of pollutant. It does not consume extra electrical energy like the supersonic and ultraviolet ray (may produce magnetic field by permanent magnet), is advantageous for application.
    Under not sur-magnetic field condition, a magnetic field which being from the molecular interior (is called partial magnetic field) could provide the magnetic moment for the change of the spinning condition of the free radical. Under sur-magnetic field condition, the Larmor spinning velocity of the spinning vector of the free radical can be changed. The difference of the spinning velocity of two spinning vectors (Dw) can be expressed by the formula

    In the formula, Dg =|g₁-g₂|, g₁ g₂ respectively notes the g value of two free radicals alone electron, g value is related with the system nature, m_B is a Bohr's magneton, h is the Planck constant, H₀ is the intensity of sur-magnetic field, a₁, a₂ are ultra fine coupling constants of two free radicals, I is the nuclear spin quantum number. The transformation speed which the two spinning vectors of free radicals from S state to T₀ state is decided by Dw value. According to above formula, the above transformation speed can increase with Dg or Ho enhancing^[4]. Speaking of the reactive blue dye simulative wastewater, Dg is a definite value in the microscopic structure, therefore the difference of the Larmor spinning velocity (Dw) is only decided by the intensity of macroscopic sur-magnetic field. According to Dg mechanism, the bigger H₀, the shorter transformation time and the quicker transformation speed from S state to T₀ state will be. Namely the more little-singlet state total, the smaller possibility of re-combination and the quicker rate of chemical reaction will be. This is the degeneration process mechanism of magnetic-assisted micro-O₃/OH^- system.

Fig5 Sample ultraviolet visible spectrum before and after treatment
1-before treatment, the ultraviolet visible spectrum of sample
2-after oxidation under magnetic field condition, the ultraviolet visible spectrum of sample
3- after oxidation without magnetic field condition, the ultraviolet visible spectrum of sample

4 CONCLUSIONS
4.1 Ultraviolet visible spectrum of the sample before and after treatment respectively
Before treatment, the sample has the obvious absorption peaks in the ultraviolet visible range. After magnetic-assisted oxidation treatment, there are not absorption peaks in the visible light area. It shows that the color groups and bases are completely destroyed. At the same time the 300nm scan line also obviously reduced. It shows that the benzene ring is partially oxidized by the hydroxyl free radical and produced chain framework. Curve 2 (reaction time was 24min) dashed lines denotes the ultraviolet visible spectrum of sample which is oxidized by magnetic-assisted oxidation system. Curve 3 (reaction time was 30min) solid line denotes the ultraviolet visible spectrum of sample which is oxidized by only oxidation system. The two ultraviolet visible spectrums are extremely approximate (reaction time is obviously different, dashed line is add-on shows difference). From Fig5 we can see that the productivity of ·OH under sur-magnetic field was the same to no sur-magnetic field. It shows that the sur-magnetic field did not enhance the productivity of ·OH.
4.2 Conclusions
1. When 500mL simulative wastewater, pH value is 10, the density of aerated ozone is 1.167mg·L^-1·h^-1, the intensity of magnetic field is 374.1mT, the removal rate of chromaticity achieved 97.8% after oxidizing 30min without magnetic field. Comparatively, the removed rate of chromaticity achieved 97.8% after oxidizing 24min under the presence of magnetic field.
2. According to first-order reaction kinetics, the relation between g and A is fit in first-order kinetics equation under the magnetic field condition, the obtained correlation coefficient of linear equation above 0.99. It shows that the response fits in first-order kinetics, the kinetics equation is g=0.19246A.
3. The sur-magnetic field enhanced ·OH productive rate of micro-O₃/OH^- system, but has not enhanced its productivity.

REFERENCES
[1] Zheng Jilu, Fan Juan, Ruan Fuchang. Techniques and equipment for environmental pollution control, 2000, 1 (5): 29-35.
[2] Zheng Yunzhong. the measurement of the ozone density, synthesize the material aging and applied 1990,000 (002): 37-41
[3] Jiang Huanwei, Wang Yu , Li Fengkai et al.  Journal of East China University of Science and Technology ( natural science version), 2003, 29 (2): 166-169.
[4] WangGuoquan, WuZhongyun, magnetic chemistry and medicine. BeiJing: Weapon Industry Press，1997，21-23.

磁强化微臭氧氧化体系对活性蓝染料废水脱色的实验研究
鲁秀国 翟建 赵春霞 李辉
（河北大学化学与环境科学学院环境科学系 河北保定 071002）
摘要  本文利用磁强化微臭氧(O₃) 氧化法协同体系对活性蓝染料废水进行了脱色处理实验研究，筛选出了最佳实验条件, 并对降解机理进行了简要讨论。实验结果表明，无磁场条件下, 通入适量O₃，反应30 min后,色度去除率达97.8%。外加磁场作用，反应24 min后，色度去除率即可达到97.8 %。磁场的存在强化了O₃生成·OH的速率, 进一步提高氧化的效率。
关键词 磁场 微臭氧 氧化 活性蓝染料