Efficiency of activated carbon to transform ozone into *OH radicals: influence of operational parameters

Based on previous findings (Jans, U., Hoigné, J., 1998. Ozone Sci. Eng. 20, 67-87), the activity of activated carbon for the transformation of ozone into *OH radicals including the influence of operational parameters (carbon dose, ozone dose, carbon-type and carbon treatment time) was quantified. The ozone decomposition constant (k(D)) was increased by the presence of activated carbon in the system and depending on the type of activated carbon added, the ratio of the concentrations of *OH radicals and ozone, the R(ct) value ([*OH]/[O3]), was increased by a factor 3-5. The results obtained show that the surface chemical and textural characteristics of the activated carbon determines its activity for the transformation of ozone into *OH radicals. The most efficient carbons in this process are those with high basicity and large surface area. The obtained results show that the interaction between ozone and pyrrol groups present on the surface of activated carbon increase the concentration of O2*- radicals in the system, enhancing ozone transformation into *OH radicals. The activity of activated carbon decreases for extended ozone exposures. This may indicate that activated carbon does not really act as a catalyst but rather as a conventional initiator or promoter for the ozone transformation into *OH radicals. Ozonation of Lake Zurich water ([O3] = 1 mg/L) in presence of activated carbon (0.5 g/L) lead to an increase in the k(D) and R(ct) value by a factor of 10 and 39, respectively, thereby favouring the removal of ozone-resistant contaminants. Moreover, the presence of activated carbon during ozonation of Lake Zurich water led to a 40% reduction in the content of dissolved organic carbon during the first 60 min of treatment. The adsorption of low concentrations of dissolved organic matter (DOM) on activated carbon surfaces did not modify its capacity to initiate/promote ozone transformation into *OH radicals.     

Comparison of the efficiency of *OH radical formation during ozonation and the advanced oxidation processes O3/H2O2 and UV/H2O2

Comparison of advanced oxidation processes (AOPs) can be difficult due to physical and chemical differences in the fundamental processes used to produce OH radicals. This study compares the ability of several AOPs, including ozone, ozone+H2O2, low pressure UV (LP)+H2O2, and medium pressure UV (MP)+H2O2 in terms of energy required to produce OH radicals. Bench scale OH radical formation data was generated for each AOP using para-chlorobenzoic acid (pCBA) as an OH radical probe compound in three waters, Lake Greifensee water, Lake Zurich water, and a simulated groundwater. Ozone-based AOPs were found to be more energy efficient than the UV/H2O2 process at all H2O2 levels, and the addition of H2O2 in equimolar concentration resulted in 35% greater energy consumption over the ozone only process. Interestingly, the relatively high UV/AOP operational costs were due almost exclusively to the cost of hydrogen peroxide while the UV portion of the UV/AOP process typically accounted for less than 10 percent of the UV/AOP cost and was always less than the ozone energy cost. As the *OH radical exposure increased, the energy gap between UV/H2O2 AOP and ozone processes decreased, becoming negligible in some water quality scenarios.     

Oxidative degradation of N-nitrosodimethylamine by conventional ozonation and the advanced oxidation process ozone/hydrogen peroxide

This study investigates the oxidative degradation of N-nitrosodimethylamine (NDMA), a probable human carcinogen, by conventional ozonation and the advanced oxidation process ozone/hydrogen peroxide (AOP O(3)/H(2)O(2)). The rate constants of reactions of NDMA with ozone and hydroxyl radical ((*)OH) were determined to be 0.052+/-0.0016M(-1)s(-1) and (4.5+/-0.21)x10(8)M(-1)s(-1), respectively. The experiments performed with buffered deionized water varying solution pH and employing H(2)O(2) and HCO(3)(-) clearly showed that the reaction with (*)OH dominates the NDMA oxidation during ozonation. Conventional ozonation with up to 160 microM (=7.7 mgL(-1)) ozone led to less than 25% NDMA oxidation in natural waters. The AOP O(3)/H(2)O(2) required 160-320 microM ozone ([O(3)](0)/[H(2)O(2)](0)=2:1) to achieve 50-75% NDMA oxidation. However, multiple injections of ozone of the same overall dose somewhat improved the oxidant utilization efficiency by minimizing (*)OH scavenging contribution of oxidants. Methylamine (MA) was found to be a major amino product from NDMA oxidation initiated by (*)OH. The mechanism of NDMA oxidation to MA is discussed based on the results obtained in this study and the previous literature. Bromate formation may be the limiting factor for NDMA oxidation during ozonation and ozone-based AOPs in bromide-containing waters.     

