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Author: Emomotimi Emily Bamuza-Pemu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Algal infestation in water bodies causes the release of soluble organic compounds that impact negatively on the taste and odour of the water. With increasing pollution in water bodies and increasing nutrient loading from agricultural activities, most water reservoirs in South Africa and around the world have become affected by this problem. In this study, an advanced oxidation process (AOP), namely, photocatalysis was evaluated for its potential to degrade aromatic compounds: and taste and odour causing bi-cyclic compounds originating from algae. Semiconductor photocatalysis is an environmentally friendly technology requiring no chemical inputs which is capable of completely mineralising organic pollutants to CO2 and H2O thereby eliminating production of unwanted by-products. Although processes involved in the photo-degradation have been reported for a wide range of pollutants, the degradative pathway in this process has not been fully established. In this study, compounds including phenol, 2-chlorophenol, 4-chlorophenol and nitrophenol were successfully eliminated from simulated wastewater. Degradation of geosmin at an environmentally significant initial concentration of 220 ng/L to levels below the lowest detectable concentration was achieved with an optimum catalyst concentration of 60 mg/L at a rate of 14.78 ng/L/min. Higher catalysts loading above 60 mg/L resulted in a decrease in degradation rates. An increase in initial geosmin concentration resulted in a decrease in rates. Ionic species commonly found in surface waters (HCO3 -, and SO4 2- ) significantly reduced the efficiency of geosmin degradation. Degradation of geosmin produced acyclic intermediates from ring fission tentatively identified as 3,5-dimethylhex-1-ene, 2,4-dimethylpentan-3-one, 2-methylethylpropanoate and 2-heptanal. The results obtained indicate that the degradation of organic pollutants in aqueous solution is as a result of synergic action from hydroxyl radicals, positive holes and direct photolysis by UV radiation, though the predominant pathway of degradation is via hydroxyl radicals in solution. Major aromatic intermediates of phenol degradation include catechol, resorcinol and hydroquinone produced in the order catechol> resorcinol> hydroquinone. All three are produced within 2 minutes of photocatalytic reaction of phenol and remain in solution until all phenol is degraded in aerated systems. Production of resorcinol in non-aerated systems is transient, further supporting the hydroxyl radical dominant reaction pathway.
Author: Emomotimi Emily Bamuza-Pemu
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Algal infestation in water bodies causes the release of soluble organic compounds that impact negatively on the taste and odour of the water. With increasing pollution in water bodies and increasing nutrient loading from agricultural activities, most water reservoirs in South Africa and around the world have become affected by this problem. In this study, an advanced oxidation process (AOP), namely, photocatalysis was evaluated for its potential to degrade aromatic compounds: and taste and odour causing bi-cyclic compounds originating from algae. Semiconductor photocatalysis is an environmentally friendly technology requiring no chemical inputs which is capable of completely mineralising organic pollutants to CO2 and H2O thereby eliminating production of unwanted by-products. Although processes involved in the photo-degradation have been reported for a wide range of pollutants, the degradative pathway in this process has not been fully established. In this study, compounds including phenol, 2-chlorophenol, 4-chlorophenol and nitrophenol were successfully eliminated from simulated wastewater. Degradation of geosmin at an environmentally significant initial concentration of 220 ng/L to levels below the lowest detectable concentration was achieved with an optimum catalyst concentration of 60 mg/L at a rate of 14.78 ng/L/min. Higher catalysts loading above 60 mg/L resulted in a decrease in degradation rates. An increase in initial geosmin concentration resulted in a decrease in rates. Ionic species commonly found in surface waters (HCO3 -, and SO4 2- ) significantly reduced the efficiency of geosmin degradation. Degradation of geosmin produced acyclic intermediates from ring fission tentatively identified as 3,5-dimethylhex-1-ene, 2,4-dimethylpentan-3-one, 2-methylethylpropanoate and 2-heptanal. The results obtained indicate that the degradation of organic pollutants in aqueous solution is as a result of synergic action from hydroxyl radicals, positive holes and direct photolysis by UV radiation, though the predominant pathway of degradation is via hydroxyl radicals in solution. Major aromatic intermediates of phenol degradation include catechol, resorcinol and hydroquinone produced in the order catechol> resorcinol> hydroquinone. All three are produced within 2 minutes of photocatalytic reaction of phenol and remain in solution until all phenol is degraded in aerated systems. Production of resorcinol in non-aerated systems is transient, further supporting the hydroxyl radical dominant reaction pathway.
