Effect of MnOx/TiO2 Oxidation State on Ozone Concentration in a Nonthermal Plasma-Driven Catalysis Reactor

Manganese oxides on titanium dioxide were prepared by impregnation method at various calcination temperatures and by deposition-precipitation method and the catalysts were characterized using TG-DTA, XRD, XPS, and N₂ adsorption. Various oxidation states for manganese were obtained and activity towards ozone decomposition inside a nonthermal plasma catalysis reactor was investigated. Activity tests show that with increasing manganese oxidation state, the greater the degree of ozone decomposition inside the reactor. MnOx/TiO₂ prepared by impregnation method calcined at 350 °C showed the highest decrease in ozone concentration.     

Comparison of Different Advanced Oxidation Processes Involving Ozone to Eliminate Atrazine

The oxidation of the herbicide atrazine by advanced oxidation processes (AOP) has been studied. The experiments were carried out in a tubular photoreactor, 2.5 L capacity, capable of providing good contact between the liquid and gas reactants. The decomposition rate of atrazine was determined at different pH using UV radiation, Hydrogen Peroxide, Ozone, Ozone/UV, Ozone/H₂O₂, H₂O₂/UV and Ozone/H₂O₂/UV processes. The effect of three different pH values was studied (4.7, 6.8, 11.7).     

Higher Oxidation State Responsible for Ozone Decomposition at Room Temperature over Manganese and Cobalt Oxides: Effect of Calcination Temperature

The heterogeneous catalytic decomposition of ozone was investigated over unsupported manganese and cobalt oxide at room temperature. All catalysts were characterized by X-ray diffraction (XRD), N₂ adsorption–desorption (Brunauer–Emmet–Teller method), H₂-temperature programmed reduction (H₂-TPR) and X-ray photoelectron spectroscopy (XPS). The catalytic activity test indicated that these oxides had a good activity on ozone conversion meanwhile the catalysts remained highly active over time under reaction conditions. The treated temperature of the catalyst had a significant impact on the performance of ozone abatement and the samples treated at lower temperature showed higher activity. The surface area decreased obviously when developing the calcination temperature and H₂-TPR results demonstrated that much higher oxidation state of metal ions and active oxygen species were maintained on the surface under low treated temperature. XPS analysis showed that there were higher oxidation states of metal ions (Mn⁴⁺ and Co³⁺) and adsorbed oxygen species on the surface of catalysts treated at lower temperature, both of which play a significant role in ozone decomposition. However, the activity of manganese oxide was higher than that of cobalt oxide and the possible reason for this phenomenon was discussed.     

Effect of Mn Dispersion on Gas Phase Ozone Decomposition at Room Temperature Using Natural Manganese Oxides

In this study, various analyses were performed to evaluate the ozone removal characteristics using natural manganese ore (NMO) at room temperature. NMO exists primarily in the form of MnO₂, and the specific forms of manganese oxide are formed as the calcination temperature increases. The activity tests, XRD, BET, and XPS analyses confirmed that the dispersion of manganese site exposed to the surface was a critical factor for ozone removal using NMO. To evaluate the actual application of NMO as a catalyst for ozone decomposition, NMO was also made as a form of monolith; as a result, the catalyst showed an excellent conversion rate (over 80%) even at space velocity 30,000 h^?1.     

Influence of Carbonate on the Ozone/Hydrogen Peroxide Based Advanced Oxidation Process for Drinking Water Treatment

The influence of carbonate on the ozone/hydrogen peroxide process has been investigated. Carbonate radicals, which are formed from the reaction of bicarbonate/carbonate with OH radicals, act as a chain carrier for ozone decomposition due to their reaction with hydrogen peroxide. The efficiency of bicarbonate/carbonate as a promoter for the radical-based chain reaction in presence of hydrogen peroxide has been calibrated and compared to a well-known chain promoter (methanol) and an inhibitor (tert-butanol). Relative to tert-butanol, the hydrogen peroxide induced ozone decomposition is accelerated by bicarbonate/carbonate. Relative to methanol, bicarbonate/carbonate in presence of hydrogen peroxide is less effective as a promoter under comparable experimental conditions.     

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.     

Combination of Ozone with Activated Carbon as an Alternative to Conventional Advanced Oxidation Processes

The objective of this study was to compare the efficiency of O₃/granular activated carbon (GAC) to enhance ozone transformation into ·OH radicals, with the common advanced oxidation processes (O₃/OH^?, O₃/H₂O₂). The results obtained with model systems under the given experimental conditions showed that the system O₃/OH^? (pH 9) and O₃/H₂O₂ (pH 7, [H₂O₂] = 1·10^?5 M) are more efficient than O₃/GAC (pH 7, [GAC] = 0.5 g/L) to enhance ozone transformation into ·OH radicals. However, in Lake Zurich water the O₃/GAC process has a similar efficiency as O₃/H₂O₂ for ozone transformation into ·OH radicals. The results also show that the presence of GAC during Lake Zurich water ozonation leads to (i) removal of hydrophilic and hydrophobic micropollutants, (ii) reduction of the concentration of CO₃ ^2?/HCO₃ ^?, and (iii) decrease of the concentration of dissolved organic carbon (DOC) present in the system.     

