Quinoxaline Ozonation in Aqueous Solution

The oxidation of quinoxaline by ozone in aqueous solution is investigated. The chemical and kinetic evolution of the oxidation process at varying pH are followed by means of semi-batch and batch ozonation experiments. Results indicate that quinoxaline ozonation can develop according to both radical and ionic mechanisms whose relative occurrence can be varied by means of addition to the reacting system of radical scavengers or ozone decomposition promoters. It is shown that each mechanism involves an initial attack of ozone to both the homocyclic and heterocyclic rings of quinoxaline. Pyrazinedicarboxylic acid is formed as a stable final product in ionic ozonation, whereas it appears as an intermediate still reactive towards ozone in radical ozonation. Despite this, the radical ozonation of quinoxaline appears to be more selective than ionic zonation with respect to production of pyrazinedicarboxylic acid. Reaction schemes are proposed to account for the observed kinetic behaviors and product formations.

Oxidation experiments have also been extended to pyrazine, and its sensitivity to only radical ozonation is shown.     

The Ozonation of Glyoxylic Acid in Aqueous Solution: Chemical Products and Kinetics Evolution

The ozonation of glyoxylic acid in aqueous solution is investigated in semicontinuous and continuous reacting systems to follow the evolution of both chemical products and kinetics. Evidence is given of formation of small amounts of formic acid and -of the promoting effect of peroxidic intermediates upon oxalic acid ozonation. Kinetic results indicate that the ozonation process develops according to a radical chain mechanism initiated by ozone attack on glyoxylic acid.     

Ozonation of Sulfur-Containing Aliphatic Compounds in Aqueous Solution. I

In view of the possible reaction of ozone with sulfur containing natural and anthropogenic compounds, the oxidation products of sulfur-containing aliphatic model compounds in pure water in dependence on pH value were investigated.

In the first part, as a model compound for thioether, thiodiglycolic acid was investigated. The rate of elimination is independent of pH-value. At pH 3 as primary product thionyldiglycolic acid is formed, which undergoes further oxidation, but very slowly, to sulfonediacetic acid, which is very stable against ozone attack at pH 3. At pH 7 and higher, however, thionyldiglycolic acid is oxidized faster to sulfonediacetic acid, and this compound is oxidized to sulfoacetic acid, oxalic acid, glyoxylic acid, sulfateion, and CO₂ after longer reaction times. In all cases, sulfite as an inorganic intermediate product could not be identified. Also the intermediate products in pure solutions are ozonized. The mass balances show that 90 to 95% of the oxidation products could be identified. Based on these results, reaction schemes are discussed.     

Aqueous Ozonation Of Fatty Acids

The reactivity of a series of fatty acids toward ozone was examined in aqueous solution at low substrate concentration (μg.L^?1 range). Saturated fatty acids were unreactive, unsaturated fatty acids were readily consumed. A number of reaction products or their methylated derivatives were identified by gas chromatography and gas chromatography-mass spectrometry. The products identified are consistent with a 1,3-dipolar cyclo-addotion reaction.     

Catalytic Ozonation of Citric Acid by Metallic Ions in Aqueous Solution

Ozonation of citric acid in water catalyzed by different ions from the first row of transition metals (Mn²⁺, Co²⁺, Ti⁴⁺, Fe²⁺, Cu²⁺, Ni²⁺ and Zn²⁺) was investigated at room temperature. The results showed that at pH=2, where the decomposition of citric acid is negligible by only ozone, the following order of efficiency of metallic ions for the decomposition of citric acid by ozone, and also for the TOC removal, was obtained: Mn²⁺ > Co²⁺ > Ti⁴⁺ > Fe²⁺. Cu²⁺, Ni²⁺ and Zn²⁺ showed negligible efficiency under the same experimental conditions. At pH=5.5, Mn²⁺ and Co²⁺ showed slightly higher efficiency than at pH=2 while Ti⁴⁺ and Fe²⁺ showed insignificant effect at this pH value. On the other hand, at pH=7 the investigated catalysts showed no obvious catalytic efficiency for the decomposition of citric acid by ozone.     

Ozonation Kinetics Of o-phenylphenol in Aqueous Solutions

This study investigated the oxidation and reaction kinetics of biocide o-phenylphenol (o-PP) during ozonation. The second-order rate constants for direct reaction of molecular ozone with o-PP were determined in homogenous system using classical and competition kinetics. Obtained values of the second-order rate at pH 2 are equal to (3.79 ± 0.23)?×?10² M^?1 s^?1 and (4.42 ± 0.64)?×?10² M^?1 s^?1, for the two methods, respectively. The rate constant for the dissociated form of o-PP was also determined. It was found that the rate constants for the reaction of o-PP with ozone increase significantly with increasing pH.     

