Kinetics of MIB and Geosmin Oxidation during Ozonation

Ozonation is an effective means for oxidation of two common earthy/musty odorants (MIB and geosmin) in drinking waters. Second order constants were experimentally determined between the two odorants with ozone and hydroxyl radicals (HO^?). Geosmin was oxidized faster than MIB. Under most surface water treatment conditions, hydroxyl radical mediated reactions dominate over ozone reactions during MIB or geosmin oxidation. MIB and geosmin oxidation increases with greater ozone dose, higher pH, higher temperature or addition of H₂O₂.     

Removal of Atrazine Through Ozonation in the Presence of Humic Substances

The presence of pesticides in water sources and their removal by treatment processes is of particular interest currently to water companies and research scientists. Although operators and scientists are debating whether the related standards and legislation are too stringent, the current European Drinking Water Directive stipulates a maximum contaminant level (MCL) of 0.1 μg/L for an individual pesticide. Atrazine is amongst the most frequently identified pesticides in water supply sources. Since conventional treatment processes (chlorination, coagulation and filtration) are unable to reduce this micropollutant to an acceptable concentration, two advanced technologies are being investigated extensively; namely, adsorption onto activated carbon, and ozonation, particularly ozone combined with hydrogen peroxide. As for ozonation, several authors (Glaze et al., 1987; McGuire and Gaston, 1988; Terashima, 1988; Ferguson et al., 1991) have reported that the removal of refractory organics (e.g., 2-methyl isoborneol – MIB and geosmin) by ozone appears to be more effective in natural waters than in pure water solution; this was attributed to the action of natural organic material in water (such as humic substances) which promotes the radical reactions of ozone. In other more fundamental studies (Staehelin and Hoigné, 1985; Xiong and Legube, 1991), humic substances were speculated to be involved in radical decomposition of ozone in solution.     

原水深度处理过程中的生物稳定性和分子量分布

研究了水源水在"预臭氧+常规+主臭氧/生物活性炭"深度处理工艺流程净化中的各工艺段出水有机物及分子量的变化特征,建立了生物稳定性与有机物分子量的关系,实现了对深度处理后供水水质生物稳定性的评估。研究结果表明:预臭氧可将大分子的天然有机物分解为相对分子质量小于1000的有机物,并提高水的可生化性;导致常规处理工艺去除水中有机物的效率降低;主臭氧可将有机物进一步氧化,并将部分氧化成相对分子质量小于500的有机物;生物活性炭可提高出水的生物稳定性,但对相对分子质量小于1000的有机物去除有限;分子量越小生物稳定性越差,越不容易被去除。此研究结果为评估水源水质深度处理的生物稳定性提供了理论依据。     

Use of Ozone for Disinfection and Taste and Odor Control at Proposed Membrane Facility

Zone 7 of Alameda County Flood Control and Water Conservation District, in coordination with Black & Veatch, conducted a 9-month pilot study to determine preliminary design parameters for a new water treatment plant (WTP). The pilot study was performed to verify the performance of membrane filters and to establish preliminary design parameters for the submerged membrane process, followed by ozonation and biological granular activated carbon filtration. The pilot testing was conducted using water from the Patterson Pass WTP reservoir. The process included coagulation with either ferric chloride or polyaluminum chloride, flocculation, sedimentation, membrane filtration, ozonation, and filtration using biological granular activated carbon (BAC). The goals of the study were as follows:

1. Determine the potential effectiveness of ozone and BAC for removing geosmin and MIB.

2. Determine the impacts of different levels of pathogen inactivation, i.e., 0.5-log Giardia and 2-log virus inactivation.

3. Monitor the formation of bromate under various conditions of ozone oxidation for different levels of pathogen inactivation as well as for taste and odor control, and evaluate bromate mitigation strategies, if necessary.