Author: Emomotimi Emily Bamuza-Pemu
Publisher:
ISBN:
Category : Drinking water
Languages : en
Pages : 312
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Book Description
Algal infestation in water bodies causes the release of soluble organic compounds that impact negatively on the taste and odour of the water. With increasing pollution in water bodies and increasing nutrient loading from agricultural activities, most water reservoirs in South Africa and around the world have become affected by this problem. In this study, an advanced oxidation process (AOP), namely, photocatalysis was evaluated for its potential to degrade aromatic compounds; and taste and odour causing bi-cyclic compounds originating from algae. Semiconductor photocatalysis is an environmentally friendly technology requiring no chemical inputs which is capable of completely mineralising organic pollutants to CO2 and H2O thereby eliminating production of unwanted by-products. Although processes involved in the photo-degradation have been reported for a wide range of pollutants, the degradative pathway in this process has not been fully established. In this study, compounds including phenol, 2-chlorophenol, 4-chlorophenol and nitrophenol were successfully eliminated from simulated wastewater. Degradation of geosmin at an environmentally significant initial concentration of 220 ng/L to levels below the lowest detectable concentration was achieved with an optimum catalyst concentration of 60 mg/L at a rate of 14.78 ng/L/min. Higher catalysts loading above 60 mg/L resulted in a decrease in degradation rates. An increase in initial geosmin concentration resulted in a decrease in rates. Ionic species commonly found in surface waters (HCO3 -, and SO4 2-) significantly reduced the efficiency of geosmin degradation. Degradation of geosmin produced acyclic intermediates from ring fission tentatively identified as 3,5-dimethylhex-1-ene, 2,4-dimethylpentan-3-one, 2-methylethylpropanoate and 2-heptanal. The results obtained indicate that the degradation of organic pollutants in aqueous solution is as a result of synergic action from hydroxyl radicals, positive holes and direct photolysis by UV radiation, though the predominant pathway of degradation is via hydroxyl radicals in solution. Major aromatic intermediates of phenol degradation include catechol, resorcinol and hydroquinone produced in the order catechol > resorcinol > hydroquinone. All three are produced within 2 minutes of photocatalytic reaction of phenol and remain in solution until all phenol is degraded in aerated systems. Production of resorcinol in non-aerated systems is transient, further supporting the hydroxyl radical dominant reaction pathway.Description:
Author: Mika Sillanpää
Publisher: Elsevier
ISBN: 0128192267
Category : Technology & Engineering
Languages : en
Pages : 462
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Book Description
Advanced Water Treatment: Advanced Oxidation Processes reviews the most recent research findings and discusses new photocatalysts (such as TiO2, etc.) and their performance under different conditions. Furthermore, the book includes the use of UV LEDs (with H2O2) for the decomposition of organic pollutants and bacteria in various conditions and water samples. Advanced oxidation processes (AOPs) have widely been used in water and wastewater treatment. This book highlights their work towards improving energy-efficient and environmentally friendly technology for growing needs in water treatment. - Includes most recent research on advanced water treatment using photocatalysis - Covers novel photocatalysts for water purification - Presents the use of sulphide materials in water purification
Author: Elvis Fosso-Kankeu
Publisher: John Wiley & Sons
ISBN: 1119576946
Category : Science
Languages : en
Pages : 508
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Book Description
Presents recent challenges related to new forms of pollution from industries and discusses adequate state-of-the-art technologies capable to remediate such forms of pollution. Over the past few decades the boom in the industrial sector has contributed to the release in the environment of pollutants that have no regulatory status and which may have significant impact on the health of humans and animals. These pollutants also referred to as "emerging pollutants", are mostly aromatic compounds which derive from excretion of pharmaceutical, industrial effluents and municipal discharge. It is recurrent these days to find water treatment plants which no longer produce water that fits the purpose of domestic consumption based on newly established guidelines. This situation has prompted water authorities and researchers to develop tools for proper prediction and control of the dispersion of pollutants in the environment to ensure that appropriate measures are taken to prevent the occurrence of outbreaks due to sudden load of these