Advanced oxidation processes for destruction of cyanide from thermoelectric power station waste waters

Several advanced oxidation processes for the destruction of cyanide contained in waste waters from thermoelectric power stations of combined‐cycle were studied. Thus, oxidation processes involving ozonation at basic pH, ozone/hydrogen peroxide, ozone/ultraviolet radiation and ozone/hydrogen peroxide/ultraviolet radiation have been carried out in a semi‐batch reactor. All these methods showed that total cyanide can be successfully degraded but with different reaction rates, and the decrease in the total cyanide concentration can be described by pseudo‐first order kinetics. The influence of pH and initial concentration of hydrogen peroxide was studied to find the optimal conditions of the oxidation process. Experimental results of the single ozone treatment indicated that total cyanide is destroyed more rapidly at higher pH (12), while ozonation combined with H₂O₂ and/or UV is faster at pH 9.5. The optimum concentration of H₂O₂ was 20.58 × 10^?2 M because an excess of peroxide decreases the reaction rate, acting as a radical scavenger. The total cyanide degradation rate in the O₃/H₂O₂(20.58 × 10^?2 M ) treatment was the highest among all the combinations studied. However, COD reduction, in the processes using UV radiation such as O₃/UV or O₃/H₂O₂/UV was about 75%, while in the processes with H₂O₂ and/or O₃/H₂O₂ was lower than 57% and was insignificant, when using ozone alone. Copyright © 2003 Society of Chemical Industry     

Decomposition of Detergents in Industrial Wastewater by AOP in Flow Systems

The present studies covered investigations of advanced oxidation of detergents in industrial wastewater with the use of ozone, hydrogen peroxide, UV and ionizing radiation separately and in combinations: O₃+UV, UV+H₂O₂, H₂O₂+O₃, O₃+H₂O₂+UV, O₃+ ionizing radiation in the flow systems taking into account specific features of subsequent versions. The aim of these studies was to present results of detergent decomposition in the applied versions and also in the flow systems compared to stationary systems. The radiation processes were carried out with high efficiency in all stationary and flow systems tested. The best results of detergent decomposition were achieved in the samples exposed to simultaneous radiation and ozonation.     

Ozone-Based Advanced Oxidation Processes for the Decomposition of N-Methyl-2-Pyrolidone in Aqueous Medium

The present study investigates the decomposition of N-Methyl-2-Pyrolidone (NMP) using conventional ozonation (O₃), ozonation in the presence of UV light (UV/O₃), hydrogen peroxide (O₃/H₂O₂), and UV/H₂O₂ processes under various experimental conditions. The influence of solution pH, ozone gas flow dosage, and H₂O₂ dosage on the degradation of NMP was studied. All ozone-based advanced oxidation processes (AOPs) were efficient in alkaline medium, whereas the UV/H₂O₂ process was efficient in acidic medium. Increasing ozone gas flow dosage would accelerate the degradation of NMP up to certain level beyond which no positive effect was observed in ozonation as well as UV light enhanced ozonation processes. Hydrogen peroxide dosage strongly influenced the degradation of NMP and a hydrogen peroxide dosage of 0.75 g/L and 0.5 g/L was found to be the optimum dosage in UV/H₂O₂ and O₃/H₂O₂ processes, respectively. The UV/O₃ process was most efficient in TOC removal. Overall it can be concluded that ozonation and ozone-based AOPs are promising processes for an efficient removal of NMP in wastewater.     

Advanced Oxidation Processes for the Elimination of Drugs Resisting Biological Membrane Treatment

The recalcitrant pharmaceutical compounds carbamazepine, clofibric acid, diazepam, and diclofenac were monitored in municipal wastewater by ESI-LC-MS and -MS-MS in positive and negative mode. Although biological treatment by conventional and membrane bioreactor failed, the advanced oxidation methods using ozone (O₃), O₃/UV or hydrogen peroxide in combination with UV (H₂O₂/UV), successfully achieved their complete elimination. Target compounds could be confirmed as permanently present pollutants in Aachen-Soers wastewater in concentrations between 0.006 and 1.9 μg L^?1 prior to AOP treatment resulting in a complete elimination.     

