Effect of Inorganic Ions on the Oxidative Efficiency of Ti(IV)-Catalyzed H2O2/O3 Process in the pH Range of 1.0 to 6.0

The oxidative efficiency of Ti(IV)-catalyzed H₂O₂/O₃ (Ti(IV)/H₂O₂/O₃) for acetic acid (HAc) degradation was investigated in the initial pH range of 1.0 to 6.0, and the effects of some common inorganic ions were also discussed in detail. The results showed that the effects of SO₄ ^2? and NO₃ ^? on the efficiency of Ti(IV)/H₂O₂/O₃ were negligible. However, adding Br^? greatly reduced the removal rate of HAc. The presence of Cl^? also reduced the efficiency of Ti(IV)/H₂O₂/O₃, but its negative effect became negligible in the initial pH range of 4.5 to 5.5. The presence of H₂PO₄ ^? could improve the removal rate of HAc, and addition of sodium carbonate had no influence on the efficiency of Ti(IV)/H₂O₂/O₃ in the initial pH range of 4.5 to 5.5.     

Performance and Mechanism on Degradation of Estriol Using O3/PS Process

In this study, enhanced ozonation of estriol (E3) with persulfate (PS) was investigated in aqueous solution. Simultaneous generation of hydroxyl radical (?OH) and sulfate radical (?SO₄^?) by O₃/PS process was proposed and experimentally verified. Kinetic results revealed that the degradation of E3 was affected by the solution pH, PS concentration, O₃ dosage and E3 initial concentration. The optimal reaction rate was observed in alkaline solutions. The mechanism for the synergistic effect was preliminarily explored by the addition of hydroxyl and sulfate radical scavengers. The enhanced degradation of E3 by O₃/PS was also observed in actual water samples, which provided impetus for practical applications. The degradation intermediates were detected using LC/MS. Results showed that the phenol structures of the estrogens were mostly oxidized to cyclohexenone moieties and quinone-like structures.     

An Effective Heterogeneous Ozone-Based Advanced Oxidation Process in Acidic Solution— Ti-MCM-41/H2O2/O3

A useful ozone-based advanced oxidation process in acidic solution- Ti-MCM-41/H₂O₂/O₃ was studied, and acetic acid (HAc) was selected to be degraded because it is a hydroxyl radical-probe compound in ozonation. The results showed that only Ti-MCM-41/H₂O₂/O₃ could effectively degrade HAc at initial pH 3.0, and that other oxidative processes such as O₃, H₂O₂/O₃ Ti-MCM-41/O₃ and MCM-41/H₂O₂/O₃, all could not, indicating the coexistence of Ti-MCM-41 and H₂O₂ was necessary for the generation of hydroxyl radicals under the experimental conditions. The optimization of parameters indicated that the rate of generation of hydroxyl radicals could be regulated by the amount of Ti-MCM-41, and that the amount of hydroxyl radicals could be controlled by the concentration of H₂O₂. The preceding results are of significance for effective treatment of acidic refractory wastewater.     

Degradation of Sulfosalicylic Acid by O3/UV O3/TiO2/UV,and O3/V-O/TiO2 : A Comparative Study

Chemical oxygen demand (COD) removal rates of sulfosalicylic acid (SSal) degraded by three advanced oxidation processes (AOPs): O₃/UV, O₃/TiO₂/UV and O₃/V-O/TiO₂ are compared in this paper. (V = Vanadium). The results show that O₃/V-O/TiO₂ is the most effective process among three AOPs and the order of degradation efficiencies at different pH values is shown as O₃/V-O/TiO₂ > O₃/TiO₂/UV > O₃/UV. For example, at the buffered solution of pH 6.8, the COD removal rate of O₃/V-O/TiO₂ reaches 70% in 30 minutes, but those of O₃/TiO₂/UV and O₃/UV are 55% and 47% at the same conditions, respectively. Furthermore, the effect of CO₃ ^{2 ?}on the COD removal rates of three AOPs shows that O₃/V-O/TiO₂ and O₃/TiO₂/UV may be considerable promising methods to overcome the limitation of the presence of radical scavenger in solution. Both the adsorption of SSal on catalysts and other oxidants (atom oxygen, photo-generated hole) must be responsible for the above result.     