pollutants in the water system. The chapters in this book cover a wide range of nano and bio-based techniques that have been designed for the real time detection of emerging contaminants in environmental water sources, geochemical models that are continuously improved for the prediction of inorganic contaminants migration from the mine solid wastes into ground and surface waters. Remediation strategies are also discussed and include effective techniques based on nanotechnology, advanced membrane filtration, oxidative and bio-degradation processes using various types of nanocatalysts, biocatalysts or supporting polymer matrices which are under advanced investigations for their implementation at large scale for the removal of recalcitrant pollutants from polluted water. Nano and Bio-Based Technologies for Wastewater Treatment: Prediction and Control Tools for the Dispersion of Pollutants in the Environment is divided is two sections. The first section covers the occurrence of emerging pollutants in environmental water while the second section covers state-of-the-art research on the removal of emerging pollutants from water using sustainable technologies. A total of 13 chapters addressing various topics related to the two sections are essentially based on recent developments in the respective field which could have a significant impact on the enhancement of the performance of wastewater treatment plants around the world, and especially in developing countries where access to clean and safe water remains a daily challenge.
Author: Jesus Moreira del Rio
Publisher:
ISBN:
Category :
Languages : en
Pages : 434
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Book Description
Abstract Scaling up a photoreactor requires both knowledge of optical properties of the slurry medium and an established kinetic model. Measuring the scattering and absorption coefficients of particles suspended in water involves the use of specialized optical equipment, as well as the partial solution of the radiative transfer equation (RTE). In addition, modeling of the radiation field in photoreactors with complicated geometries offers special challenges. On the other hand, most of the kinetic models (KM) for phenol photodegradation reported in the literature were obtained for a single organic chemical species only. In fact, neglecting all the intermediate species generated during the photoreaction, is a common oversimplification that limits the KM application. As a result, once the radiation and kinetic models fully established, energy efficiencies can be obtained. In this PhD dissertation, the photocatalytic degradation of phenol over four different TiO2 catalysts is studied. It is proven that phenol yields hydroquinone, catechol, benzoquinone, and acetic and formic acids as main intermediate species. The radiation field inside photocatalytic reactors is predicted by solving the RTE. From the solution of the RTE, the local volumetric rate of energy absorption (LVREA) is also calculated. The radiation field inside an annular photoreactor is simulated using the Monte Carlo (MC) method for different TiO2 suspensions in water. All simulations are performed by using both the spectral distribution, and the wavelength-averaged scattering and absorption coefficients. The Henyey-Greenstein phase function is adopted to represent forward, isotropic and backward scattering modes. It is assumed that the UV lamp reflects the back-scattered photons by the slurried medium. It is proven, photo-absorption rates, using MC simulations and spectral distribution of the optical coefficients, agree closely with experimental observations from a macroscopic balance (MB). It is also found that the scattering mode of the probability density function, is not a critical factor for a consistent representation of the radiation field. iv When solving the RTE, two optical parameters are needed: (1) the absorption and scattering coefficients, and (2) the phase function. In this research work, the MC method, along with an optimization technique, is shown to be effective in predicting the wavelength-averaged absorption and scattering coefficients for different TiO2 powders. To accomplish this, the LVREA and the transmitted radiation (Pt) in the photoreactor are determined by using a MB. The optimized coefficients are calculated ensuring that they comply with a number of physical constrains, falling in between bounds established via independent criteria. The optimization technique is demonstrated by finding the absorption and scattering coefficients for different semiconductors that best fit the experimental values from the MB. The objective function in this optimization is given by the least-squared error for the LVREA. A photocatalyst is synthesized and its optical properties determined by the proposed method. This approach is a general and promising one; not being restricted to reactors of concentric geometry, specific semiconductors