Aqueous Ozonation of Pesticides: A Review

The ozonation reactions of pesticides in aqueous solution have been reviewed. Degree of reaction and reaction product identity are included. Compounds are classified into five groups: chlorinated hydrocarbons, organophosphorus compounds, phenoxyalkyl acid derivatives, organonitrogen compounds, and phenolic compounds. Experimental conditions for each study are summarized. Much work has been carried out under conditions atypical of those encountered at drinking water treatment plants. Thus, the findings of the papers reviewed cannot be applied directly to potable water treatment.     

Oxidation of Cyanuric Acid in Aqueous Solution by Catalytic Ozonation

The aim of this work was studying the activity of a Ru/CeO₂ powder catalyst in the ozonation of aqueous solution of cyanuric acid (CYA). Ozonation in the presence of the catalyst significantly enhances CYA degradation. Within this work, investigation of the influence of pH and initial concentration on the catalytic ozonation of CYA has been done in a semicontinuous reactor. The removing degree of CYA at pH 5.9 show better response in comparison to pH 2.5 and pH 8.2. The mineralization of CYA by catalytic ozonation formed nitrate ions (0.7 mol of NO₃^?/mol of CYA removed for 50% initial CYA abatement) and nitrite and ammonium ions in small amounts. Three transformation products formed during catalytic ozonation were identified from LC/MS and MS/MS analyses. The impact of oxidation on the toxicity was measured from the inhibition of Vibrio fisheri, which was found to increase continuously.     

Ozonation Kinetics Of Glucosamine And N-Acetyl Glucosamine In Aqueous Medium

Glucosamine and N-acetyl glucosamine show different behaviors towards ozone in aqueous medium: while glucosamine reacts relatively fast through ozone attack on the amino group, N-acetyl glucosamine is much more resistant, resembling the reactivity of glucose. Results obtained indicate that a mechanism of viral inactivation via ozone attack on the N-acetyl glucosamine of the viral capsid is not kinetically favored.     

Kinetic Regime Changes in the Ozonation of 1,3-Cyclohexanedione in Aqueous Solutions

The reaction between ozone and 1,3-cyclohexanedione in aqueous solutions at different pH was investigated from the point of view of the film theory. The rate of ozone absorption is accompanied by a second order irreversible reaction with 1,3-cyclohexanedione. The kinetic regime of absorption was found to change from fast (the reaction being of pseudo first order) to instantaneous, according to the ozone partial pressure applied. The former kinetic regime allows the determination of the reaction rate constant, while the latter leads to the volumetric mass transfer coefficient of the system.     

Kinetic Description of Industrial Wastewater Ozonation Processes

Literary and experimental data on the ozonation kinetics of aqueous solutions and wastewater were analyzed. COD was suggested to be used as a kinetic parameter from the solution side. On the basis of the results obtained from the ozonation of model solutions and wastewater, the rate coefficient by COD of the reaction was shown to be constant during separate stages of the process. Due to the consumption of fast-reacting components and entering into the reaction of more slowly reacting intermediate products, the rate coefficient changed spasmodically with transition from one stage to another. The reaction order with respect to the COD of the solution was shown to be equal to the reaction order with respect to the pure component.     

Reactivity Towards Ozone of 2-Hydroxypyridine in Aqueous Solution

The process of ozonation of 2-hydroxypyridine in aqueous solution at pH = 5 is studied in a semi-batch reactor. The evolution of the system is followed by means of instrumental and chemical analyses performed on samples withdrawn from the reactor at different reaction times. In order to distinguish between radical and direct ozonation mechanisms, some experiments are performed with the addition of radical scavenger (tert.-BuOH) to the reacting solution. A reaction scheme is given for explaining the formation of the main intermediates and products.     

Rates of Ozonation of Cresol Isomers in Aqueous Solutions

This research used a stopped–flow spectrophotometer system to study the kinetics of the fast oxidation of cresols by ozone in aqueous solutions. The overall reaction between ozone and a cresol isotner is second order, with first order in each reactant. At the same operating condition, the ozonation rate of m–cresol is the fastest and that of o–cresol the slowest. For the oxidation of o–cresol in neutral solutions, the overall rate constant increases from 422,000 to 1,550,000 1/M–s as the temperature changes from 10 to 40°C. In aqueous solutions with the pH range of 2.4 to 9.0 at temperatures varying from 5 to 40°C, the ozonation rate of the cresols increases with temperature and pH.     

