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Solar Energy for Water and Wastewater Treatment
Published in Sampa Chakrabarti, Solar Photocatalysis for Environmental Remediation, 2019
Industrial wastewater often contains inorganic salts in addition to organic pollutants. These salts are generally ionized at experimental conditions. These ions are assumed to influence PCD. The anions commonly present in wastewater are chlorides, sulphates, carbonates, and bicarbonates. These anions generally have a negative effect on the adsorption of pollutants onto catalyst surface and the rate of PCD decreases in the presence of these ions. Moreover, these ions act as the hydroxyl radical scavenger and can absorb UV light as well. In the case of cations, the influences reported are rather contradictory. Some studies reported that only those metals that have the standard reduction potential more positive than 0.3 V can be treated with TiO2 photocatalysis. The presence of cations also has a detrimental effect on the PCD owing to reduced adsorption. The only exceptions are iron, copper, and silver ions.
Physical Pre-Treatment of Sludge
Published in Antoine Prota Trzcinski, Advanced Biological, Physical, and Chemical Treatment of Waste Activated Sludge, 2018
Ultrasonication can also cause water sonolysis whereby one water molecule is split into one hydrogen radical and one hydroxyl radical (Hua and Hoffmann, 1997). In addition to physical sludge disintegration, many toxic and recalcitrant organic pollutants, such as aromatic compounds, chlorinated aliphatic compounds, surfactants, organic dyes, etc., are also broken down into simpler forms. This is due to the generation of the highly oxidative reactive radicals hydroxyl (OH•), hydrogen (H•), hydroperoxyl (HO2•) and hydrogen peroxide (H2O2) during ultrasound pre-treatment, which leads to the oxidative breakdown of these recalcitrant compounds (Khanal et al., 2007). Hydroxyl radicals can react with organic scavengers in the sample and degrade them into simpler compounds. For example, a formic acid molecule can be degraded to carbon dioxide and water with the help of hydroxyl radicals (Navarro et al., 2011). Wang et al. (2005) tried to eliminate the influence of hydroxyl radicals on sludge solubilization by adding sodium bicarbonate, as it is known to be a very good hydroxyl radical scavenger. The authors found that hydromechanical shear forces were primarily responsible for WAS disintegration when NaHCO3 was added at an ultrasonic density of 0.384 W/mL or lower. However, the contribution of oxidizing radicals was predominant at a higher ultrasonic density of 0.72 W/mL.
Wastewater Treatment
Published in Suresh C. Ameta, Rakshit Ameta, Garima Ameta, Sonochemistry, 2018
Arpita Pandey, Arpita Paliwal, Rakshit Ameta
Beckett and Hua (2003) investigated the degradation of 1,4-dioxane using Fe(II) and US. Sodium bicarbonate is a hydroxyl radical scavenger and its addition reduced the rate of decomposition; however, it could not stop the degradation completely. Son et al. (2006) studied the effect of adding Fe(0), Fe (II) and S2O82- during the sonication of aqueous 1,4-dioxane. Nakajima et al. (2007) reported the sonochemical oxidation of 1,4-dioxane by a combination of TiO2 and SiO2. TiO2 proved to be more effective as compared to SiO2 but the photocatalytic destruction through sonolumines- cence was not the main mechanism. It seems that the process of sonication produced thermally excited holes in the TiO2 and oxygen vacancies in the TiO2 surface help in the decomposition by enhancing cavitation.
Solvent-free oxidation of ethylbenzene over LDH-hosted Co(II) Schiff base of 2-hydroxy-1-naphthaldehyde and 4-amino benzoic acid
Published in Inorganic and Nano-Metal Chemistry, 2019
Savita Khare, Jagat Singh Kirar, Swati Parashar
The quenching experiment is performed for establishing the mechanism of oxidation of ethylbenzene, a radical scavenger 2,6-di-tert-butyl-4-methylphenol (BHT) is used as a quenching reagent. Simultaneously, we have carried out two sets of reactions. The first set of reactions is carried out without BHT where conversion of ethylbenzene continuously increases up to 5 h. The second set of the reaction is initially carried out without BHT, but after 2 h of reaction, BHT is added and the reaction is continued for the next 5 h. It is observed that after adding BHT, there is no further increase in the conversion of ethylbenzene, which is confirmed by the gas chromatographic analysis. The radical scavenger inhibited the further formation of free radicals in the oxidation reaction. This indicates that oxidation of ethylbenzene using tert-butylhydroperoxide that appears to be a radical process.
Facile synthesize of CdS QDs decorated Bi2MoO6/Bi2Mo3O12 heterojunction photocatalysts and enhanced performance of visible light removal of organic pollutants
Published in Environmental Technology, 2021
Jingling Wang, Wensong Lin, Manru Dong, Yue Xing, Qicheng Zhang
During the cycle experiments, the 2-C/BMO samples were added into fresh RhB, MB and OFX solutions after each centrifugation and drying. In the radical scavenger experiment, 2-propanol (IPA), EDTA-2Na and benzoquinone (BQ) were used as hydroxyl radicals (•OH), holes (h+) and superoxide radicals () scavenger.