Kinetics of the transformation of phenyl-urea herbicides during ozonation of natural waters: rate constants and model predictions

Oxidation of four phenyl-urea herbicides (isoproturon, chlortoluron, diuron, and linuron) was studied by ozone at pH=2, and by a combination of O3/H2O2 at pH=9. These experiments allowed the determination of the rate constants for their reactions with ozone and OH radicals. For reactions with ozone, the following rate constants were obtained: 1.9 +/- 0.2, 16.5 +/- 0.6, 393.5 +/- 8.4, and 2191 +/- 259 M(-1) s(-1) for linuron, diuron, chlortoluron, and isoproturon, respectively. The rate constants for the reaction with OH radicals were (7.9 +/- 0.1) x 10(9) M(-1) s(-1) for isoproturon, (6.9 +/- 0.2) x 10(9) M(-1) s(-1) for chlortoluron, (6.6 +/- 0.1) x 10(5) M(-1) s(-1) for diuron, and (5.9 +/- 0.1) x 10(9) M(-1) s(-1) for linuron. Furthermore, the simultaneous ozonation of these selected herbicides in some natural water systems (a commercial mineral water, a groundwater, and surface water from a reservoir) was studied. The influence of operating conditions (initial ozone dose, nature of herbicides, and type of water systems) on herbicide removal efficiency was established, and the parameter Rct (proposed by Elovitz, M.S., von Gunten, U., 1999. Hydroxyl radical/ozone ratios during ozonation processes. I. The Rct concept. Ozone Sci. Eng. 21, 239-260) was evaluated from simultaneous measurement of ozone and OH radicals. A kinetic model was proposed for the prediction of the elimination rate of herbicides in these natural waters, and application of this model revealed that experimental results and predicted values agreed fairly well. Finally, the partial contributions of direct ozone and radical pathways were evaluated, and the results showed that reaction with OH radicals was the major pathway for the oxidative transformation of diuron and linuron, even when conventional ozonation was applied, while for chlortoluron and isoproturon, direct ozonation was the major pathway.     

Metal-doped carbon aerogels as catalysts during ozonation processes in aqueous solutions

The efficiency of Co(II)-, Mn(II)-, and Ti(IV)-doped carbon aerogels for the transformation of ozone into (*)OH radicals was investigated. The carbon aerogels had a markedly acid surface character (pH(PZC approximately equal) congruent with 3-4) with very high surface oxygen concentrations (O approximately equal with 20%). X-ray photoelectron spectroscopy (XPS) analyses of the samples showed the oxidation state of the metals was +2 for Co and Mn and +4 for Ti. The presence of Mn(II)-doped carbon aerogel enhanced ozone transformation into (*)OH radicals, whereas the presence of Co(II) and Ti(IV) carbon aerogels presented no activity in this process. Moreover, it was observed that an increase in the concentration of Mn in the surface of the aerogel increases its efficiency to transform ozone into (*)OH radicals, with an Rct value ([OH]/[O(3)]) of 5.36 x 10(-8) for the aerogel doped with 16% of surface Mn(II) compared to an R(ct) of 2.68 x 10(-9) for conventional ozonation. Regardless of the aerogel used, XPS analysis of the ozonated aerogel samples showed an increase in the concentration of surface oxygen when the exposure to ozone was longer. However, presence of oxidized metal species after ozone treatment was only detected in the case of the Mn-doped aerogel, (Mn(III) and Mn(IV)). CO(2) activation of carbon aerogel produced a marked increase in its efficiency to transform ozone into (*)OH radicals compared with non-activated sample. The efficiency of Mn activated carbon aerogel to transform ozone into (*)OH radicals was greater than that of Witco commercial activated carbon or H(2)O(2) in the ozonation of water from Lake Zurich (Zurich, Switzerland).     

Removal of pharmaceuticals and kinetics of mineralization by O(3)/H(2)O(2) in a biotreated municipal wastewater

The ozonation of an effluent from the secondary clarifier of two Municipal Wastewater Treatment Plants was performed by using alkaline ozone and a combination of ozone and hydrogen peroxide. Alkaline ozonation achieved only a moderate degree of mineralization, essentially concentrated during the first few minutes; but the addition of hydrogen peroxide eventually led to a complete mineralization. The evolution of total organic carbon (TOC) as a measure of the extent of mineralization and the concentration of dissolved ozone were analyzed and linked in a kinetic model whose parameter represented the product of the exposure to hydroxyl radicals and the kinetic constant of indirect ozonation. This rate parameter yielded the highest values during the first part of O(3)/H(2)O(2) runs. The kinetic constant for the decomposition of ozone at the end of the run was also measured and computed for the non-oxidizable water matrix and yielded essentially the same values regardless of whether or not hydrogen peroxide was used. A group of 33 organic compounds, mainly pharmaceuticals and some relevant metabolites present in the wastewater effluents, were evaluated before and after the ozonation process using a liquid chromatography-hybrid triple-quadrupole linear ion trap system (LC-QqLIT-MS). The results demonstrate that the ozonation degrades these compounds with efficiencies of over 99% in most cases, even under low mineralization conditions in alkaline ozonation.     

