Aqueous meta-Chloronitrobenzene Degradation by Ozonation and Its Kinetics

The kinetics and degradation process of meta-Chloronitrobenzene by ozonation in aqueous solution were investigated. Compared to para-chlorobenzoic acid, the rate constant of meta-Chloronitrobenzene with O₃ was 0.59 L/(mol·s), while that of the reaction with ^?OH was 2.07 × 10⁹ L/(mol·s). The main intermediate products were chloronitrophenols and some carboxylic acids. Neither chlorophenols nor nitrophenols was detected. The five-day biochemical oxygen demand and chemical oxygen demand were determined. The ratio of the former to the latter was above 0.3 at 20 min. It was feasible to perform a continuous biotreatment step after 20 min of ozonation.     

Ozonation Kinetics of Six Dichlorophenol Isomers

This paper investigates the kinetics of reactions between dichlorophenol (DCP) isomers and dissolved ozone in solutions of pH varying from 2 to 6 at 5 to 35 °C. A DCP can exist as dichlorophenol molecules and dichlorophenoxide anions in the aqueous solution, and both forms are reactive toward ozone. The overall reaction is second order requiring two moles of ozone for conversion of each mole of DCP. The ozonation rate of 2,6-DCP is the fastest and that of 3,4-DCP is the slowest at an identical condition. The Arrhenius equation is applicable to correlate temperature effects; the activation energy ranges from 46.5 to 55.3 kJ/mol. The reaction rate increases very rapidly as the acidity decreases, and the overall rate constant is greater than 1x106 M-1s-1 in solutions with pH of 5 or larger at 25 °C. The results of this study suggest that DCPs can be removed rapidly from wastewaters by ozone treatment.     

Henry And Mass Transfer Coefficients In The Ozonation Of Wastewaters

A procedure for the determination of Henry and mass transfer coefficients in an ozone-industrial wastewater system is presented. The method is applied to the ozonation of a tomato plant industrial wastewater, developed in the slow kinetic regime. In so doing, molar balances of ozone (in gas and water phases) are used together with gas-liquid reaction kinetic theory. While Henry's coefficients obtained are similar to those corresponding to ozonation in organic-free water, significant deviations are observed regarding the mass transfer coefficient.     

Kinetics Analysis on the Ozonation of MIB and Geosmin

The ozonation of 2-methylisoborneol (MIB) and geosmin was investigated in both pure and raw water. In a semi-batch reactor, a series of experiments was performed to determine the effect of pH on the ozonation of MIB and geosmin. The results show that pH has a significant effect on the ozonation of both compounds, which supports the theory that OH radical plays an important role on the destruction of MIB and geosmin. Compared with MIB, geosmin is more readily destroyed by ozonation. The ozonation kinetics follow approximately a first-order equation with respect to MIB and geosmin at the pH of 5, 7 and 9, and their rate orders of C_O3 at pH 7 are 0.44 and 0.61, respectively. Ozonation of organic matters in the water decreases the ozone concentration leading to a lower removal of MIB and geosmin; at the same time, the formation of OH radical initiated by the organic matters accelerates the ozonation of MIB and geosmin. The ozonation of MIB and geosmin spiked in raw water, settled water and pure water shows that background organics have no significant effect on the removal of MIB and geosmin; hence, the simplified rate equations acquired in pure water may have potential application in real water.     

Reaction Kinetics of Ozone Gas in Green Gram (Vigna radiate)

This study was carried out to evaluate the reaction kinetics of ozone gas in different height (5 and 10 cm), moisture content (10.6 and 13.4% (d.b.)) and gas flow rate (2 and 4 L/min). The decomposition kinetics obtained was first-order model. As far as the half-life of ozone is considered, the highest value obtained was equivalent to 8.72 min for grains ozonated at 5 cm height, 10.6% (d.b.) moisture content and 2 L/min gas flow rate. In the process of ozone reaction rate in green gram grains, height (p < 0.01) and moisture content (p < 0.01) were found to be the key factor for the effectiveness of ozone fumigation.     

