Advanced Oxidation Processes Against Phenolic Compounds In Wastewater Treatment

Experimental research into the oxidative treatment of aqueous solutions and wastewaters containing phenolic compounds was undertaken. Ozone, supported by short wavelength UV-irradiation, hydrogen peroxide and titanium dioxide catalyst, was selected as an oxidant in the following combinations: O₃, O₃/H₂O₂, O₃/UV, O₃/TiO₂, O₃/UV/H₂O₂ and O₃/UV/TiO₂. 5-Methylresorcinol was chosen as a model compound for the experiments with synthetic phenolic solutions. The results obtained from these experiments were compared with the results of oxidative purification of wastewaters produced from the thermal treatment of oil shale in Estonia.     

Influence of Ozone on the Photocatalytic Oxidation of Organic Compounds

Heterogeneous photocatalytic oxidation processes using titanium oxide as a photocatalyst are widely discussed topics in research for water and waste water treatment. Oxygen fed into the systems is normally used as oxidizing agent. However few investigations exist concerning the use of ozone as an additional oxidant. In this work the influence of ozone on the photocatalytic degradation of organic compounds are described. The results are compared with those by using ozone, UV/O₃ and UV/TiO₂/O₂. The oxidation reactions were performed at pH 3 and 7.

In this research compounds of the different classes were used: glyoxal, pyrrole-2-carboxylic acid, p-toluenesulfonic acid and naphthalene-1,5-disulfonic acid. Depending on the classes of compounds in some cases the elimination rates of the initial compounds is enhanced by using UV/TiO₂/O₃ compared to UV/O₃ or O₃ alone. But in all cases greatest DOC elimination is achieved by using UV/TiO₂/O₃.     

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.     

Ozone Oxidation of Endocrine Disruptors and Pharmaceuticals in Surface Water and Wastewater

The oxidative removal of a diverse group of trace organic contaminants from surface water and wastewater was evaluated using ozone (O₃) and O₃ combined with hydrogen peroxide (O₃/H₂O₂). Target compounds included estrogenic and androgenic steroids, pharmaceuticals, pesticides, and industrial chemicals. Bench- and pilot- scale experiments were conducted with surface water spiked with the target compounds and wastewater effluent containing ambient concentrations of target compounds. Full-scale water treatment plants were sampled before and after ozonation to determine if bench- and pilot-scale results accurately predict full-scale removal. In both drinking water and wastewater experiments, the majority of target compounds were removed by greater than 90% at O₃ exposures commonly used for disinfection. Atrazine, iopromide, meprobamate, and tris-chloroethylphosphate (TCEP) were the most recalcitrant compounds to oxidize using O₃, with removals generally less than 50%. The addition of H₂O₂ for advanced oxidation was of little benefit for contaminant removal as compared to O₃ alone. O₃/H₂O₂ provided a marginal increase in the removal of dilantin, diazepam, DEET, iopromide, and meprobamate, while decreasing the removal efficacy of pentoxifylline, caffeine, testosterone, progesterone, and androstenedione. In wastewater experiments, O₃ and O₃/H₂O₂ were shown to remove in vitro estrogenicity. Collectively, these data provide evidence that O₃ is a highly effective oxidant for removing the majority of trace organic contaminants from water.     

Treatability of Organic Constituents in the Paşaköy Wastewater Treatment Plant Effluent by O3 and O3/H2O2

Effluent from the Pa?aköy Wastewater Treatment Plant was oxidized by using O₃ and O₃/H₂O₂. DOC, COD, UV₂₅₄, total coliform, dissolved ozone and some endocrine disrupting compounds were monitored during oxidation. Results showed that O₃ provided superior disinfection, however, lower reductions in DOC, COD and endocrine disrupting compounds were exhibited compared to O₃/H₂O_2. The highest removal efficiency of DOC, COD and endocrine disrupting compounds were achieved at 0.5 molar ratio of O₃/H₂O_2. The benefit of H₂O₂ addition for advanced oxidation reduced significantly when the mole ratio was increased to 2. Therefore, the mole ratio of H₂O₂ to O₃ is a critical parameter for the design of wastewater oxidation by O₃/H₂O₂.     

Manganese-Based Catalysts for the Catalytic Remediation of Phenolic Acids by Ozone

Manganese-based catalysts supported on Al₂O₃, TiO₂, ZrO₂ and CeO₂ were tested for the catalytic ozonation of a simulated wastewater involving phenolic acids. Comparing the Mn-Ce catalysts preparation method, wetness impregnation and co-precipitation, the last one showed to be more active. Moreover, the increase of Mn/Ce molar proportion from 22/78 to 70/30 increased the ozonation efficiency. The catalysts stability in terms of Mn leaching, carbon adsorption and effluent biodegradability was evaluated. Mn-Ce-O (70/30) CP shows to be the most suitable catalyst to improve phenolic wastewaters catalytic remediation by ozone.     