The results of the study showed that the use of ozone achieved 2.0-log virus inactivation and 0.5-log Giardia inactivation. It also decreased the disinfection by-product formation and effectively controlled geosmin and removed a significant fraction of the MIB during a taste and odor event. Because the raw water bromide concentrations were low, bromate formation remained below the regulated level of 0.010 mg/L. However, in one instance, bromate mitigation was utilized by applying sulfuric acid to lower the pH to less than 7.1, which reduced bromate formation to less than 0.010 mg/L.     

Fenton试剂在给水除藻中的应用

研究Fe2+-H2O2氧化絮凝耦合除去藻类污染。结果表明Fe2+-H2O2在原水pH值为7.8的条件下,对藻细胞和有机物的去除率可达到90%以上。Fe2+-H2O2对藻类污染的去除主要是利用.OH自由基的氧化作用和中间Fe3+络合物的絮凝作用的有效耦合实现的。对藻细胞的去除主要受絮凝作用控制,对其代谢有机物的去除主要受.OH自由基氧化作用控制。     

水/载O3有机溶剂两相臭氧氧化法降解水体中氯霉素

以水/载O₃有机溶剂（全氟萘烷）为新型两相臭氧氧化体系,研究了臭氧在全氟萘烷中的溶解度和稳定性,并考察了pH、NaHCO₃和叔丁醇对两相体系中臭氧稳定性的影响;以水体中氯霉素为研究对象,考察了初始pH值和自由基抑制剂对两相臭氧氧化体系降解氯霉素效果的影响。结果表明：初始水相pH增大有利于氯霉素的降解;自由基抑制剂对两相体系氧化降解氯霉素影响不显著。     

Kinetic Analysis On The Effects Of Dissolved Inorganic And Organic Substances In Raw Water On The Ozonation Of Geosmin And 2–MIB

The kinetics of geosmin and 2–MIB decomposition by ozonation in the presence of dissolved inorganic and organic substances were studied. As a first approximation, the decomposition rate of geosmin and 2–MIB were analyzed as a first–order reaction with respect to their concentration. The first–order rate constants decreased significantly with increase in the concentration of carbonate ion, free chlorine, alcohols and volatile fatty acids. Small amounts of humic acids or fulvic acids, however, enhanced the rate of decomposition. It was also demonstrated that the decomposition rates in natural waters were influenced mainly by the concentrations of carbonate and humic substances.     

Catalytic ozonation for the degradation of nitrobenzene in aqueous solution by ceramic honeycomb-supported manganese

Catalytic ozonation of nitrobenzene in aqueous solution has been carried out in a semi-continuous laboratory reactor where ceramic honeycomb and Mn–ceramic honeycomb have been used as the catalysts. The presences of the two catalysts significantly improve the degradation efficiency of nitrobenzene, the utilization efficiency of ozone and the production of oxidative intermediate species compared to the results from non-catalytic ozonation, and the improvement of them is even more pronounced in the presence of Mn–ceramic honeycomb. Adsorptions of nitrobenzene on the two catalytic surfaces have no remarkable influence on the degradation efficiency. Addition of tert-butanol causes the obvious decrease of degradation efficiency, suggesting that degradation of nitrobenzene follows the mechanism of hydroxyl radical (OH) oxidation. Some of the main operating variables like amount of catalyst and reaction temperature exert a positive influence on the degradation efficiency of nitrobenzene. Initial pH also presents a positive effect in the ozonation alone system while the optimum working initial pH is found to be around 8.83 and 10.67 to the processes of ozonation/ceramic honeycomb and ozonation/Mn–ceramic honeycomb, respectively. The surface characteristics measurement of the two catalysts indicates that the loading of Mn increases the specific surface area, the pH at the point of zero charge (pH_PZC) and the density of surface hydroxyl groups, and results in the appearance of new crystalline phase of MnO₂. The results of mechanism research confirm that the loading of Mn promotes the initiation of OH.     

