References
1. Glaze WH, Kang JW, Chapin DH. The chemistry of water of water treatment processes involving ozone, hydrogen peroxide and ultraviolet radiation. Ozone Sci Eng 1987 9 335-342. 2. Sayre JM. International standards for drinking water. J Am Water Works Assoc 1988 80 53-60. 3. Organisation Mondiale de la Santee. Directives de qualitee pour l'eau de boisson. Vol. 1. Recommandations. Geneve Organization Mondiale de la Sante, 1994. 4. Rowe DR, Abdel-Magid IM. Handbook of wastewater reclamation and...
NearMegahertz Sonochemistry
In the past, it was argued that 20-50 kHz was the optimal frequency range for sonochemistry 1,33 . More recently, however, a large number of experiments have shown that this is often not the case. Generally, sonochemistry progresses as well, if not better, at the near-megahertz frequencies i.e., 1001000 kHz see Sec. II.C.1 . It is expected that near-megahertz ultrasonic frequencies will soon become as important to sonochemistry as 20-50 kHz has been in the past. Generally, higher-frequency...
Ozone Solubility Rate Constants and Mass Transfer Coefficients
Similar to ozone decomposition, ozone solubility has been the subject of multiple studies. These studies usually propose an empirical equation for the Henry's law constant as a function of pH, ionic strength, and temperature 59,60 . For example, Sotelo et al. 60 found the following equation valid for phosphate buffer aqueous solutions at temperatures between 0 and 20 C, pH range of 2 to 8.5, and ionic strength varying from 10-3 to 10-1 M He 1.85 x 107exp -2119 r exp 0.961 cO'H1-2 kPaM-1 11...
II FENTON REAGENT MECHANISMS AND KINETICS A Fenton Reaction
The second-order rate constant k1 for reaction 1 has been reported as 76 M-1 sec-1 3 no detailed conditions provided and as 41.4 M-1 sec-1 4 in the presence of 0.1 M HClO4. The fundamental mechanism for reaction 1 has been proposed as 4 Fe2 HOOH Fe OH 2 HO- 8 with reaction 8 being rate-limiting. If excess Fe2 is present in acidic solution, an additional reaction reaction 11 results in stoichiometric conversion of hydrogen peroxide to water, representing a two-electron reduction of the peroxide...
B Reductive Degradation
As can be seen from reactions 2 , 6 , 16 , and 17 , the reducing species HO2- hydroperoxyl radical and O2- superoxide are formed in Fenton Table 2 Observed Enhancements in Degradation Rate Constants with CMCD Added k koa no NOM k ko with NOM k ko with NOM a k ko ratio of observed rate constant with additives k to observed rate constant without additives ko . Additives were either CMCD or NOM. b Ratio of total amount of PCB degraded with CMCD to total amount of PCB degraded without CMCD....
B Examples of ScaleUp Environmental Application and Industrial Application
Over a dozen pilot demonstrations of SCWO treatment for a variety of waste streams ranging from industrial waste to military waste e.g., chemical weapons are currently in operation or planned for near-future operation. Among them, the most visible are government-funded demonstrations such as those at Los Alamos, Tyndall Air Force Base, U.S. Army facilities, and U.S. Navy facilities. Currently, SCWO is being evaluated under the U.S. government's Assembled Chemical Weapons Assessment ACWA program...
F Ferryl Ion or Other HighValent Iron Species
Although applications of Fenton chemistry to pollutant degradation most likely involve hydroxyl radical as the primary oxidant, an alternative mech- H2O2 hm 2HO-Fe OH 2 hv Fe2 HO-Fe3 L- hv Fe2 L- anism that does not involve hydroxyl radical has also been proposed 4 . In this mechanism, instead of reaction 8 , the following rate-limiting step occurs The importance of FeO2 the ferryl ion as an alternate oxidant, instead of hydroxyl radical, has been extensively debated. Much of the debate exists...
Kinetics of Ozonation
The design of ozonation contactors requires knowledge of kinetic information see later , that is, the rate at which pollutants or matter present in water react with ozone, both directly and or indirectly, and hence the rate of ozone absorption. Reaction rates can be calculated if rate constants of these reactions are known. Thus, the determination of rate constants represents a crucial point in contactor design. In practice, ozonation is a heterogeneous process involving ozone transfer from air...
Air Treatment
To our knowledge, all photocatalytic purifiers deodorizers for indoor air comprise cylindrical UV lamps consuming a few tens of electrical watts and a TiO2-coated material through which, or along which, the air passes 40,132 . Because of size limitations, the geometrical surface of this material is on the order of 500-2000 cm2 for an apparatus designed for an ordinary room i.e., a volume of 20-40 m3 . An incorporated fan allows the air in the Figure 4 View of the demonstration plant built in...