Effect of Application of Ozone and Ozone Combined with Hydrogen Peroxide and Titanium Dioxide in the Removal of Pesticides From Water

The aim of this research work is to study the influence of hydrogen peroxide and titanium dioxide in the ozone-based treatment to degrade 44 organic pesticides present in natural water, which are systematically detected in the Ebro River Basin (Spain). The studied pesticides are: alachlor, aldrin, ametryn, atrazine, chlorfenvinfos, chlorpyrifos, pp'-DDD, op'-DDE, op'-DDT. pp'-DDT, desethylatrazine, 3,4-dichloroaniline, 4,4'-dichlorobenzophenone, dicofol, dieldrin, dimethoate, diuron, α-endosulphan, endosulphan-sulphate, endrin, α-HCH, β-HCH, γ-HCH, δ-HCH, heptachlor, heptachlor epoxide A, heptachlor epoxide B, hexachlorobenzene, isodrin, 4-isopropylaniline, isoproturon, metholachlor, methoxychlor, molinate, parathion methyl, parathion ethyl, prometon, prometryn, propazine, simazine, terbuthylazine, terbutryn, tetradifon and trifluralin. The ozonation using 3 mg O₃ L^?1 produces a pesticides removal close to 23%, whereas the application of O₃/H₂O₂ and O₃/TiO₂ treatments achieves average degradation yields lower than the ozonation. However, the application of O₃/H₂O₂ /TiO₂ process improves considerably the pesticides degradation and an average degradation yield of 36% is obtained.     

Bactericidal Effectiveness of O3, O3/H2O2 and O3/TiO2 on Clostridium perfringens

The purpose of this research is to evaluate the bactericidal capacity of different Advanced Oxidation Treatments (AOTs) based on ozone: ozone, ozone/hydrogen peroxide and ozone/titanium dioxide on a wild strain of Clostridium perfringens, a fecal bacterial indicator in drinking water. The dose of ozone consumed ranges from 0.6 mg L^?1 min^?1 to 5.13 mg L^?1 min^?1 depending on the process and on the sample. In the treatments combined with O₃, H₂O₂ dose utilized is 0.04 mM and TiO₂ dose, 1 g L^?1. In order to evaluate the influence of natural organic matter and suspension solids over the disinfection rate, treatments are performed with two types of water – natural water from Ebro River (Zaragoza, Spain) and NaCl solution 0.9%. To achieve 4 log units of inactivation, 3.6 mg O₃ L^?1 is necessary in O₃ treatment, 4.25 mg O₃ L^?1 in O₃/TiO₂ system and 2.7 mg O₃ L^?1 in O₃/H₂O₂ after processing the natural water. In NaCl solution, to get the same inactivation, 0.42 mg O₃ L^?1 is necessary in O₃ treatment, 1.15 mg O₃ L^?1 in O₃/TiO₂ system and 0.06 mg O₃ L^?1 in O₃/H₂O₂ process. Even though the three treatments studied have a high bactericidal activity due to the number of surviving bacteria decreases to non-detectable levels, O₃/H₂O₂ is the most effective system for eliminating C. perfringens cells in a lower contact time, followed by O₃ and finally O₃/TiO₂ system.     

Evaluation of O3/UV and O3/H2O2 as Practical Advanced Oxidation Processes for Degradation of 1,4-Dioxane

The degradation of 1,4-dioxane was investigated on a laboratory scale. The extents of degradation and/or removal of 1,4-dioxane by ozonation at pH 6–8, UV irradiation, aeration, and addition of H₂O₂ were very limited. On the other hand, the degradation of 1,4-dioxane by O₃/UV and O₃/H₂O₂ was accelerated compared with the above respective methods. The amounts of 1,4-dioxane degraded per amount of ozone consumed in O₃/UV and O₃/H₂O₂ were also higher than in ozonation. The amount of 1,4-dioxane degraded in O₃/UV was affected by the intensity of UV irradiation, and that in O₃/H₂O₂ was affected by the amount of H₂O₂ added only in the case of a high initial concentration of 1,4-dioxane.     

Theoretical Aspects Of The Kinetics Of Competitive First Reactions Of Ozone In The O3/H2O2 And O3/UV Oxidation Processes

Kinetics of competition between the ozone direct reaction with compounds in water, ozone-hydroperoxide ion reaction leading to free radicals in the O₃/H₂O₂ process, and the photolysis of ozone in the O₃/UV process are discussed in terms of diffusion and reaction times to establish conditions for these reactions to be competitive. Film theory and chemical kinetic concepts then are applied to estimate initial rates of ozone absorption and consumption, removal rates of compounds present in water, and the importance of the radical oxidation path versus direct ozone and/or photolysis reactions.     

