Direct Ozonation Research Articles

Modelling of Chlorophenol Treatment in Aqueous Solutions. 1. Ozonation and Ozonation Combined with UV Radiation under Acidic Conditions

Treatment of 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) in aqueous solutions with direct photolysis (254 nm), ozonation and ozonation with photolysis was studied. A model was developed to simulate chlorophenol treatment in a semibatch column using these processes under acidic conditions in which the chemical reactions are slow. Satisfactory results were obtained in simulating the chlorophenol and ozone concentrations, and the concentrations of an aromatic quinone, hydrogen peroxide and chloride ions formed in the course of the processes. Chlorophenol oxidation systems, however, appeared to be very complex and the formation of intermediate and final products were dependent on the reaction conditions. The degradation rate of chlorophenols was not enhanced by the combination of ozone with UV radiation compared with ozonation alone. Oxidation at low pH in both processes proceeded mainly through reactions with molecular ozone.

Kinetic modelling of aqueous trichloroethylene direct ozonation in a continuous tank

The kinetics of continous direct ozonation of trichloroethylene, a water priority pollutant, is investigated. The influence of water flow type on the kinetics is studied by the use of the residence time distribution function. In accordance with this, the actual reactor used behaves as two perfectly mixed continous stirred reactors. A kinetic model accounting for rates of volatilization, direct ozonation and mass transfer together with non‐idealk water flow is presented. The results obtained indicate that water flow type should be considered to, predict more accurately removal rates of trichloroethylene during direct ozonation.

Elimination pathways during water ozonation of volatile organochlorine compounds

Ozonation of trichloroethylene, TCE and 1,1,1 trichloroethane, TCA in water has been studied. The effect of gas flow rate, pH, ozone partial pressure and water nature has been investigated. These variables exert positive effects on the elimination rates. Gas flow rate effect is specially important in the case of TCA which, at 20 Lh‐1, is mainly transferred from the water to the air rather than being decomposed through ozonation. On the contrary, TCE is mainly oxidised through hydroxyl radicals. The rate constant of the TCE‐ozone direct reaction was found to be 17.1 M‐1s‐1 which confirms that direct ozonation represents a rather poor contribution (in most cases between 2 to 5%) of the total TCE elimination rate. Therefore, ozonation of these compounds is basically an advanced oxidation process due to the participation of hydroxyl radicals. At high gas flow rates (20 Lh‐1) ozonation rates of VOC elimination were similar in ultrapure laboratory and surface waters used, except for the case of TCE that at 2.5 Lh‐1 gas flow rate, decomposes in ultrapure water faster than in surface water.

Oxidation of Polynuclear Aromatic Hydrocarbons in Water. 4. Ozone Combined with Hydrogen Peroxide

Three polynuclear aromatic hydrocarbons, fluorene, phenanthrene, and acenaphthene, have been treated in water with ozone combined with hydrogen peroxide. The effect of hydrogen peroxide concentration, pH, and bicarbonate ions has been investigated. The process goes through direct and radical reactions in the case of fluorene and phenanthrene oxidation, while acenapthene is removed exclusively by direct ozonation. At concentrations of hydrogen peroxide higher than 10-5 M, ozone mass transfer controls the process rate, regardless of pH. In any case, however, the presence of hydrogen peroxide does not improve the oxidation rate compared to ozonation alone due to the importance of the direct reactions. Intermediate compounds identified during oxidation with ozone alone and combined with UV radiation or hydrogen peroxide are similar and justify the high consumption of ozone in these processes.

The effect of lead exposure on a human chorio carcinoma cell line BeWo b24. A first step in the development of a embryotoxicity predicting in vitro model

The ozonation of four pharmaceuticals (metoprolol, naproxen, amoxicillin, and phenacetin) in ultra-pure (UP) water was studied in the pH range between 2.5 and 9. The experiments allowed the determination of the apparent rate constants for the reactions between ozone and the selected compounds. The values obtained varied depending on the pH, and ranged between 239 and 1.27 × 104 M−1 s−1 for metoprolol; 2.62 × 104 and 2.97 × 105 M−1 s−1 for naproxen; 2.31 × 103 and 1.21 × 107 M−1 s−1 for amoxicillin; and 215 and 1.57 × 103 M−1 s−1 for phenacetin. Due to the acidic nature of these substances, the degree of dissociation of each pharmaceutical was determined at every pH of work, and the specific rate constants of the neutral and ionic species formed were evaluated. Additionally, the simultaneous ozonation of the pharmaceuticals in different water matrices was carried out by considering a groundwater, a surface water from a public reservoir, and three secondary effluents from municipal wastewater treatment plants. The influence of the operating conditions (initial ozone dose, nature of pharmaceuticals and type of water) on the pharmaceuticals elimination efficiency was established, and a kinetic model was proposed for the evaluation of the partial contribution to the global oxidation of both, the direct ozonation reaction and the radical pathway.