Kinetic and Mechanistic Studies of the Ozonation of Alicyclic Amines

Studies about the ozonation of the polar and mobile alicyclic amines pyrrolidine, piperidine, morpholine and piperazine were carried out in model water at pH 7.0. According to a pseudo-first order rate law the reaction-rate constants were determined from the decrease of the amine concentration vs. the reaction time. The order of degradation of the alicyclic amines by ozone, resulting from the kinetic constants obtained, is piperazine > morpholine ? piperidine > pyrrolidine. The pH value of the water, the chemical structure of the amines and their pK_A values are recognized to be parameters influencing the reactionrates of the amines.     

Ozonation,Ozone/UV and UV/H2O2 Degradation of Chlorophenols

The performance of the O₃, O₃/UV and UV/H₂O₂ processes for degradation of six chlorophenols (4-chlorophenol, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol and pentachlorophenol) were studied in laboratory reactors. Comparative study showed that chlorophenols can be degraded successfully by all of the methods studied, whilst traditional ozonation at high pH was determined to be the most effective method to treat chlorophenols. Even though the molar absorptivity of chlorophenols is known to be relatively high in the UV-region, the combination of UV-radiation with ozone did not accelerate the degradation of chlorophenols further. The toxicity of degradation products formed during ozonation of chlorophenols has been compared with the toxicity of pure chlorophenols utilizing Daphnia magna 24 hours test. Ozonation of chlorophenols yielded less toxic or even nontoxic products for Daphnia magna compared with parent compounds.     

Cost Effectiveness of Ozonation and AOPs for Aromatic Compound Removal from Water: A Preliminary Study

The capital and operating costs for several aromatic compounds (phenanthrene, 2,4-dimethylphenol, 2,4,6-trichlorophenol, nitrobenzene) removal from polluted groundwater using ozonation and advanced oxidation have been estimated on the basis of the laboratory experiments in semibatch conditions. The pollutants initial concentration was in the range of 0.01–1.0 mM. In the calculations the polluted groundwater flow rate was taken 40 m³/h with the initial pH = 7.0. It is shown that polluted groundwater purification from the aromatic pollutants with the initial concentration in the range of 0.01–1.0 mM using ozonation and advanced oxidation is economically feasible.     

Iron Behavior in the Ozonation and Filtration of Groundwater

In Finnish groundwater, the main substances that require treatment are iron and manganese. In addition to this, groundwaters are soft and acidic. Iron removal is usually relatively effective by oxidizing dissolved iron into an insoluble form, either by aeration or chemical oxidization and removing the formed precipitate by sand filtration. Sometimes, if the untreated water contains high amounts of organic matter, problems may arise for iron removal. In Finland, it is quite common that groundwater contains high levels of both iron and natural organic matter, mainly as humic substances. The groundwater of the Kukkala intake plant in Liminka has been found to be problematic, due to its high level of natural organic matter. This research studied the removal of iron from this water by means of oxidation with ozone and filtration. While the oxidation of iron by ozone was rapid, the precipitate particles formed were small, and thus could not be removed by sand and anthracite filtration, and the iron residue in the treated water was more than 2 mgL^?1. And while the filtration was able to remove iron well without the feed of ozone, the iron residue in the treated water was only 0.30 mgL^?1. In this case, iron was led to the filter in a bivalent dissolved form. So, the result of iron removal was the best when the sand/anthracite filter functioned largely as an adsorption filter.     

