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Advanced treatment technologies for removal of contaminants of emerging concern
Published in Manish Kumar, Sanjeeb Mohapatra, Kishor Acharya, Contaminants of Emerging Concerns and Reigning Removal Technologies, 2022
Om Prakash, Deepak Panchal, Abhishek Sharma, Sukdeb Pal
Photolysis can be defined as the oxidation of any compound (compatible for oxidation) in the presence of light irradiation. It can be divided into two photolytic transformation groups such as direct and indirect photolysis. Direct photolysis encompasses the decomposition of organic compounds by direct absorption of UV light, whereas, in indirect decomposition, UV light facilitated the formation of reactive species (radicals) involving catalysts, which in turn oxidize the organic by chemical reactions. There are a number of factors affecting the photolysis such as light intensity, absorption spectra of the compound, quantum yields, formation or availability of O3, H2O2, nascent oxygen [O], and the solution matrix. Photolysis using polychromatic UV light for the degradation of CIP, oxytetracycline (OTC), and SMX was found to be pH dependent. An increase in pH from 5 to 7 increases the degradation of OTC and CIP while the degradation of SMX decreases (Avisar et al., 2010). Photoreduction of isopropanol (1%) initiated the formation of many radicles, improving the degradation of IBU, naproxen, clofibric acid, and DIC (Packer et al., 2003). There was a significant increment (58%–67%) in the photo-degradation of metronidazole when UV/H2O2 was employed, while direct exposure to UV only resulted in 6%–12% degradation (Shemer et al., 2006). UV irradiation initiates the formation of the hydroxyl radicals from H2O2, which then attacked metronidazole.
Environmental Fate and Transport of Solvent-Stabilizer Compounds
Published in Thomas K.G. Mohr, William H. DiGuiseppi, Janet K. Anderson, James W. Hatton, Jeremy Bishop, Barrie Selcoe, William B. Kappleman, Environmental Investigation and Remediation, 2020
Thomas K.G. Mohr, James Hatton
Photolysis occurs when a chemical absorbs light energy and undergoes chemical transformation. Light is said to excite electrons and destabilize bonds in some compounds. Absorption of light does not result in degradation in the majority of compounds; instead, absorbed energy is released through fluorescence, and the compounds return to their beginning energy state (Hemond and Fechner, 1994). Photolysis, also called direct photodegradation, is more likely to occur in compounds that have double carbon bonds, such as alkenes (e.g., perchloroethylene and TCE) and aromatic rings (e.g., benzene and toluene). Shorter-wavelength light has higher frequency and energy and is therefore the primary agent in photolysis. Visible light in the wavelength range from 280 to 730 nm (nanometers) is primarily responsible for photolysis of chemicals in the upper atmosphere (Seinfeld, 1986). Photolysis of some compounds may occur in both the atmosphere and in surface-water bodies; however, because light in the lower atmosphere has longer wavelengths, many compounds are not directly photolyzed.
Principles of Ecotoxicology
Published in Lorris G. Cockerham, Barbara S. Shane, Basic Environmental Toxicology, 2019
Photochemical reactions can occur in air and water compartments but are of little significance in soils. Chemicals undergo photochemical reactions after they have absorbed light in the UV range that has enough energy to break existing chemical bonds. The principal reactions are photooxidation and photoreduction, both of which proceed through the formation of free radicals which then either react with molecular oxygen or abstract hydrogen from organic compounds. Transformation of pollutants in the atmosphere is mediated by sunlight, particularly short wavelengths in the ultraviolet range, and by catalytic reactions on particulates in the atmosphere. Photolysis of pollutants depends on the energy of the incident light, the absorption spectrum of the molecule, and the presence of photosensitizers in the environment. Absorption of ultraviolet light can result in the cleavage of bonds, oxidation, hydrolysis, dimerization, and rearrangement.
Ozonation and UV photolysis for removing anticancer drug residues from hospital wastewater
Published in Journal of Environmental Science and Health, Part A, 2022
Darliana Mello Souza, Jaqueline Fabiane Reichert, Vanessa Ramos do Nascimento, Ayrton Figueiredo Martins
Also noteworthy are the photochemical processes for the degradation of contaminants, such as the use of UV photolysis as an alternative water treatment process for disinfecting pathogens due to its cost-benefit ratio and its compatibility with the environment. UV technology does not require adding chemicals to the process.[43]