Effects Of Ozone-Hydrogen Peroxide Combination On The Formation Of Biodegradable Dissolved Organic Carbon

The effects of ozone and ozone/hydrogen peroxide on BDOC formation were studied with the “Ozotest” method, a laboratory technique that permits the assessment of oxidation efficiency. Oxidation treatments were performed on river water and sand filter effluent samples. Ozone consumption, reduction of UV absorbance, and BDOC formation were monitored during the experiments. The ratio of 0.35-0.45 mg H₂O₂ per mg O₃ used to degrade pesticides also was optimal for the oxidation of organic matter. BDOC formation versus ozone dose curves with ozone alone or ozone/peroxide system were similar. BDOC formation was optimum at an applied ozone dose of 0.5-1 mg O₃/mg C (contact time = 10 min). The ozone/peroxide system yielded lower BDOC values than ozone alone, a phenomenon related to differences in byproducts generated by the two oxidative systems. Moreover, reduction of the concentration of DOC was higher with ozone/hydrogen peroxide than with ozone alone. For both oxidant systems, BDOC formation occurred during the first minute of treatment.     

Advanced Oxidation of Textile Wastewaters

Model dyeing and laundering wastewaters produced during two basic technological operations of the textile industry were subjected to treatment by advanced oxidation processes (AOPs). The following agents were used: ozone (O₃), hydrogen peroxide (H₂O₂) and UV radiation. They were applied separately and in all possible combinations: O₃ + UV, O₃ + H₂O₂, UV + H₂O₂, as well as all three at the same time: O₃ + UV + H₂O₂. Effluents before and after the treatment were analyzed according to requirements of the Polish Standards that included pH, color threshold, COD and concentration of anionic and non-ionic surfactants. Ozonation was carried out in a lab-scale bubble column reactor with a centrally located UV burner. The most effective version of AOPs proved to be the simultaneous use of all three agents. In the case of such treatment of dyeing wastewaters nearly complete discoloration and full decomposition of surface-active substances were obtained at 80% reduction of COD. A similar tendency was observed in the case of laundering wastewater, though in that case the results were slightly worse, which may be explained by much higher initial concentrations of the pollutants. Good treatment effects have also been obtained in combined treatment by simultaneous use of hydrogen peroxide and ozone.     

Treatability Study on Membrane Concentrate Containing Pesticides Using Advanced Oxidation Processes

This treatability study evaluated the overall effectiveness of advanced oxidation processes (AOPs) to treat membrane concentrates containing the pesticides bromoxynil and trifluralin. The results of study indicate that high levels of pesticide degradation were achieved using ozone (O₃) plus hydrogen peroxide (H₂O₂) for all concentrate matrices. However, the toxicity of the samples during the O₃/H₂O₂ process was higher than that obtained during ultraviolet (UV) light combined with H₂O₂. Low levels of pesticide oxidation were observed in experiments using a mixture of pesticides during all treatment options.     

Simultaneous oxidation of nitrogen oxides and sulfur dioxide with ozone and hydrogen peroxide

The use of ozone and hydrogen peroxide for the simultaneous oxidation of nitrogen and sulfur oxides was studied in experiments carried out in a stirred cell. It was found that in a gas mixture, containing both nitrogen and sulfur oxides, only the nitrogen oxides are oxidized by ozone. Contrary to earlier results, sulfur dioxide does not disturb the oxidation of nitrogen oxides under dry conditions. The consumption of ozone in the oxidation of nitric oxide was slightly below the stoichiometric level because the ozone was introduced into the reactor in the oxygen flow. When the molar ratio between ozone and nitric oxide was more than 0.4, some of the nitric oxide was oxidized to higher oxides of nitrogen, the final product being a solid mixture of N₂O₅ and (NO)₂S₂O₇. Some nitrosyl sulfuric acid was formed in the aqueous solution of hydrogen peroxide in addition to sulfuric acid under wet conditions. Some white solid was found on the walls of the reactor. This solid is said it the literature to consist of H₂SO₄, HNOSO₄ and (NO)₂S₂O₇.     

H2O2 Generation during Carbon Ozonation – Factors Influencing the Process and Their Implications

Hydrogen peroxide generation during contact of aqueous ozone with activated carbon surface is an established process. However, no systematic research concerning this phenomenon has been conducted. In this paper, factors affecting H₂O₂ generation are presented. Formation of hydrogen peroxide in contact of ozone with carbon is a surface phenomenon, strongly affected by the solution pH. Re-ozonation of the same carbon sample does not lead to H₂O₂ generation. Additionally, the amount of generated H₂O₂ is significant only in strongly acidic environment. It implies that hydrogen peroxide generated by surface of activated carbon cannot be ozone decomposition initiator in catalytic ozonation based on activated carbon as a catalyst.     