Oxidation of Polynuclear Aromatic Hydrocarbons in Water. 2. UV Radiation and Ozonation in the Presence of UV Radiation

Direct photolysis with UV radiation (254 nm) and oxidation with ozone combined with UV radiation of three polynuclear aromatic hydrocarbons, fluorene, phenanthrene, and acenaphthene, has been studied. Quantum yields of the direct photolysis of the PAHs determined were 7.5 {times} 10{sup {minus}3}, 6.9 {times} 10{sup {minus}3}, and 52 {times} 10{sup {minus}3} mol(photon){sup {minus}1} for fluorene, phenanthrene, and acenaphthene, respectively. Contributions of direct ozonation, direct photolysis, and radical oxidation have also been estimated for the oxidation with ozone combined with UV radiation. Fluorene is oxidized by direct photolysis and radical reactions, phenanthrene through direct mechanisms, ozonation, and photolysis, and acenaphthene mainly by direct ozonation.

P-Coumaric acid abatement by ozone in aqueous solution

The ozonation process of p-coumaric acid in aqueous solution is studied by identification and quantitative evaluation of intermediates and final oxidation products. In all the investigated pH range (2.0–8.0) the initial oxidation step is represented by the direct attack of ozone to the exocyclic double bond, following oxidation steps being regulated by the intervention of also the radical ozonation mechanism. The competition degree between the two mechanisms is significantly influenced by pH of the reacting mixture with a remarkable occurrence of the radical mechanism at basic pH. The high reactivities exhibited towards ozone by p-coumaric acid and p-hydroxybenzaldehyde intermediate make the rate of the ozonation process strictly controlled by diffusion. Product analysis allows to assess that direct ozonation mechanism of p-hydroxybenzaldehyde significantly proceeds through the anomalous reaction pathway.

Advanced oxidation of atrazine in water—II. Ozonation combined with ultraviolet radiation

The combination of ozone with ultraviolet radiation (254 nm) to oxidise atrazine is investigated. The importance of the three routes of atrazine elimination: direct photolysis, direct ozonation and hydroxyl radical oxidation is established in percentages. At neutral pH and 20°C 87% of the oxidation rate is due to the radical way while direct ozonation only represents 1%. Mass transfer and kinetic data obtained in previous works [Beltrán F. J., Ovejero G. and Acedo B. (1993) Wat. Res. 27, 1013–1021; Beltrán F. J., Garciá-Araya J. F. and Acedo B. (1994) Wat. Res. 28, 2153–2164.] have been applied to mol. balance equations of atrazine, ozone (both in the gas and water) and hydrogen peroxide to obtain their corresponding concentrations in different conditions. It was necessary to include a hydroxyl radical initiating rate factor to account for radical ways not included in the basic mechanism of ozone decomposition. Comparison between different ways of oxidation and photolysis of atrazine (ozone, ozone/u.v. radiation, hydrogen peroxide/u.v. radiation) is also presented.

1,2 phenylenediamine abatement in aqueous solution by ozone

Abstract The ozonation of 1,2 phenylenediamine (PDA) in aqueous solution is investigated in the pH range 1.7–8.1. Chemical analyses performed at varying ozonation times indicate that both PDA and monoprotonated PDA are sensitive to direct and radical ozonation mechanisms. Increasing competition of the radical mechanism is observed with decreasing pH. Main reaction steps regulating direct and radical process development are detailed.

Quinoline ozonation in aqueous solution

The ozonation of quinoline in aqueous solution has been studied at varying pH (1.8–6.5). The effects of direct and radicalic ozonation mechanisms upon process development are separately investigated by means of radical scavenger (t-BuOH 20 mM) addition to the reacting system. Direct ozonation of both quinoline and quinolinium ion leads mainly to production of quinolinic acid with a minor occurrence of cleavage reactions of the heterocyclic ring. Higher system reactivities are observed for ozonation experiments with no radical scavenger addition with small changes occurring in the distribution of products deriving from quinoline oxidation. System behaviors at varying experimental conditions are explained on the basis of chemical reaction schemes.

Reactivity Towards Ozone of 2-Hydroxypyridine in Aqueous Solution

Abstract 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.