Ozonation of Phenol-Containing Wastewater Using O3/Ca(OH)2 System in a Micro Bubble Gas-Liquid Reactor

The degradation of phenol in aqueous solution was investigated in an integrated process consisting of O₃/Ca(OH)₂ system and a newly developed micro bubble gas-liquid reactor. The effects of operating parameters such as Ca(OH)₂ dosage, reactor pressure, liquid phase temperature, initial phenol concentration and inlet ozone concentration on degradation and mineralization (TOC removal) were studied in order to know the ozonation performance of this new integrated process. It is demonstrated that the degradation and TOC removal efficiency increased with increasing inlet ozone concentration and increasing Ca(OH)₂ dosage before 2 g/L, as well as decreasing initial phenol concentration. The optimum Ca(OH)₂ dosage should exceed Ca(OH)₂ solubility in liquid phase. The reactor pressure and liquid phase temperature have little effects on the removal and TOC removal efficiency. When Ca(OH)₂ dosage exceeded 3 g/L, the degradation and TOC removal of phenol almost reached 100% at 30 and 55 min, respectively. The intensification mechanism of Ca(OH)₂ assisted ozonation was explored through analysis of the precipitated substances. The mechanism for Ca(OH)₂ intensified mineralization of phenol solution is the simultaneous removal of CO₃^2- ions, as hydroxyl radical scavengers, due to the presence of Ca²⁺ ions. Results indicated that the proposed new integrated process is a highly efficient ozonation process for persistent organic wastewater treatment.     

Efficiency of Ozonation and AOP for Methyl-tert-Butylether (MTBE) Removal in Waterworks

Methyl-tert-butylether (MTBE) is attracting more and more attention since it was discovered in groundwater and other raw water sources for waterworks and proved to difficult to remove during conventional treatment steps in drinking water production. Therefore advanced treatment processes have to be evaluated in addition to established treatment technologies. Laboratory based experiments were carried out studying ozonation with varying ozone concentrations at different pH values. For the elimination of MTBE the degradation through hydroxyl radicals was identified as the main degradation pathway. No decline of MTBE concentration occurred in experiments with molecular ozone, but AOP (Advanced Oxidation Processes) experiments where hydrogen peroxide (H₂O₂) was added showed a more efficient elimination. However, no complete mineralization was achieved — tert-butyl alcohol (tBA) and tert-butyl formate (tBF) were identified as metabolites. In natural waters (i.e., groundwater, bank filtrated water, and drinking water) the efficiency of MTBE removal was strongly dependent on the content of natural organic matter and alkalinity because of their scavenging characteristics. However, bromate formation was observed as well and could cause problems for drinking water production. Comparison with data gained from waterworks showed that conventional ozonation techniques as applied in waterworks are not able to remove MTBE efficiently.     

Assistance of Magnesium Cations on Degradation of Refractory Organic Pollutant by Ozone: Nitrobenzene as Model Compound

Selecting nitrobenzene as a model compound, the assistance of magnesium cations on ozon ation of refractory organic pollutant was investigated in pure water background. It is interesting to find that the presence of magnesium cations with a level of tens of millimoles per liter can obviously increase the degradation and mineralization efficiency of nitrobenzene compared with the case of ozonation alone. At lower pH condition, the magnesium cations still effectively assisted the ozonation of nitrobenzene. Ozone decomposition was accelerated by the presence of magnesium cations. It was confirmed that the presence of magnesium cations promoted the generation of hydroxyl radicals. It was speculated that the formation of hydroxyl group by the deprotonation of the hexaqueous magnesium cations complex Mg[H₂O]₆ ²⁺ promoted the hydroxyl radical formation. However, the promotion was found to be unremarkable and should not be the sole reason for the assistance of magnesium cations on ozonation. The complexation reaction between the hexaqueous magnesium cations complex and carboxylic group may be part of the reason for the magnesium cation- assisted ozonation of organic pollutants. This finding will provide fundamental support for the applications of ozone to treat the concentrated water from membrane filtration which contains both high concentration of magnesium cations and organic pollutants.     

Potential Ozone Applications for Water/Wastewater Treatment

Abstract

Several applications of ozonation were examined in this study for:

1. the treatment of stabilized high strength municipal landfill leachates,

2. the reclamation potential and toxicity reduction of municipal secondary effluents, and

3. the removal potential of phytoplanktons from surface waters.