Bromate Formation in Ozone and Advanced Oxidation Processes

Both the direct ozone reaction and the indirect hydroxyl radical reaction are important in ozonation of drinking water. This article investigates the effectiveness of ozone versus the advanced oxidation process of ozone coupled with hydrogen peroxide in the formation of bromate. The investigation was conducted on a pilot scale at various H₂O₂:O₃ dose ratios of 0.1, 0.2, and 0.35 at different times of the year. The results of this study show a reduction in bromate with the addition of hydrogen peroxide to an ozone system versus ozone alone. It was also observed that bromate increased with increased H₂O₂:O₃ ratios; however, concentrations were still lower than those in the ozone only system.     

Study Of The Advanced Oxidation Processes Of Chlorobenzenes In Water

The focus of this study was to investigate the use of advanced oxidation processes to oxidize a residual water in which chlorobenzenes were found in the range of 1 mg/L to 10 mg/L and whose TOC was about 1,000 mg/L, and a solution of chlorobenzenes whose concentration was 0.03 mg/L, which was prepared from stock solutions. Ozone in basic medium (pH = 9) and ozone in the presence of hydrogen peroxide (H₂O₂) were compared.     

Removal of diazinon by various advanced oxidation processes

Diazinon is a widely used organophosphorus insecticide that is an important pollutant in aquatic environments. The chemical removal of diazinon has been studied using UV radiation, ozone, Fenton's reagent, UV radiation plus hydrogen peroxide, ozone plus hydrogen peroxide and photo‐Fenton as oxidation processes. In the photodegradation process the observed quantum yields had values ranging between 2.42 × 10^?2 and 6.36 × 10^?2 mol E^?1. Similarly, the ozonation reaction gave values for the rate constant ranging between 0.100 and 0.193 min^?1. In the combined systems UV/H₂O₂ and O₃/H₂O₂ the partial contributions to the global oxidation reaction of the direct and radical pathways were deduced. In the Fenton's reagent and photo‐Fenton systems, the mechanism of reaction has been partially discussed, and the predominant role of the radical pathway pointed out. Additionally, the rate constant for the reaction between diazinon and the hydroxyl radicals was determined, with the value 8.4 × 10⁹ L mol^?1 s^?1 obtained. A comparison of the different oxidation systems tested under the same operating conditions revealed that UV radiation alone had a moderate oxidation efficiency, which is enhanced in the case of ozone, while the most efficient oxidant is the photo‐Fenton system. Copyright © 2007 Society of Chemical Industry     

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%.     

Modeling the oxidation of atrazine by H2O2/UV. Estimation of kinetic parameters

A kinetic model for the oxidation of atrazine by H₂O₂/UV in dilute aqueous solutions ([Atrazine]₀ < 2 μM) has been tested in a batch reactor. In this model, direct photolysis and oxidation by hydroxyl radicals are assumed to be the main reactions in the decomposition of atrazine by H₂O₂/UV. The data showed that the model can be used to predict the effects of some parameters (hydrogen peroxide dose, pH, bicarbonate alkalinity, …) and to estimate values of quantum yield of photolysis, rate constants for the reaction of hydroxyl radicals with atrazine and of the scavenging term (Sk_iS_i) of natural waters.     

ELIMINATION OF BENZENE AND CHLOROBENZENES BY PHOTODEGRADATION AND OZONATION PROCESSES

Benzene (B) and two representative chlorobenzenes (1,4-dichlorobenzene (DCB) and 1,2,3-trichlorobenzene (TCB)) were oxidized by means of UV irradiation alone, ozone alone, and the combinations UV/H₂O₂ and O₃/H₂O₂. In the single photolytic process, the influence on the photodegradation of the pH, temperature, and type of radiation source used was established. A kinetic study was performed by evaluating the first-order rate constants and the quantum yields. The effect of the additional presence of hydrogen peroxide was pointed out in the combined process UV/H₂O₂,with the determination of the specific contribution of the radical pathway to the overall photodegradation system. In the oxidation by ozone based systems (ozone alone and the combination O₃/H₂O₂), the rate constants at 20°C for the reaction of each compound with ozone and hydroxyl radicals were determined.     

