Kinetic Study and Optimum Control of the Ozone/UV Process Measuring Hydrogen Peroxide Formed In-situ

This study was conducted to develop a kinetic model of the ozone/UV process by monitoring the trend of in-situ hydrogen peroxide formation. A specifically devised setup, which could continuously measure the concentration of hydrogen peroxide as low as 10 μg/L, was used. The kinetic equations, comprised of several intrinsic constants with semi-empirical parameters (k_chain and k_R3) were developed to predict the time varied residual ozone and hydrogen peroxide formed in situ along with the hydroxyl radical concentration at steady state,[OH°]_ss, in the ozone/UV process. The optimum ozone dose was also investigated at a fixed UV dose using the removal rate of UV absorbance at 254 nm (A₂₅₄) in raw drinking water. The result showed that the continuous monitoring of hydrogen peroxide formed in situ in an ozone/UV process could be used as an important tool to optimize the operation of the process.     

Fluidized Bed GAC Filtration for the Control of Ozone Residuals

A laboratory scale study was conducted in order to investigate upflow granular activated carbon (GAC) filtration for the removal of aqueous ozone. The experimental results showed that fluidized bed GAC filtration operated at hydraulic loadings of 60 — 100 m/h is a promising process for the safe destruction of ozone residuals at the end of ozone contactors. The key parameters in terms of ozone destruction are empty bed contact time, the specific ozone destruction capability of the different GACs and the specific surface of the carbon. Ozone removal in such filters was well described with first order kinetics and external mass transfer was not limiting. Under given conditions in terms of ozone influent concentration, GAC granulometry, GAC density and bed depth, hydraulic loading and available headloss have to be traded off in order to design a well adapted and robust system.     

Facile Synthesis of Activated Carbon-Supported Porous Manganese Oxide via in situ Reduction of Permanganate for Ozone Decomposition

Lichen-like porous manganese oxides (MnO_x) with birnessite-type structure, which were assembled with curled nanosheets (less than 10 nm in thickness), were deposited in situ on the surface of activated carbon (AC) via facile reduction of permanganate by AC, and were tested for the decomposition of ozone, a common air pollutant. Despite the low Mn loading (typically 0.04%–0.14%), the as-synthesized MnO_x/AC catalysts exhibited high catalytic activity and stability for ozone decomposition at room temperature and high relative humidity, which can be attributed to the enrichment of the Mn element on the catalyst surface and a well-organized porous surface morphology of MnO_x.     

Control of Iron and Manganese Ozone Removal by Differential Turbidity Measurements

A new method for continuous monitoring of ozone concentration and the effective removal of iron and manganese was tested. The offered alternative to the ORP system was comprised of two self-cleaning turbidimeters. The turbidimeters were installed at the same locations as the ORP sensors and initial calibration test was performed with different ozone dosage. The conducted long term monitoring study showed stable performance of the differential turbidity system. The system confirmed the continuous and desired result of increased turbidity immediately after oxidation of the unwanted iron and manganese species. Therefore, the method can be expanded to other similar applications involving ozone.     

The Treatment of Spa Water with Ozone Produced by UV Light

Some North American manufacturers are selling devices which produce ozone from UV radiation, which is pumped or sucked into spas, presumably to disinfect the water, without having to use chlorine. To test this claim, a private spa used by two people at least once a day was equipped with a UV radiation unit and an ozone (generating by UV) unit. Bacterial analyses were conducted during experiments carried out using chlorine alone, ozone generated by UV radiation, unit and an ozone (generating by UV) unit. Bacterial analyses were conducted during experiments carried out using chlorine alone, ozone generaed by UV radiation, and ozoen in combination with UV radiation.

Heterotrophic plate counts, and counts of Staphyiococcus aureus and Pseudomonas aeruginosa were lowest when using chlorine, next lowest when using ozone #x002B; UV radiation, and highest when using UV-generated ozone. It is concluded that insufficient dissolved ozone is present for a sufficient reaction time to effect disinfection of these organisms by ozone generated by UV radiation. The fact that the odor of ozone was present above the spa water indicates that contacting also was inefficient.     

Effect of Application of Ozone and Ozone Combined with Hydrogen Peroxide and Titanium Dioxide in the Removal of Pesticides From Water

The aim of this research work is to study the influence of hydrogen peroxide and titanium dioxide in the ozone-based treatment to degrade 44 organic pesticides present in natural water, which are systematically detected in the Ebro River Basin (Spain). The studied pesticides are: alachlor, aldrin, ametryn, atrazine, chlorfenvinfos, chlorpyrifos, pp'-DDD, op'-DDE, op'-DDT. pp'-DDT, desethylatrazine, 3,4-dichloroaniline, 4,4'-dichlorobenzophenone, dicofol, dieldrin, dimethoate, diuron, α-endosulphan, endosulphan-sulphate, endrin, α-HCH, β-HCH, γ-HCH, δ-HCH, heptachlor, heptachlor epoxide A, heptachlor epoxide B, hexachlorobenzene, isodrin, 4-isopropylaniline, isoproturon, metholachlor, methoxychlor, molinate, parathion methyl, parathion ethyl, prometon, prometryn, propazine, simazine, terbuthylazine, terbutryn, tetradifon and trifluralin. The ozonation using 3 mg O₃ L^?1 produces a pesticides removal close to 23%, whereas the application of O₃/H₂O₂ and O₃/TiO₂ treatments achieves average degradation yields lower than the ozonation. However, the application of O₃/H₂O₂ /TiO₂ process improves considerably the pesticides degradation and an average degradation yield of 36% is obtained.     