REFERENCES Ivj
1. Mason TJ, Lorimer JP. Sonochemistry Theory, Applications and Uses of Ultrasound in Chemistry. Chichester Ellis Horwood Limited, 1988. 2. Thompson LH, Doraiswamy LK. Sonochemistry science and engineering. Ind Eng Chem Res 1999 38 1215-1249. 3. Leighton TG. The Acoustic Bubble. London Academic Press, 1992. Brennen CE. Cloud cavitation observations, calculations and shock waves. Multiph Sci Technol 1998 10 303-321. Margulis MA, Margulis IM. Theory of local electrification of cavitation bubbles...
Interferences
Effects of Inorganic Anions on Photocatalytic Water Treatment. Inorganic ions can significantly affect photocatalytic treatment only if they are located at the photocatalyst surface or in the Helmholtz layer. This location depends both on the chemical affinity of the ions for titania and on the point of zero charge PZC of this solid. At pH greater than the TiO2 PZC between 6 and 6.5 , the surface is negatively charged and anions are repelled. At pH values below the TiO2 PZC, the excess anion...
REFERENCES Mzq
1. Zimmermann FJ. Waste disposal. U.S. Patent 2,665,249, Jan. 5, 1954. 2. Copa WM, Gitchel WB. Wet oxidation. In Freeman HM, ed. Standard Handbook of Hazardous Waste Treatment and Disposal. New York McGraw-Hill, 1989, Section 8.8. 3. Joshi JB, Shah YT, Parulekar SJ. Engineering aspects of the treatment of aqueous waste streams. Indian Chem Eng 1985 37 3-37. 4. Laughlin RGW, Gallow T, Robey H. Wet air oxidation for hazardous waste control. J Hazard Mater 1983 8 1-9. 5. Mishra VS, Mahajani VV,...
Other Practical Considerations and Limitations
Because water can be considered as one of the most benign solvents available, together with its solvation powers at high temperature, its applicability for a variety of wastes is tremendous. However, based on the current developments of the process, its applicability remains limited to pumpable waste streams. In addition, it is generally understood that the waste streams with organic content in the 1-20 wt. range is most suitable for this technology. Waste streams with 100 wt. can be treated...
Products from SCWO
Identifying the products both intermediates and final products from the SCWO process is an essential prerequisite for evaluating the environmental impact of the technology. Additionally, identification of products is key to optimizing the process parameters to obtain the desired conversion for the destruction of the pollutant. The intermediate products and their composition depend on the temperature, water density or pressure , oxidant concentration, concentrations of other additives, if...
Iii Hydroxyl Radical Reactions With Organic Compounds
Although there is still debate as to whether hydroxyl radicals or ferryl species are the key oxidants in Fenton systems, most literature reports on the mechanisms of degradation of organic compounds invoke the hydroxyl radical. Based on the reports discussed above, it seems likely that hydroxyl radical is a major oxidant during Fenton degradations. Although ferryl ions or other highly oxidized forms of iron may occur, either to a limited extent or more abundantly under specific conditions, this...
References 1
1. Blake DM. Bibliography of Work on the Photocatalytic Removal of Hazardous Compounds from Water and Air. NREL TP-510-31319, Golden, CO National Renewable Energy Laboratory htpp www.nrel.gov chemistry bioenergy chemistry.html . 2. Pichat P. Heterogeneous photocatalysis. In Ertl G, Knozinger H, Weitkamp J, eds. Handbook of Heterogeneous Catalysis Vol. 4. Weinheim Wiley-VCH, 1997 2111-2122. 3. Mills A, Le Hunte S. An overview of semiconductor photocatalysis. J Photo-chem Photobiol A Chem 1997...
Contributors
Fernando J. Beltran Departamento de Ingenieria Quimica y Energetica, Universidad de Extremadura, Badajoz, Spain Enric Brillas Laboratori de Ciencia i Tecnologia Electroquimica de Materials, Departament de Quimica Fisica, Universitat de Barcelona, Barcelona, Spain Pere-Llu s Cabot Laboratori de Ciencia i Tecnologia Electroquimica de Materials, Departament de Quimica Fisica, Universitat de Barcelona, Barcelona, Spain Juan Casado Departamento de Investigacion, Carburos Metalicos S.A., Barcelona,...
General Advantages and Disadvantages of Treatments by TiO Photocatalysis
Photocatalytic treatments of gases and solutions offer several advantages 2. TiO2 is a nontoxic compound used as an additive in the food and pharmaceutical industries. Its cost is on the order of a few dollars per kilogram ca. 2 kg-1 for the pigment grade presumably 5-10 times more for a photocatalytic grade, depending on the future development of TiO2 photocatalysis . It is synthesized in very large quantities for other purposes, so that its preparation is well mastered. It is stable and, in...