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

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

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.     

Cost analysis for the degradation of highly concentrated textile dye wastewater with chemical oxidation H2O2/UV and biological treatment

The efficiency and cost‐effectiveness of H₂O₂/UV for the complete decolorization and mineralization of wastewater containing high concentrations of the textile dye Reactive Black 5 was examined. Oxidation until decolorization removed 200–300 mg g^?1 of the dissolved organic carbon (DOC). The specific energy consumption was dependent on the initial dye concentration: the higher concentration required a lower specific energy input on a weight basis (160 W h g^?1 RB5 for 2.1 g L^?1 versus 354 W h g^?1 RB5 for 0.5 g L^?1). Biodegradable compounds were formed, so that DOC removal could be increased by 30% in a following biological stage. However, in order to attain 800 mg g^?1 overall mineralization, 500 mg g^?1 of the DOC had to be oxidized in the H₂O₂/UV stage. A cost analysis showed that although the capital costs are much less for a H₂O₂/UV stage compared to ozonation, the operating costs are almost double those of ozonation. Thus, while H₂O₂/UV can compete with ozonation when the treatment goal only requires decolorization, ozonation is more cost‐effective in this case when mineralization is desired. Copyright © 2006 Society of Chemical Industry     

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

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

Decomposition of phenols in aqueous solution by a UV/O3 process

The decomposition of several non‐biodegradable phenols by the UV/O₃ and ozonation processes was studied and compared under various solution pH values, O₃ input mass flow rates and UV intensities to investigate the removal efficiencies of reactants and organic intermediates. The decomposition rate of phenols by the UV/O₃ process was found to increase with increasing O₃ input dosage, light intensity and solution pH value. The mineralization efficiencies of phenols in aqueous solution would be above 98% under adequate reaction conditions within three hours, but would be retarded for alkaline solutions because of the dissolution of CO₂ formed by mineralization of phenols. The increment of ozone input dosage had little effect on the mineralization of organic intermediates at the latter course of the reaction. The order of the decomposition rate of the phenols used in this research was 2,4‐dichlorophenol > 2‐chlorophenol > 2‐nitrophenol for low and neutral pH solutions, whereas they were nearly alike for alkaline solutions. The two‐step consecutive kinetic model was found to fit well in modeling the behavior of species during the decomposition of phenols in aqueous solutions by the UV/O₃ process.     

The Combination of Ozone/Hydrogen Peroxide and Ozone/UV Radiation for Reduction of Trihalomethane Formation Potential in Surface Water

Applied ozone dosages of 20, 25, and 30 mg/L to lake water utilized by the city of Shreveport, LA produced no significant reductions in trihalomethane formation potentials (THMFP). However, the addition of 20 mg/L of hydrogen peroxide and/or 0.67 W/L of UV radiation (254 nm) in combination with ozone produced decreases in THMFP of over 60% in 60 minutes. Smaller THMFP decreases were seen with shorter contact times. The use of H₂O₂ and/or UV in combination with O₃ increased the percentage of applied ozone consumed by the lake water (i.e., enhanced the ozone mass transfer) five times over simple ozonation.     

Evaluation of Decolorization,Mineralization, and Toxicity Reduction of Tropaeolin O in Water by Ozonation with UV Irradiation

The combination of ozonation with UV irradiation can remove Tropaeolin O (AO6) and its by-products effectively and completely. The ozone dose affects the rate of decolorization, AO6 species removal, and dissolved organic carbon (DOC) reduction significantly. After 240 minutes of ozonation, the average DOC removal efficiency (η_DOC) for O₃ alone was about 0.79, while η_DOC for O₃/UV was 1.0. The average DOC removal rate was low at early stage of ozonation due to decolorization and low DOC. At later stage of ozonation, average DOC removal rate decreases because of the formation of persistent intermediates. The ozone consumption was consistent with η_DOC. The ratio of ozone consumption to ozone applied decreased from 14 to 12% when η_DOC < 40% because the decolorization in the early stage of the ozonation of AO6 may consume a relatively large amount of ozone. It was found that NO₂, NO, CO₂, and small amount of SO₂ was detected in the off-gas. The effective concentration (EC50) increased from 23.48% to 100%, suggesting that the toxic reduction was achieved, and O₃/UV system was superior to O₃ alone system     