ZnO/O3工艺降解水中微量有机物的研究

以实验室制备的粉末氧化锌(ZnO)为催化剂,考察了ZnO/O3工艺去除水中有机物的效能.采用总有机碳(TOC)指标反映水中有机污染物的含量.结果表明:臭氧投量为1 mg/L、ZnO投量为300 mg/L时,反应60 min后ZnO-O3工艺对TOC的去除率为46%,比单独臭氧化提高了1倍;反应温度明显影响该工艺对有机物的降解效果,在水温为5,10,20和25 ℃时,TOC的去除率分别为17.5%,31.5%,45.9%和51.3%.臭氧浓度和催化剂投量的增加,可以提高TOC的氧化降解效率.     

Oxidation of metal-diethylenetriaminepentaacetate (DTPA)--complexes during drinking water ozonation

This study investigates the oxidative transformation of diethylenetriaminepentaacetate (DTPA), a synthetic ligand, during drinking water ozonation. The rate coefficients for the reactions of CaDTPA3- and ZnDTPA3- with ozone were determined to be 6200 and 3500 +/- 150 M-1 s-1, respectively. The reactivity of Fe(III)DTPA2- towards ozone was found to be much lower (< 10 M-1 s-1), but near neutral pH the reactivity of the Fe(III)-complexes is dominated by [Fe(III)(OH)]DTPA3-. For the reaction of Fe[(III)(OH)]DTPA3- with ozone a rate coefficient of 2.4 +/- 0.2 x 10(5) M-1 s-1 was measured. The rate coefficients of the reactions of the ZnDTPA- and Fe(III)DTPA with OH radicals have been determined by a competitive method as 2.4 +/- 0.4 x 10(9) and 1.5 +/- 0.1 x 10(9) M-1 s-1, respectively at pH = 7. The degradation of low concentrations of DTPA complexes during ozonation was investigated in natural waters under drinking water relevant conditions. Based on our findings CaDTPA3- and ZnDTPA3- are judged as easily degradable. Fe(III)DTPA complexes showed a somewhat lower reactivity, but were still typically degraded by one order of magnitude at ozone dosages of approximately 20 microM (1 mg L-1) in the three natural waters tested. Molecular ozone was found to be the major oxidant for the metal-DTPA complexes during ozonation.     

Degradation and estrogenic activity removal of 17beta-estradiol and 17alpha-ethinylestradiol by ozonation and O3/H2O2

This work investigated the degradation of a natural (17beta-estradiol) and a synthetic (17alpha-ethinylestradiol) estrogens (pure or in the mixture) and the removal of estrogenic activity by the ozonation and O3/H2O2 process in three different pHs (3, 7 and 11). The effect of oxidation via OH radical was evaluated adding a radical scavenger (t-butanol) in the medium. Estrogenic activity was performed using the YES assay. 17beta-estradiol and 17alpha-ethinylestradiol presented similar estrogenic potential and the association of these estrogens resulted in an addictive effect for estrogenic activity. Ozonation and O3/H2O2 processes were effective in removing the estrogens in aqueous solution. In the mixture at pH 11, removals were higher than 98% and 96% for 17beta-estradiol and 17alpha-ethinylestradiol, respectively. In pH 3, 17beta-estradiol and 17alpha-ethinylestradiol removals were 100% and 99.7%, respectively. When estrogens were treated separately, the removals in pH 11 were superior to 99.7 and 98.8%, while in pH 3 were 100% and 99.5% for 17beta-estradiol and 17alpha-ethinylestradiol, respectively. 17alpha-ethinylestradiol has been always removed at lower rates (pure or in the mixture) for all applied conditions. Estrogenic activity was completely removed in pH 3 for ozonation or O3/H2O2. The samples oxidized in pH 11 presented higher estrogenic activity than those in pH 7. Estrogens removal was lower at pHs 7 and 11, when the scavenger was added to the media. The higher estrogen residual concentrations found in ozonation in presence of tert-butanol are contributing for higher estrogenic activity observed in pHs 7 and 11. By-products with estrogenic activity were formed by oxidation via OH radical. Only a few compounds could be identified in pHs 7 and 11 and they have a phenolic ring, which, probably is contributing to the estrogenic activity observed.     

