Photocatalytic oxidation and ozonation of catechol over carbon-black-modified nano-TiO2 thin films supported on Al sheet

The photocatalytic activity of the carbon-black-modified nano-TiO2) (CB-TiO2) thin films was 1.5 times higher than that of TiO2 thin films in degrading Reactive Brilliant Red X-3B. Photocatalytic oxidation and ozonation of catechol over CB-TiO2 thin films supported on Al sheet was investigated. The experiments showed that ozone concentrations had an important effect on TOC removal. The combined photocatalysis with UV irradiation and ozonation (TiO2/UV/O3) process considerably increased TOC removal rate compared to combined photocatalysis with UV irradiation and oxygen oxidation (TiO2/UV/O2) process, ozonation alone (O3) process, combined ozonation and UV irradiation (UV/O3) process. The complete mineralization of catechol followed pseudo-zero-order kinetics dependent upon ozone (oxygen) concentration and indicated catechol concentration did not affect the kinetics during UV/O3 and TiO2/UV/O3 (O2) processes. The kinetic study showed that the rate constants in the complete mineralization of catechol with TiO2/UV/O3 are 1.32-1.80 times higher than that of UV/O3 with the same concentration of ozone. The rate constants are 2.56-5.36 times higher than the maximal rate constants of TiO2/UV/O2 and 4.68-9.8 times higher than the maximal rate constants of TiO2/UV.     

Ozone and photocatalytic processes to remove the antibiotic sulfamethoxazole from water

In this study, water containing the pharmaceutical compound sulfamethoxazole (SMT) was subjected to the various treatments of different oxidation processes involving ozonation, and photolysis and catalysis under different experimental conditions. Removal rates of SMT and total organic carbon (TOC), from experiments of simple UVA radiation, ozonation (O(3)), catalytic ozonation (O(3)/TiO(2)), ozone photolysis (O(3)/UVA), photocatalytic oxidation (O(2)/TiO(2)/UVA) and photocatalytic ozonation (O(3)/UVA/TiO(2)), have been compared. Photocatalytic ozonation leads to the highest SMT removal rate (pH 7 in buffered systems, complete removal is achieved in less than 5min) and total organic carbon (in unbuffered systems, with initial pH=4, 93% TOC removal is reached). Also, lowest ozone consumption per TOC removed and toxicity was achieved with the O(3)/UVA/TiO(2) process. Direct ozone and free radical reactions were found to be the principal mechanisms for SMT and TOC removal, respectively. In photocatalytic ozonation, with buffered (pH 7) aqueous solutions phosphates (buffering salts) and accumulation of bicarbonate scavengers inhibit the reactions completely on the TiO(2) surface. As a consequence, TOC removal diminishes. In all cases, hydrogen peroxide plays a key role in TOC mineralization. According to the results obtained in this work the use of photocatalytic ozonation is recommended to achieve a high mineralization degree of water containing SMT type compounds.     

Removal of nitrogenous compounds from aqueous solution by ozonation and ion exchange

Experiments were conducted to investigate the ammonia, nitrite and nitrate removal from aqueous solution using ozonation and ion exchange. The operating variables of the combined ozonation and ion exchange processes include the pH, initial concentration of nitrogenous compounds and flow rate of aqueous solution. The effects of those variables on the removal efficiencies of the nitrogeneous compounds by ozonation, or ion exchange or both were explored. Ozonation was found able to completely convert nitrite to nitrate. However its capability of ammonia removal is much limited. The anionic and cationic ion exchange resins were able to efficiently remove nitrate and residual ammonia. An optimal operating range of OH for ammonia removal by the combined ozonation and ion exchange was obtained. However, removal of nitrite and/or nitrate by combined ozonation and ion exchange was found to be relatively insensitive to pH. It was observed that the combined process is capable of efficiently maintaining the nitrogeneous compounds in the aqueous solution at very low concentration levels.     