Comparison of Activated Carbon and Hydrophobic Zeolite Efficiencies in 2,4-Dichlorophenol Advanced Ozonation

This study aims at comparing the removal of 2,4-dichlorophenol (2,4-DCP) by 3 methods; adsorption using hydrophobic zeolite (faujasite) or activated carbon (S-23 and L-27), conventional ozonation and hybrid adsorption/ozonation treatment. On the one hand, the three materials correctly adsorb 2,4-DCP; however the adsorption kinetics using zeolite is very low. On the other hand, ozonation totally removes 2,4-DCP after 1 h experiment and the simultaneous combination of adsorbent and ozone does not change the 2,4-DCP degradation. But, though ozonation and hybrid process appear to be equivalent for 2,4-DCP removal, activated carbons are able to decompose ozone and to improve chemical oxygen demand (COD) removal, whereas the zeolite does not show this catalytic effect. Similar results were also observed in a former study with nitrobenzene. Adsorbent degradation is evaluated by Brunauer, Emmet and Teller (BET) and differential thermogravimetric (DTG) analysis, which evidence that Faujasite and S-23 activated carbon are resistant to ozone exposure whereas the pore volume and the surface area of L-27 activated carbon decrease during ozonation.     

Correlations Between Chemical Structure and Ozonation Kinetics: Preliminary Observations

The kinetics of the heterogeneous ozonation of o, p-activated aromatic organic compounds have been correlated with structural parameters defined by Linear Free Energy Relationships. The gross first order rate constants for these reactions were found to correlate excellently with the Hammett Polar Constant for a series of substituted phenols and pyrimidines. Strong correlation also was obtained for the kinetics of ozonation of an homologous series of 2-alkyl-4,6-dinitrophenols and the Steric Parameter. The reaction rate was observed to increase as the electron density in the ring increased and decreased with increasing size of the substituent alkyl group. A preliminary model structured around the kinetics of a gas diffusion controlled reaction with infinitely fast chemical kinetics has been proposed along with a program of research to evaluate such a model.     

The Kinetics of Ozonolysis of Synthetic Dyes

Synthetic organic dyes were decomposed rapidly by ozone. The dyes all adhered well to first order kinetics with the exception of the Direct Yellow 12 which showed an initial zero order phase at pH 5. This has been tentatively ascribed to attack by unhydrolyzed ozone on the ethylenlc double bond. From one to four millimoles per liter of ozone was sufficient to attain a 5O% reduction in the concentration of all dyes during the first order ozonations.     

Heterogeneous Catalytic Ozonation of Refinery Wastewater over Alumina-Supported Mn and Cu Oxides Catalyst

An economical method was proposed to develop an efficient alumina-supported manganese (Mn) and copper (Cu) oxides (Mn-Cu-O/Al₂O₃) catalyst with a high surface area, 184.06 cm² g^?1. The catalyst was utilized for degradation refinery wastewater by heterogeneous catalytic ozonation. The effects of various operating variables including pH, ozone and catalyst dosages, and temperature were systematically investigated in detail to obtain the optimized conditions for accelerated degradation of refinery wastewater. The optimum values were as follows: ozone dose 50.0 mg L^?1, catalyst dose 3.0 g L^?1, initial pH = 6.8, T = 17 °C. Refinery wastewater samples were analyzed by chemical oxygen demand (COD) and the results indicated that kinetics of COD followed a pseudo–first-order degradation. Moreover, hydroxyl radical mechanism rather than absorption was proposed, indicating that the surface hydroxyl groups were the active sites that played a significant role in catalytic ozonation.     

Vapor and Liquid Phase Ozonation of Benzene

A comparative study is made of the benzene-ozone reaction in the gaseous and aqueous phase reactors at atmospheric pressure and 25°C. The vapor phase ozonation of benzene is first order in ozone and independent of benzene concentration. In distilled water (pH ranging from 5.2 to 5.4), the reaction is one-half order with respect to both concentrations of dissolved benzene and ozone. The overall rate constants are 0.0011 and 2.67 s^?1, respectively, in the vapor and liquid phase reactions. Results of this study suggest that it is technically feasible to remove benzene from a gas stream by the ozonation process, although the reaction rate is slow.     