A comparative study on the performance of different advanced oxidation processes (UV/O3/H2O2) treating linear alkyl benzene (LAB) production plant's wastewater

A detailed investigation on photooxidation of linear alkyl benzene (LAB) industrial wastewater is presented in this study. The process analysis was performed by varying four significant independent variables including two numerical factors (initial pH (3–11) and initial H₂O₂ concentration (0–20 mM)) and two categorical factors (UV irradiation and ozonation). The experiments were conducted based on a central composite design (CCD) and analyzed using response surface methodology (RSM). To assess the process performance, two parameters viz. TCOD removal efficiency and BOD₅/COD were measured throughout the experiments. A maximum reduction in TCOD was 58, 53, 51, and 49%, respectively for UV/H₂O₂/O₃, H₂O₂/O₃, UV/O₃ and UV/H₂O₂ processes at the optimum conditions (initial pH of 7, initial H₂O₂ concentration of 100 mM, and reaction time of 180 min). A considerable increase in BOD₅/COD ratio was obtained in the combined processes (0.46, 0.51, 0.53, and 0.55 for UV/H₂O₂, UV/O₃, H₂O₂/O₃ and UV/H₂O₂/O₃, respectively) compared to the single oxidant process (0.35). The results showed that mineralization of the LAB industrial wastewater in neutral pH is more favored than in acidic and basic pH. Gas chromatography–mass spectrometry (GC–MS) was applied to show the fate of organic compounds. In conclusion, the photooxidation process (UV/H₂O₂/O₃, H₂O₂/O₃, UV/O₃ and UV/H₂O₂) could be an appropriate pretreatment method prior to a biological treatment process.     

Ti-MWW Synthesis and Catalytic Applications in Partial Oxidation Reactions

Ti-MWW was hydrothermally synthesized employing a SiO₂–TiO₂ xerogel. Characterization was performed using XRD, SEM, ICP, NH₃-TPD, FT-IR, UV–vis spectroscopy, and the catalytic properties of Ti-MWW was evaluated over 1-hexene epoxidation, oxidative desulfurization of model sulfur compounds, direct conversion of methanol to dimethoxymethane, and allyl chloride epoxidation using H₂O₂.     

Oxidation of Propylene Glycol Methyl Ether Acetate Using Ozone-Based Advanced Oxidation Processes

The present study investigates the degradation of PGMEA and its TOC removal using O₃, UV/O₃, O₃/H₂O₂, and UV/H₂O₂ processes under various experimental conditions. Ozonation of PGMEA was substantially enhanced in the presence of UV light and H₂O₂. Approximately 33% of TOC enhancement was noted in UV/O₃ process over ozonation process. A linear relationship between PGMEA and H₂O₂ decomposition was observed in O₃/H₂O₂ and UV/H₂O₂ processes. The influence of solution pH on the decomposition of PGMEA was investigated and found that basic medium was the most efficient in all AOPs. After 60 minutes 62.4%, 100%, 90% and 54% of PGMEA decomposition at pH 10.0 was observed in O₃, UV/O₃, O₃/H₂O₂, and UV/H₂O₂ processes, respectively. It is concluded that UV/O₃ process is a promising approach for the oxidation and removal of PGMEA.     

Removal of organic contaminants in paper pulp effluents by AOPs: an economic study

The degradation of the organic content of a bleaching Kraft mill effluent was carried out using Advanced Oxidation Processes (AOPs). The study was focused on the identification of the AOP, or combination of AOPs, that showed the highest efficiency together with the lowest cost. Direct UV photolysis (UV), TiO₂ assisted‐photocatalysis (TiO₂/UV), Fenton, Fenton‐like, and photo‐Fenton reactions (Fe(II)/H₂O/UV), UV‐assisted ozonation (O₃/UV) and addition of Fe²⁺ and/or H₂O₂ to the TiO₂/UV and the O₃/UV systems, were used for the degradation of a conventional cellulose bleaching effluent. The effluent was characterized by the general parameters TOC, COD and color, and analyzed for chlorinated low molecular weight compounds using GC–MS. The costs of the systems per unit of TOC reduction were compared. Fenton, Fenton‐like and photo‐Fenton reactions achieved better levels of TOC degradation than photocatalysis and with lower cost's than photocatalytic treatments. Ozonation is an effective but rather expensive process. The use of UVA light, however, increased the effectiveness of ozonation with a significant decrease (>25%) in the operational cost. © 2002 Society of Chemical Industry     

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 treatment of cork‐processing wastewaters for potential reuse