Degradation of Aqueous Phenol and Chlorinated Phenols by Ozone

The degradation of phenol and its chlorinated derivatives with ozone is studied. The studied compounds are phenol (Ph), 4-chlorophenol (4-CPh) and 2,4-dichlorophenol (2,4-DCPh). The kinetic performances of each phenolic compound and their model mixture are examined. The pH influence on the decomposition dynamics for different phenolic compounds in the range 2–12 is investigated. The increase of the decomposition rate under increasing pH was observed. In the pH range studied, phenol and chlorophenols ozonation proceeds rapidly. The UV absorbency is used for the preliminary control of the degree of decomposition. The HPLC analysis is used to identify intermediates and final products formed during ozonation. It is shown that the basic intermediates are muconic and fumaric acids, malonic and maleic acids, catechol and hydroquinone. The final products are oxalic acid and formic acid. In the case of alkaline media, the principal final product is oxalic acid. Furthermore, intermediates and final decomposition products obtained at different pH are compared. According to the results obtained, the possible mechanism of ozonation by the reaction of hydroxylation and dechloration in the early stage is proposed. The BOD₅/COD ratio is used as a biodegradability measure for the comparison of biodegradability of initial compounds and final products composition.     

Photooxidation of Some Mono-, Di-, and Tri-chlorophenols in Aqueous Solution by Hydrogen Peroxide/UV Combinations

A number of chlorophenols, namely 2-, 3-, and 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol, have been decomposed in aqueous solution by using hydrogen peroxide as the oxidizing agent under UV radiation emitted by a 400 W high-pressure mercury lamp in a thermostatted Pyrex-glass column photoreactor, and the organic-bound chlorine has been converted into the environmentally harmless inorganic chloride. For H₂O₂/chlorophenol mole ratios between 1: 1 and 16: 1, the photooxidation reaction approached pseudo-first order kinetics, and the rate constants increased with increasing ratio of the oxidant. A theoretical model for the degradation pathway is proposed. The fact that the reaction order was not simply unity could be attributed to the complex reaction sequence processing via a radical mechanism through colored intermediates possibly comprising hydroquinone, catechol and resorcinol.     

Oxidation of Parachloronitrobenzene in Dilute Aqueous Solution by O3 + UV and H2O2 + UV : A Comparative Study

This laboratory study was designed to investigate the degradation of 4-chloronitrobenzene ([CNB] = 2.4 × 10^?6 mol L^?1; pH = 7.5) by H₂O₂/UV and by O₃/UV oxidation processes which involve the generation of very reactive and oxidizing hydroxyl free radicals. The effects of the oxidant doses (H₂O₂ or aqueous O₃), liquid flow rate (or the contact time), and bicarbonate ions acting as OH· radical scavengers on the CNB removal rates were studied. For a constant oxidant dose, the results show that the O₃/UV system appears to be more efficient than the H₂O₂/UV system to remove CNB because of the greatest rate of OH· generation by ozone photodecomposition compared to H₂O₂ photolysis. However, for a given amount of oxidant decomposed, the H₂O₂/UV oxidant system was found to be more efficient than O₃/UV. Moreover, high levels of bicarbonate ions in solution (4 × 10^?3 mol L^?1) significantly decrease the efficiency of CNB removal by H₂O₂/UV and by O₃/UV oxidation processes.     

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.     

Application of Response Surface Methodology for Coffee Effluent Treatment by Ozone and Combined Ozone/UV

This paper reports a study using ozone (O₃) and combined ozone/ultraviolet (O₃/UV) processes for color removal and caffeine degradation from synthetic coffee wastewater using a second-order response surface methodology (RSM) with a three-level central composite face-centered (CCF) design. The effects of O₃ concentration, initial pH, and reaction time were examined for both processes. The reaction time and pH were statistically significant for caffeine degradation and color removal. In the ozonation process, higher caffeine degradation and color removal were observed in alkaline pH, indicating that ozone attacks indirectly, consequently generating hydroxyl radicals. Regarding the ozone/UV process, it was observed that lower caffeine degradation and color removal occurred at neutral pH, indicating an adverse effect due to lower ozone dissolution and consequently the production of a smaller amount of free hydroxyl radicals. The achieved results showed that the techniques were efficient for color removal (85% and 99%, respectively) and caffeine degradation (88% and 98%, respectively).     