Ozonation des amines dans l'eau ozonation of amines in aqueous solutions

Amines are nitrogenated compounds which may be found in water and in the atmosphere. The use of ozone for micropollution removal is growing; the aim of our study is to specify the behaviour of these compounds during ozonation.The studied amines are: methylamine. ethylamine, propylamine, cyclohexylamine, dimethylamine. N-methyl-butylamine and trimethylamine; the tests are classified in two groups.The first group of tests is carried out with concentrated aqueous solutions (7% in weight) to find the ozonation products. the identifications are carried out by the coupling gas chromatography with mass spectroscopy. The second group of tests is carried out with diluted aqueous solutions concentrations (10 ppm) are of which nearer to the usual effluent concentrations than the concentrated solutions ones.1. The identifed compounds in concentrated solution (Table 1) lead us to propose a reaction diagram (Fig. 3) for the ozonation of primary, secondary, tertiary amines. In any case, we notice an electrophilic attack of ozone on nitrogen lone pair of electrons, with: oxidation products of nitrogen (hydroxylamines, oximes and nitrogen oxides) and of carbon in α position (amides): breakdown products from initial molecules (aldehydes, ketones and acids) associated with the formation of mineral nitrogen (NO₂^-. NO₃^-) condensing products as polyamide types. Figure 5 shows the evolution of the different products of ozonation in terms of the ozone consumption for the cyclohexylamine instance.2. In diluted solutions, the oxidation rate of the various amines is linked to the available quantity of ozone (Figs 1 and 2): we find aldehydes, carboxylic acids and nitrates as ozonation products. According to these results, ozone is the choice oxidant for the treatment of industrial sewages and malodorous gas containing amines. The ozone used for the production of drinking water contributes to the removal of this kind of pollution.     

pH sequential ozonation of domestic and wine-distillery wastewaters

Domestic and wine-distillery wastewaters were treated by semi-batch and continuous pH sequential ozonations. The process involves a succession of acidic and alkaline wastewater pH conditions. The alkaline periods allow oxidation of organic matter by hydroxyl radical and produce carbonates that eventually would inhibit the oxidation. On the other hand, the acidic periods favour the development of direct ozone reactions and strip off carbonates as carbon dioxide from the wastewater. Experimental results of pH sequential ozonation showed degradation and removal rates of wastewater pollutants higher than those achieved at constant either acidic or basic pH. The most significant improvement of ozone efficiency and pollutants removal were obtained by controlling the number of cycles, pH and time of acidic and alkaline phases. Also, ozonated wastewaters showed high biodegradability as deduced from their BOD/COD ratios. The feasibility of treating domestic and wine-distillery wastewater by an integrated activated sludge (ASP)-pH sequential ozonation system was evaluated. Integrated ASP-ozonation at constant pH processes were also carried out for comparative purposes. In these combined experiments, pH sequential ozonation showed advantages compared to ozonation at constant pH in reducing global parameters such as COD, TOC and TKN, but ozonation at constant pH led to higher removal of polyphenols and UV254 absorbing compounds.     

臭氧催化氧化与BAC联用控制氯化消毒副产物

研究了臭氧催化氧化与生物活性炭联用技术对氯化消毒副产物（DBPs）的控制效能。结果表明：常规工艺出水中分子质量为2000u左右的疏水性有机物是氯化消毒副产物的主要前质，其占DOC与UV254的比例分别为70％和80％，并与UV254有良好的线性相关性，故可用UV254作为DBPs前质的替代指标。臭氧催化氧化与生物活性炭联用对DBPs前质的去除效果显著，其中臭氧催化氧化可有效去除三卤甲烷（THMs）前质中的疏水性有机物及部分亲水性有机物，并提高了DBPs前质的可生化性，是给水深度处理中控制THMs前质的主要工艺环节。臭氧催化氧化／生物活性炭对UV254的控制是减少DBPs生成的一条有效途径。     

Degradation of protocatechuic acid by two advanced oxidation processes: Ozone/UV radiation and H2O2UV radiation

Two advanced oxidation processes: the combinations of ozone and UV radiation, and hydrogen peroxide and UV radiation, have been used in the chemical degradation of protocatechuic acid, a phenolic pollutant present in the wastewaters from olive oil manufacturing. In the first case, the kinetic study is carried out by taking into account the contributions of the single ozonation and the photochemical reaction and applying the film theory model. The apparent kinetic constants and reaction orders for the combined reaction are deduced and correlated as a function of pH and temperature. In the second case, an empirical reaction rate expression which considers the contribution of both oxidants, UV radiation and hydrogen peroxide, is proposed. The kinetic rate constants for this combined reaction are also obtained and correlated as a function of temperature and pH.     