The major parameters examined were the applied ozone dosage and the respective contact time. The application of single ozonation on leachates resulted in the efficient removal of color and organic loading, due to the respective oxidation, induced by ozonation. In addition, ozonation was found to be effective for the removal of the residual organic content of secondary municipal effluents. However, acute toxic effects after ozonation were observed on V. fischeri and were related to ozone concentration and contact time. Furthermore, the surface water used for drinking water production, was subjected to ozonation treatment for the removal of harmful cyanobacteria. Ozonation resulted in the reduction of the number of cyanobacteria species and in the breakage of the chain‐type species to cells with a lower number of atoms.     

Ozonation of chloronitrobenzenes in aqueous solution: kinetics and mechanism

BACKGROUND: Chloronitrobenzenes (ClNBs) are a family of toxic and bio‐resistant organic compounds. Ozone treatment is specifically suitable for partial or complete oxidation of non‐biodegradable components. However, few studies on the decomposition of ClNBs by ozone are available, and kinetics and mechanisms of ClNBs ozonation have not been thoroughly investigated. The kinetics and mechanism of ozonation degradation of ClNBs in aqueous solution were investigated, and the contribution of both molecular ozone and hydroxyl radicals was also evaluated. RESULTS: The results demonstrated that the decomposition of ClNBs was a pseudo‐first‐order reaction with respect to the pollutant concentration and the overall rate constant increased with an increase in pH. It declined, however, with an increase in pollutant and radical scavenger concentration. Furthermore, TOC removal rate was significantly lower than that of ClNBs, but the same order o‐ClNB < m‐ClNB < p‐ClNB was followed. Ozonation could not reduce TOC significantly, p‐chlorophenol, p‐nitrophenol, 2‐chloro‐5‐nitrophenol and 5‐chloro‐2‐nitrophenol were detected as primary degradation intermediates in ozonation of p‐ClNB. Rate constants of the direct reaction between ozone and ClNBs at 25 °C had been found to be lower than 1 M^?1S^?1. More than 95% of ClNBs removal was due to hydroxyl radical oxidation at pH ≥ 7. CONCLUSION: Advanced oxidation processes may be the preferred choice for the elimination of ClNBs from the environment. Copyright © 2008 Society of Chemical Industry     

Effect of Zeolite Chemical Surface Properties on Catalytic Ozonation of Methylene Blue Contaminated Waters

Heterogeneous catalytic ozonation using natural zeolite has been recently reported. However, there is a lack in the information related to the influence of zeolite active surface sites in this combined system. This work presents experimental results on the effect of zeolite chemical surface properties on catalytic ozonation. Zeolite samples with different chemical surface compositions were prepared from natural zeolite. The effect of pH, and the presence of radical scavengers were assessed at laboratory scale. Results obtained here indicate that hydrous oxide sites present on zeolite surface (S–OH₂ ⁺, S–OH, S–O^?) play a key role on the catalytic ozonation mechanism.     

Degradation of Refractory Organic Pollutants by Catalytic Ozonation—Activated Carbon and Mn-Loaded Activated Carbon as Catalysts

A novel catalyst for the ozonation process was prepared by loading manganese on the granular activated carbon (GAC). Nitrobenzene was used as a model refractory organic micropollutant in this study. The catalytic activity of GAC and the Mn-loaded GAC were studied respectively. The removal efficiency of nitrobenzene by Mn-loaded GAC catalyzed ozonation could reach 34.2–49.9%, with the oxidation efficiency being about 1.5–2.0 times higher than that achieved in GAC catalyzed ozonation and 2.0–3.0 times higher than that achieved by ozonation alone. The effect of pH and the t -butanol on the GAC/ozone process was discussed. The optimum condition for preparing the catalyst was studied.     

