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Degradation Pathways of Various Plastics
Published in Hyunjung Kim, Microplastics, 2023
Hyunjung Kim, Sadia Ilyas, Gukhwa Hwang
The most significant damage occurs from highly reactive ozone in the atmosphere, which can attack the double bonds of some plastics and elastomers by ozonolysis. The ozonolysis leads to the interaction of ozone molecule reacts with the double bond to produce an unstable, reactive ozonide (polyatomic anion). The rapid decomposition of the ozonide results in double bond cleavage and ultimately polymer chain breaking. The chain breaking by ozonolysis leads to a decrease in molecular weight and a reduction in material strength that can further cause brittlement and material cracking. For example, in elastomers, ozone can induce cracking on surfaces exposed to the atmosphere, and this ozone-cracking effect is often seen in old car tires. However, elastomers like Neoprene have good ozone resistance because the double bonds in the polymer chain are protected from attack by ozone due to the presence of chlorine in polymer backbone which decreases the electron density in the double bonds, thereby reducing the tendency to react with ozone (Davis et al., 2010).
Advanced Oxidation Processes for Wastewater Treatment
Published in Sreedevi Upadhyayula, Amita Chaudhary, Advanced Materials and Technologies for Wastewater Treatment, 2021
Gunjan Deshmukh, Haresh Manyar
Ozone is a highly reactive molecule that breaks down to dioxygen and oxygen radicals. It is a powerful oxidizing agent with E0 = +2.07 eV. Ozone readily reacts with a double bond capable of degrading several organic molecules containing double bonds. Ozone may react with water to produce a hydroxyl radical as a source of reactive oxygen molecule. The decomposition of ozone leads to the formation of H2O2, as elaborated in Scheme 8.3. The literature reports different mechanisms based on the catalyst system used. The efficiency of ozonolysis is pH-, temperature-, and pressure-dependent. The activity of ozone is controlled at low pH to prevent discriminative reaction of ozone with organic and inorganic constituents of the mixture. Further, the process demands optimum pressure and temperature to keep a check on the dissolution of ozone in the water. This directly affects the rate of the desired reaction.
Oxidation Reactions
Published in Michael B. Smith, A Q&A Approach to Organic Chemistry, 2020
Ozone (O3) adds to alkenes, but the initially formed product rearranges to a more stable product called an ozonide, even at low temperatures. Subsequent treatment with an oxidizing or reducing agent leads to net cleavage of the carbon–carbon double bond and formation of aldehydes, ketones, or carboxylic acids. The process of cleavage of alkenes by reaction with ozone into carbonyl derivatives is called ozonolysis. How many resonance forms can be drawn for ozone?
Ozonolysis Post-Treatment of Anaerobically Digested Distillery Wastewater Effluent
Published in Ozone: Science & Engineering, 2019
Benton Otieno, Seth Apollo, John Kabuba, Bobby Naidoo, Aoyi Ochieng
Anaerobically digested DWW has an intense dark brown color and sludge, which require abatement prior to discharge to receiving streams. In this study, ozonolysis of real anaerobically digested DWW has been found to be feasible post-treatment to the AD. The ozonolysis process was significantly affected by pH, ozone flowrate and initial substrate concentration with optimal conditions of 4, 45 mg/L/min and initial COD of 1500 mg/L, respectively, obtained after 60 minutes of ozonolysis. The optimal conditions achieved adequate ozone utilization efficiency >95% and color removal >80%. This study has shown that high ozone dosages resulting in reduced mass transfer led to low ozone utilization and ultimately low color reductions in addition to being uneconomical. Through ozonolysis, the complex aromatic compounds are broken down to simple aliphatic compounds resulting in an increased oxidation state and improved biodegradability. Apart from color abatement, the ozonolysis process also achieved 88% sludge solubilization.
Role of Ozone in Post-Harvest Disinfection and Processing of Horticultural Crops: A Review
Published in Ozone: Science & Engineering, 2022
S Vijay Rakesh Reddy, D.V Sudhakar Rao, R.R. Sharma, P. Preethi, R Pandiselvam
The action of ozone on hydrocarbons resulted in the formation of carboxyl and carboxyl oxides. Carboxyl oxide is a criegee intermediate, which is either isomerized into keto-hydroperoxide or decomposes to hydrocarbonic acid. During ozonolysis of ethylene, ozone cleaves the double bond of ethylene and forms an unstable cyclic primary ozonoide, i.e., 1,2,3-trioxolane, which quickly gets transformed into formaldehyde (HCHO) and an unstable hydroperoxyacetaldehyde (CH2OO*). With prolonged ozonolysis, the hydroperoxyacetaldehyde might recombine with formaldehyde to form secondary ozonoide—an isomer of primary ozonoide, i.e., 1,2,4-trioxolane or decomposes to form free radicals and carbon gases (Alam et al. 2011) (Figure 2).
Ozone: An Advanced Oxidation Technology to Enhance Sustainable Food Consumption through Mycotoxin Degradation
Published in Ozone: Science & Engineering, 2022
O. J. Sujayasree, A. K. Chaitanya, R. Bhoite, R. Pandiselvam, Anjineyulu Kothakota, Mohsen Gavahian, Amin Mousavi Khaneghah
The ozone technology in mycotoxin degradation can be well explored to develop a detoxification method to ensure food quality and safety. O3 inhibits fungal growth, sporulation, and germination. To degrade the mycotoxins by ozonation, it follows a pseudo-first-order rate (Aguilar et al., 2018). Ozonation efficiency increases with higher temperature and more prolonged exposure. The efficiency of the ozonolysis process depends on the concentration of ozone, exposure time, and temperature. Ozone decomposes quickly at temperatures higher than 50°C (Diao, Hou, and Dong 2013). The efficacy of ozone is determined by factors, such as treatment method (Aqueous or gaseous phase), dosage rate, and exposure time of its application, fungal population or contaminants, and the kind of food or feed. Due to its short half-life of 20–30 min at ambient temperature and 7.0 pH (Khadre, Yousef, and Kim 2001), its permanence in the aqueous phase is influenced by the pH and exposure time. The greater the pH, the poorer is the stability of O3 (i.e., shorter half-life). For fungal and pathogenic microbes, minimal exposure time and dose are needed to attain the required deactivation (Cullen et al. 2009; Gujer and von Gunten 2003; Karaca and Velioglu, 2007). The ozone application should not surpass a certain threshold level as a high ozone concentration and long exposure times can have deteriorative impacts on the food quality traits. The processing efficiency is dependent on fungal species, the age of culture, the population density, the existence of compounds having demand for O3, modes of O3 application (aqueous/gaseous), precision of procedures, and method to assess the antimicrobial efficiency (Guzel-Seydim, Greene, and Seydim 2004).