The chemical treatment of cork‐processing wastewater by ozonation, alone and in combination with hydrogen peroxide and UV radiation was investigated. A reduction of the chemical oxygen demand (COD) ranging from 42% to 76% was obtained during ozonation after 3 h of reaction, depending on the experimental conditions. The additional presence of hydrogen peroxide and UV radiation enhanced the efficiency of the ozonation treatment due to the contribution of the OH radicals formed in the decomposition of ozone. Thus, final reductions of the COD higher than 90% and a complete elimination of phenolic compounds and absorbance at 254 nm were achieved in both Advanced Oxidation Processes (AOPs), O₃/H₂O₂ and O₃/UV. Therefore the effluent resulting from the ozonation treatments can be reused in the cork‐processing industry. In a second step, the chemical treatment was conducted by means of UV radiation alone and by the action of hydroxyl radicals, which were generated by the following AOPs: UV/H₂O₂, Fenton's reagent, and photo‐Fenton system. The single photochemical process resulted in 9% of the organic matter present being removed, while the AOPs significantly enhanced this reduction with values in the range 20–75%. Kinetic studies for both groups of treatments were performed, and apparent kinetic rate constants were evaluated. In the ozone‐based experiments, the rate constants ranged from 1846 to 10922 dm³ mol^?1 O₃ h^?1, depending on the operating conditions. In the oxidation experiments using oxidants other than ozone, the rate constants varied between 0.06 and 1.19 h^?1. Copyright © 2004 Society of Chemical Industry     

The Chemistry of Water Treatment Processes Involving Ozone,Hydrogen Peroxide and Ultraviolet Radiation

Advanced oxidation processes are defined as those which involve the generation of hydroxyl radicals in sufficient quantity to affect water purification. The theoretical and (practical yield of OH from O₃ at high pH, 0₃/H₂0₂, O₃/UV and H₂O₂/UV systems is reviewed. New data is presented which illustrates the importance of direct photolysis in the O₃/UV process, the effect of the H₂0₂:0₃ ratio in the O₃/H₂O₂ process, and the impact of the low extinction coefficient of H₂O₂ in the H₂0₂/UV process.     

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 microwave,UV, and O3 on propylene gas degradation via photocatalytic reaction with CVD TiO2 films

A microwave/UV/ozone/TiO₂ photocatalyst hybrid process system, which is a combination of various propylene gas treatment techniques, is evaluated for use as an advanced, efficient technology for air pollution treatment. TiO₂ photocatalyst balls were prepared using low-pressure metal-organic chemical vapor deposition. The microwave/UV/TiO₂ photocatalyst hybrid process exhibited the higher degradation efficiency than the microwave/UV/alumina ball hybrid system. The degradation efficiency increased almost linearly with increasing ozone dose. The lower the propylene inlet concentration was the higher degradation efficiency. The double bond of propylene is broken by ozone and OH, resulting in production of CH₄ and C₂H₆. These two intermediate products are mineralized into CO₂, H₂O, and CO. C₂H₄ and C₃H₈ may be produced from CH₄, whereas C₂H₆ and C₃H₆ are produced by microwave irradiation.     

Fabrication of chain-like TiO2 hollow microspheres with enhanced photocatalytic activity

TiO₂ hollow microspheres (TiO₂-HMSs) have attracted much attention due to their low density, high photoreactivity and easy recovery. However, fabrication of TiO₂-HMSs is time-consuming and costly. In this paper, effect of H₂O₂ on the formation of chain-like TiO₂-HMSs was studied using (NH₄)₂TiF₆ as titanium source and urea as neutralizer through a one-pot hydrothermal reaction strategy. The prepared TiO₂-HMSs were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and scanning electron microscopy (SEM). The photocatalytic activity of TiO₂-HMSs was evaluated by photocatalytic degradation of an anionic dye X3B under UV irradiation. It was found that the presence of H₂O₂ not only influences the nucleation, but also enhances the hollowing process of TiO₂-HMSs by accelerating the “inside-outside” mass transfer. TiO₂-HMSs prepared in the presence of H₂O₂ showed enhanced photocatalytic activity due to the synergistic effects of well crystallization and hollow structures.     

Heterogeneous photocatalytic removal of the herbicide clopyralid and its comparison with UV/H2O2 and ozone oxidation techniques

Clopyralid is a herbicide that has recently been reported to occur in drinking water at concentrations above the Permitted Concentration Value (PCV) of 0.1 μg/L for an individual pesticide (EU directive 98/83/EC). An extensive laboratory study on clopyralid removal with UV/TiO₂, was carried out and was compared to UV/H₂O₂ and O₃ removal efficiencies. The effectiveness of three TiO₂ photocatalysts (Degussa P25, VP Aeroperl, Hombifine N) was studied and Degussa P25 was selected since it outperformed the other two. Complete removal of clopyralid was achieved with UV/TiO₂ in about 90 min at an optimum catalyst concentration of 1 g/L. Pseudo-zero-order kinetics were suitable to describe the first stage of the photocatalytic reaction in the concentration range 0.078–0.521 mM. pH was found to significantly affect the removal rates of clopyralid due to changes in TiO₂ surface charges and clopyralid ionisation degree. The rate constant was maximum at pH 5 and its value was 2.1 × 10⁻⁶ ± 4.3 × 10⁻⁷ M min⁻¹. Pure oxygen bubbled in solution was found to slightly affect unfavourably the photocatalytic removal of clopyralid as compared to air. With UV/H₂O₂ and O₃ systems, the initial removal rates were high but these systems were not effective in achieving high removal percentages overall.     