Removal of the UV Filter Benzophenone-2 in Aqueous Solution by Ozonation: Kinetics,Intermediates, Pathways and Toxicity

Benzophenone-2 (BP-2) is an important type of UV filter that has been widely used and detected in the aquatic environment with greater estrogenic toxicity. In our work, the removal of BP-2 with the initial concentration of 25 mg L^?1 was first carried out by ozone at different pH (ranging from pH 3.0 to 11.0), and we found a positive correlation between the pH values and the degradation efficiency of BP-2, among which the more rapid removal of BP-2 in alkaline condition was observed than acidic and neutral conditions. For the influence of aqueous humic acid (HA, the concentration ranged from 0 ppm to 100 ppm), the degradation rate of BP-2 by ozonation was first increased with the growth of humic acid concentration (from 0 ppm to 5 ppm), reaching to maximum at 5 ppm of HA and subsequently decreased with the growth of HA concentration (from 5 ppm to 100 ppm). Fourteen intermediate products in the ozonation process were distinguished by an electrospray time-of-flight mass spectrometer and then two degradation pathways were proposed. Through the theoretical calculation, we found the carbanyl group of BP-2 has the most reactivity to be easily attacked by ozone, providing us guides and theoretical basis on the supposed intermediate products. Furthermore, the P. phosphoreum acute toxicity test was conducted to evaluate the potential toxicity during the ozonation process.     

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

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

Study of photochemical and sonochemical processes efficiency for degradation of dyes in aqueous solution

The degradation of two commercially available dyestuffs (C.I. Reactive Black 5 and C.I. Disperse Orange 25) by ultraviolet radiation (UV), ultrasonic irradiation (US), UV/H₂O₂ and US/H₂O₂ processes was investigated in a laboratory-scale batch photoreactor equipped with a 55 W immersed-type low-pressure mercury vapor lamp and a sonoreactor with low frequency (42 kHz) plate type transducer at 170 W of acoustic power. The toxicity was also evaluated in acute toxicity studies using Daphnia magna. Results showed that color removal efficiencies by US and US/H₂O₂ processes were negligible for both dyes. Almost complete disappearance of Reactive Black 5 (97.9%) in UV/H₂O₂ process was possible after 5 min of irradiation. The maximum color removal efficiency of Disperse Orange 25 after 10 min of irradiation, however, was only 9.2% and reached a maximum value of 41% after 120 min of irradiation. Pseudo-first order kinetics with respect to dyestuffs concentrations was found to fit all the experimental data. The results clearly showed that both dyes examined were toxic to D. magna and resulted in quite low LC₅₀ values.     

Degradation of benzene,toluene ethylbenzene and p‐xylene (BTEX) in aqueous solutions using UV/H2O2 system

The homogeneous degradation of benzene (B), toluene (T), ethylbenzene (E) and p‐xylene (X) (BTEX) was studied in aqueous solutions, at pH 3.0, of hydrogen peroxide (5.8 mM ) under UV irradiation in a photoreactor equipped with a 300 nm lamp of light intensity 3.5 × 10^?5 Ein L^?1 min^?1. BTEX was substantially degraded by the H₂O₂/UV system, with >90% disappearing in 10 min of irradiation. The decomposition of BTEX was studied either as single or as multi‐component systems. The effects of irradiation time, amounts of H₂O₂ in molar ratios, rate of degradation and competition between components were thoroughly examined. It can be stated that the rate of BTEX degradation in mixture was higher than those for the individual components due to external effects of the absorption of UV light by the mixture, and their effects on enhancing the formation of OH^? radicals. The appropriate figure of merit, the electrical energy per mass (EE/M), was estimated at various molar ratios and it was confirmed that the best value was the one depicted for p‐xylene (0.065 kWh kg^?1). A theoretical model for the degradation pathway was proposed. Copyright © 2004 Society of Chemical Industry     

Aqueous meta-Chloronitrobenzene Degradation by Ozonation and Its Kinetics

The kinetics and degradation process of meta-Chloronitrobenzene by ozonation in aqueous solution were investigated. Compared to para-chlorobenzoic acid, the rate constant of meta-Chloronitrobenzene with O₃ was 0.59 L/(mol·s), while that of the reaction with ^?OH was 2.07 × 10⁹ L/(mol·s). The main intermediate products were chloronitrophenols and some carboxylic acids. Neither chlorophenols nor nitrophenols was detected. The five-day biochemical oxygen demand and chemical oxygen demand were determined. The ratio of the former to the latter was above 0.3 at 20 min. It was feasible to perform a continuous biotreatment step after 20 min of ozonation.     