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.     

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.     

Removal of pharmaceutical compounds, nitroimidazoles, from waters by using the ozone/carbon system

The main objective of this study was to analyze the effectiveness of technologies based on the use of ozone and activated carbon for the removal of nitroimidazoles from water, considering them as model of pharmaceutical compounds. A study was undertaken of the influence of the different operational variables on the effectiveness of each system studied (O(3), O(3)/activated carbon), and on the kinetics involved in each process. Ozone reaction kinetics showed that nitroimidazoles have a low reactivity, with [Formula: see text] values <350M(-1)s(-1) regardless of the nitroimidazole and solution pH considered. However, nitroimidazoles have a high affinity for HO radicals, with radical rate constant (k(HO)) values of around 10(10)M(-1)s(-1). Among the nitroimidazole ozonation by-products, nitrate ions and 3-acetyl-2-oxazolidinone were detected. The presence of activated carbon during nitroimidazole ozonation produces (i) an increase in the removal rate, (ii) a reduction in the toxicity of oxidation by-products, and (iii) a reduction in the concentration of dissolved organic matter. These results are explained by the generation of HO radicals at the O(3)-activated carbon interface.     

Effectiveness of different oxidizing agents for removing sodium dodecylbenzenesulphonate in aqueous systems

The present study investigates the efficacy of various oxidizing treatments (ClO⁻, ClO₂, KMnO₄, O₃, O₃/H₂O₂, O₃/activated carbon) to remove from waters sodium dodecylbenzenesulphonate (SDBS), considered as model surfactant. Results obtained show that the use of ClO⁻ and ClO₂ does not cause appreciable SDBS degradation. Additionally, in the case of ClO⁻, trihalomethanes are generated, increasing system toxicity. Because the reaction kinetics between SDBS and KMnO₄ is very slow, a decrease in contaminant concentration is not observed, even at very acid pH values. SDBS reactivity with ozone is very low, with a kinetic constant (kO3) of 3.68 M⁻¹ s⁻¹, but its reactivity with HO radicals is very high (k_OH = 1.16 × 10¹⁰ M⁻¹ s⁻¹), therefore O₃/H₂O₂ and O₃/activated carbon, which can also generate HO, appear as promising advanced oxidation processes to remove this contaminant from waters. The method based on ozone and activated carbon was the only process studied that produced both an increase in SDBS removal rate (due to the generation of HO radicals in the O₃-PAC or O₃-GAC interaction) and a considerable reduction in the concentration of dissolved organic carbon in the system due to the PAC adsorbent properties.     

Characterization of raw water for the ozone application measuring ozone consumption rate.

This study was conducted to illustrate an ideal method for characterizing natural waters for ozonation processes in drinking water treatment plants. A specific instrument designed with the flow injection analysis (FIA) technique enabled us to measure accurately the ozone decomposition rate, which was found to consist of two stages: the instantaneous ozone consumption stage and the slower ozone decay stage. The ozone consumption rate was measured at the initial and secondary stages by determining certain parameters called the instantaneous ozone demand (ID) and the pseudo first-order decay rate constant (k(c)). Using the OH*-probe, the yield of OH* per consumed ozone was also measured to determine its potential to produce OH* for the oxidation of micropollutants during the ozonation process. The ozone consumption of the ID values was significant in most natural waters, and substantial amounts of OH* were found to generate during the instantaneous ozone consumption stage. This study also investigated the effects of particulates, ozone doses, and sequential ozone injection on ozone decomposition kinetics and OH* formation yield.     

Optimization of Coagulation and Ozonation Processes for Disinfection by–Products Formation Potential Reduction

Optimization of coagulation and ozonation processes for removal of disinfection by–products (DBP) formation potential in raw water was conducted by a pilot scale system. Proper poly–aluminum–chloride–sulfates (PACS), pre–ozone and post–ozone dosages are required for improving the removal performance of DBP formation potential to guarantee the safety of drinking water. Considering the treatment performances and economic costs, the optimum PACS, pre–ozone and post–ozone dosages for treating raw water with high organic concentration should be around 8.9 mg/L Al₂O₃, 0.5 and 2.5 mg/L, respectively. The combined drinking water treatment system of pre–ozonation, coagulation/sedimentation, sand filtration, post–ozonation, granular activated carbon filtration and disinfection is a promising process to reduce DBP formation potential from raw water in southern China. Under the optimum conditions, this combined system removed total trihalomethanes and haloacetic acids formation potential 50.16 and 69.10%, respectively.     