Degradation and Transformation of Organic Compounds in Songhua River Water by Catalytic Ozonation in the Presence of TiO2/Zeolite

This paper presents experimental results of the catalytic ozonation of Songhua River water in the presence of nano-TiO₂ supported on Zeolite. The removal efficiency of TOC and UV₂₅₄, the variation of AOC and molecular weight distribution of organics was studied. Results showed that TOC and UV₂₅₄ removal efficiency by ozone was improved in the presence of TiO₂/Zeolite, and increased by 20% and 25%, respectively. The part of organic compounds less than 1000 Da increased in ozonation, but decreased in catalytic ozonation. The AOC of water increased in catalytic ozonation, and the increase of AOC was particularly obvious when ozone dose increased from 28.8 mg·L^?1 to 46.6 mg·L^?1. The degradation and transformation of organic compounds was analyzed by means of GC-MS. The total number of organic compounds was reduced from 50 in the untreated water to 36 and 20, respectively, in ozonation and catalytic ozonation. The removal efficiency of the total organic compounds peak area in ozonation and catalytic ozonation were 23.5% and 62.5%, respectively. Most of the hydrocarbons could be removed easily in ozonation and catalytic ozonation. The organic compounds having hydroxyl, carboxyl or carbonyl groups were hard to be removed in ozonation, but could be removed efficiently in the presence of TiO₂/Zeolite.     

Gallic acid water ozonation using activated carbon

The ozonation of gallic acid in water in the presence of activated carbon has been studied at pH 5. Hydrogen peroxide, ketomalonic and oxalic acids were identified as by-products. The process involves two main periods of reaction. The first period, up to complete disappearance of gallic acid, during which ozonation rates are slightly improved by the presence of activated carbon. The second one, during which activated carbon plays an important role as promoter, and total mineralization of the organic content of the water is achieved. The organic matter removal is due to the sum of contributions of ozone direct reactions and adsorption during the first period and to a free radical mechanism likely involving surface reactions of ozone and hydrogen peroxide on the carbon surface during the second period. There is a third transition period where by-products concentration reach maximum values and ozonation is likely due to both direct and free radical mechanisms involving ozone and adsorption. Discussion on the mechanism and kinetics of the process is also presented both for single ozonation and activated carbon ozonation.     

Ozonation of organic compounds in alkaline aqueous media

Effect of pH on the aqueous phase ozonation of various organic compounds was investigated. The reaction was accelerated in alkaline media due to the formation of active hydroxyl radical by an interaction of ozone with hydroxide ion. However, in a strongly alkaline media (pH < 11.9), hydroxyl radical dissociated into less reactive oxygen ion and the efficiency of ozonation decreased. By means of the theory of gas absorption accompanied by chemical reaction, it was found that the rate of the decomposition of ozone in the presence of about 300 ppm of 1-butanol was 5-80 times larger than that catalyzed only by hydroxide ion in the pH range of 11-13. Efficiency of ozonation showed that an optimum range of pH for the removal of total organic carbon was 9-10.     

Diclofenac removal from water by ozone and photolytic TiO2 catalysed processes

BACKGROUND: The aim of this work was to establish the efficiency of single ozonation at different pH levels (5, 7 and 9) and with different TiO₂ photolytic oxidizing systems (O₂/UV‐A/TiO₂, O₃/UV‐A/TiO₂ or UV‐A/TiO₂) for diclofenac removal from water, with especial emphasis on mineralization of the organic matter. RESULTS: In the case of single ozonation processes, results show fast and practically complete elimination of diclofenac, with little differences in removal rates that depend on pH and buffering conditions. In contrast, total organic carbon (TOC) removal rates are slow and mineralization degree reaches 50% at best. As far as photocatalytic processes are concerned, diclofenac is completely removed from the aqueous solutions at high rates. However, unlike single ozonation processes, TOC removal can reach 80%. CONCLUSION: In single ozonation processes, direct ozone reaction is mainly responsible for diclofenac elimination. Once diclofenac has disappeared, its by‐products are removed by reaction with hydroxyl radicals formed in the ozone decomposition and also from the reaction of diclofenac with ozone. In the photocatalytic processes hydroxyl radicals are responsible oxidant species of diclofenac removal as well as by‐products. Copyright © 2010 Society of Chemical Industry