Ozonation of pyridine in aqueous solution: Mechanistic and kinetic aspects

Direct and radicalic ozonation of pyridine in aqueous solution is investigated. Experiments are performed in a semibatch apparatus with continuous admission of ozone to the reacting solution. Reaction processes are followed by means of HPLC and chemical analyses at different ozonation times. Direct ozonation is performed by addition of t-butanol to the reacting system to prevent radicalic development. In these conditions the ozonation of pyridine mainly leads to production of pyridine N-oxide according to first-order kinetics with respect to both ozone and pyridine. Ozonation experiments at different pHs (3.0–6.0) indicate that pyridinium ion has no appreciable reactivity towards ozone. A direct ozonation process thus occurs through the electrophilic attack of ozone on the nitrogen atom of pyridine with a rate constant k = 2.0 ± 0.3 mol −1 ls −1 at 298 K. Ozonation experiments which allow radicalic development of the reaction process show that pyridine oxidation occurs with a strong cleavage of the heterocyclic ring even in the initial ozonation stage. Ammonia, nitrate and amidic compounds, among which is N-formyl oxamic acid, are produced. Formation also of nitroso and/or nitro derivatives can be inferred by the experimental results. Radicalic ozonation of pyridine exhibits an autocatalytic character as shown by the rapid increase of the reaction rate in the initial ozonation stage. Autocatalysis is likely due to reaction intermediates coming from slow direct attack of ozone on pyridine and is capable of promoting the ozone decomposition in aqueous solution. A reaction scheme based on the addition of hydroxyl radicals to the aromatic ring of pyridine is proposed to explain the observed products distribution.

Application of Ozone with Physical Wastewater Treatments to Recondition Poultry Process Waters

Several wastewater treatments, including direct ozonation and a combination of ozonation with either slow sand filtration, dissolved air flotation, or diatomaceous earth (DE) filtration, were tested for their ability to recondition broiler process waters. The quality of broiler prechiller overflow water was significantly improved with all wastewater treatments examined, surpassing the USDA’s recycling requirements in nearly all trials. A combination of screening, DE filtration, and ozonation yielded the highest quality water. With this treatment, significant reductions in chemical oxygen demand, total solids, and the total microbial load including coliform bacteria and salmonellae of 87, 65, and 99.9%, respectively, were detected in the reconditioned prechiller water. Percentage of light transmission at 500 nm (%T) of treated water increased to 97% of tap water and compared favorably with %T of potable water. This same water treatment was tested on final carcass rinse and neck chiller overflow waters. The quality of these treated waters was also significantly improved. It was concluded that poultry process waters could be effectively reconditioned for recycling by screening, DE filtration, and ozonation. Furthermore, wastewater organic loads discharged to wastewater treatment facilities can be effectively reduced through these reconditioning practices.

Improved Sewage Treatment with Ozonated Activated Sludge

ABSTRACTActivated SLUDGE SEWAGE treatment processes are often inadequate to comply with effluent criteria as promulgated in anti‐pollution legislation. Ozonation was studied as a means of improving nutrient removal activated sludge processes without the salinity and other disadvantages of the often used polyvalent metal salt addition. Direct ozonation into the aeration basin of a 150 I/d Phoredox (modified Bardenpho) system led to improved removal of organic substances. Nitrification was improved while phosphate removal was not adversely affected. Beneficial biological activity in the activated sludge was enhanced. The trihalomethane formation potential was reduced. Pollutional loads could be lessened, while an effluent with increased reuse potential was produced.

Sludge Bulking Control with Ozone

ABSTRACTOzonation was studied as a non‐specific means of sludge bulking control. Direct ozonation at 6 g/m3 influent, i.e. 4 gO3/kg sludge per day into the aeration basin of a 150 l/d Phoredox system controlled the growth of filamentous organisms and improved the settleability of the sludge. Bulking control with ozone is not significantly more expensive than with chlorine or with larger settler capacity.

A comparison of the rates of ozonation of biological antioxidants and oleate and linoleate esters

The rates of reaction with ozone of some biological antioxidants and simple polyunsaturated fatty acids (PUFA) have been measured in water or in aqueous micellar solutions. At pH 7.0 the rate constants are ca . 10 6 M −1sec −1 for urate, alpha-tocopherol, and PUFA, and 6 × 10 7 M −1sec −1 for ascorbate. When ozone-containing air is breathed, ascorbate in the lung may undergo direct ozonation. However, alpha-tocopherol is probably spared direct reaction with ozone because it doesn't effectively compete with PUFA in pulmonary membranes; rather, tocopherol is used to scavenge radicals produced from the ozone-PUFA reaction.

Improved ammonia oxidation by ozone in the presence of bromide ion during water treatment

Ammonia oxidation by ozone proceeds more rapidly in the presence of bromide ion than in its absence. Unlike the direct ozonation of ammonia, the bromide-catalyzed process is little affected by changes in pH. A reaction scheme is proposed in which bromide is oxidized to HOBr, which then brominates ammonia to produce NH 2Br. NH 2Br in turn reacts with O 3 to form NO 3 − and also to generate Br −, which thus acts as a catalyst. In accordance with the reaction model, zero-order kinetics for ammonia consumption are observed. This work points out once again the importance of Br − as a water quality parameter due to its role as a catalyst in both ozonation and chlorination processes in general.

The synthesis of enantiomers of 4-ketocyclophosphamide

Oxidation with Fenton's reagent and by direct ozonation of the enantiomers of the antitumour agent cyclophosphamide afforded optically pure enantiomers of 4-ketocyclophosphamide. Oxidation with potassium permanganate, however, gave the corresponding racemate.