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.     

Ozonation of reverse osmosis concentrate: kinetics and efficiency of beta blocker oxidation

Reverse osmosis (RO) concentrate samples were obtained from a RO-membrane system that uses effluents of wastewater treatment plants (WWTP) as feed water for the production of drinking water. A number of different pharmaceuticals (e.g. antibiotics, contrast media, beta blockers) were found in the WWTP effluent as well as in the RO-concentrate. Overall, a concentration factor (feed:concentrate) of approximately 3-4 was measured. Beta blockers (acebutolol, atenolol, bisoprolol, celiprolol, metoprolol, propranolol, timolol) were found in the range of low ng/L to low microg/L. Because metoprolol and propranolol are classified as potentially toxic to aquatic organisms and all beta blocker molecules have moieties, which are reactive towards ozone (amine groups, activated aromatic rings), it was tested whether ozonation can be applied for their mitigation. Rate constants for the reaction of acebutolol, atenolol, metoprolol and propranolol with ozone and OH radicals were determined. At pH 7 acebutolol, atenolol and metoprolol react with ozone with an apparent second-order rate constant ( [Formula: see text] ) of about 2,000 M(-1)s(-1), whereas propranolol reacts with approximately 10(5)M(-1)s(-1). The rate constants for the reaction of the selected compounds with OH radicals were determined to be 0.5-1.0 x 10(10)M(-1)s(-1). Experiments with RO concentrate showed that an ozone dose of only 5mg/L resulted in a quantitative removal of propranolol in 0.8s and 10mg O(3)/L oxidized 70% of metoprolol in only 1.2s. Tests with chlorinated and non-chlorinated WWTP effluent showed an increase of ozone stability but a decrease of hydroxyl radical exposure in the samples after chlorination. This may shift the oxidation processes towards direct ozone reactions and favor the degradation of compounds with high [Formula: see text].     

Reactions of thiocarbamate, triazine and urea herbicides, RDX and benzenes on EPA Contaminant Candidate List with ozone and with hydroxyl radicals

Second-order rate constants of the direct ozone reactions [formula: see text] and the indirect OH radical reactions [formula: see text] for nine chemicals on the US EPA's Drinking Water Contaminant Candidate List (CCL) were studied during the ozonation and ozone/hydrogen peroxide advanced oxidation process (O(3)/H(2)O(2) AOP) using batch reactors. Except for the thiocarbamate herbicides (molinate and EPTC), all other CCL chemicals (linuron, diuron, prometon, RDX, 2,4-dinitrotoluene, 2,6-dinitrotoluene and nitrobenzene) show low reactivity toward ozone. The general magnitude of ozone reactivity of the CCL chemicals can be explained by their structures and the electrophilic nature of ozone reactions. The CCL chemicals (except RDX) are highly reactive toward OH radicals as demonstrated by their high [formula: see text] values. Ozonation at low pH, which involves mainly the direct ozone reaction, is only efficient for the removal of the thiocarbamates. Ozonation at high pH and O(3)/H(2)O(2) AOP will be highly efficient for the treatment of all chemicals in this study except RDX, which shows the lowest OH radical reactivity. Removal of a contaminant does not mean complete mineralization and reaction byproducts may be a problem if they are recalcitrant and are likely to cause health concerns.     

不同水源下臭氧/生物活性炭运行参数的优化

近年来,臭氧/生物活性炭工艺在国内得到广泛应用,在控制饮用水中消毒副产物的生成方面起到了重要作用。研究与生产实践表明,臭氧/生物活性炭运行参数的优化对其净水效能的发挥至关重要。针对江苏J水厂采用的H和X两个水质差异较大的水源,建立了中试装置,开展了以控制消毒副产物为目标的臭氧/生物活性炭运行参数优化研究。结果表明:随着臭氧投加量的增加,系统对H与X水源中三卤甲烷生成势(THMFP)的去除率先上升后逐渐平稳,对卤乙酸生成势(HAAFP)的去除率呈现先增加后降低的趋势;随着炭床停留时间的延长,生物活性炭工艺对THMFP、HAAFP的去除率均呈先上升后平稳的趋势。综合考虑THMFP和HAAFP的去除效能,优化后的臭氧/生物活性炭工艺运行参数如下:针对H水源,臭氧投加量为0. 5 mg/L,炭床停留时间为12 min;针对X水源,臭氧投加量为2. 0 mg/L,炭床停留时间为12 min。     

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.