Decomposition of Carboxylic Acids in Water by O3, O3/H2O2, and O3/Catalyst

This paper studies the decomposition of formic, oxalic and maleic acids by O₃, O₃/catalyst, and O₃/H₂O₂. The catalytic effect of Co²⁺, Ni²⁺, Cu²⁺, Mn²⁺, Zn²⁺, Cr³⁺, and Fe²⁺ ions is investigated. The results showed that—Co²⁺ and Mn²⁺ have the highest catalytic activity for the decomposition of oxalic acid while the catalytic effect of the studied ions is insignificant on the rate of decomposition of formic acid. Maleic acid decomposes by ozone into formic acid and glyoxylic acid, which subsequently oxidizes to oxalic acid. Though the studied ions have no effect on the decomposition of maleic acid, they have a significant effect on the produced oxalic and glyoxylic acids. In the presence of Cu²⁺ ions glyoxylic acid is mainly transformed into formic acid and traces of oxalic acid. In such case, a complete decomposition of maleic acid and its degradation products is achieved within 45 min. The results also show that combining H₂O₂ with O₃ results in an increase in the rate of decomposition of oxalic acid. However, O₃/H₂O₂ system is less active than O₃/Co²⁺ or O₃/Mn²⁺.     

The Advanced Oxidation Process of Phenol Solution by O3/H2O2 in a Rotating Packed Bed

This article presents experimental investigation on the oxidative treatment of phenol in water by O₃/H₂O₂ in a rotating packed bed (RPB). It was found that the phenol degradation ratio increased with increasing rotation speed, initial pH value of phenol solution, and temperature. The degradation ratio of phenol had a peak value with increasing H₂O₂ concentration. The optimum operating conditions in this study were determined as an H₂O₂ concentration of 6.5 mM and a rotation speed of 1200 rpm. Phenol degradation ratio reached 100% at an initial phenol concentration of 40 mg/L in the O₃/H₂O₂ process.     

Comparative Efficiency Of Three Systems (O3, O3/H2O2, and O3/TiO2) For The Oxidation Of Natural Organic Matter In Water

CATAZONE is a new process of heterogeneous catalytic ozonation in which water is ozonated in the presence of a solid catalyst composed of titanium dioxide. The efficiency of this O₃/TiO₂ system has been compared to the two well-known oxidant systems: ozone alone and ozone combined with hydrogen peroxide.

This comparison was undertaken on three models of natural organic compounds : an aquatic fulvic acid, a protein and a disaccharide. The first results showed the following order of relative efficiency: O₃/TiO₂ > O₃/H₂O₂ > O₃ as far as Total Organic Carbon (TOC) removal was concerned.     

Influence of Carbonate on the Ozone/Hydrogen Peroxide Based Advanced Oxidation Process for Drinking Water Treatment

The influence of carbonate on the ozone/hydrogen peroxide process has been investigated. Carbonate radicals, which are formed from the reaction of bicarbonate/carbonate with OH radicals, act as a chain carrier for ozone decomposition due to their reaction with hydrogen peroxide. The efficiency of bicarbonate/carbonate as a promoter for the radical-based chain reaction in presence of hydrogen peroxide has been calibrated and compared to a well-known chain promoter (methanol) and an inhibitor (tert-butanol). Relative to tert-butanol, the hydrogen peroxide induced ozone decomposition is accelerated by bicarbonate/carbonate. Relative to methanol, bicarbonate/carbonate in presence of hydrogen peroxide is less effective as a promoter under comparable experimental conditions.     

O3/H2O2 Treatment of Methyl-terf-Butyl Ether in Contaminated Waters: Effect of Background COD on the O3-Dose

The destruction of methyl-tert-butyl ether (MTBE) in contaminated waters by O₃/H₂0₂ process was studied and the influence background COD, alkalinity, and hydrogen peroxide and MTBE concentrations on process treatment efficiency and ozone dosage was investigated. The treatment efficiency was evaluated by an Efficiency Index, which is based on electrical energy requirement for ozone production. It was found that the treatment efficiency decreases linearly with increasing concentrations of MTBE at constant background COD and with background COD at constant MTBE concentration. A simplified kinetic scheme was presented to account for these observations.     

Fluorescent Brightener 28 Removal by Ozonation or Advanced Oxidation Processes (O3/H2O2)

The aim of this work is to study the reaction of ozone and combined ozone/hydrogen peroxide mixtures with the fluorescent brightener 28 in dilute aqueous solution using controlled experimental conditions. The kinetics were also evaluated under various experimental conditions. The main ozonation by-products have been identified by High Pressure Anionic Exchange Chromatography (HPAEC) and Gas Chromatography coupled with Mass Spectrometry (GC-MS) techniques and a reaction pathway is proposed. In order to confirm this mechanism, melamine and s-triazine have been treated under the same reaction conditions and their decomposition pathways were studied.     