Oxidation by UV and Ozone of Organic Contaminants Dissolved in Deionized and Raw Mains Water

Organic contaminants dissolved in deionized pretreated and raw mains water were reacted with ultraviolet light and ozone. Ozone first was used for partial oxidation followed by ozone combined with ultraviolet radiation to produce total oxidation. The reduction of TOC level and direct oxidation of halogenated compounds were measured throughout the treatment process. The rate of TOC reduction was compared for ozone injected upstream and inside the reactor.     

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).     

Impact of Ozone and Hydrogen Peroxide vs. UV and Hydrogen Peroxide on Chlorine Residual

The current study undertaken by the Walkerton Clean Water Centre (WCWC) is to evaluate the application of Advanced Oxidation Processes (AOPs) involving Ozone and UV with the addition of hydrogen peroxide, as one of the methods used in the process of the removal of PPCPs and EDCs, or taste and odor. The amount of hydrogen peroxide used with UV is much higher than that used with the ozone application. The concern is the impact of the hydrogen peroxide on the chlorine residual in the water that is pumped to the distribution system. One of the methods used to deal with this problem is to increase the chlorine addition to maintain the required residual. That could increase the disinfectant by-products (DBPs), namely Trihalomethanes (THMs), in addition to increase to the cost of operation. The findings of these experiments would provide useful information regarding the AOPs application using ozone vs. UV with hydrogen peroxide.     

Guideline for Measurement of Ozone Concentration in the Process Gas From an Ozone Generator

A joint meeting of members of the Quality Assurance Committees of the International Ozone Association Pan American Group (PAG), European-African Group (EAG), and Nippon Islands Group (NIG) was held in Oxford, Ohio on November 8 and 9, 1995. The purpose of the meeting was to establish a single, shared guideline for ozone concentration measurement in the gas phase and, in particular, from commercial ozone generators.     

Synergistic Evaluation of Ozone and UV at the Coquitlam Source for Enhanced DBP Control and Cryptosporidium Inactivation

A study was performed for the GVRD to select the ozone dose that results in a higher UVT (UV Transmittance) and reduced DBP formation potential, at the most economical life cycle costs of ozone and UV treatment. The GVRD treats its Coquitlam source with ozone, to meet Giardia and virus inactivation requirements. Currently, the Coquitlam Facility does not meet Cryptosporidium inactivation requirements (3-log). Because the ozone dosage required for Cryptosporidium inactivation is cost prohibitive, UV treatment was selected to provide for adequate log inactivation. Based on pilot and full-scale test results, a model was developed to predict the ozone treated water UVT, which was applied to historical water quality data to evaluate life cycle costs of ozone and UV treatment. In addition, the dosage necessary for control of DBPs, the change in ozone decay rate with increases in pH, and the impact of three quenching chemicals on treated water UVT were evaluated.     

Determination of Residual Ozone or Chlorine Dioxide in Water with ACVK – an Updated Version

The determination of residual ozone or residual chlorine dioxide can be carried out with Acid Chrome Violet K (C.I. code no. 61710, formerly 6170), now available as dye for analytical use under the name of Alizarin Violet 3R (Aldrich 22, 783-8; MW 622.25). The discoloration of the dye in an NH₃-NH₄CI buffered solution of pH 8.1 to 8.5 is specific both for ozone and for chlorine dioxide without interference of chlorine, chloramines, chlorite or chlorate ions in concentrations possibly encountered in treated drinking water.

Detection limit : 0.02 mg L^?l: standard deviation : 0.01 mg L^?l are obtained both for ozone and chlorine dioxide.     

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.     

Ozonation Dynamics and Its Implication for Off-Gas Ozone Control in Treating Pulp Mill Wastewaters

Ozonation of biologically pretreated pulp mill wastewaters was studied using both bench and pilot scale fine bubble contactors to determine the oxidation efficiencies, mass transfer coefficients (k_La) and enhancement factors (E) due to the occurrence of chemical reactions. A sensitivity analysis based on the measured process parameters was then used to reveal the interrelated effects of key factors on off-gas ozone concentrations. It was shown that the removal efficiencies of color and AOX were simply related to the amount of utilized ozone, regardless of variation of other operating conditions. Furthermore, the rate of absorption fell within the fast or instantaneous kinetics regimes due to the occurrence of rapid chemical reactions. The Ek_La values were found to vary substantially during the course of ozonation, indicating that the enhancement factors were not only affected not only by operating conditions but also by wastewater characteristics. To effectively control the off-gas ozone emission, measures should be taken to minimize the backmixing, use a counter-current flow arrangement and provide adequate contact time.     