Assessment of Microwave/UV/O<Subscript>3</Subscript> in the Photo-Catalytic Degradation of Bromothymol Blue in Aqueous Nano TiO<Subscript>2</Subscript> Particles Dispersions

In this study, a microwave/UV/TiO₂/ozone/H₂O₂ hybrid process system, in which various techniques that have been used for water treatment are combined, is evaluated to develop an advanced technology to treat non-biodegradable water pollutants efficiently. In particular, the objective of this study is to develop a novel advanced oxidation process that overcomes the limitations of existing single-process water treatment methods by adding microwave irradiation to maximize the formation of active intermediate products, e.g., OH radicals, with the aid of UV irradiation by microwave discharge electrodeless lamp, photo-catalysts, and auxiliary oxidants. The results of photo-catalytic degradation of BTB showed that the decomposition rate increased with the TiO₂ particle dosages and microwave intensity. When an auxiliary oxidant such as ozone or hydrogen peroxide was added to the microwave-assisted photo-catalysis, however, a synergy effect that enhanced the reaction rate considerably was observed.     

Post-Treatment of Pulp and Paper Industry Wastewater by Advanced Oxidation Processes

The aim of this study was to investigate the effectiveness of chemical oxidation by applying ozonation, combination of ozone and hydrogen peroxide and Fenton's processes for decolorization and residual chemical oxygen demand (COD) removal of biologically pretreated pulp and paper industry effluents. The batch tests were performed to determine the optimum operating conditions including pH, O₃, H₂O_2, and Fe²⁺ dosages. H₂O₂ addition reduced the reaction times for the same ozone dosages; however combinations of ozone/hydrogen peroxide were only faintly more effective than ozone alone for COD and color removals. In the Fenton‘s oxidation studies, the removal efficiencies of COD, color and ultraviolet absorbance at 254 nm (UV₂₅₄) for biologically treated pulp and paper industry effluents were found to be about 83, 95, and 89%, respectively. Experimental studies indicated that Fenton oxidation was a more effective process for the reduction of COD, color, and UV₂₅₄when compared to ozonation and ozone/hydrogen peroxide combination. Fenton oxidation was found to have less operating cost for color removal from wastewater per cubic meter than the cost for ozone and ozone/hydrogen peroxide applications.     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

Chemical beneficiation of coal with aqueous hydrogen peroxide/sulphuric acid solutions

The removal of sulphur and ash from coal treated with aqueous hydrogen peroxide/sulphuric acid solutions has been studied at ambient temperature, under a variety of experimental conditions. Almost complete elimination of the sulphate and the pyritic sulphur was observed in most cases, as well as substantial reduction in the ash content. The other components of the organic coal matrix were not affected to a significant extent, indicating high selectivity of the $\text{H}{}_2\text{O}{}_2\text{H}{}_2\text{SO4}$ system towards sulphur oxidation. An optimal H₂SO₄ concentration was established, above which the acid was found to have an adverse effect on the oxidation of pyrite by hydrogen peroxide.     

Advanced oxidation processes for the degradation of p‐hydroxybenzoic acid 2: Photo‐assisted Fenton oxidation

Oxidation of p‐hydroxybenzoic acid in aqueous solution by the photo‐assisted Fenton reaction (Fe²⁺ + H₂O₂ + UV) has been studied. The effects of ferrous ion concentration (0.05, 0.14 and 0.29 mmol dm^?3), temperature (10, 20, 30 and 40 °C), and initial hydrogen peroxide concentration (0.7, 1.4, 2.2 and 2.9 mmol dm^?3) on the p‐hydroxybenzoic acid conversion were established. Experimental results indicate that the kinetics of this oxidation process fits pseudo‐first‐order kinetics well. The overall kinetic rate constant was split into two components: direct oxidation by UV radiation (photolysis) and oxidation by free radicals (mainly OH·) generated in the system. The importance of these two reaction paths for each specific value of ferrous ion concentration, temperature and initial hydrogen peroxide concentration was evaluated. A semi‐empirical expression is proposed for the overall reaction rate which takes into account both oxidation pathways and is a function of operating variables. © 2001 Society of Chemical Industry