Effect of Ozone and Peroxone on Helminth Hymenolepis nana Eggs

In this study the effect of ozone and peroxone on the structure of Hymenolepis nana eggs at different pH (5, 7 and 10) was evaluated. Experiments were conducted with an ozone dose of 1.1 mg/min for 60 min; peroxone tests were done with the same conditions of ozonation process plus 0.33 mL of 33% hydrogen peroxide. Studies with scanning and transmission electron microscopy did not show ultrastructural changes after the treatment with ozone and peroxone at pH 5 and 7, but at pH 10 the eggs lost their external layer, making them more vulnerable.     

Ozonation and Advanced Oxidation of Wastewater: Effect of O3 Dose,pH, DOM and HO•-Scavengers on Ozone Decomposition and HO• Generation

The decomposition of ozone in wastewater is observed starting 350 milliseconds after ozone addition. It seems not to be controlled by the autocatalytic chain reaction, but rather by direct reactions with reactive moieties of the dissolved organic matter (DOM). A larger ozone dose increases ozone consumption prior to 350 milliseconds but decreases the rate of ozone decomposition later on; this effect is predicted by a second-order kinetic model. Transferred Ozone Dose (TOD) is poorly correlated with ozone exposure (= ∫[O₃]dt) indicating that TOD is not a suitable parameter for the prediction of disinfection or oxidation in wastewater. HO^? concentrations (> 10^?10 M) and R_ct (=∫[HO^?]dt/∫[O₃]dt > 10^?6) are larger than in most advanced oxidation processes (AOP) in natural waters, but rapidly decrease over time. R_ct also decreases with increasing pre-ozonation doses. An increase in pH accelerates ozone decomposition and HO^? generation; this effect is predicted by a kinetic model taking into account deprotonation of reactive moieties of the DOM. DOC emerges as a crucial water quality parameter that might be of use to normalize ozone doses when comparing ozonation in different wastewaters. A rapid drop of absorbance in the water matrix—with a maximum between 255–285 nm—is noticeable in the first 350 milliseconds and is directly proportional to ozone consumption. The rate of absorbance decrease at 285 nm is first order with respect to ozone concentration. A kinetic model is introduced to explore ozone decomposition induced by distributions of reactive moieties at sub-stoichiometric ozone concentrations. The model helps visualize and comprehend the operationally-defined “instantaneous ozone demand” observed during ozone batch experiments with DOM-containing waters.     

工业废气中H2S和R—SH的臭氧氧化去除试验

介绍了臭氧氧化法去除工业废气中的硫化氢、硫醇的试验情况,考察了臭氧浓度、停留时间和催化剂等不同因素对去除率的影响。试验结果表明能达到较好的去除效果,硫化氢、硫醇的最终氧化产物可以不是二氧化硫,而是凝聚态的硫化物。     

低低温电除尘对烟气烟尘脱除的影响

对某百万燃煤机组进行低低温电除尘进出口烟尘浓度测试,研究低低温电除尘对烟尘的脱除情况以及不同负荷和改造前后对低低温电除尘除尘效率的影响。试验结果表明:测试结果合理,低低温电除尘除尘效果可达99.9%以上且对不同负荷适应性较好;与改造前相比,低低温电除尘改造后烟气比电阻降低,烟气流量降低,更有利于烟尘的捕集与脱除,除尘效率由99.65%增加到99.92%,     

Hydroxyl Radical/Ozone Ratios During Ozonation Processes. II. The Effect of Temperature,pH, Alkalinity,and DOM Properties

The influence of temperature, pH, alkalinity, and type and concentration of the dissolved organic matter (DOM) on the rate of ozone (O₃) decomposition, O₃-exposure, ?OH-exposure and the ratio R_ct of the concentrations of ?OH and O₃ has been studied. For a standardized single ozone dose of 1 mg/L in all experiments, considerable variations in O₃-exposure and ?OH-exposure were found. This has important implications for water treatment plants regarding the efficiency of oxidation and disinfection by O₃. In oligotrophic surface waters and groundwaters, minimal calibration experiments are needed to model and control the ozonation process, whereas in eutrophic surface waters more frequent measurements of O₃ kinetics and R_ct values are required to evaluate seasonal variations.     

Evaluation and Comparison of Conventional and Advanced Oxidation Processes for the Removal of PPCPs and EDCs and Their Effect on THM-Formation Potentials

Pharmaceuticals and personal care products (PPCPs), endocrine disrupting compounds (EDCs) and disinfection by-products are suspected to have potential adverse impact on humans and hence their elimination during drinking water treatment is often desired or regulated. Based on pilot-plant experiments with three raw water sources, conventional treatment poorly removed the selected PPCPs and EDCs, while ozone/H₂O₂ and UV/H₂O₂ (both) with conventional treatment effectively removed PPCPs and EDCs. In most of the experiments, ozone/H₂O₂ + conventional treatment additionally removed THM formation potentials (THM-FPs) compared to those of conventional treatment. However, UV/H₂O₂ treatment was found to increase THM-FPs compared to conventionally treated water.