and/or particular photocatalytic reactor unit scale. Based on the proposed intermediate reactions, a phenomenological based unified kinetic model is proposed for describing the obtained experimental observations in phenol photodegradation. This Langmuir-Hinshelwood (L-H) kinetic model is based on a Series- Parallel reaction network. This reaction model is found to be applicable to the various TiO2 photocatalyst in the present study. This unified kinetic network is based on the identified and quantified chemical species in the photoconversion of phenol and its intermediates. In order to minimize the number of optimized parameters, the adsorption constants of the different intermediate species on the different catalysts configuration, are obtained experimentally. It is shown that the unified kinetic model requires a number of significant assumptions to be effective; avoiding overparametization. As a result, the unified kinetic model is adapted for each specific TiO2 photocatalyst under study. These different models adequately describe the experimental results. It is shown that this approach results in good and objective parameter estimates in the L-H kinetic model, which is typically applied to photocatalytic reactors. Finally, two efficiency factors, the quantum yield and the photochemical and thermodynamic efficiency factor, are obtained, in this PhD dissertation. These factors are based on the kinetic model proposed and the radiation being absorbed by the photocatalyst particles. The v efficiency calculations consider stoichiometric relationships involving observable chemical species and OH- groups. The obtained efficiency factors point toward a high degree of photon utilization and, as a result, the value of photocatalysis and Photo-CREC-Water reactors for the conversion of organic pollutants in water is confirmed.
Author: Martin M. Halmann
Publisher: CRC Press
ISBN: 9780849324598
Category : Technology & Engineering
Languages : en
Pages : 322
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Book Description
Photodegradation of Water Pollutants, the only complete survey available of current photocatalytic methods for treating water pollutants, covers all aspects of light-stimulated detoxification. Ideal for researchers and students, this new book explains methods for pollution treatment that have proven more effective than conventional biodegradation. Photodegradation of Water Pollutants examines advanced oxidation processes that have been successful in treating the chemical substances produced by industrial effluents and intensive agriculture. These oxidation processes include irradiation with ultraviolet or visible light, the use of homogenous sensitizers, such as dyes, and the use of heterogeneous photocatalysts, such as dispersed semiconductors. In addition, Photodegradation of Water Pollutants addresses the naturally occurring self-cleaning of some pollutants in sunlit surface waters, as well as several alternative non-photochemical approaches to water treatment. Available treatment options are discussed for the main groups of water pollutants, including toxic inorganic ions (cyanides, heavy metals), hydrocarbon derivatives (oil spills, surfactants, pulp and paper wastes), halocarbons, organo-N, organo-P, and organo-S compounds. The text also contains a unique section on the economics of advanced oxidation pollution treatments.
Author: Martin M. Halmann
Publisher: CRC Press
ISBN: 1040286240
Category : Technology & Engineering
Languages : en
Pages : 319
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Book Description
Photodegradation of Water Pollutants, the only complete survey available of current photocatalytic methods for treating water pollutants, covers all aspects of light-stimulated detoxification. Ideal for researchers and students, this new book explains methods for pollution treatment that have proven more effective than conventional biodegradation. Photodegradation of Water Pollutants examines advanced oxidation processes that have been successful in treating the chemical substances produced by industrial effluents and intensive agriculture. These oxidation processes include irradiation with ultraviolet or visible light, the use of homogenous sensitizers, such as dyes, and the use of heterogeneous photocatalysts, such as dispersed semiconductors. In addition, Photodegradation of Water Pollutants addresses the naturally occurring self-cleaning of some pollutants in sunlit surface waters, as well as several alternative non-photochemical approaches to water treatment. Available treatment options are discussed for the main groups of water pollutants, including toxic inorganic ions (cyanides, heavy metals), hydrocarbon derivatives (oil spills, surfactants, pulp and paper wastes), halocarbons, organo-N, organo-P, and organo-S compounds. The text also contains a unique section on the economics of advanced oxidation pollution treatments.