The effect of humic acids on nitrobenzene oxidation by ozonation and O3/UV processes

Three types of commercially available humic acids from different sources were used to simulate natural organic matter in water for the investigation of nitrobenzene oxidation by ozonation and O(3)/UV. Despite the structural differences among the Fluka, Aldrich and Suwanee River humic acids as reflected by the UV absorptivity, their effects on nitrobenzene removal rate was observed to be similar for the two processes. Removal rate of nitrobenzene was hindered by the addition of humic acids in ozonation as well as in O(3)/UV processes. However, the hindrance by the humic acids was more pronounced in O(3)/UV as compared to the ozonation process. The effect of humic acid in O(3)/UV was primarily a UV light screening. Addition of humic acids above a certain concentration did not cause any further retardation on nitrobenzene removal rate by ozonation and O(3)/UV.Accumulation of hydrogen peroxide as well as probable formation of peroxy radicals in the solutions might induce chain promoting reactions to produce hydroxyl radical during the nitrobenzene oxidation. For waters containing high levels of humic acid, ozonation alone might be as effective as O(3)/UV process for the removal of nitrobenzene.     

Advanced oxidation of a reactive dyebath effluent: comparison of O3, H2O2/UV-C and TiO2/UV-A processes

In the present study the treatment efficiency of different AOPs (O3/OH- H2O2/UV-C and TiO2/UV-A) were compared for the oxidation of simulated reactive dyebath effluent containing a mixture of monochlorotriazine type reactive dyes and various dye auxiliary chemicals at typical concentrations encountered in exhausted reactive dyebath liquors. A525 (color), UV280 (aromaticity) and TOC removal rates were assessed to screen the most appropriate oxidative process in terms of reactive dyebath effluent treatment. Special emphasis was laid on the effect of reaction pH and applied oxidant (O3, H2O2) dose on the observed reaction kinetics. It was established that the investigated AOPs were negatively affected by the Na2CO3 content (= 867 mg/L) which is always present at high concentrations in dychouse effluents since it is applied as a pH buffer and dye fixation agent during the reactive dyeing process. The ozonation reaction exhibited almost instantaneous decolorization kinetics and a reasonable TOC reduction rate. It appeared to be stable under the investigated advanced oxidation conditions and outranked the other studied AOPs based on the above mentioned criteria. Besides, the electrical energy requirements based on the EE/O parameter (the electrical energy required per order of pollutant removal in 1 m3 wastewater) was calculated for the homogenous AOPs in terms of decolorization kinetics. In view of the electrical energy efficiency, ozonation and H2O2/UV-C oxidation at the selected treatment conditions appear to be promising candidates for full-scale dyehouse effluent decolorization.     

光催化协同臭氧降解蒽醌染料废水

采用光催化协同臭氧技术降解蒽醌染料分散艳蓝E-4R,研究了光催化／臭氧法处理染料的主要影响参数,结果表明：增加臭氧的流量有利于提高脱色率,溶液初始pH值则对降解的影响较小,在光催似臭氧体系中,对降解起到主要作用的是·OH的氧化作用。     

Calcium enhanced COD removal for the ozonation of phenol solution

In order to improve the chemical oxygen demand (COD) removal rate for the ozonation of phenol solution, ozonation combined with calcium binding was investigated. The results show that the addition of Ca(2+) can effectively enhance the COD removal rate. During the ozonation, calcium ion can bind with some of the intermediate products of phenol, including high molecular weight products, maleic acid and oxalic acid, to form insoluble precipitates. These calcium binding effects are responsible for the enhancement of COD removal. The variations of ADMI value during ozonation are similar for solutions with and without Ca(2+). However, the peak ADMI value in calcium-contained solution is lower than that without Ca(2+). As the phenol was completely decomposed, the ozone gas outlet concentration rapidly increases. The increasing rate of the ozone gas outlet concentration for ozonation with the presence of Ca(2+) is faster than that without Ca(2+). The optimal initial calcium dosage shows linear relationship with the initial phenol concentration, which is useful for practical application.     