Aqueous Pesticide Degradation by Ozonation and Ozone-Based Advanced Oxidation Processes: A Review (Part I)

Pesticide pollution of surface water and groundwater has been recognized as a major problem in many countries because of their persistence in aquatic environment and potential adverse health effects. Among various water and wastewater treatment options, ozonation and ozone-based advanced oxidation processes, such as ozone/hydrogen peroxide, ozone/ultraviolet irradiation, and ozone/hydrogen peroxide/ultraviolet irradiation, are likely key technologies for degrading and detoxifying these pollutants in water and wastewater. In this paper, ozone-based treatment of four major groups of pesticides, namely carbamates, chlorophenoxy compounds, organochlorines, and organophosphates, are reviewed. Degree of pesticide degradation, reaction kinetics, identity and characteristics of degradation by-products and intermediates, and possible degradation pathways are covered and discussed.     

Degradation of Pesticides by Ozonation and Advanced Oxidation

In the Netherlands many water supply companies are upgrading their surface water treatment plants in order to guarantee the water supply and water quality in the coming years. The Water Supply Company North West Brabant (WNWB) has plans to upgrade their treatment plant at Zevenbergen. In the retrofit plant chlorination will be abandoned and probably ozonation will be the major barrier against microorganisms. Pesticide concentrations will be decreased by three barriers: storage, ozonation and activated carbon filtration.

If the ozone dosage is restricted just to reach the required disinfection level at pH 7.2, ozonation is a poor barrier against pesticides. Out of 23 selected pesticides, only 6 were effectively degraded: dimethoate, chlortoluron, diuron, isoproturon, metoxuron and vinclozolin (O₃/DOC = 0.55 g/g). Application of an (O₃/DOC ratio of 1.0 g/g results in an effective barrier for roughly 50% of the tested pesticides (also for diazinon, parathion-methyl, linuron, methabenzthiazuron, metobromuron, MCPA and MCPP). Pesticides were degraded more effectively at high pH and high temperature.

For additional degradation of high concentrations of persistent pesticides, advanced oxidation may be applied. Atrazine, propazine, simazine, chlor-fenvinphos, tetrachlorvinphos, 2,4-D, 2,4-DP and 2,4,5-T were degraded by O₃/DOC = 1.4 g/g and H₂O₂/O₃ = 0.5 g/g. Dicamba and dikegulac were most persistent. pH has a minor effect on the degradation of pesticides by advanced oxidation. Higher hydrogen peroxide dosages showed no improvement in degradation. After ozonation and advanced oxidation, about 50% of totally reacted atrazine and propazine was converted into desethylatrazine. No desisopropylatrazine formation was observed.     

TiO2光催化降解2,4-二氯酚动力学及机理的研究

以TiO2作为催化剂,500 W汞灯作为光源,对水体中2,4-二氯酚（2,4-DCP）的光催化降解特性进行了研究。实验结果表明,TiO2光催化降解2,4-DCP效果较好,降解的最佳pH为7,催化剂的最佳投加量为200 mg·L-1。2,4-DCP的初始浓度越小,光催化的效率越高。在初始浓度为5 mg·L-1时,光催化1 h的降解率达90%。在实验的四种不同初始浓度（5 mg·L-1、10 mg·L-1、20 mg·L-1、40 mg·L-1）下,2,4-DCP的光降解速率常数近似与其初始质量浓度成一级反应动力学关系。结合高效液相色谱、气相色谱-质谱的测定结果以及Cl-、COD的变化,认为2,4-DCP的主要降解过程为：脱氯-开环-矿化、中间产物相互作用-进一步矿化。     

Tube Diameter and Height Influence on the Ozonation Operating Conditions with a U-Tube

Ozone has been used for a number of years in water treatment for viricidal and bactericidal action, as well as for its oxidizing properties. Energy consumption during its use depends on the performance of the ozone generators, but also on the ozone transfer efficiency from the gas phase to the liquid phase. Therefore, it is important to use a contactor with a high transfer efficiency.A new ozonation reactor has been developed: the Deep U-Tube (DUT). This reactor works under pressure, which increases the saturation concentration of ozone at equilibrium (C ). and creates a great turbulence, which breaks the gas bubbles and increases the interfacial area of exchange. Further, this new contactor has a piston hydraulic behavior in the liquid phase, which leads to a very great efficiency and to a better reduction for all reaction kinetics.