Decolorization of Brown Chitooligomers in Aqueous Solution by Ozonation

Brown chitooligomers were obtained by gamma irradiation. Decolorization of brown chitooligomers in aqueous solution by ozonation was investigated. It was found that ozone could decolorize the brown chitooligomers in aqueous solution. When the pH value was below 2.93, the ozone treatment could inhibit yellowing and browning of chitooligomers in aqueous solution. As a result, the chitooligomers were slightly depolymerized by ozonation. The characterization showed that the decolorization by ozonation did not lead to the significant modification of chemical structure of the chitooligomers.     

Aqueous Ozonation Of Surfactants: A Review

The aqueous ozonation reactions of surfactants have been reviewed, including the degree of reaction and ozonation byproduct identity. Compounds are classified into three groups: anionic, cationic and non-ionic surfactants. Experimental conditions for each study reviewed are summarized. Much work has been carried out under conditions unlikely to occur during drinking water treatment. Thus, most of the findings of the papers reviewed cannot be directly applied to potable water treatment. However this review can serve to indicate the likely reactivity of the individual surfactants towards ozone and the possible byproducts formed. This reactivity depends mainly upon the chemical structure of the surfactants. The removal of surfactants is pH dependent, with the best results being obtained in alkaline media. High ozone doses usually do not cause complete disruption of the surfactants, while smaller doses are sufficient to enhance their biodegradation.     

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.     

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.     

Studies in Radiation Chemistry: Application to Ozonation and Other Advanced Oxidation Processes

Advanced oxidation/reduction processes (AORPs) are an alternative water treatment that is becoming more widely utilized. Our radiation-chemistry based studies are being used to develop a fundamental understanding of AOP treatment options, and are divided into three complementary types of contaminants; disinfection by-products (DBPs), emerging pollutants of concern (EPoCs), and natural organic matter (NOM). More than 600 DBPs have been identified, and one class that appears to have severe potential adverse health effects is the halonitromethanes (HNMs). Of the nine HNMs, trichloronitromethane (chloropicrin) is the most common, with levels up to 180 nM in US drinking waters. EPoCs are of interest because of their biological activity at low concentrations in water and while the initial focus was on endocrine disruptor chemicals (EDCs) this class has now been expanded to include many other recalcitrant chemicals such as hormones, antibiotics, industrial contaminants, and health care products. Natural organic matter is one of the most common radical scavengers in natural waters and therefore may adversely affect AOPs. Our approach is to study NOM both directly and using model compounds thought to be representative of structural components of this complex material.     

Determination of Rate Constants for Ozonation of Ofloxacin in Aqueous Solution

The ozonation of the quinolone antibiotic ofloxacin in water has been investigated with focus on kinetic parameters determination. The apparent stoichiometric factor and the second-order rate constants of the reactions of ozone and hydroxyl radical with ofloxacin were determined at 20 °C in the pH range of 4–9. The apparent stoichiometric factor was found to be about 2.5 mol O₃/mol ofloxacin regardless of the pH. The rate constant of the reaction between ozone and ofloxacin was determined by a competitive method (pH = 6–9) and a direct ozonation method (pH = 4). It was found that this rate constant increases with pH due to the dissociation of ofloxacin in water. The direct rate constants of ofloxacin species were determined to be 1.0?×?10², 4.3?×?10⁴ and 3.7?×?10⁷ for cationic, neutral-zwitterion and anionic species, respectively. Accordingly, the attack of ozone to ofloxacin mainly takes place at the tertiary amine group of the piperazine ring, though some reactivity is also due to the quinolone structure and oxazine substituent. The rate constant of the reaction between ofloxacin and hydroxyl radical was obtained from UV/H₂O₂ photodegradation experiments. It was found that this rate constant varies with pH from 3.2?×?10⁹ at pH 4 to 5.1?×?10⁹ at pH 9.     

Ozonation Of Sulfur-Containing Aliphatic Compounds In Aqueous Solutions. II. Cysteine,Cystine and Thioglycolic Acid

In view of the possible reaction of ozone with sulfur-containing natural and anthropogenic compounds, the ozonation of cysteine, cystine, thioglycolic acid and their oxidation products at pH 3 and 7 (initial concentration 1 mmol/L) was investigated. The oxidation of cysteine at pH 3 leads to cysteic acid; at pH 7 sulfoacetic acid, sulfate, ammonia and nitrate are formed besides cysteic acid. Cysteinesulfinic acid as intermediate oxidation product was not identified because of the very fast reaction with ozone forming cysteic acid.