Comparison of different advanced oxidation processes for phenol degradation

Advanced Oxidation Processes (O3, O3/H2O2, UV, UV/O3, UV/H2O2, O3/UV/H2O2, Fe2+ /H2O2 and photocatalysis) for degradation of phenol in aqueous solution have been studied in earlier works. In this paper, a comparison of these techniques is undertaken: pH influence, kinetic constants, stoichiometric coefficient and optimum oxidant/pollutant ratio. Of the tested processes, Fenton reagent was found to the fastest one for phenol degradation. However, lower costs were obtained with ozonation. In the ozone combinations, the best results were achieved with single ozonation. As for the UV processes, UV/H2O2 showed the highest degradation rate.     

亚硝酸盐氮对臭氧氧化有机物的影响研究

在臭氧氧化处理微污染原水的工艺中，臭氧对有机物的去除效果与水中还原性无机物的含量有关。通过试验考察了水中NO2^--N对臭氧氧化有机物的影响。结果表明，水中较高浓度的NO2^--N可消耗臭氧投加量的40％左右，并降低了臭氧对THMs前体物的去除率，也影响其提高水中可生物降解有机物浓度的能力；碱度的增加可增强NO2^--N对臭氧的竞争利用，降低臭氧对TOC和UV254的去除率。     

UV-based processes for reactive azo dye mineralization

In the present study, advanced oxidation processes, UV/H2O2, UV/O3, and UV/H2O2/O3 have been applied to bleach and degrade organic dye C.I. Reactive Red 45 in water solution. Influence of pH and hydrogen peroxide dosage on process efficiency was investigated. The rate of color removal was studied by measuring the absorbance at the characteristic wavelength while mineralization rates were obtained on the basis of total organic carbon (TOC) and adsorbable organic halides (AOX) measurements. Complete bleaching was achieved by all applied processes after 60 min while the maximal mineralization extent depended on the reaction conditions for each of the processes. It has been found that UV/H2O2/O3 process was the most efficient with 61.1% TOC removal and 72.0% AOX removal, respectively, achieved after a 1-h treatment. Time required for complete mineralization of RR45 by UV/H2O2 and UV/H2O2/O3 processes was determined as well.     

Removal of textile basic dye from aqueous solutions using sawdust as bio‐adsorbent

The ability of low cost bio‐adsorbent sawdust to remove basic dye (methylene blue) from aqueous solution is investigated using it in two different forms: in raw form and in chemically treated (with sulphuric acid) form. The effect of contact time, dye concentration, adsorbent dose and the kinetics of adsorption were studied in batch experiments. At neutral pH and 4?gm/l of chemically activated and raw sawdust adsorbents, removal of 98.12% and 97.18% of methylene blue dye (at 100?mg/l concentration) from the aqueous solution, was the best result obtained during study. An average percentage removal difference of less than 5%, between two adsorbents was achieved under different conditions in the experiments. The data fit well in Freundlich isotherm.     

Oxidation of phenolic compounds by ozone and ozone + u.v. radiation: A comparative study

This study was designed to investigate the reaction mechanisms of oxidation of various phenolic compounds by ozone and ozone + u.v. radiation at pH 2.5, 7.0 and 9.0. Experimental results indicated that the molecular ozone is the predominant oxidant only at acidic pH; at neutral and basic pH, in the absence or presence of u.v. radiation, free radical reaction is the major pathway in the oxidation of phenolic compounds. The overall removal of phenols and the removal of TOC increase with increasing pH during ozonation with or without u.v. light. For a specific pH, the removal rates of phenol and TOC are highest for ozone + u.v. light followed by ozone and then u.v. light alone.     