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.     

过程装备与控制工程专业加强过程教学的认识与实践

从理解过程装备与控制工程专业的内涵出发,本文阐述了对本专业加强过程教学的认识,介绍了加强过程教学的一些具体措施及体会。     

Removal Characteristics of Organic Pollutants in Sewage Treatment by a Pre-Coagulation,Ozonation and Ozone/Hydrogen Peroxide Process

The applicability of a sequential process of ozonation and ozone/hydrogen peroxide process for the removal of soluble organic compounds from a pre-coagulated municipal sewage was examined. 6–25% of initial T-COD_Cr was removed at the early stage of ozonation before the ratio of consumed ozone to removed T-COD_Cr dramatically increased. Until dissolved ozone was detected, 0.3 mgO₃/mgTOC₀ (Initial TOC) of ozone was consumed. When an ozone/hydrogen peroxide process was applied, additional COD_Cr was removed. And we elucidated that two following findings are important for the better performance of ozone/hydrogen peroxide process; those are to remove readily reactive organic compounds with ozone before the application of ozone/hydrogen peroxide process and to avoid the excess addition of hydrogen peroxide. Based on these two findings, we proposed a sequential process of ozonation and multi-stage ozone/hydrogen peroxide process and the appropriate addition of hydrogen peroxide. T-COD_Cr, TOC and ATU-BOD₅ were reduced to less than 7 mg/L, 6 mgC/L and 5 mg/L, respectively after total treatment time of 79 min. Furthermore, we discussed the transformation of organic compounds and the removal of organic compounds. The removal amount of COD_Cr and UV₂₅₄ had good linear relationship until the removal amounts of COD_Cr and UV₂₅₄ were 30 mg/L and 0.11 cm^?1, respectively. Therefore UV₂₅₄ would be useful for an indicator for COD_Cr removal at the beginning of the treatment. The accumulation of carboxylic acids (formic acid, acetic acid and oxalic acid) was observed. The ratio of carbon concentration of carboxylic acids to TOC remaining was getting higher and reached around 0.5 finally. Removal of TOC was observed with the accumulation of carboxylic acids. When unknown organic compounds (organic compounds except for carboxylic acids) were oxidized, 70% was apparently removed as carbon dioxide and 30% was accumulated as carboxylic acids. A portion of biodegradable organic compounds to whole organic compounds was enhanced as shown by the increase ratio of BOD/COD_Cr.     

Influence of Water Vapor on Photochemical Ozone Generation with Efficient 172 nm Xenon Excimer Lamps

The influence of water vapor on photochemical ozone generation has been investigated. Tests of a coaxial ozone generator driven by an efficient, tubular, 172 nm xenon excimer lamp revealed that ozone saturation concentration strongly depends on moisture concentration in the process gas. In order to adequately model the data, catalytic ozone destruction by OH and HO₂ radicals formed by reactions with trace amounts of water vapor in the process gas had to be included in the photochemical ozone production rate equation system. Based on the model, optimized ozone photoreactor designs for ambient air, dry air and dry oxygen are described.     

Numerical Study of NOx Abatement Using Ozone Injection Integrated with Wet Absorption

Nitrogen oxides emitted from power plants and the chemical industry are poisonous to humans and animals, contribute to ozone depletion, and cause acid rain. More than 90% of nitrogen oxides (NO_x) consist of nitric oxide (NO), which is insoluble in water. Among the various available techniques of NO_x abatement, ozone injection is a promising method in which NO is oxidized to higher-order nitrogen oxides (NO₃, N₂O₃, N₂O₄, and N₂O₅), which can easily be absorbed in a wet scrubber. In this article, the ozone injection process integrated with an absorber column is numerically modeled and simulated at various operating conditions. The predicted results of NO_x oxidation with ozone injection and absorption in water agree with the published experimental results. The ozone injection process is modeled using a plug flow reactor, while the wet absorption is based on a rigorous rate-based RateFrac model. Detailed kinetic mechanisms of O₃-NO_x oxidation and absorption of nitrogen oxides in water are incorporated in the model to simultaneously predict the performance efficiency of the ozone reactor and absorber column. Thermodynamic properties of the components are estimated using an Electrolyte NRTL model. The influence of performance parameters (such as feed gas flow rate, inlet gas temperature, reactor configurations, ozone concentration, and NO/NO₂ molar ratio) on the oxidation efficiency of NO_x in the reactor and absorber column is investigated to predict the optimal operating conditions.