Comparison of Hydroxyl Radical Generation for Various Advanced Oxidation Combinations as Applied to Foundries

The authors monitored hydrogen peroxide (H₂O₂), ozone (O₃), and apparent hydroxyl radical (OH·) concentrations in the liquid phase, along with gas phase ozone when operating an advanced oxidation (AO) system that included H₂O₂, O₃, sonication, and underwater plasma (UWAP). The OH· radical converted non-fluorescent terephthalic acid to fluorescent hydroxyterephthalic acid (HTA). As determined from HTA formation, when a 500 ppm H₂O₂ dose in tap water was combined with O₃ and sonication, nearly twice as much OH· (0.72 ppm) accumulated than with H₂O₂ alone. When UWAP accompanied H₂O₂, O₃, and sonication, these together generated 15–35% more OH· than when UWAP was excluded. When ozone was introduced into this AO system, the AO system decomposed almost all the O₃. This research has been conducted as a part of a study that has appraised this advanced oxidation system (Sonoperoxone) in green sand foundries, where it has diminished volatile organic compound (VOC) and hazardous air pollutant (HAP) emissions by 20–75%; and clay and coal consumption by 20–35%.     

Degradation of Acid Black 210 by advanced oxidative processes: O3 and O3/UV

Acid Black 210 (AB-210) dye is one of the most black dyes used by the leather industry. In the present work, AB-210 degradation in aqueous solution by ozonation (O₃) and ozonation with ultraviolet (UV) radiation (O₃/UV) was investigated. The effects of pH, initial dye concentration and UV radiation were studied in laboratory scale. Removal was evaluated in terms of residual AB-210 concentration in the treated solution and mineralization efficiency was evaluated by total organic carbon (TOC) analysis. The results indicated that AB-210 is quickly degraded after 15 min but not totally mineralized. It was observed that dye removal of 100% was achieved at pH 3, 7, and 11, while mineralization was found to increase with the pH (55% at pH 11). Concerning UV-C radiation, it enhanced AB-210 degradation at pH 3 but did not reveal any significant effect at pH 7 and 11.     

Effect of UV Radiation on the Removal of Carboxylic Acids from Water by H2O2 and O3 in the Presence of Metallic Ions

The effect of UV radiation on the removal of formic, oxalic and maleic acids from water by metallic ion (Fe²⁺ or Cu²⁺)/H₂O₂ and metallic ion/O₃ was studied and compared. The results showed that metallic ion/O₃/UV has higher efficiency than metallic ion/H₂O₂/UV for oxalic acid removal. UV radiation significantly increases the efficiency of metallic ion/H₂O₂ for formic and maleic acids removal while its effect on the efficiency of metallic ion/O₃ for formic acid removal is minor_. However, at pH 2, O₃ alone showed higher efficiency than metallic ion/H₂O₂/UV for formic acid removal. Contrary to the relative efficiency of metallic ions in the previous systems, Cu²⁺ exhibited higher rate than Fe²⁺ for the removal of the degradation products of maleic acid by O₃. UV radiation exhibited a minor effect on the efficiency of Cu²⁺/O₃, while it exhibited a large effect on the efficiency of Fe²⁺/O₃ for the removal of the degradation products of maleic acid.     

Ozonation of Trace Nitrobenzene in Water in the Presence of a TiO2/Silica-Gel Catalyst

Heterogeneous catalytic ozonation was investigated for the degradation of nitrobenzene in the presence of TiO₂ supported on Silica-gel as a solid catalyst. The conditions in preparing the catalyst are experimentally optimized. The catalytic activity of the supported TiO₂ is strongly influenced by the calcination temperature. The TiO₂/Silica-gel calcined at 500 °C showed the highest activity for the degradation of nitrobenzene. An approximate increase of 21% in removal efficiency was achieved for catalytic ozonation compared with the case of ozonation alone. Nitrobenzene degradation was significantly influenced by the presence of carbonate and t-butanol, which confirmed that TiO₂/Silica-gel catalyzed ozonation followed a radical-type mechanism. Kinetic study demonstrated that catalytic ozonation is pseudo–first-order with no respect to the initial nitrobenzene concentration. The effect of catalyst dosage and pH on the oxidation efficiency of nitrobenzene was also investigated. Catalyst dosage exerted a positive influence on nitrobenzene removal, and nitrobenzene degraded more completely under neutral or basic conditions. Finally, the catalyst stability was tested through repeated experiments.     

Degradation of Oxalic Acid and Bisphenol A by Photocatalytic Ozonation with g-C3N4 Nanosheet under Simulated Solar Irradiation

Photocatalytic ozonation of organics under simulated solar irradiation with a g-C₃N₄ nanosheet was investigated. g-C₃N₄ was prepared by calcinations of urea and characterized by TEM, BET, XRD and UV-Vis. Oxalic acid and bisphenol A were used as model substances to evaluate its catalytic ability. The results showed that g-C₃N₄ possess 2D nanosheet structure. The degradation ratio of oxalic acid and bisphenol A with g-C₃N₄/O₃/Solar was 1.50 and 1.92 times as great as the sum ratio when it was individually degraded by g-C₃N₄/Solar and O₃, separately. The results of recycling experiment indicated that g-C₃N₄ catalyst is very stable under experimental conditions.     

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.