Author: Lindelwa Jay
Publisher:
ISBN:
Category : Water
Languages : en
Pages : 0
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Book Description
The United States Environmental Protection Agency (USEPA) has enlisted phenolic compounds as pollutants of priority concern, as they tend to persist in the environment over a long period, accumulate and exert toxic effects on humans and animals. The entrance of phenolic compounds into the aquatic environment results from natural, industrial, domestic and agricultural activities. Their presence may be due to the degradation or decomposition of natural organic matter present in the water, through the disposal of industrial and domestic wastes into water bodies and through runoffs from agricultural land. Several specific new technologies, called Advanced Oxidation Processes (AOP), have been developed to eliminate dangerous organic chemicals such as phenol from polluted waters. The photocatalytic process, based on UV irradiated semiconductor (TiO2), represents one of AOP that provide an interesting route to the destruction of many organic substances to CO2, H2O and corresponding mineral acids. TiO2 is usually used as a photocatalyst in two crystal structures: Rutile and Anatase. The photoreactivity of P-25 Degussa, consisting of anatase and rutile (4/1 w/w), exceeds that of pure anatase and rutile in several reaction systems. This study characterised the three TiO2 powder forms by BET, XRD, XRF and SEM analyses to contribute to a better understanding of their physical properties. Anatase was revealed to have 98.4% purity x-ray fluorescence analysis, Degussa at 96.7% and rutile at 75.7% was reported to have the most impurities (~25%). This study investigated the UV/TiO2 photocatalytic degradation of phenol, with emphasis on the effects of; solution pH, catalyst load, initial phenol concentration, dissolved oxygen and UV radiation intensity. Degradation studies were conducted in a batch reactor with photons for catalyst (TiO2) activation supplied by a medium pressure 400 W UV lamp immersed in the pollutant solution housed in a double jacket quartz sleeve, which served as the cooling system for the lamp. Temperature control in the reactor was achieved by circulating cold water through the outer cavity of the quartz sleeve. The reactor contents in all batches were aerated at a flow rate of 10 mL/min. Thorough mixing of the contents of the reactor was achieved by continuous agitation with a magnetic stirrer. The experimental reaction time was set at 60-100minutes. Samples were monitored by GC-MS analysis. Results showed that UV/TiO2 photocatalysis is an effective method for the removal of phenol from wastewaters. The efficiency of the process depends strongly on the experimental conditions. Degradation of organic compounds in water is often accompanied by the formation of several intermediate compounds, some of which may be more toxic than the original pollutant. The carbon-13 isotopic labelling technique was employed to track the degradation mechanism of phenol to better understand the degradation pathway. Carbon-13 tracking results revealed that hydroquinone, catechol, benzoquinone, resorcinol and maleic acid were the main intermediates containing the C-13 isotope. A reaction pathway was postulated based on these findings. Kinetic isotope effect (KIE) experiments were conducted and a primary isotope effect was observed. This confirmed that the C-13 isotope position on the labelled phenol was the site of bond breaking in the rate-limiting step.
Author: Eduardo Enrique Pérez
Publisher:
ISBN:
Category : Science
Languages : en
Pages :
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Book Description
Phenolic compounds are important industrial wastes, and are classified as hazardous substances contaminating groundwater resources. Therefore, the removal or diminish of these organics compounds in order to reach the permitted levels before discharging becomes a challenging. Several processes have been developed to remove phenolic compounds from waters, including electrochemical oxidation, redox reactions, membrane separation and photocatalytic degradation. Recently, tendency of phenolic compounds removal involves adsorption and photocatalytic process, using synthetic or natural particles, such as carbon materials and clays. Actually, materials in nanometric scale play an important role in the processes previously mention due to their unique chemical and physical properties. In this book chapter, the first part shows the chemical properties of phenolic compounds that play an important role in the removal process. In the second part, different materials in macro, micro and nanosize used as adsorbents or photocatalysts are reviewed. In addition, other removal processes of phenolic compounds as electrochemistry and redox reactions are included. The removal conditions in these process, such as pH, adsorbate and adsorbent concentration are analyzed and discussed. Furthermore, special emphasis is included in micro and nanocarbon materials, used as adsorbents or photocatalyst to remove phenol from water in recently researches.
Author: Jill Clarke
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