Oxidation of Esculetin,a Model Pollutant Present in Cork Processing Wastewaters,by Chemical Methods

The ozonation of esculetin (6,7-dihydroxycoumarin), a major pollutant present in the wastewater generated in the cork industry, was accelerated at high pH, with apparent second-order rate constants in the range from 3.3 × 10⁴ L/(mol·s) at pH=2 to 8.4 × 10⁷ L/(mol·s) at pH=9. The acid-base equilibrium of esculetin was studied, resulting in a pK_a value of 7.37. Taking into account this pK_a, the rate constants for the reaction between ozone and the un dissociated and dissociated forms of esculetin were 3.0 × 10⁴ and L/(mol·s) 6.67 × 10⁸ L/(mol·s), respectively. Apparent first-order rate constants for the photolysis by UV irradiation were also evaluated, with values between 0.12 × 10^?2 min^?1 at pH=2 and 1.15 × 10^?2 min^?1 at pH=9, while the quantum yields for this photo-degradation reaction varied from 0.99 × 10^?2 mol/Eins to 11.1 × 10^?2 mol/Eins at these pHs. The Fenton's reagent system was used for the generation of hydroxyl radicals, and the rate constant for the reaction between esculetin and these radicals was determined to be 1.06 × 10¹⁰ L/(mol·s). Finally, several chemical oxidation systems were used in the degradation of this pollutant: single oxidants (ozone, UV irradiation) and advanced oxidation processes (Fenton's reagent, UV/H₂O₂, O₃/H₂O₂, O₃/UV, O₃/H₂O₂ /UV, and photo-Fenton system). The results revealed that the most efficient methods in terms of esculetin removal were ozonation among the single oxidants, and the photo-Fenton system among the combined processes.     

Functional ceramic and nanocomposite fibers, cellular articles and microspheres via radiation curable colloidal dispersions

We present here new cellular ceramics, fibers and microspheres produced by novel and general microshaping techniques employing colloidal dispersions in solvent free radiation curable monomer mixtures. High loading, low viscosity dispersions of functional nanoparticles such as TiO₂ and α-Fe₂O₃ and colloidal Fe(C₂O₄)·2H₂O metal salt are achieved with comb-polyelectrolyte surfactants and/or mildly polar resins. TiO₂ dispersions are spun and solidified “on the fly” by UV radiation into continuous ceramic/polymer nanocomposite fibers with dimensions below 10 μm. Fe(C₂O₄)·2H₂O dispersions provide a UV curable alternative to α-Fe₂O₃ dispersions which can only be thermally cured. The Fe(C₂O₄)·2H₂O nanocomposites transform to α-Fe₂O₃ below 550 °C. Novel cellular Al₂O₃, TiO₂ and α-Fe₂O₃ articles with porosity >80% and precise replication of the pore-forming agents have also been produced from such dispersions. Al₂O₃ nanocomposite microspheres are produced by emulsification of the dispersions in an appropriate medium and UV curing.     

Preparation and characterization of TiO2/Ti film electrodes by anodization at low voltage for photoelectrocatalytic application

Multiporous TiO₂/Ti film electrodes were prepared by different anodic oxidation processes at low voltage, in which the micro-structured TiO₂ thick films were prepared in H₂SO₄–H₂O₂–H₃PO₄–HF solution for 2 h and the nano-structured TiO₂ thin films were prepared in H₃PO₄–HF solution for 30 min with post-calcination. Both types of TiO₂/Ti films were characterized by scanning electron microscopy and X-ray diffraction analysis. The photocatalytic (PC) and photoelectrocatalytic (PEC) reactivity of the TiO₂/Ti electrodes were evaluated in terms of bisphenol A (BPA) degradation in aqueous solution. The experimental results demonstrated that the nano-structured TiO₂/Ti thin-film electrodes had higher reactivity in the BPA degradation reaction. The PEC degradation of BPA was further studied using different cathodes, either a reticulated vitreous carbon (RVC) electrode or a platinum (Pt) electrode. The experimental results confirmed that the efficiency of BPA degradation could be significantly enhanced in the TiO₂/Ti–RVC reaction system due to the generation of H₂O₂ on the RVC cathode. It is believed that such a H₂O₂-assisted TiO₂ PEC oxidation process may have good potential for water and wastewater treatment.