UV/H2O2 Treatment: A Practical Solution for Organic Contaminant Control and Primary Disinfection

PWN's water treatment plant Andijk was commissioned almost 40 years ago. It services water from the IJssel Lake by conventional surface water treatment. In view of taste and odor problems the plant was retrofitted with GAC filtration 25 years ago. The finished water quality still complies with all E.C. and Dutch drinking water standards. Nevertheless an upgrade is desired to avoid the use of chlorine and to extend the barriers against pathogenic micro-organisms and a broad range of organic micropollutants such as pesticides, rocket fuel by-products (NDMA), fuel oxygenates (MTBE), solvents (dioxane), endocrine disruptors, algae toxins, pharmaceuticals, etc. UV/H₂O₂ treatment was selected for both primary disinfection and organic contaminant control. The disinfection requirements were based on a 10^?4 health risk. The required 3 log inactivation for Giardia and Cryptosporidium was achieved by an UV dose lower than 20 mJ/cm². The highest UV dose, 105 mJ/cm², was needed for the inactivation of spores of Sulphite Reducing Clostridia. Reactivation of protozoa was established for UV doses up to 25 mJ/cm², for doses higher than 45 mJ/cm² no reactivation was observed. In view of the raw water concentrations the required organic contaminant degradation was set at 80%. Collimated beam and pilot-plant work showed that the required degradation can be achieved by the proper combination of electric energy and H₂O₂. In a UV reactor optimized for organic contaminant control, UV dose of 540 mJ/cm² (about 0.5 kWh/m³) and 6 mg/L H₂O₂ were needed. Under those conditions pesticides (atrazine), NDMA, MTBE, dioxane, endocrine disruptors (bisphenol A), microcystine and pharmaceuticals (diclofenac, ibuprofen) could be removed up to the required 80%. Bromate formation was absent while formation of primary metabolites was insignificant. The UV dose for organic contaminant control is about five times higher than the dose needed for disinfection. The UV/H₂O₂ process was implemented into the existing treatment train between the sand and GAC filters. In the GAC filters excess H₂O₂ is degraded, nitrite is converted into nitrate and biodegradable reaction products are consumed by bacteria. The full-scale installation with 3 streets of 4 Trojan Swift 16L30 reactors has been in operation since October 2004. Disinfection and organic contaminant control are as expected.     

Photo‐oxidation of cyanide in aqueous solution by the UV/H2O2 process

Photo‐oxidation of cyanide was studied in aqueous solution using a low‐pressure ultra‐violet (UV) lamp along with H₂O₂ as an oxidant. It was observed that by UV alone, cyanide degradation was slow but when H₂O₂ was used with UV, the degradation rate became faster and complete degradation occurred in 40 min. The rate of degradation increased as the lamp wattage was increased. It was also observed that cyanide oxidation is dependent on initial H₂O₂ concentration and the optimum dose of H₂O₂ was found to be 35.3 mmol dm^?3. Photo‐oxidation reactions were carried out at alkaline pH values (10–11) as at acidic pH values, cyanide ions form highly toxic HCN gas which is volatile and difficult to oxidise. By the UV/H₂O₂ process, using a 25 W low‐pressure UV lamp and at alkaline pH of 10.5 with an H₂O₂ dose of 35.3 mmol dm^?3, cyanide (100 mg dm^?3) was completely degraded in 40 min when air was bubbled through the reactor, but when pure oxygen was bubbled the time reduced to 25 min. The cyanide degradation reaction pathway has been established. It was found that cyanide was first oxidised to cyanate and later the cyanate was oxidised to carbon dioxide and nitrogen. The kinetics of cyanide oxidation were found to be pseudo‐first order and the rate constant estimated to be 9.9 × 10^?2min^?1 at 40 °C. The power required for complete degradation of 1 kg of cyanide was found to be 167 kWh (kilowatt hour). Copyright © 2004 Society of Chemical Industry     

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.