Decomposition of diazinon in aqueous solution by ozonation

The decomposition of diazinon in aqueous solution by ozonation was studied under various solution pH values, gaseous ozone dosages, gaseous pressure, alkalinity levels and solution temperatures. Ozonation has been shown to be feasible for achieving nearly complete decomposition of diazinon within 1 h. The surface tension of aqueous solution was found to be affected by the dissolved diazinon and influenced the oxidation mechanism of diazinon by ozonation in aqueous solution. The gas–liquid reaction model was well used to describe the transfer and reaction behaviors of reacting species in the system. The quasi-global kinetics based on a simplified consecutive reaction scheme was developed to describe the temporal behavior of diazinon decomposition in aqueous solution by ozonation.     

Mineralization of some natural refractory organic compounds by biodegradation and ozonation

The objective of this study was to explore the extent of mineralization, reduction in color and reduction of COD of gallic acid, tannin and lignin by ozonation and a combination of aerobic biodegradation and ozonation. Ozonation of pure aliquots (phase I experiments) resulted in the decline in TOC, COD, COD/TOC ratio, UV absorbance at 280 nm and color of the three model compounds investigated, with COD removals of greater than 80% and high removals (>90%) of UV absorbance at 280 nm and color observed in all cases at an ozone dose of 6 mg ozone/mg initial TOC or higher. Aerobic biodegradation of pure gallic acid, tannin and lignin aliquots resulted in COD decline of approximately 36-38%. Subsequent ozonation (phase II experiments) resulted in further decline in TOC, COD, COD/TOC ratio, and increase in UV absorbance at 280 nm and color removals. COD and TOC removals comparable to phase I experiments were obtained with 30-40% lower ozone absorption in phase II experiments. The biodegradation step was quite effective in removing specific UV absorbance at 280 nm, with up to 75% removal observed. Subsequent ozonation increased overall specific UV absorbance at 280 nm to greater than 90%.     

Protocatechuic acid ozonation in aqueous solutions

The oxidation of protocatechuic acid with ozone in aqueous solution has been studied varying the temperature, pH, ozone partial pressure and initial acid concentration. A stoichiometric ratio of 2 mol of ozone consumed per mol of protocatechuic acid reacted is deduced from homogeneous experiments in a discontinuous tank reactor.In the ozonation experiments, the influence of the operating variables was established and the kinetic regime of ozone absorption was shown to be fast and pseudo m-order with respect to ozone, except at pH 2, when the reaction develops in the moderate kinetic regime. After applying a mass transfer with chemical reaction model, the reaction orders are deduced and the kinetic rate constants are determined as a function of pH and temperature. A modified Arrhenius expression is proposed to correlate them.     

Oxidation of chlorfenvinphos in ultrapure and natural waters by ozonation and photochemical processes

The chemical oxidation of the organophosphorus insecticide chlorfenvinphos, a priority pollutant in aquatic environments, has been conducted in ultrapure water, by means of single degradation agents (ozone and UV radiation), and by the Advanced Oxidation Processes constituted by combinations of these oxidants (O(3)/H(2)O(2) and UV/H(2)O(2)). The influence of the operating variables was discussed, and the degradation rates were evaluated by determining the rate constants for the reactions with ozone ( [Formula: see text] =3.7+/-0.2 L mol(-1)s(-1)) and OH radicals (k(OH)=(3.2+/-0.2)x10(9) L mol(-1)s(-1)), as well as the quantum yield for the photodegradation (around 0.1 mol E(-1), depending on the pH). Additionally, the ozonation of chlorfenvinphos in a natural water system (a surface water from a reservoir) was studied. The influence of the operating conditions on the insecticide removal efficiency was established, and the R(ct) parameter was evaluated. A kinetic model was proposed for the prediction of the elimination rate of chlorfenvinphos in the ozonation process and the results obtained reveal a good agreement between experimental results and predicted values.